One document matched: draft-ietf-forces-model-07.txt
Differences from draft-ietf-forces-model-06.txt
Internet Draft J. Halpern
Expiration: April 2007 Self
File: draft-ietf-forces-model-07.txt E. Deleganes
Working Group: ForCES Intel Corp.
October 2006
ForCES Forwarding Element Model
draft-ietf-forces-model-07.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than a "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.html.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Comments are solicited and should be addressed to the working
group's mailing list at forces@peach.ease.lsoft.com and/or the
author(s).
Abstract
This document defines the forwarding element (FE) model used in the
Forwarding and Control Element Separation (ForCES) protocol. The
model represents the capabilities, state and configuration of
forwarding elements within the context of the ForCES protocol, so
that control elements (CEs) can control the FEs accordingly. More
specifically, the model describes the logical functions that are
present in an FE, what capabilities these functions support, and how
these functions are or can be interconnected. This FE model is
intended to satisfy the model requirements specified in the ForCES
requirements draft, RFC 3564 [1].
Internet Draft ForCES FE Model October 2006
Table of Contents
Abstract...........................................................1
1. Definitions.....................................................4
2. Introduction....................................................5
2.1. Requirements on the FE model...............................6
2.2. The FE Model in Relation to FE Implementations.............6
2.3. The FE Model in Relation to the ForCES Protocol............6
2.4. Modeling Language for the FE Model.........................7
2.5. Document Structure.........................................8
3. FE Model Concepts...............................................8
3.1. FE Capability Model and State Model........................8
3.2. LFB (Logical Functional Block) Modeling...................11
3.2.1. LFB Outputs..........................................13
3.2.2. LFB Inputs...........................................16
3.2.3. Packet Type..........................................19
3.2.4. Metadata.............................................19
3.2.5. LFB Events...........................................26
3.2.6. LFB Element Properties...............................27
3.2.7. LFB Versioning.......................................27
3.2.8. LFB Inheritance......................................28
3.3. FE Datapath Modeling......................................29
3.3.1. Alternative Approaches for Modeling FE Datapaths.....29
3.3.2. Configuring the LFB Topology.........................33
4. Model and Schema for LFB Classes...............................37
4.1. Namespace.................................................37
4.2. <LFBLibrary> Element......................................37
4.3. <load> Element............................................39
4.4. <frameDefs> Element for Frame Type Declarations...........39
4.5. <dataTypeDefs> Element for Data Type Definitions..........40
4.5.1. <typeRef> Element for Aliasing Existing Data Types...43
4.5.2. <atomic> Element for Deriving New Atomic Types.......43
4.5.3. <array> Element to Define Arrays.....................44
4.5.4. <struct> Element to Define Structures................47
4.5.5. <union> Element to Define Union Types................48
4.5.6. Augmentations........................................49
4.6. <metadataDefs> Element for Metadata Definitions...........50
4.7. <LFBClassDefs> Element for LFB Class Definitions..........51
4.7.1. <derivedFrom> Element to Express LFB Inheritance.....52
4.7.2. <inputPorts> Element to Define LFB Inputs............53
4.7.3. <outputPorts> Element to Define LFB Outputs..........55
4.7.4. <attributes> Element to Define LFB Operational
Attributes..................................................57
4.7.5. <capabilities> Element to Define LFB Capability
Attributes..................................................59
4.7.6. <events> Element for LFB Notification Generation.....61
4.7.7. <description> Element for LFB Operational Specification
............................................................64
4.8. Properties................................................64
Yang, et al. Expires April 2007 [Page 2]
Internet Draft ForCES FE Model October 2006
4.8.1. Basic Properties.....................................64
4.8.2. Array Properties.....................................66
4.8.3. String Properties....................................66
4.8.4. Octetstring Properties...............................67
4.8.5. Event Properties.....................................67
4.8.6. Alias Properties.....................................70
4.9. XML Schema for LFB Class Library Documents................71
5. FE Attributes and Capabilities.................................82
5.1. XML for FEObject Class definition.........................82
5.2. FE Capabilities...........................................89
5.2.1. ModifiableLFBTopology................................89
5.2.2. SupportedLFBs and SupportedLFBType...................89
5.3. FEAttributes..............................................92
5.3.1. FEStatus.............................................92
5.3.2. LFBSelectors and LFBSelectorType.....................92
5.3.3. LFBTopology and LFBLinkType..........................92
5.3.4. FENeighbors and FEConfiguredNeighborType.............93
6. Satisfying the Requirements on FE Model........................93
7. Using the FE model in the ForCES Protocol......................94
7.1. FE Topology Query.........................................96
7.2. FE Capability Declarations................................97
7.3. LFB Topology and Topology Configurability Query...........98
7.4. LFB Capability Declarations...............................98
7.5. State Query of LFB Attributes.............................99
7.6. LFB Attribute Manipulation................................99
7.7. LFB Topology Re-configuration............................100
8. Example.......................................................100
8.1. Data Handling............................................107
8.1.1. Setting up a DLCI...................................108
8.1.2. Error Handling......................................108
8.2. LFB Attributes...........................................109
8.3. Capabilities.............................................109
8.4. Events...................................................109
9. IANA Considerations...........................................111
10. Authors Emeritus.............................................111
11. Acknowledgments..............................................111
12. Security Considerations......................................112
13. Normative References.........................................112
14. Informative References.......................................112
15. Authors' Addresses...........................................113
16. Intellectual Property Right..................................113
17. Copyright Statement..........................................113
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC-2119].
Yang, et al. Expires April 2007 [Page 3]
Internet Draft ForCES FE Model October 2006
1. Definitions
Terminology associated with the ForCES requirements is defined in
RFC 3564 [1] and is not copied here. The following list of
terminology relevant to the FE model is defined in this section.
FE Model -- The FE model is designed to model the logical processing
functions of an FE. The FE model proposed in this document includes
three components: the modeling of individual logical functional
blocks (LFB model), the logical interconnection between LFBs (LFB
topology) and the FE level attributes, including FE capabilities.
The FE model provides the basis to define the information elements
exchanged between the CE and the FE in the ForCES protocol.
Datapath -- A conceptual path taken by packets within the forwarding
plane inside an FE. Note that more than one datapath can exist
within an FE.
LFB (Logical Functional Block) Class (or type) -- A template that
representing a fine-grained, logically separable aspect of FE
processing. Most LFBs relate to packet processing in the data path.
LFB classes are the basic building blocks of the FE model.
LFB Instance -- As a packet flows through an FE along a datapath, it
flows through one or multiple LFB instances, where each LFB is an
instance of a specific LFB class. Multiple instances of the same
LFB class can be present in an FE's datapath. Note that we often
refer to LFBs without distinguishing between an LFB class and LFB
instance when we believe the implied reference is obvious for the
given context.
LFB Model -- The LFB model describes the content and structures in
an LFB, plus the associated data definition. Four types of
information are defined in the LFB model. The core part of the LFB
model is the LFB class definitions; the other three types define the
associated data including common data types, supported frame formats
and metadata.
LFB Metadata -- Metadata is used to communicate per-packet state
from one LFB to another, but is not sent across the network. The FE
model defines how such metadata is identified, produced and consumed
by the LFBs, but not how the per-packet state is implemented within
actual hardware. Metadata is sent between the FE and the CE on
redirect packets.
LFB Attribute -- Operational parameters of the LFBs that must be
visible to the CEs are conceptualized in the FE model as the LFB
attributes. The LFB attributes include: flags, single parameter
Yang, et al. Expires April 2007 [Page 4]
Internet Draft ForCES FE Model October 2006
arguments, complex arguments, and tables that the CE can read or/and
write via the ForCES protocol.
LFB Topology -- A representation of the logical interconnection and
the placement of LFB instances along the datapath within one FE.
Sometimes this representation is called intra-FE topology, to be
distinguished from inter-FE topology. LFB topology is outside of
the LFB model, but is part of the FE model.
FE Topology -- A representation of how multiple FEs within a single
NE are interconnected. Sometimes this is called inter-FE topology,
to be distinguished from intra-FE topology (i.e., LFB topology). An
individual FE might not have the global knowledge of the full FE
topology, but the local view of its connectivity with other FEs is
considered to be part of the FE model. The FE topology is
discovered by the ForCES base protocol or by some other means.
Inter-FE Topology -- See FE Topology.
Intra-FE Topology -- See LFB Topology.
LFB class library -- A set of LFB classes that has been identified
as the most common functions found in most FEs and hence should be
defined first by the ForCES Working Group.
2. Introduction
RFC 3746 [2] specifies a framework by which control elements (CEs)
can configure and manage one or more separate forwarding elements
(FEs) within a networking element (NE) using the ForCES protocol.
The ForCES architecture allows Forwarding Elements of varying
functionality to participate in a ForCES network element. The
implication of this varying functionality is that CEs can make only
minimal assumptions about the functionality provided by FEs in an
NE. Before CEs can configure and control the forwarding behavior of
FEs, CEs need to query and discover the capabilities and states of
their FEs. RFC 3654 [1] mandates that the capabilities, states and
configuration information be expressed in the form of an FE model.
RFC 3444 [11] observed that information models (IMs) and data models
(DMs) are different because they serve different purposes. "The
main purpose of an IM is to model managed objects at a conceptual
level, independent of any specific implementations or protocols
used". "DMs, conversely, are defined at a lower level of
abstraction and include many details. They are intended for
implementors and include protocol-specific constructs." Sometimes
it is difficult to draw a clear line between the two. The FE model
described in this document is primarily an information model, but
also includes some aspects of a data model, such as explicit
Yang, et al. Expires April 2007 [Page 5]
Internet Draft ForCES FE Model October 2006
definitions of the LFB class schema and FE schema. It is expected
that this FE model will be used as the basis to define the payload
for information exchange between the CE and FE in the ForCES
protocol.
2.1. Requirements on the FE model
RFC 3654 [1] defines requirements that must be satisfied by a ForCES
FE model. To summarize, an FE model must define:
. Logically separable and distinct packet forwarding operations
in an FE datapath (logical functional blocks or LFBs);
. The possible topological relationships (and hence the sequence
of packet forwarding operations) between the various LFBs;
. The possible operational capabilities (e.g., capacity limits,
constraints, optional features, granularity of configuration)
of each type of LFB;
. The possible configurable parameters (i.e., attributes) of each
type of LFB;
. Metadata that may be exchanged between LFBs.
2.2. The FE Model in Relation to FE Implementations
The FE model proposed here is based on an abstraction of distinct
logical functional blocks (LFBs), which are interconnected in a
directed graph, and receive, process, modify, and transmit packets
along with metadata. The FE model should be designed such that
different implementations of the forwarding datapath can be
logically mapped onto the model with the functionality and sequence
of operations correctly captured. However, the model is not
intended to directly address how a particular implementation maps to
an LFB topology. It is left to the forwarding plane vendors to
define how the FE functionality is represented using the FE model.
Our goal is to design the FE model such that it is flexible enough
to accommodate most common implementations.
The LFB topology model for a particular datapath implementation must
correctly capture the sequence of operations on the packet.
Metadata generation by certain LFBs MUST always precede any use of
that metadata by subsequent LFBs in the topology graph; this is
required for logically consistent operation. Further, modification
of packet fields that are subsequently used as inputs for further
processing MUST occur in the order specified in the model for that
particular implementation to ensure correctness.
2.3. The FE Model in Relation to the ForCES Protocol
The ForCES base protocol is used by the CEs and FEs to maintain the
communication channel between the CEs and FEs. The ForCES protocol
may be used to query and discover the inter-FE topology. The
Yang, et al. Expires April 2007 [Page 6]
Internet Draft ForCES FE Model October 2006
details of a particular datapath implementation inside an FE,
including the LFB topology, along with the operational capabilities
and attributes of each individual LFB, are conveyed to the CE within
information elements in the ForCES protocol. The model of an LFB
class should define all of the information that needs to be
exchanged between an FE and a CE for the proper configuration and
management of that LFB.
Specifying the various payloads of the ForCES messages in a
systematic fashion is difficult without a formal definition of the
objects being configured and managed (the FE and the LFBs within).
The FE Model document defines a set of classes and attributes for
describing and manipulating the state of the LFBs within an FE.
These class definitions themselves will generally not appear in the
ForCES protocol. Rather, ForCES protocol operations will reference
classes defined in this model, including relevant attributes and the
defined operations.
Section 7 provides more detailed discussion on how the FE model
should be used by the ForCES protocol.
2.4. Modeling Language for the FE Model
Even though not absolutely required, it is beneficial to use a
formal data modeling language to represent the conceptual FE model
described in this document. Use of a formal language can help to
enforce consistency and logical compatibility among LFBs. A full
specification will be written using such a data modeling language.
The formal definition of the LFB classes may facilitate the eventual
automation of some of the code generation process and the functional
validation of arbitrary LFB topologies. These class definitions
form the LFB Library. Documents which describe LFB Classes are
therefore referred to as LFB Library documents.
Human readability was the most important factor considered when
selecting the specification language, whereas encoding, decoding and
transmission performance was not a selection factor. The encoding
method for over the wire transport is not dependent on the
specification language chosen and is outside the scope of this
document and up to the ForCES protocol to define.
XML was chosen as the specification language in this document,
because XML has the advantage of being both human and machine
readable with widely available tools support. This document uses XML
Schema to define the structure of the LFB Library documents, as
defined in [12] and [13]. While these LFB Class definitions are not
sent in the Forces protocol, these definitions comply with the
recommendations in RFC 3470 [11] on the use of XML in IETF
protocols.
Yang, et al. Expires April 2007 [Page 7]
Internet Draft ForCES FE Model October 2006
2.5. Document Structure
Section 3 provides a conceptual overview of the FE model, laying the
foundation for the more detailed discussion and specifications in
the sections that follow. Section 4 and 5 constitute the core of
the FE model, detailing the two major components in the FE model:
LFB model and FE level attributes including capability and LFB
topology. Section 6 directly addresses the model requirements
imposed by the ForCES requirement draft [1] while Section 7 explains
how the FE model should be used in the ForCES protocol.
3. FE Model Concepts
Some of the important concepts used throughout this document are
introduced in this section. Section 3.1 explains the difference
between a state model and a capability model, and describes how the
two can be combined in the FE model. Section 3.2 introduces the
concept of LFBs (Logical Functional Blocks) as the basic functional
building blocks in the FE model. Section 3.3 discusses the logical
inter-connection and ordering between LFB instances within an FE,
that is, the LFB topology.
The FE model proposed in this document is comprised of two major
components: the LFB model and FE level attributes, including FE
capabilities and LFB topology. The LFB model provides the content
and data structures to define each individual LFB class. FE
attributes provide information at the FE level, particularly the
capabilities of the FE at a coarse level. Part of the FE level
information is the LFB topology, which expresses the logical inter-
connection between the LFB instances along the datapath(s) within
the FE. Details of these components are described in Section 4 and
5. The intent of this section is to discuss these concepts at the
high level and lay the foundation for the detailed description in
the following sections.
3.1. FE Capability Model and State Model
The ForCES FE model includes both a capability and a state model.
The FE capability model describes the capabilities and capacities of
an FE by specifying the variation in functions supported and any
limitations. The FE state model describes the current state of the
FE, that is, the instantaneous values or operational behavior of the
FE.
Conceptually, the FE capability model tells the CE which states are
allowed on an FE, with capacity information indicating certain
quantitative limits or constraints. Thus, the CE has general
knowledge about configurations that are applicable to a particular
Yang, et al. Expires April 2007 [Page 8]
Internet Draft ForCES FE Model October 2006
FE. For example, an FE capability model may describe the FE at a
coarse level such as:
. this FE can handle IPv4 and IPv6 forwarding;
. this FE can perform classification on the following fields:
source IP address, destination IP address, source port number,
destination port number, etc;
. this FE can perform metering;
. this FE can handle up to N queues (capacity);
. this FE can add and remove encapsulating headers of types
including IPSec, GRE, L2TP.
While one could try and build an object model to fully represent the
FE capabilities, other efforts found this to be a significant
undertaking. The main difficulty arises in describing detailed
limits, such as the maximum number of classifiers, queues, buffer
pools, and meters the FE can provide. We believe that a good
balance between simplicity and flexibility can be achieved for the
FE model by combining coarse level capability reporting with an
error reporting mechanism. That is, if the CE attempts to instruct
the FE to set up some specific behavior it cannot support, the FE
will return an error indicating the problem. Examples of similar
approaches include DiffServ PIB [4] and Framework PIB [5].
There is one common and shared aspect of capability that will be
handled in a separate fashion. For all elements of information,
certain property information is needed. All elements need
information as to whether they are supported and if so whether the
element is readable or writeable. Based on their type, many
elements have additional common properties (for example, arrays have
their current size.) There is a specific model and protocol
mechanism for referencing this form of property information about
elements of the model.
The FE state model presents the snapshot view of the FE to the CE.
For example, using an FE state model, an FE may be described to its
corresponding CE as the following:
. on a given port, the packets are classified using a given
classification filter;
. the given classifier results in packets being metered in a
certain way, and then marked in a certain way;
. the packets coming from specific markers are delivered into a
shared queue for handling, while other packets are delivered to
a different queue;
. a specific scheduler with specific behavior and parameters will
service these collected queues.
Yang, et al. Expires April 2007 [Page 9]
Internet Draft ForCES FE Model October 2006
Figure 1 shows the concepts of FE state, capabilities and
configuration in the context of CE-FE communication via the ForCES
protocol.
+-------+ +-------+
| | FE capabilities: what it can/cannot do. | |
| |<-----------------------------------------| |
| | | |
| CE | FE state: what it is now. | FE |
| |<-----------------------------------------| |
| | | |
| | FE configuration: what it should be. | |
| |----------------------------------------->| |
+-------+ +-------+
Figure 1. Illustration of FE state, capabilities and configuration
exchange in the context of CE-FE communication via ForCES.
The concepts relating to LFBs, particularly capability at the LFB
level and LFB topology will be discussed in the rest of this
section.
Capability information at the LFB level is an integral part of the
LFB model, and is modeled the same way as the other operational
parameters inside an LFB. For example, when certain features of an
LFB class are optional, the CE MUST be able to determine whether
those optional features are supported by a given LFB instance. Such
capability information can be modeled as a read-only attribute in
the LFB instance, see Section 4.7.5 for details.
Capability information at the FE level may describe the LFB classes
that the FE can instantiate; the number of instances of each that
can be created; the topological (linkage) limitations between these
LFB instances, etc. Section 5 defines the FE level attributes
including capability information.
Once the FE capability is described to the CE, the FE state
information can be represented by two levels. The first level is
the logically separable and distinct packet processing functions,
called Logical Functional Blocks (LFBs). The second level of
information describes how these individual LFBs are ordered and
placed along the datapath to deliver a complete forwarding plane
service. The interconnection and ordering of the LFBs is called LFB
Topology. Section 3.2 discusses high level concepts around LFBs,
whereas Section 3.3 discusses LFB topology issues.
Yang, et al. Expires April 2007 [Page 10]
Internet Draft ForCES FE Model October 2006
3.2. LFB (Logical Functional Block) Modeling
Each LFB performs a well-defined action or computation on the
packets passing through it. Upon completion of its prescribed
function, either the packets are modified in certain ways (e.g.,
decapsulator, marker), or some results are generated and stored,
often in the form of metadata (e.g., classifier). Each LFB
typically performs a single action. Classifiers, shapers and meters
are all examples of such LFBs. Modeling LFBs at such a fine
granularity allows us to use a small number of LFBs to express the
higher-order FE functions (such as an IPv4 forwarder) precisely,
which in turn can describe more complex networking functions and
vendor implementations of software and hardware. These LFBs will be
defined in detail in one or more documents.
An LFB has one or more inputs, each of which takes a packet P, and
optionally metadata M; and produces one or more outputs, each of
which carries a packet P', and optionally metadata M'. Metadata is
data associated with the packet in the network processing device
(router, switch, etc.) and is passed from one LFB to the next, but
is not sent across the network. In general, multiple LFBs are
contained in one FE, as shown in Figure 2, and all the LFBs share
the same ForCES protocol termination point that implements the
ForCES protocol logic and maintains the communication channel to and
from the CE.
Yang, et al. Expires April 2007 [Page 11]
Internet Draft ForCES FE Model October 2006
+-----------+
| CE |
+-----------+
^
| Fp reference point
|
+--------------------------|-----------------------------------+
| FE | |
| v |
| +----------------------------------------------------------+ |
| | ForCES protocol | |
| | termination point | |
| +----------------------------------------------------------+ |
| ^ ^ |
| : : Internal control |
| : : |
| +---:----------+ +---:----------| |
| | :LFB1 | | : LFB2 | |
| =====>| v |============>| v |======>...|
| Inputs| +----------+ |Outputs | +----------+ | |
| (P,M) | |Attributes| |(P',M') | |Attributes| |(P",M") |
| | +----------+ | | +----------+ | |
| +--------------+ +--------------+ |
| |
+--------------------------------------------------------------+
Figure 2. Generic LFB Diagram
An LFB, as shown in Figure 2, has inputs, outputs and attributes
that can be queried and manipulated by the CE indirectly via an Fp
reference point (defined in RFC 3746 [2]) and the ForCES protocol
termination point. The horizontal axis is in the forwarding plane
for connecting the inputs and outputs of LFBs within the same FE.
The vertical axis between the CE and the FE denotes the Fp reference
point where bidirectional communication between the CE and FE
occurs: the CE to FE communication is for configuration, control and
packet injection while FE to CE communication is used for packet re-
direction to the control plane, monitoring and accounting
information, errors, etc. Note that the interaction between the CE
and the LFB is only abstract and indirect. The result of such an
interaction is for the CE to indirectly manipulate the attributes of
the LFB instances.
A namespace is used to associate a unique name or ID with each LFB
class. The namespace MUST be extensible so that a new LFB class can
be added later to accommodate future innovation in the forwarding
plane.
Yang, et al. Expires April 2007 [Page 12]
Internet Draft ForCES FE Model October 2006
LFB operation is specified in the model to allow the CE to
understand the behavior of the forwarding datapath. For instance,
the CE must understand at what point in the datapath the IPv4 header
TTL is decremented. That is, the CE needs to know if a control
packet could be delivered to it either before or after this point in
the datapath. In addition, the CE MUST understand where and what
type of header modifications (e.g., tunnel header append or strip)
are performed by the FEs. Further, the CE MUST verify that the
various LFBs along a datapath within an FE are compatible to link
together.
There is value to vendors if the operation of LFB classes can be
expressed in sufficient detail so that physical devices implementing
different LFB functions can be integrated easily into an FE design.
Therefore, a semi-formal specification is needed; that is, a text
description of the LFB operation (human readable), but sufficiently
specific and unambiguous to allow conformance testing and efficient
design, so that interoperability between different CEs and FEs can
be achieved.
The LFB class model specifies information such as:
. number of inputs and outputs (and whether they are
configurable)
. metadata read/consumed from inputs;
. metadata produced at the outputs;
. packet type(s) accepted at the inputs and emitted at the
outputs;
. packet content modifications (including encapsulation or
decapsulation);
. packet routing criteria (when multiple outputs on an LFB are
present);
. packet timing modifications;
. packet flow ordering modifications;
. LFB capability information;
. Events that can be detected by the LFB, with notification to
the CE;
. LFB operational attributes, etc.
Section 4 of this document provides a detailed discussion of the LFB
model with a formal specification of LFB class schema. The rest of
Section 3.2 only intends to provide a conceptual overview of some
important issues in LFB modeling, without covering all the specific
details.
3.2.1. LFB Outputs
An LFB output is a conceptual port on an LFB that can send
information to another LFB. The information is typically a packet
Yang, et al. Expires April 2007 [Page 13]
Internet Draft ForCES FE Model October 2006
and its associated metadata, although in some cases it might consist
of only metadata, i.e., with no packet data.
A single LFB output can be connected to only one LFB input. This is
required to make the packet flow through the LFB topology
unambiguously.
Some LFBs will have a single output, as depicted in Figure 3.a.
+---------------+ +-----------------+
| | | |
| | | OUT +-->
... OUT +--> ... |
| | | EXCEPTIONOUT +-->
| | | |
+---------------+ +-----------------+
a. One output b. Two distinct outputs
+---------------+ +-----------------+
| | | EXCEPTIONOUT +-->
| OUT:1 +--> | |
... OUT:2 +--> ... OUT:1 +-->
| ... +... | OUT:2 +-->
| OUT:n +--> | ... +...
+---------------+ | OUT:n +-->
+-----------------+
c. One output group d. One output and one output group
Figure 3. Examples of LFBs with various output combinations.
To accommodate a non-trivial LFB topology, multiple LFB outputs are
needed so that an LFB class can fork the datapath. Two mechanisms
are provided for forking: multiple singleton outputs and output
groups, which can be combined in the same LFB class.
Multiple separate singleton outputs are defined in an LFB class to
model a pre-determined number of semantically different outputs.
That is, the LFB class definition MUST include the number of
outputs, implying the number of outputs is known when the LFB class
is defined. Additional singleton outputs cannot be created at LFB
instantiation time, nor can they be created on the fly after the LFB
is instantiated.
For example, an IPv4 LPM (Longest-Prefix-Matching) LFB may have one
output(OUT) to send those packets for which the LPM look-up was
successful, passing a META_ROUTEID as metadata; and have another
output (EXCEPTIONOUT) for sending exception packets when the LPM
Yang, et al. Expires April 2007 [Page 14]
Internet Draft ForCES FE Model October 2006
look-up failed. This example is depicted in Figure 3.b. Packets
emitted by these two outputs not only require different downstream
treatment, but they are a result of two different conditions in the
LFB and each output carries different metadata. This concept
assumes the number of distinct outputs is known when the LFB class
is defined. For each singleton output, the LFB class definition
defines the types of frames and metadata the output emits.
An output group, on the other hand, is used to model the case where
a flow of similar packets with an identical set of metadata needs to
be split into multiple paths. In this case, the number of such paths
is not known when the LFB class is defined because it is not an
inherent property of the LFB class. An output group consists of a
number of outputs, called the output instances of the group, where
all output instances share the same frame and metadata emission
definitions (see Figure 3.c). Each output instance can connect to a
different downstream LFB, just as if they were separate singleton
outputs, but the number of output instances can differ between LFB
instances of the same LFB class. The class definition may include a
lower and/or an upper limit on the number of outputs. In addition,
for configurable FEs, the FE capability information may define
further limits on the number of instances in specific output groups
for certain LFBs. The actual number of output instances in a group
is an attribute of the LFB instance, which is read-only for static
topologies, and read-write for dynamic topologies. The output
instances in a group are numbered sequentially, from 0 to N-1, and
are addressable from within the LFB. The LFB has a built-in
mechanism to select one specific output instance for each packet.
This mechanism is described in the textual definition of the class
and is typically configurable via some attributes of the LFB.
For example, consider a re-director LFB, whose sole purpose is to
direct packets to one of N downstream paths based on one of the
metadata associated with each arriving packet. Such an LFB is
fairly versatile and can be used in many different places in a
topology. For example, a redirector can be used to divide the data
path into an IPv4 and an IPv6 path based on a FRAMETYPE metadata
(N=2), or to fork into color specific paths after metering using the
COLOR metadata (red, yellow, green; N=3), etc.
Using an output group in the above LFB class provides the desired
flexibility to adapt each instance of this class to the required
operation. The metadata to be used as a selector for the output
instance is a property of the LFB. For each packet, the value of
the specified metadata may be used as a direct index to the output
instance. Alternatively, the LFB may have a configurable selector
table that maps a metadata value to output instance.
Yang, et al. Expires April 2007 [Page 15]
Internet Draft ForCES FE Model October 2006
Note that other LFBs may also use the output group concept to build
in similar adaptive forking capability. For example, a classifier
LFB with one input and N outputs can be defined easily by using the
output group concept. Alternatively, a classifier LFB with one
singleton output in combination with an explicit N-output re-
director LFB models the same processing behavior. The decision of
whether to use the output group model for a certain LFB class is
left to the LFB class designers.
The model allows the output group to be combined with other
singleton output(s) in the same class, as demonstrated in Figure
3.d. The LFB here has two types of outputs, OUT, for normal packet
output, and EXCEPTIONOUT for packets that triggered some exception.
The normal OUT has multiple instances, thus, it is an output group.
In summary, the LFB class may define one output, multiple singleton
outputs, one or more output groups, or a combination thereof.
Multiple singleton outputs should be used when the LFB must provide
for forking the datapath, and at least one of the following
conditions hold:
. the number of downstream directions are inherent from the
definition of the class and hence fixed;
. the frame type and set of metadata emitted on any of the
outputs are substantially different from what is emitted on
the other outputs (i.e., they cannot share frame-type and
metadata definitions);
An output group is appropriate when the LFB must provide for forking
the datapath, and at least one of the following conditions hold:
. the number of downstream directions is not known when the LFB
class is defined;
. the frame type and set of metadata emitted on these outputs are
sufficiently similar or ideally identical, such they can share
the same output definition.
3.2.2. LFB Inputs
An LFB input is a conceptual port on an LFB where the LFB can
receive information from other LFBs. The information is typically a
packet and associated metadata, although in some cases it might
consist of only metadata, without any packet data.
For LFB instances that receive packets from more than one other LFB
instance (fan-in). There are three ways to model fan-in, all
supported by the LFB model and can be combined in the same LFB:
. Implicit multiplexing via a single input
Yang, et al. Expires April 2007 [Page 16]
Internet Draft ForCES FE Model October 2006
. Explicit multiplexing via multiple singleton inputs
. Explicit multiplexing via a group of inputs (input group)
The simplest form of multiplexing uses a singleton input (Figure
4.a). Most LFBs will have only one singleton input. Multiplexing
into a single input is possible because the model allows more than
one LFB output to connect to the same LFB input. This property
applies to any LFB input without any special provisions in the LFB
class. Multiplexing into a single input is applicable when the
packets from the upstream LFBs are similar in frame-type and
accompanying metadata, and require similar processing. Note that
this model does not address how potential contention is handled when
multiple packets arrive simultaneously. If contention handling
needs to be explicitly modeled, one of the other two modeling
solutions must be used.
The second method to model fan-in uses individually defined
singleton inputs (Figure 4.b). This model is meant for situations
where the LFB needs to handle distinct types of packet streams,
requiring input-specific handling inside the LFB, and where the
number of such distinct cases is known when the LFB class is
defined. For example, a Layer 2 Decapsulation/Encapsulation LFB may
have two inputs, one for receiving Layer 2 frames for decapsulation,
and one for receiving Layer 3 frames for encapsulation. This LFB
type expects different frames (L2 vs. L3) at its inputs, each with
different sets of metadata, and would thus apply different
processing on frames arriving at these inputs. This model is
capable of explicitly addressing packet contention by defining how
the LFB class handles the contending packets.
+--------------+ +------------------------+
| LFB X +---+ | |
+--------------+ | | |
| | |
+--------------+ v | |
| LFB Y +---+-->|input Meter LFB |
+--------------+ ^ | |
| | |
+--------------+ | | |
| LFB Z |---+ | |
+--------------+ +------------------------+
(a) An LFB connects with multiple upstream LFBs via a single input.
Yang, et al. Expires April 2007 [Page 17]
Internet Draft ForCES FE Model October 2006
+--------------+ +------------------------+
| LFB X +---+ | |
+--------------+ +-->|layer2 |
+--------------+ | |
| LFB Y +------>|layer3 LFB |
+--------------+ +------------------------+
(b) An LFB connects with multiple upstream LFBs via two separate
singleton inputs.
+--------------+ +------------------------+
| Queue LFB #1 +---+ | |
+--------------+ | | |
| | |
+--------------+ +-->|in:0 \ |
| Queue LFB #2 +------>|in:1 | input group |
+--------------+ |... | |
+-->|in:N-1 / |
... | | |
+--------------+ | | |
| Queue LFB #N |---+ | Scheduler LFB |
+--------------+ +------------------------+
(c) A Scheduler LFB uses an input group to differentiate which queue
LFB packets are coming from.
Figure 3. Input modeling concepts (examples).
The third method to model fan-in uses the concept of an input group.
The concept is similar to the output group introduced in the
previous section, and is depicted in Figure 4.c. An input group
consists of a number of input instances, all sharing the properties
(same frame and metadata expectations). The input instances are
numbered from 0 to N-1. From the outside, these inputs appear as
normal inputs, i.e., any compatible upstream LFB can connect its
output to one of these inputs. When a packet is presented to the
LFB at a particular input instance, the index of the input where the
packet arrived is known to the LFB and this information may be used
in the internal processing. For example, the input index can be
used as a table selector, or as an explicit precedence selector to
resolve contention. As with output groups, the number of input
instances in an input group is not defined in the LFB class.
However, the class definition may include restrictions on the range
of possible values. In addition, if an FE supports configurable
topologies, it may impose further limitations on the number of
instances for a particular port group(s) of a particular LFB class.
Within these limitations, different instances of the same class may
have a different number of input instances. The number of actual
input instances in the group is an attribute of the LFB class, which
Yang, et al. Expires April 2007 [Page 18]
Internet Draft ForCES FE Model October 2006
is read-only for static topologies, and is read-write for
configurable topologies.
As an example for the input group, consider the Scheduler LFB
depicted in Figure 3.c. Such an LFB receives packets from a number
of Queue LFBs via a number of input instances, and uses the input
index information to control contention resolution and scheduling.
In summary, the LFB class may define one input, multiple singleton
inputs, one or more input groups, or a combination thereof. Any
input allows for implicit multiplexing of similar packet streams via
connecting multiple outputs to the same input. Explicit multiple
singleton inputs are useful when either the contention handling must
be handled explicitly, or when the LFB class must receive and
process a known number of distinct types of packet streams. An
input group is suitable when contention handling must be modeled
explicitly, but the number of inputs are not inherent from the class
(and hence is not known when the class is defined), or when it is
critical for LFB operation to know exactly on which input the packet
was received.
3.2.3. Packet Type
When LFB classes are defined, the input and output packet formats
(e.g., IPv4, IPv6, Ethernet, etc.) MUST be specified. These are the
types of packets a given LFB input is capable of receiving and
processing, or a given LFB output is capable of producing. This
requires distinct packet types be uniquely labeled with a symbolic
name and/or ID.
Note that each LFB has a set of packet types that it operates on,
but does not care whether the underlying implementation is passing a
greater portion of the packets. For example, an IPv4 LFB might only
operate on IPv4 packets, but the underlying implementation may or
may not be stripping the L2 header before handing it over -- whether
that is happening or not is opaque to the CE.
3.2.4. Metadata
Metadata is the per-packet state that is passed from one LFB to
another. The metadata is passed with the packet to assist subsequent
LFBs to process that packet. The ForCES model captures how the per-
packet state information is propagated from one LFB to other LFBs.
Practically, such metadata propagation can happen within one FE, or
cross the FE boundary between two interconnected FEs. We believe
that the same metadata model can be used for either situation;
however, our focus here is for intra-FE metadata.
Yang, et al. Expires April 2007 [Page 19]
Internet Draft ForCES FE Model October 2006
3.2.4.1. Metadata Vocabulary
Metadata has historically been understood to mean "data about data".
While this definition is a start, it is inadequate to describe the
multiple forms of metadata, which may appear within a complex
network element. The discussion here categorizes forms of metadata
by two orthogonal axes.
The first axis is "internal" versus "external", which describes
where the metadata exists in the network model or implementation.
For example, a particular vendor implementation of an IPv4 forwarder
may make decisions inside of a chip that are not visible externally.
Those decisions are metadata for the packet that is "internal" to
the chip. When a packet is forwarded out of the chip, it may be
marked with a traffic management header. That header, which is
metadata for the packet, is visible outside of the chip, and is
therefore called "external" metadata.
The second axis is "implicit" versus "expressed", which specifies
whether or not the metadata has a visible physical representation.
For example, the traffic management header described in the previous
paragraph may be represented as a series of bits in some format, and
that header is associated with the packet. Those bits have physical
representation, and are therefore "expressed" metadata. If the
metadata does not have a physical representation, it is called
"implicit" metadata. This situation occurs, for example, when a
particular path through a network device is intended to be traversed
only by particular kinds of packets, such as an IPv4 router. An
implementation may not mark every packet along this path as being of
type "IPv4", but the intention of the designers is that every packet
is of that type. This understanding can be thought of as metadata
about the packet, which is implicitly attached to the packet through
the intent of the designers.
In the ForCES model, we do not discuss or represent metadata
"internal" to vendor implementations of LFBs. Our focus is solely
on metadata "external" to the LFBs, and therefore visible in the
ForCES model. The metadata discussed within this model may, or may
not be visible outside of the particular FE implementing the LFB
model. In this regard, the scope of the metadata within ForCES is
very narrowly defined.
Note also that while we define metadata within this model, it is
only a model. There is no requirement that vendor implementations
of ForCES use the exact metadata representations described in this
document. The only implementation requirement is that vendors
implement the ForCES protocol, not the model.
Yang, et al. Expires April 2007 [Page 20]
Internet Draft ForCES FE Model October 2006
3.2.4.2. Metadata lifecycle within the ForCES model
Each metadata can be conveniently modeled as a <label, value> pair,
where the label identifies the type of information, (e.g., "color"),
and its value holds the actual information (e.g., "red"). The tag
here is shown as a textual label, but it can be replaced or
associated with a unique numeric value (identifier).
The metadata life-cycle is defined in this model using three types
of events: "write", "read" and "consume". The first "write"
implicitly creates and initializes the value of the metadata, and
hence starts the life-cycle. The explicit "consume" event
terminates the life-cycle. Within the life-cycle, that is, after a
"write" event, but before the next "consume" event, there can be an
arbitrary number of "write" and "read" events. These "read" and
"write" events can be mixed in an arbitrary order within the life-
cycle. Outside of the life-cycle of the metadata, that is, before
the first "write" event, or between a "consume" event and the next
"write" event, the metadata should be regarded non-existent or non-
initialized. Thus, reading a metadata outside of its life-cycle is
considered an error.
To ensure inter-operability between LFBs, the LFB class
specification must define what metadata the LFB class "reads" or
"consumes" on its input(s) and what metadata it "produces" on its
output(s). For maximum extensibility, this definition should
neither specify which LFBs the metadata is expected to come from for
a consumer LFB, nor which LFBs are expected to consume metadata for
a given producer LFB.
While it is important to define the metadata types passing between
LFBs, it is not appropriate to define the exact encoding mechanism
used by LFBs for that metadata. Different implementations are
allowed to use different encoding mechanisms for metadata. For
example, one implementation may store metadata in registers or
shared memory, while another implementation may encode metadata in-
band as a preamble in the packets. In order to allow the CE to
understand and control the meta-data related operations, the model
represents each metadata tag as a 32-bit integer. Each LFB
definition indicates in its metadata declarations the 32-bit value
associated with a given metadata tag. Ensuring consistency of usage
of tags is important, and outside the scope of the model.
At any link between two LFBs, the packet is marked with a finite set
of active metadata, where active means the metadata is within its
life-cycle. There are two corollaries of this model:
1. No un-initialized metadata exists in the model.
Yang, et al. Expires April 2007 [Page 21]
Internet Draft ForCES FE Model October 2006
2. No more than one occurrence of each metadata tag can be
associated with a packet at any given time.
3.2.4.3. LFB Operations on Metadata
When the packet is processed by an LFB (i.e., between the time it is
received and forwarded by the LFB), the LFB may perform read, write
and/or consume operations on any active metadata associated with the
packet. If the LFB is considered to be a black box, one of the
following operations is performed on each active metadata.
. IGNORE: ignores and forwards the metadata
. READ: reads and forwards the metadata
. READ/RE-WRITE: reads, over-writes and forwards the metadata
. WRITE: writes and forwards the metadata
(can also be used to create new metadata)
. READ-AND-CONSUME: reads and consumes the metadata
. CONSUME consumes metadata without reading
The last two operations terminate the life-cycle of the metadata,
meaning that the metadata is not forwarded with the packet when the
packet is sent to the next LFB.
In our model, a new metadata is generated by an LFB when the LFB
applies a WRITE operation to a metadata type that was not present
when the packet was received by the LFB. Such implicit creation may
be unintentional by the LFB, that is, the LFB may apply the WRITE
operation without knowing or caring if the given metadata existed or
not. If it existed, the metadata gets over-written; if it did not
exist, the metadata is created.
For LFBs that insert packets into the model, WRITE is the only
meaningful metadata operation.
For LFBs that remove the packet from the model, they may either
READ-AND-CONSUME (read) or CONSUME (ignore) each active metadata
associated with the packet.
3.2.4.4. Metadata Production and Consumption
For a given metadata on a given packet path, there MUST be at least
one producer LFB that creates that metadata and SHOULD be at least
one consumer LFB that needs that metadata. In this model, the
producer and consumer LFBs of a metadata are not required to be
adjacent. In addition, there may be multiple producers and
consumers for the same metadata. When a packet path involves
multiple producers of the same metadata, then subsequent producers
overwrite that metadata value.
Yang, et al. Expires April 2007 [Page 22]
Internet Draft ForCES FE Model October 2006
The metadata that is produced by an LFB is specified by the LFB
class definition on a per output port group basis. A producer may
always generate the metadata on the port group, or may generate it
only under certain conditions. We call the former an
"unconditional" metadata, whereas the latter is a "conditional"
metadata. In the case of conditional metadata, it should be
possible to determine from the definition of the LFB when a
"conditional" metadata is produced.
The consumer behavior of an LFB, that is, the metadata that the LFB
needs for its operation, is defined in the LFB class definition on a
per input port group basis. An input port group may "require" a
given metadata, or may treat it as "optional" information. In the
latter case, the LFB class definition MUST explicitly define what
happens if an optional metadata is not provided. One approach is to
specify a default value for each optional metadata, and assume that
the default value is used if the metadata is not provided with the
packet.
When a consumer LFB requires a given metadata, it has dependencies
on its up-stream LFBs. That is, the consumer LFB can only function
if there is at least one producer of that metadata and no
intermediate LFB consumes the metadata.
The model should expose these inter-dependencies. Furthermore, it
should be possible to take inter-dependencies into consideration
when constructing LFB topologies, and also that the dependencies can
be verified when validating topologies.
For extensibility reasons, the LFB specification SHOULD define what
metadata the LFB requires without specifying which LFB(s) it expects
a certain metadata to come from. Similarly, LFBs SHOULD specify
what metadata they produce without specifying which LFBs the
metadata is meant for.
When specifying the metadata tags, some harmonization effort must be
made so that the producer LFB class uses the same tag as its
intended consumer(s), or vice versa.
3.2.4.5. Fixed, Variable and Configurable Tag
When the produced metadata is defined for a given LFB class, most
metadata will be specified with a fixed tag. For example, a Rate
Meter LFB will always produce the "Color" metadata.
A small subset of LFBs need the capability to produce one or more of
their metadata with tags that are not fixed in the LFB class
definition, but instead can be selected per LFB instance. An
example of such an LFB class is a Generic Classifier LFB. We call
this capability "variable tag metadata production". If an LFB
Yang, et al. Expires April 2007 [Page 23]
Internet Draft ForCES FE Model October 2006
produces metadata with a variable tag, the corresponding LFB
attribute, called the tag selector, specifies the tag for each such
metadata. This mechanism improves the versatility of certain multi-
purpose LFB classes, since it allows the same LFB class to be used
in different topologies, producing the right metadata tags according
to the needs of the topology. This selection of tags is variable in
that the produced output may have any number of different tags. The
meaning of the various tags is still defined by the metadata
declaration associated with the LFB class definition. This also
allows the CE to correctly set the tag values in the table to match
the declared meanings of the metadata tag values.
Depending on the capability of the FE, the tag selector can be
either a read-only or a read-write attribute. If the selector is
read-only, the tag cannot be modified by the CE. If the selector is
read-write, the tag can be configured by the CE, hence we call this
"configurable tag metadata production." Note that using this
definition, configurable tag metadata production is a subset of
variable tag metadata production.
Similar concepts can be introduced for the consumer LFBs to satisfy
different metadata needs. Most LFB classes will specify their
metadata needs using fixed metadata tags. For example, a Next Hop
LFB may always require a "NextHopId" metadata; but the Redirector
LFB may need a "ClassID" metadata in one instance, and a
"ProtocolType" metadata in another instance as a basis for selecting
the right output port. In this case, an LFB attribute is used to
provide the required metadata tag at run-time. This metadata tag
selector attribute may be read-only or read-write, depending on the
capabilities of the LFB instance and the FE.
3.2.4.6. Metadata Usage Categories
Depending on the role and usage of a metadata, various amounts of
encoding information MUST be provided when the metadata is defined,
where some cases offer less flexibility in the value selection than
others.
There are three types of metadata related to metadata usage:
. Relational (or binding) metadata
. Enumerated metadata
. Explicit/external value metadata
The purpose of the relational metadata is to refer in one LFB
instance (producer LFB) to a "thing" in another downstream LFB
instance (consumer LFB), where the "thing" is typically an entry in
a table attribute of the consumer LFB.
Yang, et al. Expires April 2007 [Page 24]
Internet Draft ForCES FE Model October 2006
For example, the Prefix Lookup LFB executes an LPM search using its
prefix table and resolves to a next-hop reference. This reference
needs to be passed as metadata by the Prefix Lookup LFB (producer)
to the Next Hop LFB (consumer), and must refer to a specific entry
in the next-hop table within the consumer.
Expressing and propagating such a binding relationship is probably
the most common usage of metadata. One or more objects in the
producer LFB are bound to a specific object in the consumer LFB.
Such a relationship is established by the CE explicitly by properly
configuring the attributes in both LFBs. Available methods include
the following:
The binding may be expressed by tagging the involved objects in both
LFBs with the same unique, but otherwise arbitrary, identifier. The
value of the tag is explicitly configured by the CE by writing the
value into both LFBs, and this value is also carried by the metadata
between the LFBs.
Another way of setting up binding relations is to use a naturally
occurring unique identifier of the consumer's object as a reference
and as a value of the metadata (e.g., the array index of a table
entry). In this case, the index is either read or inferred by the
CE by communicating with the consumer LFB. Once the CE obtains the
index, it needs to write it into the producer LFB to establish the
binding.
Important characteristics of the binding usage of metadata are:
. The value of the metadata shows up in the CE-FE communication
for both the consumer and the producer. That is, the metadata
value MUST be carried over the ForCES protocol. Using the
tagging technique, the value is written to both LFBs. Using
the other technique, the value is written to only the producer
LFB and may be READ from the consumer LFB.
. The metadata value is irrelevant to the CE, the binding is
simply expressed by using the same value at the consumer and
producer LFBs.
. Hence the metadata definition is not required to include value
assignments. The only exception is when some special value(s)
of the metadata must be reserved to convey special events.
Even though these special cases must be defined with the
metadata specification, their encoded values can be selected
arbitrarily. For example, for the Prefix Lookup LFB example, a
special value may be reserved to signal the NO-MATCH case, and
the value of zero may be assigned for this purpose.
Yang, et al. Expires April 2007 [Page 25]
Internet Draft ForCES FE Model October 2006
The second class of metadata is the enumerated type. An example is
the "Color" metadata that is produced by a Meter LFB. As the name
suggests, enumerated metadata has a relatively small number of
possible values, each with a specific meaning. All possible cases
must be enumerated when defining this class of metadata. Although a
value encoding must be included in the specification, the actual
values can be selected arbitrarily (e.g., <Red=0, Yellow=1, Green=2>
and <Red=3, Yellow=2, Green 1> would be both valid encodings, what
is important is that an encoding is specified).
The value of the enumerated metadata may or may not be conveyed via
the ForCES protocol between the CE and FE.
The third class of metadata is the explicit type. This refers to
cases where the metadata value is explicitly used by the consumer
LFB to change some packet header fields. In other words, the value
has a direct and explicit impact on some field and will be visible
externally when the packet leaves the NE. Examples are: TTL
increment given to a Header Modifier LFB, and DSCP value for a
Remarker LFB. For explicit metadata, the value encoding MUST be
explicitly provided in the metadata definition. The values cannot
be selected arbitrarily and should conform to what is commonly
expected. For example, a TTL increment metadata should be encoded
as zero for the no increment case, one for the single increment
case, etc. A DSCP metadata should use 0 to encode DSCP=0, 1 to
encode DSCP=1, etc.
3.2.5. LFB Events
During operation, various conditions may occur that can be detected
by LFBs. Examples range from link failure or restart to timer
expiration in special purpose LFBs. The CE may wish to be notified
of the occurrence of such events. The PL protocol provides for such
notifications. The LFB definition includes the necessary
declarations of events. The declarations include identifiers
necessary for subscribing to events (so that the CE can indicate to
the FE which events it wishes to receive) and to indicate in event
notification messages which event is being reported.
The declaration of an event defines a condition that an FE can
detect, and may report. From a conceptual point of view, event
processing is split into triggering (the detection of the condition)
and reporting (the generation of the notification of the event.) In
between these two conceptual points there is event filtering.
Properties associated with the event in the LFB instance can define
filtering conditions to suppress the reporting of that event. The
model thus describes event processing as if events always occur, and
filtering may suppress reporting. Implementations may function in
this manner, or may have more complex logic that eliminates some
Yang, et al. Expires April 2007 [Page 26]
Internet Draft ForCES FE Model October 2006
event processing if the reporting would be suppressed. Any
implementation producing an effect equivalent to the model
description is valid.
3.2.6. LFB Element Properties
LFBs are made up of elements, containing the information that the CE
needs to see and / or change about the functioning of the LFB.
These elements, as described in detail elsewhere, may be basic
values, complex structures, or tables (containing values,
structures, or tables.) Some of these elements are optional. Some
elements may be readable or writeable at the discretion of the FE
implementation. The CE needs to know these properties.
Additionally, certain kinds of elements (arrays, aliases, and events
as of this writing) have additional property information that the CE
may need to read or write. This model defines the structure of the
property information for all defined data types.
The reports with events are designed to allow for the common,
closely related information that the CE can be strongly expected to
need to react to the event. It is not intended to carry information
the CE already has, nor large volumes of information, nor
information related in complex fashions.
3.2.7. LFB Versioning
LFB class versioning is a method to enable incremental evolution of
LFB classes. In general, an FE is not allowed to contain an LFB
instance for more than one version of a particular class.
Inheritance (discussed next in Section 3.2.6) has special rules. If
an FE datapath model containing an LFB instance of a particular
class C also simultaneously contains an LFB instance of a class C'
inherited from class C; C could have a different version than C'.
LFB class versioning is supported by requiring a version string in
the class definition. CEs may support multiple versions of a
particular LFB class to provide backward compatibility, but FEs MUST
NOT support more than one version of a particular class.
Versioning is not restricted to making backwards compatible changes.
It is specifically expected to be used to make changes that cannot
be represented by inheritance. Often this will be to correct
errors, and hence may not be backwards compatible. It may also be
used to remove elements which are not considered useful
(particularly if they were previously mandatory, and hence were an
implementation impediment.)
Yang, et al. Expires April 2007 [Page 27]
Internet Draft ForCES FE Model October 2006
3.2.8. LFB Inheritance
LFB class inheritance is supported in the FE model as a method to
define new LFB classes. This also allows FE vendors to add vendor-
specific extensions to standardized LFBs. An LFB class
specification MUST specify the base class and version number it
inherits from (the default is the base LFB class). Multiple-
inheritance is not allowed, however, to avoid unnecessary
complexity.
Inheritance should be used only when there is significant reuse of
the base LFB class definition. A separate LFB class should be
defined if little or no reuse is possible between the derived and
the base LFB class.
An interesting issue related to class inheritance is backward
compatibility between a descendant and an ancestor class. Consider
the following hypothetical scenario where a standardized LFB class
"L1" exists. Vendor A builds an FE that implements LFB "L1" and
vendor B builds a CE that can recognize and operate on LFB "L1".
Suppose that a new LFB class, "L2", is defined based on the existing
"L1" class by extending its capabilities incrementally. Let us
examine the FE backward compatibility issue by considering what
would happen if vendor B upgrades its FE from "L1" to "L2" and
vendor C's CE is not changed. The old L1-based CE can interoperate
with the new L2-based FE if the derived LFB class "L2" is indeed
backward compatible with the base class "L1".
The reverse scenario is a much less problematic case, i.e., when CE
vendor B upgrades to the new LFB class "L2", but the FE is not
upgraded. Note that as long as the CE is capable of working with
older LFB classes, this problem does not affect the model; hence we
will use the term "backward compatibility" to refer to the first
scenario concerning FE backward compatibility.
Backward compatibility can be designed into the inheritance model by
constraining LFB inheritance to require the derived class be a
functional superset of the base class (i.e. the derived class can
only add functions to the base class, but not remove functions).
Additionally, the following mechanisms are required to support FE
backward compatibility:
1. When detecting an LFB instance of an LFB type that is unknown
to the CE, the CE MUST be able to query the base class of such
an LFB from the FE.
2. The LFB instance on the FE SHOULD support a backward
compatibility mode (meaning the LFB instance reverts itself
back to the base class instance), and the CE SHOULD be able to
configure the LFB to run in such a mode.
Yang, et al. Expires April 2007 [Page 28]
Internet Draft ForCES FE Model October 2006
3.3. FE Datapath Modeling
Packets coming into the FE from ingress ports generally flow through
multiple LFBs before leaving out of the egress ports. How an FE
treats a packet depends on many factors, such as type of the packet
(e.g., IPv4, IPv6 or MPLS), actual header values, time of arrival,
etc. The result of LFB processing may have an impact on how the
packet is to be treated in downstream LFBs. This differentiation of
packet treatment downstream can be conceptualized as having
alternative datapaths in the FE. For example, the result of a 6-
tuple classification performed by a classifier LFB could control
which rate meter is applied to the packet by a rate meter LFB in a
later stage in the datapath.
LFB topology is a directed graph representation of the logical
datapaths within an FE, with the nodes representing the LFB
instances and the directed link depicting the packet flow direction
from one LFB to the next. Section 3.3.1 discusses how the FE
datapaths can be modeled as LFB topology; while Section 3.3.2
focuses on issues related to LFB topology reconfiguration.
3.3.1. Alternative Approaches for Modeling FE Datapaths
There are two basic ways to express the differentiation in packet
treatment within an FE, one represents the datapath directly and
graphically (topological approach) and the other utilizes metadata
(the encoded state approach).
. Topological Approach
Using this approach, differential packet treatment is expressed by
splitting the LFB topology into alternative paths. In other
words, if the result of an LFB operation controls how the packet
is further processed, then such an LFB will have separate output
ports, one for each alternative treatment, connected to separate
sub-graphs, each expressing the respective treatment downstream.
. Encoded State Approach
An alternate way of expressing differential treatment is by using
metadata. The result of the operation of an LFB can be encoded in
a metadata, which is passed along with the packet to downstream
LFBs. A downstream LFB, in turn, can use the metadata and its
value (e.g., as an index into some table) to determine how to
treat the packet.
Theoretically, either approach could substitute for the other, so
one could consider using a single pure approach to describe all
Yang, et al. Expires April 2007 [Page 29]
Internet Draft ForCES FE Model October 2006
datapaths in an FE. However, neither model by itself results in the
best representation for all practically relevant cases. For a given
FE with certain logical datapaths, applying the two different
modeling approaches will result in very different looking LFB
topology graphs. A model using only the topological approach may
require a very large graph with many links or paths, and nodes
(i.e., LFB instances) to express all alternative datapaths. On the
other hand, a model using only the encoded state model would be
restricted to a string of LFBs, which is not an intuitive way to
describe different datapaths (such as MPLS and IPv4). Therefore, a
mix of these two approaches will likely be used for a practical
model. In fact, as we illustrate below, the two approaches can be
mixed even within the same LFB.
Using a simple example of a classifier with N classification outputs
followed by other LFBs, Figure 5(a) shows what the LFB topology
looks like when using the pure topological approach. Each output
from the classifier goes to one of the N LFBs where no metadata is
needed. The topological approach is simple, straightforward and
graphically intuitive. However, if N is large and the N nodes
following the classifier (LFB#1, LFB#2, ..., LFB#N) all belong to
the same LFB type (e.g., meter), but each has its own independent
attributes, the encoded state approach gives a much simpler topology
representation, as shown in Figure 5(b). The encoded state approach
requires that a table of N rows of meter attributes is provided in
the Meter node itself, with each row representing the attributes for
one meter instance. A metadata M is also needed to pass along with
the packet P from the classifier to the meter, so that the meter can
use M as a look-up key (index) to find the corresponding row of the
attributes that should be used for any particular packet P.
What if those N nodes (LFB#1, LFB#2, ..., LFB#N) are not of the same
type? For example, if LFB#1 is a queue while the rest are all
meters, what is the best way to represent such datapaths? While it
is still possible to use either the pure topological approach or the
pure encoded state approach, the natural combination of the two
appears to be the best option. Figure 5(c) depicts two different
functional datapaths using the topological approach while leaving
the N-1 meter instances distinguished by metadata only, as shown in
Figure 5(c).
Yang, et al. Expires April 2007 [Page 30]
Internet Draft ForCES FE Model October 2006
+----------+
P | LFB#1 |
+--------->|(Attrib-1)|
+-------------+ | +----------+
| 1|------+ P +----------+
| 2|---------------->| LFB#2 |
| classifier 3| |(Attrib-2)|
| ...|... +----------+
| N|------+ ...
+-------------+ | P +----------+
+--------->| LFB#N |
|(Attrib-N)|
+----------+
5(a) Using pure topological approach
+-------------+ +-------------+
| 1| | Meter |
| 2| (P, M) | (Attrib-1) |
| 3|---------------->| (Attrib-2) |
| ...| | ... |
| N| | (Attrib-N) |
+-------------+ +-------------+
5(b) Using pure encoded state approach to represent the LFB
topology in 5(a), if LFB#1, LFB#2, ..., and LFB#N are of the
same type (e.g., meter).
+-------------+
+-------------+ (P, M) | queue |
| 1|------------->| (Attrib-1) |
| 2| +-------------+
| 3| (P, M) +-------------+
| ...|------------->| Meter |
| N| | (Attrib-2) |
+-------------+ | ... |
| (Attrib-N) |
+-------------+
5(c) Using a combination of the two, if LFB#1, LFB#2, ..., and
LFB#N are of different types (e.g., queue and meter).
Figure 5. An example of how to model FE datapaths
From this example, we demonstrate that each approach has a distinct
advantage depending on the situation. Using the encoded state
approach, fewer connections are typically needed between a fan-out
node and its next LFB instances of the same type because each packet
carries metadata the following nodes can interpret and hence invoke
Yang, et al. Expires April 2007 [Page 31]
Internet Draft ForCES FE Model October 2006
a different packet treatment. For those cases, a pure topological
approach forces one to build elaborate graphs with many more
connections and often results in an unwieldy graph. On the other
hand, a topological approach is the most intuitive for representing
functionally different datapaths.
For complex topologies, a combination of the two is the most
flexible. A general design guideline is provided to indicate which
approach is best used for a particular situation. The topological
approach should primarily be used when the packet datapath forks to
distinct LFB classes (not just distinct parameterizations of the
same LFB class), and when the fan-outs do not require changes, such
as adding/removing LFB outputs, or require only very infrequent
changes. Configuration information that needs to change frequently
should be expressed by using the internal attributes of one or more
LFBs (and hence using the encoded state approach).
+---------------------------------------------+
| |
+----------+ V +----------+ +------+ |
| | | | |if IP-in-IP| | |
---->| ingress |->+----->|classifier|---------->|Decap.|---->---+
| ports | | |----+ | |
+----------+ +----------+ |others+------+
|
V
(a) The LFB topology with a logical loop
+-------+ +-----------+ +------+ +-----------+
| | | |if IP-in-IP | | | |
--->|ingress|-->|classifier1|----------->|Decap.|-->+classifier2|->
| ports | | |----+ | | | |
+-------+ +-----------+ |others +------+ +-----------+
|
V
The LFB topology without the loop utilizing two independent
classifier instances.
Figure 6. An LFB topology example.
It is important to point out that the LFB topology described here is
the logical topology, not the physical topology of how the FE
hardware is actually laid out. Nevertheless, the actual
implementation may still influence how the functionality is mapped
to the LFB topology. Figure 6 shows one simple FE example. In this
example, an IP-in-IP packet from an IPSec application like VPN may
go to the classifier first and have the classification done based on
the outer IP header; upon being classified as an IP-in-IP packet,
the packet is then sent to a decapsulator to strip off the outer IP
Yang, et al. Expires April 2007 [Page 32]
Internet Draft ForCES FE Model October 2006
header, followed by a classifier again to perform classification on
the inner IP header. If the same classifier hardware or software is
used for both outer and inner IP header classification with the same
set of filtering rules, a logical loop is naturally present in the
LFB topology, as shown in Figure 6(a). However, if the
classification is implemented by two different pieces of hardware or
software with different filters (i.e., one set of filters for the
outer IP header and another set for the inner IP header), then it is
more natural to model them as two different instances of classifier
LFB, as shown in Figure 6(b).
To distinguish between multiple instances of the same LFB class,
each LFB instance has its own LFB instance ID. One way to encode
the LFB instance ID is to encode it as x.y where x is the LFB class
ID and y is the instance ID within each LFB class.
3.3.2. Configuring the LFB Topology
While there is little doubt that an individual LFB must be
configurable, the configurability question is more complicated for
LFB topology. Since the LFB topology is really the graphic
representation of the datapaths within an FE, configuring the LFB
topology means dynamically changing the datapaths, including
changing the LFBs along the datapaths on an FE (e.g., creating,
instantiating or deleting LFBs) and setting up or deleting
interconnections between outputs of upstream LFBs to inputs of
downstream LFBs.
Why would the datapaths on an FE ever change dynamically? The
datapaths on an FE are set up by the CE to provide certain data
plane services (e.g., DiffServ, VPN, etc.) to the Network Element's
(NE) customers. The purpose of reconfiguring the datapaths is to
enable the CE to customize the services the NE is delivering at run
time. The CE needs to change the datapaths when the service
requirements change, such as adding a new customer or when an
existing customer changes their service. However, note that not all
datapath changes result in changes in the LFB topology graph.
Changes in the graph are dependent on the approach used to map the
datapaths into LFB topology. As discussed in 3.3.1, the topological
approach and encoded state approach can result in very different
looking LFB topologies for the same datapaths. In general, an LFB
topology based on a pure topological approach is likely to
experience more frequent topology reconfiguration than one based on
an encoded state approach. However, even an LFB topology based
entirely on an encoded state approach may have to change the
topology at times, for example, to bypass some LFBs or insert new
LFBs. Since a mix of these two approaches is used to model the
datapaths, LFB topology reconfiguration is considered an important
aspect of the FE model.
Yang, et al. Expires April 2007 [Page 33]
Internet Draft ForCES FE Model October 2006
We want to point out that allowing a configurable LFB topology in
the FE model does not mandate that all FEs are required to have this
capability. Even if an FE supports configurable LFB topology, the
FE may impose limitations on what can actually be configured.
Performance-optimized hardware implementations may have zero or very
limited configurability, while FE implementations running on network
processors may provide more flexibility and configurability. It is
entirely up to the FE designers to decide whether or not the FE
actually implements reconfiguration and if so, how much. Whether a
simple runtime switch is used to enable or disable (i.e., bypass)
certain LFBs, or more flexible software reconfiguration is used, is
implementation detail internal to the FE and outside of the scope of
FE model. In either case, the CE(s) MUST be able to learn the FE's
configuration capabilities. Therefore, the FE model MUST provide a
mechanism for describing the LFB topology configuration capabilities
of an FE. These capabilities may include (see Section 5 for full
details):
. Which LFB classes the FE can instantiate
. Maximum number of instances of the same LFB class that can be
created
. Any topological limitations, For example:
o The maximum number of instances of the same class or any
class that can be created on any given branch of the graph
o Ordering restrictions on LFBs (e.g., any instance of LFB
class A must be always downstream of any instance of LFB
class B).
Note that even when the CE is allowed to configure LFB topology for
the FE, the CE is not expected to be able to interpret an arbitrary
LFB topology and determine which specific service or application
(e.g. VPN, DiffServ, etc.) is supported by the FE. However, once
the CE understands the coarse capability of an FE, the CE MUST
configure the LFB topology to implement the network service the NE
is supposed to provide. Thus, the mapping the CE has to understand
is from the high level NE service to a specific LFB topology, not
the other way around. The CE is not expected to have the ultimate
intelligence to translate any high level service policy into the
configuration data for the FEs. However, it is conceivable that
within a given network service domain, a certain amount of
intelligence can be programmed into the CE to give the CE a general
understanding of the LFBs involved to allow the translation from a
high level service policy to the low level FE configuration to be
done automatically. Note that this is considered an implementation
issue internal to the control plane and outside the scope of the FE
model. Therefore, it is not discussed any further in this draft.
Yang, et al. Expires April 2007 [Page 34]
Internet Draft ForCES FE Model October 2006
+----------+ +-----------+
---->| Ingress |---->|classifier |--------------+
| | |chip | |
+----------+ +-----------+ |
v
+-------------------------------------------+
+--------+ | Network Processor |
<----| Egress | | +------+ +------+ +-------+ |
+--------+ | |Meter | |Marker| |Dropper| |
^ | +------+ +------+ +-------+ |
| | |
+----------+-------+ |
| | |
| +---------+ +---------+ +------+ +---------+ |
| |Forwarder|<------|Scheduler|<--|Queue | |Counter | |
| +---------+ +---------+ +------+ +---------+ |
|--------------------------------------------------------------+
(a) The Capability of the FE, reported to the CE
+-----+ +-------+ +---+
| A|--->|Queue1 |--------------------->| |
------>| | +-------+ | | +---+
| | | | | |
| | +-------+ +-------+ | | | |
| B|--->|Meter1 |----->|Queue2 |------>| |->| |
| | | | +-------+ | | | |
| | | |--+ | | | |
+-----+ +-------+ | +-------+ | | +---+
classifier +-->|Dropper| | | IPv4
+-------+ +---+ Fwd.
Scheduler
(b) One LFB topology as configured by the CE and
accepted by the FE
Yang, et al. Expires April 2007 [Page 35]
Internet Draft ForCES FE Model October 2006
Queue1
+---+ +--+
| A|------------------->| |--+
+->| | | | |
| | B|--+ +--+ +--+ +--+ |
| +---+ | | | | | |
| Meter1 +->| |-->| | |
| | | | | |
| +--+ +--+ | Ipv4
| Counter1 Dropper1 Queue2| +--+ Fwd.
+---+ | +--+ +--->|A | +-+
| A|---+ | |------>|B | | |
------>| B|------------------------------>| | +--->|C |->| |->
| C|---+ +--+ | +->|D | | |
| D|-+ | | | +--+ +-+
+---+ | | +---+ Queue3| | Scheduler
Classifier1 | | | A|------------> +--+ | |
| +->| | | |--+ |
| | B|--+ +--+ +-------->| | |
| +---+ | | | | +--+ |
| Meter2 +->| |-+ |
| | | |
| +--+ Queue4 |
| Marker1 +--+ |
+---------------------------->| |----+
| |
+--+
(c) Another LFB topology as configured by the CE and
accepted by the FE
Figure 7. An example of configuring LFB topology.
Figure 7 shows an example where a QoS-enabled router has several
line cards that have a few ingress ports and egress ports, a
specialized classification chip, a network processor containing
codes for FE blocks like meter, marker, dropper, counter, queue,
scheduler and Ipv4 forwarder. Some of the LFB topology is already
fixed and has to remain static due to the physical layout of the
line cards. For example, all of the ingress ports might be hard-
wired into the classification chip so all packets flow from the
ingress port into the classification engine. On the other hand, the
LFBs on the network processor and their execution order are
programmable. However, certain capacity limits and linkage
constraints could exist between these LFBs. Examples of the capacity
limits might be: 8 meters; 16 queues in one FE; the scheduler can
handle at most up to 16 queues; etc. The linkage constraints might
dictate that the classification engine may be followed by a meter,
marker, dropper, counter, queue or IPv4 forwarder, but not a
scheduler; queues can only be followed by a scheduler; a scheduler
Yang, et al. Expires April 2007 [Page 36]
Internet Draft ForCES FE Model October 2006
must be followed by the IPv4 forwarder; the last LFB in the datapath
before going into the egress ports must be the IPv4 forwarder, etc.
Once the FE reports these capabilities and capacity limits to the
CE, it is now up to the CE to translate the QoS policy into a
desirable configuration for the FE. Figure 7(a) depicts the FE
capability while 7(b) and 7(c) depict two different topologies that
the CE may request the FE to configure. Note that both the ingress
and egress are omitted in (b) and (c) to simplify the
representation. The topology in 7(c) is considerably more complex
than 7(b) but both are feasible within the FE capabilities, and so
the FE should accept either configuration request from the CE.
4. Model and Schema for LFB Classes
The main goal of the FE model is to provide an abstract, generic,
modular, implementation-independent representation of the FEs. This
is facilitated using the concept of LFBs, which are instantiated
from LFB classes. LFB classes and associated definitions will be
provided in a collection of XML documents. The collection of these
XML documents is called a LFB class library, and each document is
called an LFB class library document (or library document, for
short). Each of the library documents will conform to the schema
presented in this section. The root element of the library document
is the <LFBLibrary> element.
It is not expected that library documents will be exchanged between
FEs and CEs "over-the-wire". But the model will serve as an
important reference for the design and development of the CEs
(software) and FEs (mostly the software part). It will also serve
as a design input when specifying the ForCES protocol elements for
CE-FE communication.
4.1. Namespace
A namespace is needed to uniquely identify the LFB type in the LFB
class library. The reference to the namespace definition is
contained in Section 9, IANA Considerations.
4.2. <LFBLibrary> Element
The <LFBLibrary> element serves as a root element of all library
documents. It contains one or more of the following main blocks:
. <frameTypeDefs> for the frame declarations;
. <dataTypeDefs> for defining common data types;
. <metadataDefs> for defining metadata, and
. <LFBClassDefs> for defining LFB classes.
Yang, et al. Expires April 2007 [Page 37]
Internet Draft ForCES FE Model October 2006
Each block is optional, that is, one library document may contain
only metadata definitions, another may contain only LFB class
definitions, yet another may contain all of the above.
In addition to the above main blocks, a library document can import
other library documents if it needs to refer to definitions
contained in the included document. This concept is similar to the
"#include" directive in C. Importing is expressed by the <load>
elements, which must precede all the above elements in the document.
For unique referencing, each LFBLibrary instance document has a
unique label defined in the "provide" attribute of the LFBLibrary
element.
The <LFBLibrary> element also includes an optional <description>
element, which can be used to provide textual description about the
library document.
The following is a skeleton of a library document:
<?xml version="1.0" encoding="UTF-8"?>
<LFBLibrary xmlns="http://ietf.org/forces/1.0/lfbmodel"
provides="this_library">
<description>
...
</description>
<!-- Loading external libraries (optional) -->
<load library="another_library"/>
...
<!-- FRAME TYPE DEFINITIONS (optional) -->
<frameTypeDefs>
...
</frameTypeDefs>
<!-- DATA TYPE DEFINITIONS (optional) -->
<dataTypeDefs>
...
</dataTypeDefs>
<!-- METADATA DEFINITIONS (optional) -->
<metadataDefs>
...
</metadataDefs>
Yang, et al. Expires April 2007 [Page 38]
Internet Draft ForCES FE Model October 2006
<!--
-
-
LFB CLASS DEFINITIONS (optional) -->
<LFBCLassDefs>
...
</LFBCLassDefs>
</LFBLibrary>
4.3. <load> Element
This element is used to refer to another LFB library document.
Similar to the "#include" directive in C, this makes the objects
(metadata types, data types, etc.) defined in the referred library
document available for referencing in the current document.
The load element MUST contain the label of the library document to
be included and may contain a URL to specify where the library can
be retrieved. The load element can be repeated unlimited times.
Three examples for the <load> elements:
<load library="a_library"/>
<load library="another_library" location="another_lib.xml"/>
<load library="yetanother_library"
location="http://www.petrimeat.com/forces/1.0/lfbmodel/lpm.xml"/>
4.4. <frameDefs> Element for Frame Type Declarations
Frame names are used in the LFB definition to define the types of
frames the LFB expects at its input port(s) and emits at its output
port(s). The <frameDefs> optional element in the library document
contains one or more <frameDef> elements, each declaring one frame
type.
Each frame definition MUST contain a unique name (NMTOKEN) and a
brief synopsis. In addition, an optional detailed description may
be provided.
Uniqueness of frame types MUST be ensured among frame types defined
in the same library document and in all directly or indirectly
included library documents.
The following example defines two frame types:
<frameDefs>
<frameDef>
<name>ipv4</name>
<synopsis>IPv4 packet</synopsis>
<description>
Yang, et al. Expires April 2007 [Page 39]
Internet Draft ForCES FE Model October 2006
This frame type refers to an IPv4 packet.
</description>
</frameDef>
<frameDef>
<name>ipv6</name>
<synopsis>IPv6 packet</synopsis>
<description>
This frame type refers to an IPv6 packet.
</description>
</frameDef>
...
</frameDefs>
4.5. <dataTypeDefs> Element for Data Type Definitions
The (optional) <dataTypeDefs> element can be used to define commonly
used data types. It contains one or more <dataTypeDef> elements,
each defining a data type with a unique name. Such data types can be
used in several places in the library documents, including:
. Defining other data types
. Defining attributes of LFB classes
This is similar to the concept of having a common header file for
shared data types.
Each <dataTypeDef> element MUST contain a unique name (NMTOKEN), a
brief synopsis, an optional longer description, and a type
definition element. The name MUST be unique among all data types
defined in the same library document and in any directly or
indirectly included library documents. For example:
<dataTypeDefs>
<dataTypeDef>
<name>ieeemacaddr</name>
<synopsis>48-bit IEEE MAC address</synopsis>
... type definition ...
</dataTypeDef>
<dataTypeDef>
<name>ipv4addr</name>
<synopsis>IPv4 address</synopsis>
... type definition ...
</dataTypeDef>
...
</dataTypeDefs>
Yang, et al. Expires April 2007 [Page 40]
Internet Draft ForCES FE Model October 2006
There are two kinds of data types: atomic and compound. Atomic data
types are appropriate for single-value variables (e.g. integer,
string, byte array).
The following built-in atomic data types are provided, but
additional atomic data types can be defined with the <typeRef> and
<atomic> elements:
<name> Meaning
---- -------
char 8-bit signed integer
uchar 8-bit unsigned integer
int16 16-bit signed integer
uint16 16-bit unsigned integer
int32 32-bit signed integer
uint32 32-bit unsigned integer
int64 64-bit signed integer
uint64 64-bit unsigned integer
boolean A true / false value where
0 = false, 1 = true
string[N] A UTF-8 string represented in at most
N Octets.
string A UTF-8 string without a configured
storage length limit.
byte[N] A byte array of N bytes
octetstring[N] A buffer of N octets, which may
contain fewer than N octets. Hence
the encoded value will always have
a length.
float16 16-bit floating point number
float32 32-bit IEEE floating point number
float64 64-bit IEEE floating point number
These built-in data types can be readily used to define metadata or
LFB attributes, but can also be used as building blocks when
defining new data types. The boolean data type is defined here
because it is so common, even though it can be built by sub-ranging
the uchar data type.
Compound data types can build on atomic data types and other
compound data types. Compound data types can be defined in one of
four ways. They may be defined as an array of elements of some
compound or atomic data type. They may be a structure of named
elements of compound or atomic data types (ala C structures). They
may be a union of named elements of compound or atomic data types
Yang, et al. Expires April 2007 [Page 41]
Internet Draft ForCES FE Model October 2006
(ala C unions). They may also be defined as augmentations
(explained below in 4.5.6) of existing compound data types.
Given that the FORCES protocol will be getting and setting attribute
values, all atomic data types used here must be able to be conveyed
in the FORCES protocol. Further, the FORCES protocol will need a
mechanism to convey compound data types. However, the details of
such representations are for the protocol document to define, not
the model document. Strings and octetstrings must be conveyed with
their length, as they are not delimited, and are variable length.
With regard to strings, this model defines a small set of
restrictions and definitions on how they are structured. String and
octetstring length limits can be specified in the LFB Class
definitions. The element properties for string and octetstring
elements also contain actual lengths and length limits. This
duplication of limits is to allow for implementations with smaller
limits than the maximum limits specified in the LFB Class
definition. In all cases, these lengths are specified in octets,
not in characters. In terms of protocol operation, as long as the
specified length is within the FE’s supported capabilities, the FE
stores the contents of a string exactly as provided by the CE, and
returns those contents when requested. No canonicalization,
transformations, or equivalences are performed by the FE. Elements
of type string (or string[n]) may be used to hold identifiers for
correlation with elements in other LFBs. In such cases, an exact
octet for octet match is used. No equivalences are used by the FE
or CE in performing that matching. The ForCES protocol does not
perform or require validation of the content of UTF-8 strings.
However, UTF-8 strings SHOULD be encoded in the shortest form to
avoid potential security issues described in [15]. Any entity
displaying such strings is expected to perform its own validation
(for example for correct multi-byte characters, and for ensuring
that the string does not end in the middle of a multi-byte
sequence.) Specific LFB class definitions may restrict the valid
contents of a string as suited to the particular usage (for example,
an element that holds a DNS name would be restricted to hold only
octets valid in such a name.) FEs should validate the contents of
SET requests for such restricted elements at the time the set is
performed, just as range checks for range limited elements are
performed. The ForCES protocol behavior defines the normative
processing for requests using that protocol.
For the definition of the actual type in the <dataTypeDef> element,
the following elements are available: <typeRef>, <atomic>, <array>,
<struct>, and <union>.
The predefined type alias is somewhere between the atomic and
compound data types. It behaves like a structure, one element of
Yang, et al. Expires April 2007 [Page 42]
Internet Draft ForCES FE Model October 2006
which has special behavior. Given that the special behavior is tied
to the other parts of the structure, the compound result is treated
as a predefined construct.
4.5.1. <typeRef> Element for Aliasing Existing Data Types
The <typeRef> element refers to an existing data type by its name.
The referred data type MUST be defined either in the same library
document, or in one of the included library documents. If the
referred data type is an atomic data type, the newly defined type
will also be regarded as atomic. If the referred data type is a
compound type, the new type will also be compound. Some usage
examples follow:
<dataTypeDef>
<name>short</name>
<synopsis>Alias to int16</synopsis>
<typeRef>int16</typeRef>
</dataTypeDef>
<dataTypeDef>
<name>ieeemacaddr</name>
<synopsis>48-bit IEEE MAC address</synopsis>
<typeRef>byte[6]</typeRef>
</dataTypeDef>
4.5.2. <atomic> Element for Deriving New Atomic Types
The <atomic> element allows the definition of a new atomic type from
an existing atomic type, applying range restrictions and/or
providing special enumerated values. Note that the <atomic> element
can only use atomic types as base types, and its result MUST be
another atomic type.
For example, the following snippet defines a new "dscp" data type:
<dataTypeDef>
<name>dscp</name>
<synopsis>Diffserv code point.</synopsis>
<atomic>
<baseType>uchar</baseType>
<rangeRestriction>
<allowedRange min="0" max="63"/>
</rangeRestriction>
<specialValues>
<specialValue value="0">
<name>DSCP-BE</name>
<synopsis>Best Effort</synopsis>
</specialValue>
...
Yang, et al. Expires April 2007 [Page 43]
Internet Draft ForCES FE Model October 2006
</specialValues>
</atomic>
</dataTypeDef>
4.5.3. <array> Element to Define Arrays
The <array> element can be used to create a new compound data type
as an array of a compound or an atomic data type. The type of the
array entry can be specified either by referring to an existing type
(using the <typeRef> element) or defining an unnamed type inside the
<array> element using any of the <atomic>, <array>, <struct>, or
<union> elements.
The array can be "fixed-size" or "variable-size", which is specified
by the "type" attribute of the <array> element. The default is
"variable-size". For variable size arrays, an optional "max-length"
attribute specifies the maximum allowed length. This attribute
should be used to encode semantic limitations, not implementation
limitations. The latter should be handled by capability attributes
of LFB classes, and should never be included in data type
definitions. If the "max-length" attribute is not provided, the
array is regarded as of unlimited-size.
For fixed-size arrays, a "length" attribute MUST be provided that
specifies the constant size of the array.
The result of this construct MUST always be a compound type, even if
the array has a fixed size of 1.
Arrays MUST only be subscripted by integers, and will be presumed to
start with index 0.
In addition to their subscripts, arrays may be declared to have
content keys. Such a declaration has several effects:
. Any declared key can be used in the ForCES protocol to select
an element for operations (for details, see the protocol).
. In any instance of the array, each declared key must be unique
within that instance. No two elements of an array may have the
same values on all the fields which make up a key.
Each key is declared with a keyID for use in the protocol, where the
unique key is formed by combining one or more specified key fields.
To support the case where an array of an atomic type with unique
values can be referenced by those values, the key field identifier
may be "*" (i.e., the array entry is the key). If the value type of
the array is a structure or an array, then the key is one or more
fields, each identified by name. Since the field may be an element
Yang, et al. Expires April 2007 [Page 44]
Internet Draft ForCES FE Model October 2006
of the structure, the element of an element of a structure, or
further nested, the field name is actually a concatenated sequence
of part identifiers, separated by decimal points ("."). The syntax
for key field identification is given following the array examples.
The following example shows the definition of a fixed size array
with a pre-defined data type as the array elements:
<dataTypeDef>
<name>dscp-mapping-table</name>
<synopsis>
A table of 64 DSCP values, used to re-map code space.
</synopsis>
<array type="fixed-size" length="64">
<typeRef>dscp</typeRef>
</array>
</dataTypeDef>
The following example defines a variable size array with an upper
limit on its size:
<dataTypeDef>
<name>mac-alias-table</name>
<synopsis>A table with up to 8 IEEE MAC addresses</synopsis>
<array type="variable-size" max-length="8">
<typeRef>ieeemacaddr</typeRef>
</array>
</dataTypeDef>
The following example shows the definition of an array with a local
(unnamed) type definition:
<dataTypeDef>
<name>classification-table</name>
<synopsis>
A table of classification rules and result opcodes.
</synopsis>
<array type="variable-size">
<struct>
<element elementID="1">
<name>rule</name>
<synopsis>The rule to match</synopsis>
<typeRef>classrule</typeRef>
</element>
<element elementID="2">
<name>opcode</name>
<synopsis>The result code</synopsis>
<typeRef>opcode</typeRef>
</element>
Yang, et al. Expires April 2007 [Page 45]
Internet Draft ForCES FE Model October 2006
</struct>
</array>
</dataTypeDef>
In the above example, each entry of the array is a <struct> of two
fields ("rule" and "opcode").
The following example shows a table of IP Prefix information that
can be accessed by a multi-field content key on the IP Address and
prefix length. This means that in any instance of this table, no
two entries can have the same IP address and prefix length.
<dataTypeDef>
<name>ipPrefixInfo_table</name>
<synopsis>
A table of information about known prefixes
</synopsis>
<array type="variable-size">
<struct>
<element elementID="1">
<name>address-prefix</name>
<synopsis>the prefix being described</synopsis>
<typeRef>ipv4Prefix</typeRef>
</element>
<element elementID="2">
<name>source</name>
<synopsis>
the protocol or process providing this information
</synopsis>
<typeRef>uint16</typeRef>
</element>
<element elementID="3">
<name>prefInfo</name>
<synopsis>the information we care about</synopsis>
<typeRef>hypothetical-info-type</typeRef>
</element>
</struct>
<key keyID="1">
<keyField> address-prefix.ipv4addr </keyField>
<keyField> address-prefix.prefixlen </keyField>
<keyField> source </keyField>
</key>
</array>
</dataTypeDef>
Note that the keyField elements could also have been simply address-
prefix and source, since all of the fields of address-prefix are
being used.
Yang, et al. Expires April 2007 [Page 46]
Internet Draft ForCES FE Model October 2006
4.5.3.1 Key Field References
In order to use key declarations, one must refer to fields that are
potentially nested inside other fields in the array. If there are
nested arrays, one might even use an array element as a key (but
great care would be needed to ensure uniqueness.)
The key is the combination of the values of each field declared in a
keyField element.
Therefore, the value of a keyField element MUST be a concatenated
Sequence of field identifiers, separated by a "." (period)
character. Whitespace is permitted and ignored.
A valid string for a single field identifier within a keyField
depends upon the current context. Initially, in an array key
declaration, the context is the type of the array. Progressively,
the context is whatever type is selected by the field identifiers
processed so far in the current key field declaration.
When the current context is an array, (e.g., when declaring a key
for an array whose content is an array) then the only valid value
for the field identifier is an explicit number.
When the current context is a structure, the valid values for the
field identifiers are the names of the elements of the structure.
In the special case of declaring a key for an array containing an
atomic type, where that content is unique and is to be used as a
key, the value "*" can be used as the single key field identifier.
4.5.4. <struct> Element to Define Structures
A structure is comprised of a collection of data elements. Each
data element has a data type (either an atomic type or an existing
compound type) and is assigned a name unique within the scope of the
compound data type being defined. These serve the same function as
"struct" in C, etc.
The actual type of the field can be defined by referring to an
existing type (using the <typeDef> element), or can be a locally
defined (unnamed) type created by any of the <atomic>, <array>,
<struct>, or <union> elements.
A structure definition is a series of element declarations. Each
element carries an elementID for use by the ForCES protocol. In
addition, the element contains the name, a synopsis, an optional
description, an optional declaration that the element itself is
optional, and the typeRef declaration that specifies the element
type.
Yang, et al. Expires April 2007 [Page 47]
Internet Draft ForCES FE Model October 2006
For a dataTypeDef of a struct, the structure definition may be
inherited from, and augment, a previously defined structured type.
This is indicated by including the derivedFrom attribute on the
struct declaration.
The result of this construct MUST be a compound type, even when the
<struct> contains only one field.
An example:
<dataTypeDef>
<name>ipv4prefix</name>
<synopsis>
IPv4 prefix defined by an address and a prefix length
</synopsis>
<struct>
<element elementID="1">
<name>address</name>
<synopsis>Address part</synopsis>
<typeRef>ipv4addr</typeRef>
</element>
<element elementID="2">
<name>prefixlen</name>
<synopsis>Prefix length part</synopsis>
<atomic>
<baseType>uchar</baseType>
<rangeRestriction>
<allowedRange min="0" max="32"/>
</rangeRestriction>
</atomic>
</element>
</struct>
</dataTypeDef>
4.5.5. <union> Element to Define Union Types
Similar to the union declaration in C, this construct allows the
definition of overlay types. Its format is identical to the
<struct> element.
The result of this construct MUST be a compound type, even when the
union contains only one element.
4.5.6 <alias> Element
It is sometimes necessary to have an element in an LFB or structure
refer to information in other LFBs. The <alias> declaration creates
the constructs for this. The content of an <alias> element MUST be a
Yang, et al. Expires April 2007 [Page 48]
Internet Draft ForCES FE Model October 2006
named type. It can be a base type of a derived type. The actual
value referenced by an alias is known as its target. When a GET or
SET operation references the alias element, the value of the target
is returned or replaced. Write access to an alias element is
permitted if write access to both the alias and the target are
permitted.
The target of an <alias> element is determined by its properties.
Like all elements, the properties MUST include the support / read /
write permission for the alias. In addition, there are several
fields in the properties which define the target of the alias.
These fields are the ID of the LFB class of the target, the ID of
the LFB instance of the target, and a sequence of integers
representing the path within the target LFB instance to the target
element. The type of the target element must match the declared
type of the alias. Details of the alias property structure in the
section of this document on properties.
Note that the read / write property of the alias refers to the
value. The CE can only determine if it can write the target
selection properties of the alias by attempting such a write
operation. (Property elements do not themselves have properties.)
4.5.6. Augmentations
Compound types can also be defined as augmentations of existing
compound types. If the existing compound type is a structure,
augmentation may add new elements to the type. The type of an
existing element can only be replaced with an augmentation derived
from the current type, an existing element cannot be deleted. If
the existing compound type is an array, augmentation means
augmentation of the array element type.
One consequence of this is that augmentations are compatible with
the compound type from which they are derived. As such,
augmentations are useful in defining attributes for LFB subclasses
with backward compatibility. In addition to adding new attributes
to a class, the data type of an existing attribute may be replaced
by an augmentation of that attribute, and still meet the
compatibility rules for subclasses.
For example, consider a simple base LFB class A that has only one
attribute (attr1) of type X. One way to derive class A1 from A can
be by simply adding a second attribute (of any type). Another way
to derive a class A2 from A can be by replacing the original
attribute (attr1) in A of type X with one of type Y, where Y is an
augmentation of X. Both classes A1 and A2 are backward compatible
with class A.
Yang, et al. Expires April 2007 [Page 49]
Internet Draft ForCES FE Model October 2006
The syntax for augmentations is to include a derivedFrom element in
a structure definition, indicating what structure type is being
augmented. Element names and element IDs within the augmentation
must not be the same as those in the structure type being augmented.
4.6. <metadataDefs> Element for Metadata Definitions
The (optional) <metadataDefs> element in the library document
contains one or more <metadataDef> elements. Each <metadataDef>
element defines a metadata.
Each <metadataDef> element MUST contain a unique name (NMTOKEN).
Uniqueness is defined to be over all metadata defined in this
library document and in all directly or indirectly included library
documents. The <metadataDef> element MUST also contain a brief
synopsis, the mandatory tag value to be used for this metadata, an
optional detailed description, and a mandatory type definition
information. Only atomic data types can be used as value types for
metadata.
Two forms of type definitions are allowed. The first form uses the
<typeRef> element to refer to an existing atomic data type defined
in the <dataTypeDefs> element of the same library document or in one
of the included library documents. The usage of the <typeRef>
element is identical to how it is used in the <dataTypeDef>
elements, except here it can only refer to atomic types.
The latter restriction is not yet enforced by the XML schema.
The second form is an explicit type definition using the <atomic>
element. This element is used here in the same way as in the
<dataTypeDef> elements.
The following example shows both usages:
<metadataDefs>
<metadataDef>
<name>NEXTHOPID</name>
<synopsis>Refers to a Next Hop entry in NH LFB</synopsis>
<metadataID>17</metaDataID>
<typeRef>int32</typeRef>
</metadataDef>
<metadataDef>
<name>CLASSID</name>
<synopsis>
Result of classification (0 means no match).
</synopsis>
<metadataID>21</metadataID>
<atomic>
<baseType>int32</baseType>
Yang, et al. Expires April 2007 [Page 50]
Internet Draft ForCES FE Model October 2006
<specialValues>
<specialValue value="0">
<name>NOMATCH</name>
<synopsis>
Classification didn’t result in match.
</synopsis>
</specialValue>
</specialValues>
</atomic>
</metadataDef>
</metadataDefs>
4.7. <LFBClassDefs> Element for LFB Class Definitions
The (optional) <LFBClassDefs> element can be used to define one or
more LFB classes using <LFBClassDef> elements. Each <LFBClassDef>
element MUST define an LFB class and include the following elements:
. <name> provides the symbolic name of the LFB class. Example:
"ipv4lpm"
. <synopsis> provides a short synopsis of the LFB class. Example:
"IPv4 Longest Prefix Match Lookup LFB"
. <version> is the version indicator
. <derivedFrom> is the inheritance indicator
. <inputPorts> lists the input ports and their specifications
. <outputPorts> lists the output ports and their specifications
. <attributes> defines the operational attributes of the LFB
. <capabilities> defines the capability attributes of the LFB
. <description> contains the operational specification of the LFB
. The LFBClassID attribute of the LFBClassDef element defines the
ID for this class. These must be globally unique.
. <events> defines the events that can be generated by instances
of this LFB.
LFB Class Names must be unique, in order to enable other documents
to reference the classes by name, and to enable human readers to
understand references to class names. While a complex naming
structure could be created, simplicity is preferred. As given in the
IANA considerations section of this document, the IANA will maintain
a registry of LFB Class names and Class identifiers, along with a
reference to the document defining the class.
Here is a skeleton of an example LFB class definition:
<LFBClassDefs>
<LFBClassDef LFBClassID="12345">
<name>ipv4lpm</name>
<synopsis>IPv4 Longest Prefix Match Lookup LFB</synopsis>
<version>1.0</version>
Yang, et al. Expires April 2007 [Page 51]
Internet Draft ForCES FE Model October 2006
<derivedFrom>baseclass</derivedFrom>
<inputPorts>
...
</inputPorts>
<outputPorts>
...
</outputPorts>
<attributes>
...
</attributes>
<capabilities>
...
</capabilities>
<description>
This LFB represents the IPv4 longest prefix match lookup
operation.
The modeled behavior is as follows:
Blah-blah-blah.
</description>
</LFBClassDef>
...
</LFBClassDefs>
The individual attributes and capabilities will have elementIDs for
use by the ForCES protocol. These parallel the elementIDs used in
structs, and are used the same way. Attribute and capability
elementIDs must be unique within the LFB class definition.
Note that the <name>, <synopsis>, and <version> elements are
required, all other elements are optional in <LFBClassDef>. However,
when they are present, they must occur in the above order.
4.7.1. <derivedFrom> Element to Express LFB Inheritance
The optional <derivedFrom> element can be used to indicate that this
class is a derivative of some other class. The content of this
element MUST be the unique name (<name>) of another LFB class. The
referred LFB class MUST be defined in the same library document or
in one of the included library documents.
It is assumed that the derived class is backwards compatible with
the base class.
Yang, et al. Expires April 2007 [Page 52]
Internet Draft ForCES FE Model October 2006
4.7.2. <inputPorts> Element to Define LFB Inputs
The optional <inputPorts> element is used to define input ports. An
LFB class may have zero, one, or more inputs. If the LFB class has
no input ports, the <inputPorts> element MUST be omitted. The
<inputPorts> element can contain one or more <inputPort> elements,
one for each port or port-group. We assume that most LFBs will have
exactly one input. Multiple inputs with the same input type are
modeled as one input group. Input groups are defined the same way
as input ports by the <inputPort> element, differentiated only by an
optional "group" attribute.
Multiple inputs with different input types should be avoided if
possible (see discussion in Section 3.2.1). Some special LFBs will
have no inputs at all. For example, a packet generator LFB does not
need an input.
Single input ports and input port groups are both defined by the
<inputPort> element; they are differentiated by only an optional
"group" attribute.
The <inputPort> element MUST contain the following elements:
. <name> provides the symbolic name of the input. Example: "in".
Note that this symbolic name must be unique only within the scope
of the LFB class.
. <synopsis> contains a brief description of the input. Example:
"Normal packet input".
. <expectation> lists all allowed frame formats. Example: {"ipv4"
and "ipv6"}. Note that this list should refer to names specified
in the <frameDefs> element of the same library document or in any
included library documents. The <expectation> element can also
provide a list of required metadata. Example: {"classid",
"vifid"}. This list should refer to names of metadata defined in
the <metadataDefs> element in the same library document or in any
included library documents. For each metadata, it must be
specified whether the metadata is required or optional. For each
optional metadata, a default value must be specified, which is
used by the LFB if the metadata is not provided with a packet.
In addition, the optional "group" attribute of the <inputPort>
element can specify if the port can behave as a port group, i.e., it
is allowed to be instantiated. This is indicated by a "yes" value
(the default value is "no").
An example <inputPorts> element, defining two input ports, the
second one being an input port group:
Yang, et al. Expires April 2007 [Page 53]
Internet Draft ForCES FE Model October 2006
<inputPorts>
<inputPort>
<name>in</name>
<synopsis>Normal input</synopsis>
<expectation>
<frameExpected>
<ref>ipv4</ref>
<ref>ipv6</ref>
</frameExpected>
<metadataExpected>
<ref>classid</ref>
<ref>vifid</ref>
<ref dependency="optional" defaultValue="0">vrfid</ref>
</metadataExpected>
</expectation>
</inputPort>
<inputPort group="yes">
... another input port ...
</inputPort>
</inputPorts>
For each <inputPort>, the frame type expectations are defined by the
<frameExpected> element using one or more <ref> elements (see
example above). When multiple frame types are listed, it means that
"one of these" frame types is expected. A packet of any other frame
type is regarded as incompatible with this input port of the LFB
class. The above example list two frames as expected frame types:
"ipv4" and "ipv6".
Metadata expectations are specified by the <metadataExpected>
element. In its simplest form, this element can contain a list of
<ref> elements, each referring to a metadata. When multiple
instances of metadata are listed by <ref> elements, it means that
"all of these" metadata must be received with each packet (except
metadata that are marked as "optional" by the "dependency" attribute
of the corresponding <ref> element). For a metadata that is
specified "optional", a default value MUST be provided using the
"defaultValue" attribute. The above example lists three metadata as
expected metadata, two of which are mandatory ("classid" and
"vifid"), and one being optional ("vrfid").
The schema also allows for more complex definitions of metadata
expectations. For example, using the <one-of> element, a list of
metadata can be specified to express that at least one of the
specified metadata must be present with any packet. For example:
Yang, et al. Expires April 2007 [Page 54]
Internet Draft ForCES FE Model October 2006
<metadataExpected>
<one-of>
<ref>prefixmask</ref>
<ref>prefixlen</ref>
</one-of>
</metadataExpected>
The above example specifies that either the "prefixmask" or the
"prefixlen" metadata must be provided with any packet.
The two forms can also be combined, as it is shown in the following
example:
<metadataExpected>
<ref>classid</ref>
<ref>vifid</ref>
<ref dependency="optional" defaultValue="0">vrfid</ref>
<one-of>
<ref>prefixmask</ref>
<ref>prefixlen</ref>
</one-of>
</metadataExpected>
Although the schema is constructed to allow even more complex
definitions of metadata expectations, we do not discuss those here.
4.7.3. <outputPorts> Element to Define LFB Outputs
The optional <outputPorts> element is used to define output ports.
An LFB class may have zero, one, or more outputs. If the LFB class
has no output ports, the <outputPorts> element MUST be omitted. The
<outputPorts> element can contain one or more <outputPort> elements,
one for each port or port-group. If there are multiple outputs with
the same output type, we model them as an output port group. Some
special LFBs may have no outputs at all (e.g., Dropper).
Single output ports and output port groups are both defined by the
<outputPort> element; they are differentiated by only an optional
"group" attribute.
The <outputPort> element MUST contain the following elements:
. <name> provides the symbolic name of the output. Example: "out".
Note that the symbolic name must be unique only within the scope
of the LFB class.
. <synopsis> contains a brief description of the output port.
Example: "Normal packet output".
. <product> lists the allowed frame formats. Example: {"ipv4",
"ipv6"}. Note that this list should refer to symbols specified in
Yang, et al. Expires April 2007 [Page 55]
Internet Draft ForCES FE Model October 2006
the <frameDefs> element in the same library document or in any
included library documents. The <product> element may also
contain the list of emitted (generated) metadata. Example:
{"classid", "color"}. This list should refer to names of metadata
specified in the <metadataDefs> element in the same library
document or in any included library documents. For each generated
metadata, it should be specified whether the metadata is always
generated or generated only in certain conditions. This
information is important when assessing compatibility between
LFBs.
In addition, the optional "group" attribute of the <outputPort>
element can specify if the port can behave as a port group, i.e., it
is allowed to be instantiated. This is indicated by a "yes" value
(the default value is "no").
The following example specifies two output ports, the second being
an output port group:
<outputPorts>
<outputPort>
<name>out</name>
<synopsis>Normal output</synopsis>
<product>
<frameProduced>
<ref>ipv4</ref>
<ref>ipv4bis</ref>
</frameProduced>
<metadataProduced>
<ref>nhid</ref>
<ref>nhtabid</ref>
</metadataProduced>
</product>
</outputPort>
<outputPort group="yes">
<name>exc</name>
<synopsis>Exception output port group</synopsis>
<product>
<frameProduced>
<ref>ipv4</ref>
<ref>ipv4bis</ref>
</frameProduced>
<metadataProduced>
<ref availability="conditional">errorid</ref>
</metadataProduced>
</product>
</outputPort>
</outputPorts>
Yang, et al. Expires April 2007 [Page 56]
Internet Draft ForCES FE Model October 2006
The types of frames and metadata the port produces are defined
inside the <product> element in each <outputPort>. Within the
<product> element, the list of frame types the port produces is
listed in the <frameProduced> element. When more than one frame is
listed, it means that "one of" these frames will be produced.
The list of metadata that is produced with each packet is listed in
the optional <metadataProduced> element of the <product>. In its
simplest form, this element can contain a list of <ref> elements,
each referring to a metadata type. The meaning of such a list is
that "all of" these metadata are provided with each packet, except
those that are listed with the optional "availability" attribute set
to "conditional". Similar to the <metadataExpected> element of the
<inputPort>, the <metadataProduced> element supports more complex
forms, which we do not discuss here further.
4.7.4. <attributes> Element to Define LFB Operational Attributes
Operational parameters of the LFBs that must be visible to the CEs
are conceptualized in the model as the LFB attributes. These
include, for example, flags, single parameter arguments, complex
arguments, and tables. Note that the attributes here refer to only
those operational parameters of the LFBs that must be visible to the
CEs. Other variables that are internal to LFB implementation are
not regarded as LFB attributes and hence are not covered.
Some examples for LFB attributes are:
. Configurable flags and switches selecting between operational
modes of the LFB
. Number of inputs or outputs in a port group
. Metadata CONSUME vs.PROPAGATE mode selector
. Various configurable lookup tables, including interface tables,
prefix tables, classification tables, DSCP mapping tables, MAC
address tables, etc.
. Packet and byte counters
. Various event counters
. Number of current inputs or outputs for each input or output
group
There may be various access permission restrictions on what the CE
can do with an LFB attribute. The following categories may be
supported:
. No-access attributes. This is useful when multiple access
modes may be defined for a given attribute to allow some
flexibility for different implementations.
. Read-only attributes.
. Read-write attributes.
Yang, et al. Expires April 2007 [Page 57]
Internet Draft ForCES FE Model October 2006
. Write-only attributes. This could be any configurable data for
which read capability is not provided to the CEs. (e.g., the
security key information)
. Read-reset attributes. The CE can read and reset this
resource, but cannot set it to an arbitrary value. Example:
Counters.
. Firing-only attributes. A write attempt to this resource will
trigger some specific actions in the LFB, but the actual value
written is ignored.
The LFB class may define more than one possible access mode for a
given attribute (for example, "write-only" and "read-write"), in
which case it is left to the actual implementation to pick one of
the modes. In such cases, a corresponding capability attribute must
inform the CE about the access mode the actual LFB instance supports
(see next subsection on capability attributes).
The attributes of the LFB class are listed in the <attributes>
element. Each attribute is defined by an <attribute> element. An
<attribute> element MUST contain the following elements:
. <name> defines the name of the attribute. This name must be
unique among the attributes of the LFB class. Example:
"version".
. <synopsis> should provide a brief description of the purpose of
the attribute.
. <optional/> indicates that this attribute is optional.
. The data type of the attribute can be defined either via a
reference to a predefined data type or providing a local
definition of the type. The former is provided by using the
<typeRef> element, which must refer to the unique name of an
existing data type defined in the <dataTypeDefs> element in the
same library document or in any of the included library
documents. When the data type is defined locally (unnamed
type), one of the following elements can be used: <atomic>,
<array>, <struct>, and <union>. Their usage is identical to how
they are used inside <dataTypeDef> elements (see Section 4.5).
. The optional <defaultValue> element can specify a default value
for the attribute, which is applied when the LFB is initialized
or reset.
The attribute element also MUST have an elementID attribute, which
is a numeric value used by the ForCES protocol.
In addition to the above elements, the <attribute> element includes
an optional "access" attribute, which can take any of the following
values or even a list of these values: "read-only", "read-write",
"write-only", "read-reset", and "trigger-only". The default access
mode is "read-write".
Yang, et al. Expires April 2007 [Page 58]
Internet Draft ForCES FE Model October 2006
Whether optional elements are supported, and whether elements
defined as read-write can actually be written can be determined for
a given LFB instance by the CE by reading the property information
of that element.
The following example defines two attributes for an LFB:
<attributes>
<attribute access="read-only" elementID=’’1’’>
<name>foo</name>
<synopsis>number of things</synopsis>
<typeRef>uint32</typeRef>
</attribute>
<attribute access="read-write write-only" elementID=’’2’’>
<name>bar</name>
<synopsis>number of this other thing</synopsis>
<atomic>
<baseType>uint32</baseType>
<rangeRestriction>
<allowedRange min="10" max="2000"/>
</rangeRestriction>
</atomic>
<defaultValue>10</defaultValue>
</attribute>
</attributes>
The first attribute ("foo") is a read-only 32-bit unsigned integer,
defined by referring to the built-in "uint32" atomic type. The
second attribute ("bar") is also an integer, but uses the <atomic>
element to provide additional range restrictions. This attribute has
two possible access modes, "read-write" or "write-only". A default
value of 10 is provided.
Note that not all attributes are likely to exist at all times in a
particular implementation. While the capabilities will frequently
indicate this non-existence, CEs may attempt to reference non-
existent or non-permitted attributes anyway. The FORCES protocol
mechanisms should include appropriate error indicators for this
case.
The mechanism defined above for non-supported attributes can also
apply to attempts to reference non-existent array elements or to set
read-only elements.
4.7.5. <capabilities> Element to Define LFB Capability Attributes
The LFB class specification provides some flexibility for the FE
implementation regarding how the LFB class is implemented. For
Yang, et al. Expires April 2007 [Page 59]
Internet Draft ForCES FE Model October 2006
example, the instance may have some limitations that are not
inherent from the class definition, but rather the result of some
implementation limitations. For example, an array attribute may be
defined in the class definition as "unlimited" size, but the
physical implementation may impose a hard limit on the size of the
array.
Such capability related information is expressed by the capability
attributes of the LFB class. The capability attributes are always
read-only attributes, and they are listed in a separate
<capabilities> element in the <LFBClassDef>. The <capabilities>
element contains one or more <capability> elements, each defining
one capability attribute. The format of the <capability> element is
almost the same as the <attribute> element, it differs in two
aspects: it lacks the access mode attribute (because it is always
read-only), and it lacks the <defaultValue> element (because default
value is not applicable to read-only attributes).
Some examples of capability attributes follow:
. The version of the LFB class that this LFB instance complies
with;
. Supported optional features of the LFB class;
. Maximum number of configurable outputs for an output group;
. Metadata pass-through limitations of the LFB;
. Maximum size of configurable attribute tables;
. Additional range restriction on operational attributes;
. Supported access modes of certain attributes (if the access
mode of an operational attribute is specified as a list of two
or mode modes).
The following example lists two capability attributes:
<capabilities>
<capability elementID="3">
<name>version</name>
<synopsis>
LFB class version this instance is compliant with.
</synopsis>
<typeRef>version</typeRef>
</capability>
<capability elementID="4">
<name>limitBar</name>
<synopsis>
Maximum value of the "bar" attribute.
</synopsis>
<typeRef>uint16</typeRef>
</capability>
</capabilities>
Yang, et al. Expires April 2007 [Page 60]
Internet Draft ForCES FE Model October 2006
4.7.6. <events> Element for LFB Notification Generation
The <events> element contains the information about the occurrences
for which instances of this LFB class can generate notifications to
the CE.
The <events> definition needs a baseID attributevalue, which is
normally <events baseID=’’number’’>. The value of the baseID is the
starting element for the path which identifies events. It must not
be the same as the elementID of any top level attribute or
capability of the LFB class. In derived LFBs (i.e. ones with a
<derivedFrom> element) where the parent LFB class has an events
declaration, the baseID must not be present. Instead, the value
from the parent class is used.
The <events> element contains 0 or more <event> elements, each of
which declares a single event. The <event> element has an eventID
attribute giving the unique ID of the event. The element will
include:
. <eventTarget> element indicating which LFB field is tested to
generate the event;
. condition element indicating what condition on the field will
generate the event from a list of defined conditions;
. <eventReports> element indicating what values are to be
reported in the notification of the event.
4.7.6.1 <eventTarget> Element
The <eventTarget> element contains information identifying a field
in the LFB. Specifically, the <target> element contains one or more
<eventField> or <eventSubscript> elements. These elements represent
the textual equivalent of a path select component of the LFB. The
<eventField> element contains the name of an element in the LFB or
struct. The first element in a <target> MUST be an <eventField>
element and MUST name a field in the LFB. The following element
MUST identify a valid field within the containing context. If an
<eventField> identifies an array, and is not the last element in the
target, then the next element MUST be an <eventSubscript>.
<eventSubscript> elements MUST occur only after <eventField> names
that identifies an array. An <eventSubscript> may contain a numeric
value to indicate that this event applies to a specific element of
the array. More commonly, the event is being defined across all
elements of the array. In that case, <eventSubscript> will contain
a name. The name in an <eventSubscript> element is not a field
name. It is a variable name for use in the <report> elements of
this LFB definition. This name MUST be distinct from any field name
that can validly occur in the <eventReport> clause. Hence it SHOULD
Yang, et al. Expires April 2007 [Page 61]
Internet Draft ForCES FE Model October 2006
be distinct from any field name used in the LFB or in structures
used within the LFB.
The <eventTarget> provides additional components for the path used
to reference the event. The path will be the baseID for events,
followed by the ID for the specific event, followed by a value for
each <eventSubscript> element in the <eventTarget>. This will
identify a specific occurrence of the event. So, for example, it
will appear in the event notification LFB. It is also used for the
SET-PROPERTY operation to subscribe to a specific event. A SET-
PROPERTY of the subscription property (but not of any other
writeable properties) may be sent by the CE with any prefix of the
path of the event. So, for an event defined on a table, a SET-
PROPERTY with a path of the baseID and the eventID will subscribe
the CE to all occurrences of that event on any element of the table.
This is particularly useful for the <eventCreated/> and
<eventDestroyed/> conditions. Events using those conditions will
generally be defined with a field / subscript sequence that
identifies an array and ends with an <eventSubscript> element.
Thus, the event notification will indicate which array entry has
been created or destroyed. A typical subscriber will subscribe for
the array, as opposed to a specific element in an array, so it will
use a shorter path.
Thus, if there is an LFB with an event baseID of 7, and a specific
event with an event ID of 8, then one can subscribe to the event by
referencing the properties of the LFB element with path 7.8. If the
event target has no subscripts (for example, it is a simple
attribute of the LFB) then one can also reference the event
threshold and filtering properties via the properties on element
7.8. If the event target is defined as an element of an array, then
the target definition will include an <eventSubscript> element. In
that case, one can subscribe to the event for the entire array by
referencing the properties of 7.8. One can also subscribe to a
specific element, x, of the array by referencing the subscription
property of 7.8.x and also access the threshold and filtering
properties of 7.8.x. If the event is targeting an element of an
array within an array, then there will be two (or conceivably more)
<eventSubscript> elements in the target. If so, for the case of two
elements, one would reference the properties of 7.8.x.y to get to
the threshold and filtering properties of an individual event.
Threshold and filtering conditions can only be applied to individual
events. For events defined on elements of an array, this
specification does not allow for defining a threshold or filtering
condition on an event for all elements of an array.
Yang, et al. Expires April 2007 [Page 62]
Internet Draft ForCES FE Model October 2006
4.7.6.2 <events> Element Conditions
The condition element represents a condition that triggers a
notification. The list of conditions is:
. <eventCreated/> the target must be an array, ending with a
subscript indication. The event is generated when an entry in
the array is created. This occurs even if the entry is created
by CE direction.
. <eventDeleted/> the target must be an array, ending with a
subscript indication. The event is generated when an entry in
the array is destroyed. This occurs even if the entry is
destroyed by CE direction.
. <eventChanged/> the event is generated whenever the target
element changes in any way. For binary attributes such as
up/down, this reflects a change in state. It can also be used
with numeric attributes, in which case any change in value
results in a detected trigger.
. <eventGreaterThan/> the event is generated whenever the target
element becomes greater than the threshold. The threshold is
an event property.
. <eventLessThan/> the event is generated whenever the target
element becomes less than the threshold. The threshold is an
event property.
As described in the Event Properties section, event items have
properties associated with them. These properties include the
subscription information (indicating whether the CE wishes the FE to
generate event reports for the event at all, thresholds for events
related to level crossing, and filtering conditions that may reduce
the set of event notifications generated by the FE. Details of the
filtering conditions that can be applied are given in that section.
The filtering conditions allow the FE to suppress floods of events
that could result from oscillation around a condition value. For FEs
that do not wish to support filtering, the filter properties can
either be read only or not supported.
4.7.6.3 <eventReports> Element
The <eventReports> element of an <event> describes the information
to be delivered by the FE along with the notification of the
occurrence of the event. The <reports> element contains one or more
<eventReport> elements. Each <report> element identifies a piece of
data from the LFB to be reported. The notification carries that
data as if the collection of <eventReport> elements had been defined
in a structure. Each <eventReport> element thus MUST identify a
field in the LFB. The syntax is exactly the same as used in the
<eventTarget> element, using <eventField> and <eventSubscript>
elements. <eventSubcripts> may contain integers. If they contain
Yang, et al. Expires April 2007 [Page 63]
Internet Draft ForCES FE Model October 2006
names, they MUST be names from <eventSubscript> elements of the
<eventTarget>. The selection for the report will use the value for
the subscript that identifies that specific element triggering the
event. This can be used to reference the structure / field causing
the event, or to reference related information in parallel tables.
This event reporting structure is designed to allow the LFB designer
to specify information that is likely not known a priori by the CE
and is likely needed by the CE to process the event. While the
structure allows for pointing at large blocks of information (full
arrays or complex structures) this is not recommended. Also, the
variable reference / subscripting in reporting only captures a small
portion of the kinds of related information. Chaining through index
fields stored in a table, for example, is not supported. In
general, the <eventReports> mechanism is an optimization for cases
that have been found to be common, saving the CE from having to
query for information it needs to understand the event. It does not
represent all possible information needs.
If any elements referenced by the eventReport are optional, then the
report MUST support optional elements. Any components which do not
exist are not reported.
4.7.7. <description> Element for LFB Operational Specification
The <description> element of the <LFBClass> provides unstructured
text (in XML sense) to verbally describe what the LFB does.
4.8.Properties
Elements of LFBs have properties which are important to the CE. The
most important property is the existence / readability /
writeability of the element. Depending up the type of the element,
other information may be of importance.
The model provides the definition of the structure of property
information. There is a base class of property information. For
the array, alias, and event elements there are subclasses of
property information providing additional fields. This information
is accessed by the CE (and updated where applicable) via the PL
protocol. While some property information is writeable, there is no
mechanism currently provided for checking the properties of a
property element. Writeability can only be checked by attempting to
modify the value.
4.8.1. Basic Properties
The basic property definition, along with the scalar for
accessibility is below. Note that this access permission
information is generally read-only.
Yang, et al. Expires April 2007 [Page 64]
Internet Draft ForCES FE Model October 2006
<dataTypeDef>
<name>accessPermissionValues</name>
<synopsis>
The possible values of attribute access permission
</synopsis>
<atomic>
<baseType>uchar</baseType>
<specialValues>
<specialValue value="0">
<name>None</name>
<synopsis>Access is prohibited</synopsis>
</specialValue>
<specialValue value="1">
<name> Read-Only </name>
<synopsis>Access is read only</synopsis>
</specialValue>
<specialValue value="2">
<name>Write-Only</name>
<synopsis>
The attribute may be written, but not read
</synopsis>
</specialValue>
<specialValue value="3">
<name>Read-Write</name>
<synopsis>
The attribute may be read or written
</synopsis>
</specialValue>
</specialValues>
</atomic>
</dataTypeDef>
<dataTypeDef>
<name>baseElementProperties</name>
<synopsis>basic properties, accessibility</synopsis>
<struct>
<element elementID="1">
<name>accessibility</name>
<synopsis>
does the element exist, and
can it be read or written
</synopsis>
<typeRef>accessPermissionValues</typeRef>
</element>
</struct>
</dataTypeDef>
Yang, et al. Expires April 2007 [Page 65]
Internet Draft ForCES FE Model October 2006
4.8.2. Array Properties
The properties for an array add a number of important pieces of
information. These properties are also read-only.
<dataTypeDef>
<name>arrayElementProperties</name>
<struct>
<derivedFrom>baseElementProperties</derivedFrom>
<element elementID=’’2’’>
<name>entryCount</name>
<synopsis>the number of entries in the array</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’3’’>
<name>highestUsedSubscript</name>
<synopsis>the last used subscript in the array</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’4’’>
<name>firstUnusedSubscript</name>
<synopsis>
The subscript of the first unused array element
</synopsis>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
4.8.3. String Properties
The properties of a string specify the actual octet length and the
maximum octet length for the element. The maximum length is
included because an FE implementation may limit a string to be
shorter than the limit in the LFB Class definition.
<dataTypeDef>
<name>stringElementProperties</name>
<struct>
<derivedFrom>baseElementProperties</derivedFrom>
<element elementID=’’2’’>
<name>stringLength</name>
<synopsis>the number of octets in the string</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’3’’>
<name>maxStringLength</name>
<synopsis>
the maximum number of octets in the string
Yang, et al. Expires April 2007 [Page 66]
Internet Draft ForCES FE Model October 2006
</synopsis>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
4.8.4. Octetstring Properties
The properties of an octetstring specify the actual length and the
maximum length, since the FE implementation may limit an octetstring
to be shorter than the LFB Class definition.
<dataTypeDef>
<name>octetstringElementProperties</name>
<struct>
<derivedFrom>baseElementProperties</derivedFrom>
<element elementID=’’2’’>
<name>octetstringLength</name>
<synopsis>
the number of octets in the octetstring
</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’3’’>
<name>maxOctetstringLength</name>
<synopsis>
the maximum number of octets in the octetstring
</synopsis>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
4.8.5. Event Properties
The properties for an event add three (usually) writeable fields.
One is the subscription field. 0 means no notification is
generated. Any non-zero value (typically 1 is used) means that a
notification is generated. The hysteresis field is used to suppress
generation of notifications for oscillations around a condition
value, and is described in the text for events. The threshold field
is used for the <eventGreaterThan/> and <eventLessThan/> conditions.
It indicates the value to compare the event target against. Using
the properties allows the CE to set the level of interest. FEs
which do not supporting setting the threshold for events will make
this field read-only.
Yang, et al. Expires April 2007 [Page 67]
Internet Draft ForCES FE Model October 2006
<dataTypeDef>
<name>eventElementProperties</name>
<struct>
<derivedFrom>baseElementProperties</derivedFrom>
<element elementID=’’2’’>
<name>registration</name>
<synopsis>
has the CE registered to be notified of this event
</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’3’’>
<name>threshold</name>
<synopsis> comparison value for level crossing events
</synopsis>
</optional
<typeRef>uint32</typeRef>
</element>
<element elementID=’’4’’>
<name>eventHysteresis</name>
<synopsis> region to suppress event recurrence notices
</synopsis>
</optional>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’5’’>
<name>eventCount</name>
<synopsis> number of occurrences to suppress
</synopsis>
</optional>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’6’’>
<name>eventHysteresis</name>
<synopsis> time interval in ms between notifications
</synopsis>
</optional>
<typeRef>uint32</typeRef>
</element>
</struct>
<dataTypeDef>
4.8.5.1. Common Event Filtering
The event properties have values for controlling several filter
conditions. Support of these conditions is optional, but all
conditions SHOULD be supported. Events which are reliably known not
to be subject to rapid occurrence or other concerns may not support
all filter conditions.
Yang, et al. Expires April 2007 [Page 68]
Internet Draft ForCES FE Model October 2006
Currently, three different filter condition variables are defined.
These are eventCount, eventInterval, and eventHysteresis. Setting
the condition variables to 0 (their default value) means that the
condition is not checked.
Conceptually, when an event is triggered, all configured conditions
are checked. If no filter conditions are triggered, or if any
trigger conditions are met, the event notification is generated. If
there are filter conditions, and no condition is met, then no event
notification is generated. Event filter conditions have reset
behavior when an event notification is generated. If any condition
is passed, and the notification is generated, the notification reset
behavior is performed on all conditions, even those which had not
passed. This provides a clean definition of the interaction of the
various event conditions.
An example of the interaction of conditions is an event with an
eventCount property set to 5 and an eventInterval property set to
500 milliseconds. Suppose that a burst of occurrences of this event
is detected by the FE. The first occurrence will cause a
notification to be sent to the CE. Then, if four more occurrences
are detected rapidly (less than 0.5 seconds) they will not result in
notifications. If two more occurrences are detected, then the
second of those will result in a notification. Alternatively, if
more than 500 milliseconds has passed since the notification and an
occurrence is detected, that will result in a notification. In
either case, the count and time interval suppression is reset no
matter which condition actually caused the notification.
4.8.5.2. Event Hysteresis Filtering
Events with numeric conditions can have hysteresis filters applied
to them. The hysteresis level is defined by a property of the
event. This allows the FE to notify the CE of the hysteresis
applied, and if it chooses, the FE can allow the CE to modify the
hysteresis. This applies to <eventChanged/> for a numeric field,
and to <eventGreaterThan/> and <eventLessThan/>. The content of a
<variance> element is a numeric value. When supporting hysteresis,
the FE MUST track the value of the element and make sure that the
condition has become untrue by at least the hysteresis from the
event property. To be specific, if the hysteresis is V, then
. For a <eventChanged/> condition, if the last notification was
for value X, then the <changed/> notification MUST NOT be
generated until the value reaches X +/- V.
. For a <eventGreaterThan/> condition with threshold T, once the
event has been generated at least once it MUST NOT be generated
Yang, et al. Expires April 2007 [Page 69]
Internet Draft ForCES FE Model October 2006
again until the field first becomes less than or equal to T -
-
V, and then exceeds T.
. For a <eventLessThan/> condition with threshold T, once the
event has been generate at least once it MUST NOT be generated
again until the field first becomes greater than or equal to T
+ V, and then becomes less than T.
4.8.5.3. Event Count Filtering
Events may have a count filtering condition. This property, if set
to a non-zero value, indicates the number of occurrences of the event
that should be considered redundant and not result in a notification.
Thus, if this property is set to 1, and no other conditions apply,
then every other detected occurrence of the event will result in a
notification. This particular meaning is chosen so that the value 1
has a distinct meaning from the value 0.
A conceptual implementation (not required) for this might be an
internal suppression counter. Whenever an event is triggered, the
counter is checked. If the counter is 0, a notification is
generated. Whether a notification is generated or not, the counter
is incremented. If the counter exceeds the configured value, it is
reset to 0. In this conceptual implementation the reset behavior
when a notification is generated can be thought of as setting the
counter to 1.
4.8.5.4. Event Time Filtering
Events may have a time filtering condition. This property
represents the minimum time interval (in the absence of some other
filtering condition being passed) between generating notifications of
detected events. This condition MUST only be passed if the time
since the last notification of the event is longer than the
configured interval in milliseconds.
Conceptually, this can be thought of as a stored timestamp which is
compared with the detection time, or as a timer that is running that
resets a suppression flag. In either case, if a notification is
generated due to passing any condition then the time interval
detection MUST be restarted.
4.8.6. Alias Properties
The properties for an alias add three (usually) writeable fields.
These combine to identify the target element the subject alias
refers to.
Yang, et al. Expires April 2007 [Page 70]
Internet Draft ForCES FE Model October 2006
<dataTypeDef>
<name>aliasElementProperties</name>
<struct>
<derivedFrom>baseElementProperties</derivedFrom>
<element elementID=’’2’’>
<name>targetLFBClass</name>
<synopsis>the class ID of the alias target</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’3’’>
<name>targetLFBInstance</name>
<synopsis>the instance ID of the alias target</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’4’’>
<name>targetElementPath</name>
<synopsis>
the path to the element target
each 4 octets is read as one path element,
using the path construction in the PL protocol.
</synopsis>
<typeRef>octetstring[128]</typeRef>
</element>
</struct>
</dataTypeDef>
4.9. XML Schema for LFB Class Library Documents
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns="http://ietf.org/forces/1.0/lfbmodel"
xmlns:lfb="http://ietf.org/forces/1.0/lfbmodel"
targetNamespace="http://ietf.org/forces/1.0/lfbmodel"
attributeFormDefault="unqualified"
elementFormDefault="qualified">
<xsd:annotation>
<xsd:documentation xml:lang="en">
Schema for Defining LFB Classes and associated types (frames,
data types for LFB attributes, and metadata).
</xsd:documentation>
</xsd:annotation>
<xsd:element name="description" type="xsd:string"/>
<xsd:element name="synopsis" type="xsd:string"/>
<!-- Document root element: LFBLibrary -->
<xsd:element name="LFBLibrary">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="description" minOccurs="0"/>
<xsd:element name="load" type="loadType" minOccurs="0"
Yang, et al. Expires April 2007 [Page 71]
Internet Draft ForCES FE Model October 2006
maxOccurs="unbounded"/>
<xsd:element name="frameDefs" type="frameDefsType"
minOccurs="0"/>
<xsd:element name="dataTypeDefs" type="dataTypeDefsType"
minOccurs="0"/>
<xsd:element name="metadataDefs" type="metadataDefsType"
minOccurs="0"/>
<xsd:element name="LFBClassDefs" type="LFBClassDefsType"
minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="provides" type="xsd:Name" use="required"/>
</xsd:complexType>
<!-- Uniqueness constraints -->
<xsd:key name="frame">
<xsd:selector xpath="lfb:frameDefs/lfb:frameDef"/>
<xsd:field xpath="lfb:name"/>
</xsd:key>
<xsd:key name="dataType">
<xsd:selector xpath="lfb:dataTypeDefs/lfb:dataTypeDef"/>
<xsd:field xpath="lfb:name"/>
</xsd:key>
<xsd:key name="metadataDef">
<xsd:selector xpath="lfb:metadataDefs/lfb:metadataDef"/>
<xsd:field xpath="lfb:name"/>
</xsd:key>
<xsd:key name="LFBClassDef">
<xsd:selector xpath="lfb:LFBClassDefs/lfb:LFBClassDef"/>
<xsd:field xpath="lfb:name"/>
</xsd:key>
</xsd:element>
<xsd:complexType name="loadType">
<xsd:attribute name="library" type="xsd:Name" use="required"/>
<xsd:attribute name="location" type="xsd:anyURI" use="optional"/>
</xsd:complexType>
<xsd:complexType name="frameDefsType">
<xsd:sequence>
<xsd:element name="frameDef" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element ref="description" minOccurs="0"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="dataTypeDefsType">
<xsd:sequence>
Yang, et al. Expires April 2007 [Page 72]
Internet Draft ForCES FE Model October 2006
<xsd:element name="dataTypeDef" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element ref="description" minOccurs="0"/>
<xsd:group ref="typeDeclarationGroup"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<!--
Predefined (built-in) atomic data-types are:
char, uchar, int16, uint16, int32, uint32, int64, uint64,
string[N], string, byte[N], boolean, octetstring[N],
float16, float32, float64
-->
<xsd:group name="typeDeclarationGroup">
<xsd:choice>
<xsd:element name="typeRef" type="typeRefNMTOKEN"/>
<xsd:element name="atomic" type="atomicType"/>
<xsd:element name="array" type="arrayType"/>
<xsd:element name="struct" type="structType"/>
<xsd:element name="union" type="structType"/>
<xsd:element name="alias" type="typeRefNMTOKEN"/>
</xsd:choice>
</xsd:group>
<xsd:simpleType name="typeRefNMTOKEN">
<xsd:restriction base="xsd:token">
<xsd:pattern value="\c+"/>
<xsd:pattern value="string\[\d+\]"/>
<xsd:pattern value="byte\[\d+\]"/>
<xsd:pattern value="octetstring\[\d+\]"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:complexType name="atomicType">
<xsd:sequence>
<xsd:element name="baseType" type="typeRefNMTOKEN"/>
<xsd:element name="rangeRestriction"
type="rangeRestrictionType" minOccurs="0"/>
<xsd:element name="specialValues" type="specialValuesType"
minOccurs="0"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="rangeRestrictionType">
<xsd:sequence>
<xsd:element name="allowedRange" maxOccurs="unbounded">
<xsd:complexType>
Yang, et al. Expires April 2007 [Page 73]
Internet Draft ForCES FE Model October 2006
<xsd:attribute name="min" type="xsd:integer"
use="required"/>
<xsd:attribute name="max" type="xsd:integer"
use="required"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="specialValuesType">
<xsd:sequence>
<xsd:element name="specialValue" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
</xsd:sequence>
<xsd:attribute name="value" type="xsd:token"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="arrayType">
<xsd:sequence>
<xsd:group ref="typeDeclarationGroup"/>
<xsd:element name="contentKey" minOccurs="0"
maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="contentKeyField" maxOccurs="unbounded"
type="xsd:string"/>
</xsd:sequence>
<xsd:attribute name="contentKeyID" use="required"
type="xsd:integer"/>
</xsd:complexType>
<!--declare keys to have unique IDs -->
<xsd:key name="contentKeyID">
<xsd:selector xpath="lfb:contentKey"/>
<xsd:field xpath="@contentKeyID"/>
</xsd:key>
</xsd:element>
</xsd:sequence>
<xsd:attribute name="type" use="optional"
default="variable-size">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:enumeration value="fixed-size"/>
<xsd:enumeration value="variable-size"/>
</xsd:restriction>
</xsd:simpleType>
Yang, et al. Expires April 2007 [Page 74]
Internet Draft ForCES FE Model October 2006
</xsd:attribute>
<xsd:attribute name="length" type="xsd:integer" use="optional"/>
<xsd:attribute name="maxLength" type="xsd:integer"
use="optional"/>
</xsd:complexType>
<xsd:complexType name="structType">
<xsd:sequence>
<xsd:element name="derivedFrom" type="typeRefNMTOKEN"
minOccurs="0"/>
<xsd:element name="element" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element name="optional" minOccurs="0"/>
<xsd:group ref="typeDeclarationGroup"/>
</xsd:sequence>
<xsd:attribute name="elementID" use="required"
type="xsd:integer"/>
</xsd:complexType>
<!-- key declaration to make elementIDs unique in a struct
-->
<xsd:key name="structElementID">
<xsd:selector xpath="lfb:element"/>
<xsd:field xpath="@elementID"/>
</xsd:key>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="metadataDefsType">
<xsd:sequence>
<xsd:element name="metadataDef" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element name="metadataID" type="xsd:integer"/>
<xsd:element ref="description" minOccurs="0"/>
<xsd:choice>
<xsd:element name="typeRef" type="typeRefNMTOKEN"/>
<xsd:element name="atomic" type="atomicType"/>
</xsd:choice>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="LFBClassDefsType">
<xsd:sequence>
Yang, et al. Expires April 2007 [Page 75]
Internet Draft ForCES FE Model October 2006
<xsd:element name="LFBClassDef" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element name="version" type="versionType"/>
<xsd:element name="derivedFrom" type="xsd:NMTOKEN"
minOccurs="0"/>
<xsd:element name="inputPorts" type="inputPortsType"
minOccurs="0"/>
<xsd:element name="outputPorts" type="outputPortsType"
minOccurs="0"/>
<xsd:element name="attributes" type="LFBAttributesType"
minOccurs="0"/>
<xsd:element name="capabilities"
type="LFBCapabilitiesType" minOccurs="0"/>
<xsd:element name="events"
type="eventsType" minOccurs="0"/>
<xsd:element ref="description" minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="LFBClassID" use="required"
type="xsd:integer"/>
</xsd:complexType>
<!-- Key constraint to ensure unique attribute names within
a class:
-->
<xsd:key name="attributes">
<xsd:selector xpath="lfb:attributes/lfb:attribute"/>
<xsd:field xpath="lfb:name"/>
</xsd:key>
<xsd:key name="capabilities">
<xsd:selector xpath="lfb:capabilities/lfb:capability"/>
<xsd:field xpath="lfb:name"/>
</xsd:key>
<!-- does the above ensure that attributes and capabilities
have different names?
If so, the following is the elementID constraint
-->
<xsd:key name="attributeIDs">
<xsd:selector xpath="lfb:attributes/lfb:attribute"/>
<xsd:field xpath="@elementID"/>
</xsd:key>
<xsd:key name="capabilityIDs">
<xsd:selector xpath="lfb:attributes/lfb:capability"/>
<xsd:field xpath="@elementID"/>
</xsd:key>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
Yang, et al. Expires April 2007 [Page 76]
Internet Draft ForCES FE Model October 2006
<xsd:simpleType name="versionType">
<xsd:restriction base="xsd:NMTOKEN">
<xsd:pattern value="[1-9][0-9]*\.([1-9][0-9]*|0)"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:complexType name="inputPortsType">
<xsd:sequence>
<xsd:element name="inputPort" type="inputPortType"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="inputPortType">
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element name="expectation" type="portExpectationType"/>
<xsd:element ref="description" minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="group" type="booleanType" use="optional"
default="no"/>
</xsd:complexType>
<xsd:complexType name="portExpectationType">
<xsd:sequence>
<xsd:element name="frameExpected" minOccurs="0">
<xsd:complexType>
<xsd:sequence>
<!-- ref must refer to a name of a defined frame type -->
<xsd:element name="ref" type="xsd:string"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="metadataExpected" minOccurs="0">
<xsd:complexType>
<xsd:choice maxOccurs="unbounded">
<!-- ref must refer to a name of a defined metadata -->
<xsd:element name="ref" type="metadataInputRefType"/>
<xsd:element name="one-of"
type="metadataInputChoiceType"/>
</xsd:choice>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="metadataInputChoiceType">
<xsd:choice minOccurs="2" maxOccurs="unbounded">
<!-- ref must refer to a name of a defined metadata -->
<xsd:element name="ref" type="xsd:NMTOKEN"/>
<xsd:element name="one-of" type="metadataInputChoiceType"/>
Yang, et al. Expires April 2007 [Page 77]
Internet Draft ForCES FE Model October 2006
<xsd:element name="metadataSet" type="metadataInputSetType"/>
</xsd:choice>
</xsd:complexType>
<xsd:complexType name="metadataInputSetType">
<xsd:choice minOccurs="2" maxOccurs="unbounded">
<!-- ref must refer to a name of a defined metadata -->
<xsd:element name="ref" type="metadataInputRefType"/>
<xsd:element name="one-of" type="metadataInputChoiceType"/>
</xsd:choice>
</xsd:complexType>
<xsd:complexType name="metadataInputRefType">
<xsd:simpleContent>
<xsd:extension base="xsd:NMTOKEN">
<xsd:attribute name="dependency" use="optional"
default="required">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:enumeration value="required"/>
<xsd:enumeration value="optional"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
<xsd:attribute name="defaultValue" type="xsd:token"
use="optional"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:complexType name="outputPortsType">
<xsd:sequence>
<xsd:element name="outputPort" type="outputPortType"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="outputPortType">
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element name="product" type="portProductType"/>
<xsd:element ref="description" minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="group" type="booleanType" use="optional"
default="no"/>
</xsd:complexType>
<xsd:complexType name="portProductType">
<xsd:sequence>
<xsd:element name="frameProduced">
<xsd:complexType>
<xsd:sequence>
<!-- ref must refer to a name of a defined frame type
Yang, et al. Expires April 2007 [Page 78]
Internet Draft ForCES FE Model October 2006
-->
<xsd:element name="ref" type="xsd:NMTOKEN"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="metadataProduced" minOccurs="0">
<xsd:complexType>
<xsd:choice maxOccurs="unbounded">
<!-- ref must refer to a name of a defined metadata
-->
<xsd:element name="ref" type="metadataOutputRefType"/>
<xsd:element name="one-of"
type="metadataOutputChoiceType"/>
</xsd:choice>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="metadataOutputChoiceType">
<xsd:choice minOccurs="2" maxOccurs="unbounded">
<!-- ref must refer to a name of a defined metadata -->
<xsd:element name="ref" type="xsd:NMTOKEN"/>
<xsd:element name="one-of" type="metadataOutputChoiceType"/>
<xsd:element name="metadataSet" type="metadataOutputSetType"/>
</xsd:choice>
</xsd:complexType>
<xsd:complexType name="metadataOutputSetType">
<xsd:choice minOccurs="2" maxOccurs="unbounded">
<!-- ref must refer to a name of a defined metadata -->
<xsd:element name="ref" type="metadataOutputRefType"/>
<xsd:element name="one-of" type="metadataOutputChoiceType"/>
</xsd:choice>
</xsd:complexType>
<xsd:complexType name="metadataOutputRefType">
<xsd:simpleContent>
<xsd:extension base="xsd:NMTOKEN">
<xsd:attribute name="availability" use="optional"
default="unconditional">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:enumeration value="unconditional"/>
<xsd:enumeration value="conditional"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
Yang, et al. Expires April 2007 [Page 79]
Internet Draft ForCES FE Model October 2006
<xsd:complexType name="LFBAttributesType">
<xsd:sequence>
<xsd:element name="attribute" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element ref="description" minOccurs="0"/>
<xsd:element name="optional" minOccurs="0"/>
<xsd:group ref="typeDeclarationGroup"/>
<xsd:element name="defaultValue" type="xsd:token"
minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="access" use="optional"
default="read-write">
<xsd:simpleType>
<xsd:list itemType="accessModeType"/>
</xsd:simpleType>
</xsd:attribute>
<xsd:attribute name="elementID" use="required"
type="xsd:integer"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:simpleType name="accessModeType">
<xsd:restriction base="xsd:NMTOKEN">
<xsd:enumeration value="read-only"/>
<xsd:enumeration value="read-write"/>
<xsd:enumeration value="write-only"/>
<xsd:enumeration value="read-reset"/>
<xsd:enumeration value="trigger-only"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:complexType name="LFBCapabilitiesType">
<xsd:sequence>
<xsd:element name="capability" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element ref="description" minOccurs="0"/>
<xsd:element name="optional" minOccurs="0"/>
<xsd:group ref="typeDeclarationGroup"/>
</xsd:sequence>
<xsd:attribute name="elementID" use="required"
type="xsd:integer"/>
</xsd:complexType>
</xsd:element>
Yang, et al. Expires April 2007 [Page 80]
Internet Draft ForCES FE Model October 2006
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="eventsType">
<xsd:sequence>
<xsd:element name="event" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/>
<xsd:element name="eventTarget" type="eventPathType"/>
<xsd:element ref="eventCondition"/>
<xsd:element name="eventReports" type="eventReportsType"
minOccurs="0"/>
<xsd:element ref="description" minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="eventID" use="required"
type="xsd:integer"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
<xsd:attribute name="baseID" type="xsd:integer"
use="optional"/>
</xsd:complexType>
<!-- the substitution group for the event conditions -->
<xsd:element name="eventCondition" abstract="true"/>
<xsd:element name="eventCreated"
substitutionGroup="eventCondition"/>
<xsd:element name="eventDeleted"
substitutionGroup="eventCondition"/>
<xsd:element name="eventChanged"
substitutionGroup="eventCondition"/>
<xsd:element name="eventGreaterThan"
substitutionGroup="eventCondition"/>
<xsd:element name="eventLessThan"
substitutionGroup="eventCondition"/>
<xsd:complexType name="eventPathType">
<xsd:sequence>
<xsd:element ref="eventPathPart" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<!-- the substitution group for the event path parts -->
<xsd:element name="eventPathPart" type="xsd:string"
abstract="true"/>
<xsd:element name="eventField" type="xsd:string"
substitutionGroup="eventPathPart"/>
<xsd:element name="eventSubscript" type="xsd:string"
substitutionGroup="eventPathPart"/>
<xsd:complexType name="eventReportsType">
Yang, et al. Expires April 2007 [Page 81]
Internet Draft ForCES FE Model October 2006
<xsd:sequence>
<xsd:element name="eventReport" type="eventPathType"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xsd:simpleType name="booleanType">
<xsd:restriction base="xsd:string">
<xsd:enumeration value="0"/>
<xsd:enumeration value="1"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:schema>
5. FE Attributes and Capabilities
A ForCES forwarding element handles traffic on behalf of a ForCES
control element. While the standards will describe the protocol and
mechanisms for this control, different implementations and different
instances will have different capabilities. The CE MUST be able to
determine what each instance it is responsible for is actually
capable of doing. As stated previously, this is an approximation.
The CE is expected to be prepared to cope with errors in requests
and variations in detail not captured by the capabilities
information about an FE.
In addition to its capabilities, an FE will have attribute
information that can be used in understanding and controlling the
forwarding operations. Some of the attributes will be read only,
while others will also be writeable.
In order to make the FE attribute information easily accessible, the
information will be stored in an LFB. This LFB will have a class,
FEObject. The LFBClassID for this class is 1. Only one instance of
this class will ever be present, and the instance ID of that
instance in the protocol is 1. Thus, by referencing the elements of
class:1, instance:1 a CE can get all the information about the FE.
For model completeness, this LFB Class is described in this section.
There will also be an FEProtocol LFB Class. LFBClassID 2 is
reserved for that class. There will be only one instance of that
class as well. Details of that class are defined in the ForCES
protocol document.
5.1. XML for FEObject Class definition
<?xml version="1.0" encoding="UTF-8"?>
<LFBLibrary xmlns="http://ietf.org/forces/1.0/lfbmodel"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://ietf.org/forces/1.0/lfbmodel.xsd"
Yang, et al. Expires April 2007 [Page 82]
Internet Draft ForCES FE Model October 2006
provides="FEObject">
<!--
-
-
xmlns and schemaLocation need to be fixed -->
<dataTypeDefs>
<dataTypeDef>
<name>LFBAdjacencyLimitType</name>
<synopsis>Describing the Adjacent LFB</synopsis>
<struct>
<element elementID="1">
<name>NeighborLFB</name>
<synopsis>ID for that LFB Class</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="2">
<name>ViaPorts</name>
<synopsis>
the ports on which we can connect
</synopsis>
<array type="variable-size">
<typeRef>string</typeRef>
</array>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>PortGroupLimitType</name>
<synopsis>
Limits on the number of ports in a given group
</synopsis>
<struct>
<element elementID="1">
<name>PortGroupName</name>
<synopsis>Group Name</synopsis>
<typeRef>string</typeRef>
</element>
<element elementID="2">
<name>MinPortCount</name>
<synopsis>Minimum Port Count</synopsis>
<optional/>
<typeRef>uint32</typeRef>
</element>
<element elementID="3">
<name>MaxPortCount</name>
<synopsis>Max Port Count</synopsis>
<optional/>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
Yang, et al. Expires April 2007 [Page 83]
Internet Draft ForCES FE Model October 2006
<name>SupportedLFBType</name>
<synopsis>table entry for supported LFB</synopsis>
<struct>
<element elementID="1">
<name>LFBName</name>
<synopsis>
The name of a supported LFB Class
</synopsis>
<typeRef>string</typeRef>
</element>
<element elementID="2">
<name>LFBClassID</name>
<synopsis>the id of a supported LFB Class</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=’’3’’>
<name>LFBVersion</name>
<synopsis>
The version of the LFB Class used
by this FE.
</synopsis>
<typeRef>string</typeRef>
<element elementID="4">
<name>LFBOccurrenceLimit</name>
<synopsis>
the upper limit of instances of LFBs of this class
</synopsis>
<optional/>
<typeRef>uint32</typeRef>
</element>
<!-- For each port group, how many ports can exist
-->
<element elementID="5">
<name>PortGroupLimits</name>
<synopsis>Table of Port Group Limits</synopsis>
<optional/>
<array type="variable-size">
<typeRef>PortGroupLimitType</typeRef>
</array>
</element>
<!-- for the named LFB Class, the LFB Classes it may follow -->
<element elementID="6">
<name>CanOccurAfters</name>
<synopsis>
List of LFB Classes that this LFB class can follow
</synopsis>
<optional/>
<array type="variable-size">
<typeRef>LFBAdjacencyLimitType</typeRef>
Yang, et al. Expires April 2007 [Page 84]
Internet Draft ForCES FE Model October 2006
</array>
</element>
<!-- for the named LFB Class, the LFB Classes that may follow it
-->
<element elementID="7">
<name>CanOccurBefores</name>
<synopsis>
List of LFB Classes that can follow this LFB class
</synopsis>
<optional/>
<array type="variable-size">
<typeRef>LFBAdjacencyLimitType</typeRef>
</array>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>FEStatusValues</name>
<synopsis>The possible values of status</synopsis>
<atomic>
<baseType>uchar</baseType>
<specialValues>
<specialValue value="0">
<name>AdminDisable</name>
<synopsis>
FE is administratively disabled
</synopsis>
</specialValue>
<specialValue value="1">
<name>OperDisable</name>
<synopsis>FE is operatively disabled</synopsis>
</specialValue>
<specialValue value="2">
<name>OperEnable</name>
<synopsis>FE is operating</synopsis>
</specialValue>
</specialValues>
</atomic>
</dataTypeDef>
<dataTypeDef>
<name>FEConfiguredNeighborType</name>
<synopsis>Details of the FE's Neighbor</synopsis>
<struct>
<element elementID="1">
<name>NeighborID</name>
<synopsis>Neighbors FEID</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="2">
Yang, et al. Expires April 2007 [Page 85]
Internet Draft ForCES FE Model October 2006
<name>InterfaceToNeighbor</name>
<synopsis>
FE's interface that connects to this neighbor
</synopsis>
<optional/>
<typeRef>string</typeRef>
</element>
<element elementID=’’3’’>
<name>NeighborInterface</name>
<synopsis>
The name of the interface on the neighbor to
which this FE is adjacent. This is required
In case two FE’s are adjacent on more than
one interface.
</synopsis>
<optional/>
<typeRef>string</typeRef>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>LFBSelectorType</name>
<synopsis>
Unique identification of an LFB class-instance
</synopsis>
<struct>
<element elementID="1">
<name>LFBClassID</name>
<synopsis>LFB Class Identifier</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="2">
<name>LFBInstanceID</name>
<synopsis>LFB Instance ID</synopsis>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>LFBLinkType</name>
<synopsis>
Link between two LFB instances of topology
</synopsis>
<struct>
<element elementID="1">
<name>FromLFBID</name>
<synopsis>LFB src</synopsis>
<typeRef>LFBSelectorType</typeRef>
</element>
Yang, et al. Expires April 2007 [Page 86]
Internet Draft ForCES FE Model October 2006
<element elementID="2">
<name>FromPortGroup</name>
<synopsis>src port group</synopsis>
<typeRef>string</typeRef>
</element>
<element elementID="3">
<name>FromPortIndex</name>
<synopsis>src port index</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="4">
<name>ToLFBID</name>
<synopsis>dst LFBID</synopsis>
<typeRef>LFBSelectorType</typeRef>
</element>
<element elementID="5">
<name>ToPortGroup</name>
<synopsis>dst port group</synopsis>
<typeRef>string</typeRef>
</element>
<element elementID="6">
<name>ToPortIndex</name>
<synopsis>dst port index</synopsis>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
</dataTypeDefs>
<LFBClassDefs>
<LFBClassDef LFBClassID="1">
<name>FEObject</name>
<synopsis>Core LFB: FE Object</synopsis>
<version>1.0</version>
<attributes>
<attribute access="read-write" elementID="1">
<name>LFBTopology</name>
<synopsis>the table of known Topologies</synopsis>
<array type="variable-size">
<typeRef>LFBLinkType</typeRef>
</array>
</attribute>
<attribute access="read-write" elementID="2">
<name>LFBSelectors</name>
<synopsis>
table of known active LFB classes and
instances
</synopsis>
<array type="variable-size">
<typeRef>LFBSelectorType</typeRef>
Yang, et al. Expires April 2007 [Page 87]
Internet Draft ForCES FE Model October 2006
</array>
</attribute>
<attribute access="read-write" elementID="3">
<name>FEName</name>
<synopsis>name of this FE</synopsis>
<typeRef>string[40]</typeRef>
</attribute>
<attribute access="read-write" elementID="4">
<name>FEID</name>
<synopsis>ID of this FE</synopsis>
<typeRef>uint32</typeRef>
</attribute>
<attribute access="read-only" elementID="5">
<name>FEVendor</name>
<synopsis>vendor of this FE</synopsis>
<typeRef>string[40]</typeRef>
</attribute>
<attribute access="read-only" elementID="6">
<name>FEModel</name>
<synopsis>model of this FE</synopsis>
<typeRef>string[40]</typeRef>
</attribute>
<attribute access="read-only" elementID="7">
<name>FEState</name>
<synopsis>model of this FE</synopsis>
<typeRef>FEStatusValues</typeRef>
</attribute>
<attribute access="read-write" elementID="8">
<name>FENeighbors</name>
<synopsis>table of known neighbors</synopsis>
<array type="variable-size">
<typeRef>FEConfiguredNeighborType</typeRef>
</array>
</attribute>
</attributes>
<capabilities>
<capability elementID="30">
<name>ModifiableLFBTopology</name>
<synopsis>
Whether Modifiable LFB is supported
</synopsis>
<optional/>
<typeRef>boolean</typeRef>
</capability>
<capability elementID="31">
<name>SupportedLFBs</name>
<synopsis>List of all supported LFBs</synopsis>
<optional/>
<array type="variable-size">
Yang, et al. Expires April 2007 [Page 88]
Internet Draft ForCES FE Model October 2006
<typeRef>SupportedLFBType</typeRef>
</array>
</capability>
</capabilities>
</LFBClassDef>
</LFBClassDefs>
</LFBLibrary>
5.2. FE Capabilities
The FE Capability information is contained in the capabilities
element of the class definition. As described elsewhere, capability
information is always considered to be read-only.
The currently defined capabilities are ModifiableLFBTopology and
SupportedLFBs. Information as to which attributes of the FE LFB are
supported is accessed by the properties information for those
elements.
5.2.1. ModifiableLFBTopology
This element has a boolean value that indicates whether the LFB
topology of the FE may be changed by the CE. If the element is
absent, the default value is assumed to be true, and the CE presumes
the LFB topology may be changed. If the value is present and set to
false, the LFB topology of the FE is fixed. If the topology is
fixed, the LFBs supported clause may be omitted, and the list of
supported LFBs is inferred by the CE from the LFB topology
information. If the list of supported LFBs is provided when
ModifiableLFBTopology is false, the CanOccurBefore and CanOccurAfter
information should be omitted.
5.2.2. SupportedLFBs and SupportedLFBType
One capability that the FE should include is the list of supported
LFB classes. The SupportedLFBs element, is an array that contains
the information about each supported LFB Class. The array structure
type is defined as the SupportedLFBType dataTypeDef.
Each occurrence of the SupportedLFBs array element describes an LFB
class that the FE supports. In addition to indicating that the FE
supports the class, FEs with modifiable LFB topology should include
information about how LFBs of the specified class may be connected
to other LFBs. This information should describe which LFB classes
the specified LFB class may succeed or precede in the LFB topology.
The FE should include information as to which port groups may be
connected to the given adjacent LFB class. If port group
information is omitted, it is assumed that all port groups may be
used.
Yang, et al. Expires April 2007 [Page 89]
Internet Draft ForCES FE Model October 2006
5.2.2.1. LFBName
This element has as its value the name of the LFB Class being
described.
5.2.2.2. LFBClassID
The numeric ID of the LFB Class being described. While conceptually
redundant with the LFB Name, both are included for clarity and to
allow consistency checking.
5.2.2.3. LFBVersion
The version string specifying the LFB Class version supported by
this FE. As described above in versioning, an FE can support only a
single version of a given LFB Class.
5.2.2.4. LFBOccurrenceLimit
This element, if present, indicates the largest number of instances
of this LFB class the FE can support. For FEs that do not have the
capability to create or destroy LFB instances, this can either be
omitted or be the same as the number of LFB instances of this class
contained in the LFB list attribute.
5.2.2.5. PortGroupLimits and PortGroupLimitType
The PortGroupLimits element is an array of information about the
port groups supported by the LFB class. The structure of the port
group limit information is defined by the PortGroupLimitType
dataTypeDef.
Each PortGroupLimits array element contains information describing a
single port group of the LFB class. Each array element contains the
name of the port group in the PortGroupName element, the fewest
number of ports that can exist in the group in the MinPortCount
element, and the largest number of ports that can exist in the group
in the MaxPortCount element.
5.2.2.6.CanOccurAfters and LFBAdjacencyLimitType
The CanOccurAfters element is an array that contains the list of
LFBs the described class can occur after. The array elements are
defined in the LFBAdjacencyLimitType dataTypeDef.
The array elements describe a permissible positioning of the
described LFB class, referred to here as the SupportedLFB.
Specifically, each array element names an LFB that can topologically
Yang, et al. Expires April 2007 [Page 90]
Internet Draft ForCES FE Model October 2006
precede that LFB class. That is, the SupportedLFB can have an input
port connected to an output port of an LFB that appears in the
CanOccurAfters array. The LFB class that the SupportedLFB can
follow is identified by the NeighborLFB element of the
LFBAdjacencyLimitType array element. If this neighbor can only be
connected to a specific set of input port groups, then the viaPort
element is included. This element occurs once for each input port
group of the SupportedLFB that can be connected to an output port of
the NeighborLFB.
[e.g., Within a SupportedLFBs element, each array element of the
CanOccurAfters array must have a unique NeighborLFB, and within each
array element each viaPort must represent a distinct and valid input
port group of the SupportedLFB. The LFB Class definition schema
does not yet support uniqueness declarations]
5.2.2.7. CanOccurBefores and LFBAdjacencyLimitType
The CanOccurBefores array holds the information about which LFB
classes can follow the described class. Structurally this element
parallels CanOccurAfters, and uses the same type definition for the
array element.
The array elements list those LFB classes that the SupportedLFB may
precede in the topology. In this element, the
viaPort element of the array value represents the output port group
of the SupportedLFB that may be connected to the NeighborLFB. As
with CanOccurAfters, viaPort may occur multiple times if multiple
output ports may legitimately connect to the given NeighborLFB
class.
[And a similar set of uniqueness constraints apply to the
CanOccurBefore clauses, even though an LFB may occur both in
CanOccurAfter and CanOccurBefore.]
5.2.2.8. LFBClassCapabilities
While it would be desirable to include class capability level
information, this is not included in the model. While such
information belongs in the FE Object in the supported class table,
the contents of that information would be class specific. The
currently expected encoding structures for transferring information
between the CE and FE are such that allowing completely unspecified
information would be likely to induce parse errors. We could
specify that the information is encoded in an octetstring, but then
we would have to define the internal format of that octet string.
As there also are not currently any defined LFB Class level
Capabilities that the FE needs to report, this information is not
Yang, et al. Expires April 2007 [Page 91]
Internet Draft ForCES FE Model October 2006
present now, but may be added in a future version of the FE Protocol
Object. (This is an example of a case where versioning, rather than
inheritance, would be needed, since the FE Object must have class ID
1 and instance ID 1 so that the protocol behavior can start by
finding this object.)
5.3. FEAttributes
The attributes element is included if the class definition contains
the attributes of the FE that are not considered "capabilities".
Some of these attributes are writeable, and some are read-only,
which should be indicated by the capability information.
5.3.1. FEStatus
This attribute carries the overall state of the FE. For now, it is
restricted to the strings AdminDisable, OperDisable and OperEnable.
5.3.2. LFBSelectors and LFBSelectorType
The LFBSelectors element is an array of information about the LFBs
currently accessible via ForCES in the FE. The structure of the LFB
information is defined by the LFBSelectorType.
Each entry in the array describes a single LFB instance in the FE.
The array element contains the numeric class ID of the class of the
LFB instance and the numeric instance ID for this instance.
5.3.3. LFBTopology and LFBLinkType
The optional LFBTopology element contains information about each
inter-LFB link inside the FE, where each link is described in an
LFBLinkType element. The LFBLinkType element contains sufficient
information to identify precisely the end points of a link. The
FromLFBID and ToLFBID fields specify the LFB instances at each end
of the link, and must reference LFBs in the LFB instance table. The
FromPortGroup and ToPortGroup must identify output and input port
groups defined in the LFB classes of the LFB instances identified by
FromLFBID and ToLFBID. The FromPortIndex and ToPortIndex fields
select the elements from the port groups that this link connects.
All links are uniquely identified by the FromLFBID, FromPortGroup,
and FromPortIndex fields. Multiple links may have the same ToLFBID,
ToPortGroup, and ToPortIndex as this model supports fan in of inter-
LFB links but not fan out.
Yang, et al. Expires April 2007 [Page 92]
Internet Draft ForCES FE Model October 2006
5.3.4. FENeighbors and FEConfiguredNeighborType
The FENeighbors element is an array of information about manually
configured adjacencies between this FE and other FEs. The content
of the array is defined by the FEConfiguredNeighborType element.
This array is intended to capture information that may be configured
on the FE and is needed by the CE, where one array entry corresponds
to each configured neighbor. Note that this array is not intended
to represent the results of any discovery protocols, as those will
have their own LFBs.
While there may be many ways to configure neighbors, the FE-ID is
the best way for the CE to correlate entities. And the interface
identifier (name string) is the best correlator. The CE will be
able to determine the IP address and media level information about
the neighbor from the neighbor directly. Omitting that information
from this table avoids the risk of incorrect double configuration.
Information about the intended forms of exchange with a given
neighbor is not captured here, only the adjacency information is
included.
5.3.4.1.NeighborID
This is the ID in some space meaningful to the CE for the neighbor.
If this table remains, we probably should add an FEID from the same
space as an attribute of the FE.
5.3.4.2.InterfaceToNeighbor
This identifies the interface through which the neighbor is reached.
5.3.4.3.NeighborInterface
This identifies the interface on the neighbor through which the
neighbor is reached. The interface identification is needed when
either only one side of the adjacency has configuration information,
or the two FEs are adjacent on more than one interface.
6. Satisfying the Requirements on FE Model
This section describes how the proposed FE model meets the
requirements outlined in Section 5 of RFC 3654 [1]. The
requirements can be separated into general requirements (Sections 5,
5.1 - 5.4) and the specification of the minimal set of logical
functions that the FE model must support (Section 5.5).
Yang, et al. Expires April 2007 [Page 93]
Internet Draft ForCES FE Model October 2006
The general requirement on the FE model is that it be able to
express the logical packet processing capability of the FE, through
both a capability and a state model. In addition, the FE model is
expected to allow flexible implementations and be extensible to
allow defining new logical functions.
A major component of the proposed FE model is the Logical Function
Block (LFB) model. Each distinct logical function in an FE is
modeled as an LFB. Operational parameters of the LFB that must be
visible to the CE are conceptualized as LFB attributes. These
attributes express the capability of the FE and support flexible
implementations by allowing an FE to specify which optional features
are supported. The attributes also indicate whether they are
configurable by the CE for an LFB class. Configurable attributes
provide the CE some flexibility in specifying the behavior of an
LFB. When multiple LFBs belonging to the same LFB class are
instantiated on an FE, each of those LFBs could be configured with
different attribute settings. By querying the settings of the
attributes for an instantiated LFB, the CE can determine the state
of that LFB.
Instantiated LFBs are interconnected in a directed graph that
describes the ordering of the functions within an FE. This directed
graph is described by the topology model. The combination of the
attributes of the instantiated LFBs and the topology describe the
packet processing functions available on the FE (current state).
Another key component of the FE model is the FE attributes. The FE
attributes are used mainly to describe the capabilities of the FE,
but they also convey information about the FE state.
The FE model includes only the definition of the FE Object LFB
itself. Meeting the full set of working group requirements requires
other LFBs. The class definitions for those LFBs will be provided
in other documents.
7. Using the FE model in the ForCES Protocol
The actual model of the forwarding plane in a given NE is something
the CE must learn and control by communicating with the FEs (or by
other means). Most of this communication will happen in the post-
association phase using the ForCES protocol. The following types of
information must be exchanged between CEs and FEs via the ForCES
protocol:
1) FE topology query;
2) FE capability declaration;
3) LFB topology (per FE) and configuration capabilities query;
4) LFB capability declaration;
Yang, et al. Expires April 2007 [Page 94]
Internet Draft ForCES FE Model October 2006
5) State query of LFB attributes;
6) Manipulation of LFB attributes;
7) LFB topology reconfiguration.
Items 1) through 5) are query exchanges, where the main flow of
information is from the FEs to the CEs. Items 1) through 4) are
typically queried by the CE(s) in the beginning of the post-
association (PA) phase, though they may be repeatedly queried at any
time in the PA phase. Item 5) (state query) will be used at the
beginning of the PA phase, and often frequently during the PA phase
(especially for the query of statistical counters).
Items 6) and 7) are "command" types of exchanges, where the main
flow of information is from the CEs to the FEs. Messages in Item 6)
(the LFB re-configuration commands) are expected to be used
frequently. Item 7) (LFB topology re-configuration) is needed only
if dynamic LFB topologies are supported by the FEs and it is
expected to be used infrequently.
The inter-FE topology (item 1 above) can be determined by the CE in
many ways. Neither this document nor the Forces protocol mandates a
specific mechanism. The LFB Class definition does include the
capability for an FE to be configured with, and provides to the CE
in response to a query, the identity of its neighbors. There may
also be defined specific LFB classes and protocols for neighbor
discovery. Routing protocols may be used by the CE for adjacency
determination. The CE may be configured with the relevant
information.
The relationship between the FE model and the seven post-association
messages are visualized in Figure 9:
+--------+
..........-->| CE |
/----\ . +--------+
\____/ FE Model . ^ |
| |................ (1),2 | | 6, 7
| | (off-line) . 3, 4, 5 | |
\____/ . | v
. +--------+
e.g. RFCs ..........-->| FE |
+--------+
Figure 9. Relationship between the FE model and the ForCES protocol
messages, where (1) is part of the ForCES base protocol, and the
rest are defined by the FE model.
Yang, et al. Expires April 2007 [Page 95]
Internet Draft ForCES FE Model October 2006
The actual encoding of these messages is defined by the ForCES
protocol and beyond the scope of the FE model. Their discussion is
nevertheless important here for the following reasons:
. These PA model components have considerable impact on the FE
model. For example, some of the above information can be
represented as attributes of the LFBs, in which case such
attributes must be defined in the LFB classes.
. The understanding of the type of information that must be
exchanged between the FEs and CEs can help to select the
appropriate protocol format and the actual encoding method
(such as XML, TLVs).
. Understanding the frequency of these types of messages should
influence the selection of the protocol format (efficiency
considerations).
An important part of the FE model is the port the FE uses for its
message exchanges to and from the CE. In the case that a dedicated
port is used for CE-FE communication, we propose to use a special
port LFB, called the CE-FE Port LFB (a subclass of the general Port
LFB in Section 6.1), to model this dedicated CE-FE port. The CE-FE
Port LFB acts as both a source and sink for the traffic from and to
the CE. Sometimes the CE-FE traffic does not have its own dedicated
port, instead the data fabric is shared for the data plane traffic
and the CE-FE traffic. A special processing LFB can be used to
model the ForCES packet encapsulation and decapsulation in such
cases.
The remaining sub-sections of this section address each of the seven
message types.
7.1. FE Topology Query
An FE may contain zero, one or more external ingress ports.
Similarly, an FE may contain zero, one or more external egress
ports. In other words, not every FE has to contain any external
ingress or egress interfaces. For example, Figure 10 shows two
cascading FEs. FE #1 contains one external ingress interface but no
external egress interface, while FE #2 contains one external egress
interface but no ingress interface. It is possible to connect these
two FEs together via their internal interfaces to achieve the
complete ingress-to-egress packet processing function. This provides
the flexibility to spread the functions across multiple FEs and
interconnect them together later for certain applications.
While the inter-FE communication protocol is out of scope for
ForCES, it is up to the CE to query and understand how multiple FEs
are inter-connected to perform a complete ingress-egress packet
processing function, such as the one described in Figure 10. The
Yang, et al. Expires April 2007 [Page 96]
Internet Draft ForCES FE Model October 2006
inter-FE topology information may be provided by FEs, may be hard-
coded into CE, or may be provided by some other entity (e.g., a bus
manager) independent of the FEs. So while the ForCES protocol
supports FE topology query from FEs, it is optional for the CE to
use it, assuming the CE has other means to gather such topology
information.
+-----------------------------------------------------+
| +---------+ +------------+ +---------+ |
input| | | | | | output |
---+->| Ingress |-->|Header |-->|IPv4 |---------+--->+
| | port | |Decompressor| |Forwarder| FE | |
| +---------+ +------------+ +---------+ #1 | |
+-----------------------------------------------------+ V
|
+-----------------------<-----------------------------+
|
| +----------------------------------------+
V | +------------+ +----------+ |
| input | | | | output |
+->--+->|Header |-->| Egress |---------+-->
| |Compressor | | port | FE |
| +------------+ +----------+ #2 |
+----------------------------------------+
Figure 10. An example of two FEs connected together.
Once the inter-FE topology is discovered by the CE after this query,
it is assumed that the inter-FE topology remains static. However,
it is possible that an FE may go down during the NE operation, or a
board may be inserted and a new FE activated, so the inter-FE
topology will be affected. It is up to the ForCES protocol to
provide a mechanism for the CE to detect such events and deal with
the change in FE topology. FE topology is outside the scope of the
FE model.
7.2. FE Capability Declarations
FEs will have many types of limitations. Some of the limitations
must be expressed to the CEs as part of the capability model. The
CEs must be able to query these capabilities on a per-FE basis.
Examples:
. Metadata passing capabilities of the FE. Understanding these
capabilities will help the CE to evaluate the feasibility of
LFB topologies, and hence to determine the availability of
certain services.
. Global resource query limitations (applicable to all LFBs of
the FE).
Yang, et al. Expires April 2007 [Page 97]
Internet Draft ForCES FE Model October 2006
. LFB supported by the FE.
. LFB class instantiation limit.
. LFB topological limitations (linkage constraint, ordering etc.)
7.3. LFB Topology and Topology Configurability Query
The ForCES protocol must provide the means for the CEs to discover
the current set of LFB instances in an FE and the interconnections
between the LFBs within the FE. In addition, sufficient information
should be available to determine whether the FE supports any CE-
initiated (dynamic) changes to the LFB topology, and if so,
determine the allowed topologies. Topology configurability can also
be considered as part of the FE capability query as described in
Section 9.3.
7.4. LFB Capability Declarations
LFB class specifications define a generic set of capabilities.
When an LFB instance is implemented (instantiated) on a vendor's FE,
some additional limitations may be introduced. Note that we discuss
only those limitations that are within the flexibility of the LFB
class specification. That is, the LFB instance will remain
compliant with the LFB class specification despite these
limitations. For example, certain features of an LFB class may be
optional, in which case it must be possible for the CE to determine
if an optional feature is supported by a given LFB instance or not.
Also, the LFB class definitions will probably contain very few
quantitative limits (e.g., size of tables), since these limits are
typically imposed by the implementation. Therefore, quantitative
limitations should always be expressed by capability arguments.
LFB instances in the model of a particular FE implementation will
possess limitations on the capabilities defined in the corresponding
LFB class. The LFB class specifications must define a set of
capability arguments, and the CE must be able to query the actual
capabilities of the LFB instance via querying the value of such
arguments. The capability query will typically happen when the LFB
is first detected by the CE. Capabilities need not be re-queried in
case of static limitations. In some cases, however, some
capabilities may change in time (e.g., as a result of
adding/removing other LFBs, or configuring certain attributes of
some other LFB when the LFBs share physical resources), in which
case additional mechanisms must be implemented to inform the CE
about the changes.
The following two broad types of limitations will exist:
. Qualitative restrictions. For example, a standardized multi-
field classifier LFB class may define a large number of
Yang, et al. Expires April 2007 [Page 98]
Internet Draft ForCES FE Model October 2006
classification fields, but a given FE may support only a subset
of those fields.
. Quantitative restrictions, such as the maximum size of tables,
etc.
The capability parameters that can be queried on a given LFB class
will be part of the LFB class specification. The capability
parameters should be regarded as special attributes of the LFB. The
actual values of these arguments may be, therefore, obtained using
the same attribute query mechanisms as used for other LFB
attributes.
Capability attributes will typically be read-only arguments, but in
certain cases they may be configurable. For example, the size of a
lookup table may be limited by the hardware (read-only), in other
cases it may be configurable (read-write, within some hard limits).
Assuming that capabilities will not change frequently, the
efficiency of the protocol/schema/encoding is of secondary concern.
7.5. State Query of LFB Attributes
This feature must be provided by all FEs. The ForCES protocol and
the data schema/encoding conveyed by the protocol must together
satisfy the following requirements to facilitate state query of the
LFB attributes:
. Must permit FE selection. This is primarily to refer to a
single FE, but referring to a group of (or all) FEs may
optional be supported.
. Must permit LFB instance selection. This is primarily to refer
to a single LFB instance of an FE, but optionally addressing of
a group of LFBs (or all) may be supported.
. Must support addressing of individual attribute of an LFB.
. Must provide efficient encoding and decoding of the addressing
info and the configured data.
. Must provide efficient data transmission of the attribute state
over the wire (to minimize communication load on the CE-FE
link).
7.6. LFB Attribute Manipulation
The FE Model provides for the definition of LFB Classes. Each class
has a globally unique identifier. Elements within the class are
assigned identifiers within that scope. This model also specifies
that instances of LFB Classes have identifiers. The combination of
class identifiers, instance identifiers, and element identifiers are
used by the protocol to reference the LFB information in the
protocol operations.
Yang, et al. Expires April 2007 [Page 99]
Internet Draft ForCES FE Model October 2006
7.7. LFB Topology Re-configuration
Operations that will be needed to reconfigure LFB topology:
. Create a new instance of a given LFB class on a given FE.
. Connect a given output of LFB x to the given input of LFB y.
. Disconnect: remove a link between a given output of an LFB and
a given input of another LFB.
. Delete a given LFB (automatically removing all interconnects
to/from the LFB).
8. Example
This section contains an example LFB definition. While some
properties of LFBs are shown by the FE Object LFB, this endeavors to
show how a data plain LFB might be build. This example is a
fictional case of an interface supporting a coarse WDM optical
interface carry Frame Relay traffic. The statistical information
(including error statistics) is omitted.)
<?xml version="1.0" encoding="UTF-8"?>
<LFBLibrary xmlns="http://ietf.org/forces/1.0/lfbmodel"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://ietf.org/forces/1.0/lfbmodel"
provides="LaserFrameLFB">
<frameDefs>
<frameDef>
<name>FRFrame</name>
<synopsis>
A frame relay frame, with DLCI without
stuffing)
</synopsis>
</frameDef>
<frameDef>
<name>IPFrame</name>
<synopsis>An IP Packet</synopsis>
</frameDef>
</frameDefs>
<dataTypeDefs>
<dataTypeDef>
<name>frequencyInformationType</name>
<synopsis>
Information about a single CWDM frequency
</synopsis>
<struct>
<element elementID="1">
<name>LaserFrequency</name>
<synopsis>encoded frequency(channel)</synopsis>
<typeRef>uint32</typeRef>
Yang, et al. Expires April 2007 [Page 100]
Internet Draft ForCES FE Model October 2006
</element>
<element elementID="2">
<name>FrequencyState</name>
<synopsis>state of this frequency</synopsis>
<typeRef>PortStatusValues</typeRef>
</element>
<element elementID="3">
<name>LaserPower</name>
<synopsis>current observed power</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="4">
<name>FrameRelayCircuits</name>
<synopsis>
Information about circuits on this Frequency
</synopsis>
<array>
<typeRef>frameCircuitsType</typeRef>
</array>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>frameCircuitsType</name>
<synopsis>
Information about a single Frame Relay circuit
</synopsis>
<struct>
<element elementID="1">
<name>DLCI</name>
<synopsis>DLCI of the circuit</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="2">
<name>CircuitStatus</name>
<synopsis>state of the circuit</synopsis>
<typeRef>PortStatusValues</typeRef>
</element>
<element elementID="3">
<name>isLMI</name>
<synopsis>is this the LMI circuit</synopsis>
<typeRef>boolean</typeRef>
</element>
<element elementID="4">
<name>associatedPort</name>
<synopsis>
which input / output port is associated
with this circuit
</synopsis>
Yang, et al. Expires April 2007 [Page 101]
Internet Draft ForCES FE Model October 2006
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>PortStatusValues</name>
<synopsis>
The possible values of status. Used for both
administrative and operation status
</synopsis>
<atomic>
<baseType>uchar</baseType>
<specialValues>
<specialValue value="0">
<name>Disabled </name>
<synopsis>the component is disabled</synopsis>
</specialValue>
<specialValue value="1">
<name>Enable</name>
<synopsis>FE is operatively disabled</synopsis>
</specialValue>
</specialValues>
</atomic>
</dataTypeDef>
</dataTypeDefs>
<metadataDefs>
<metadataDef>
<name>DLCI</name>
<synopsis>The DLCI the frame arrived on</synopsis>
<metadataID>12</metadataID>
<typeRef>uint32</typeRef>
</metadataDef>
<metadataDef>
<name>LaserChannel</name>
<synopsis>The index of the laser channel</synopsis>
<metadataID>34</metadataID>
<typeRef>uint32</typeRef>
</metadataDef>
</metadataDefs>
<LFBClassDefs>
<LFBClassDef LFBClassID="-255">
<name>FrameLaserLFB</name>
<synopsis>Fictional LFB for Demonstrations</synopsis>
<version>1.0</version>
<inputPorts>
<inputPort group="yes">
<name>LMIfromFE</name>
<synopsis>
Ports for LMI traffic, for transmission
Yang, et al. Expires April 2007 [Page 102]
Internet Draft ForCES FE Model October 2006
</synopsis>
<expectation>
<frameExpected>
<ref>FRFrame</ref>
</frameExpected>
<metadataExpected>
<ref>DLCI</ref>
<ref>LaserChannel</ref>
</metadataExpected>
</expectation>
</inputPort>
<inputPort>
<name>DatafromFE</name>
<synopsis>
Ports for data to be sent on circuits
</synopsis>
<expectation>
<frameExpected>
<ref>IPFrame</ref>
</frameExpected>
<metadataExpected>
<ref>DLCI</ref>
<ref>LaserChannel</ref>
</metadataExpected>
</expectation>
</inputPort>
</inputPorts>
<outputPorts>
<outputPort group="yes">
<name>LMItoFE</name>
<synopsis>
Ports for LMI traffic for processing
</synopsis>
<product>
<frameProduced>
<ref>FRFrame</ref>
</frameProduced>
<metadataProduced>
<ref>DLCI</ref>
<ref>LaserChannel</ref>
</metadataProduced>
</product>
</outputPort>
<outputPort group="yes">
<name>DatatoFE</name>
<synopsis>
Ports for Data traffic for processing
</synopsis>
<product>
Yang, et al. Expires April 2007 [Page 103]
Internet Draft ForCES FE Model October 2006
<frameProduced>
<ref>IPFrame</ref>
</frameProduced>
<metadataProduced>
<ref>DLCI</ref>
<ref>LaserChannel</ref>
</metadataProduced>
</product>
</outputPort>
</outputPorts>
<attributes>
<attribute access="read-write" elementID="1">
<name>AdminPortState</name>
<synopsis>is this port allowed to function</synopsis>
<typeRef>PortStatusValues</typeRef>
</attribute>
<attribute access="read-write" elementID="2">
<name>FrequencyInformation</name>
<synopsis>
table of information per CWDM frequency
</synopsis>
<array type="variable-size">
<typeRef>frequencyInformationType</typeRef>
</array>
</attribute>
</attributes>
<capabilities>
<capability elementID="31">
<name>OperationalState</name>
<synopsis>
whether the port over all is operational
</synopsis>
<typeRef>PortStatusValues</typeRef>
</capability>
<capability elementID="32">
<name>MaximumFrequencies</name>
<synopsis>
how many laser frequencies are there
</synopsis>
<typeRef>uint16</typeRef>
</capability>
<capability elementID="33">
<name>MaxTotalCircuits</name>
<synopsis>
Total supportable Frame Relay Circuits, across
all laser frequencies
</synopsis>
<optional/>
<typeRef>uint32</typeRef>
Yang, et al. Expires April 2007 [Page 104]
Internet Draft ForCES FE Model October 2006
</capability>
</capabilities>
<events baseID="61">
<event eventID="1">
<name>FrequencyState</name>
<synopsis>
The state of a frequency has changed
</synopsis>
<eventTarget>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>FrequencyState</eventField>
</eventTarget>
<eventChanged/>
<eventReports>
<!-- report the new state -->
<eventReport>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>FrequencyState</eventField>
</eventReport>
</eventReports>
</event>
<event eventID="2">
<name>CreatedFrequency</name>
<synopsis>A new frequency has appeared</synopsis>
<eventTarget>
<eventField>FrequencyInformation></eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
</eventTarget>
<eventCreated/>
<eventReports>
<eventReport>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>LaserFrequency</eventField>
</eventReport>
</eventReports>
</event>
<event eventID="3">
<name>DeletedFrequency</name>
<synopsis>
A frequency Table entry has been deleted
</synopsis>
<eventTarget>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
</eventTarget>
<eventDeleted/>
Yang, et al. Expires April 2007 [Page 105]
Internet Draft ForCES FE Model October 2006
</event>
<event eventID="4">
<name>PowerProblem</name>
<synopsis>
there are problems with the laser power level
</synopsis>
<eventTarget>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>LaserPower</eventField>
</eventTarget>
<eventLessThan/>
<eventReports>
<eventReport>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>LaserPower</eventField>
</eventReport>
<eventReport>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>LaserFrequency</eventField>
</eventReport>
</eventReports>
</event>
<event eventID="5">
<name>FrameCircuitChanged</name>
<synopsis>
the state of an Fr circuit on a frequency
has changed
</synopsis>
<eventTarget>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>FrameRelayCircuits</eventField>
<eventSubscript>FrameCircuitIndex</eventSubscript>
<eventField>CircuitStatus</eventField>
</eventTarget>
<eventChanged/>
<eventReports>
<eventReport>
<eventField>FrequencyInformation</eventField>
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>FrameRelayCircuits</eventField>
<eventSubscript>FrameCircuitIndex</eventSubscript>
<eventField>CircuitStatus</eventField>
</eventReport>
<eventReport>
<eventField>FrequencyInformation</eventField>
Yang, et al. Expires April 2007 [Page 106]
Internet Draft ForCES FE Model October 2006
<eventSubscript>_FrequencyIndex_</eventSubscript>
<eventField>FrameRelayCircuits</eventField>
<eventSubscript>FrameCircuitIndex</eventSubscript>
<eventField>DLCI</eventField>
</eventReport>
</eventReports>
</event>
</events>
</LFBClassDef>
</LFBClassDefs>
</LFBLibrary>
8.1.1. Data Handling
This LFB is designed to handle data packets coming in from or going
out to the external world. It is not a full port, and it lacks many
useful statistics. But it serves to show many of the relevant
behaviors.
Packets arriving without error from the physical interface come in
on a Frame Relay DLCI on a laser channel. These two values are used
by the LFB too look up the handling for the packet. If the handling
indicates that the packet is LMI, then the output index is used to
select an LFB port from the LMItoFE port group. The packet is sent
as a full Frame Relay frame (without any bit or byte stuffing) on
the selected port. The laser channel and DLCI are sent as meta-
data, even though the DLCI is also still in the packet.
Good packets that arrive and are not LMI and have a frame relay type
indicator of IP are sent as IP packets on the port in the DatatoFE
port group, using the same index field from the table based on the
laser channel and DLCI. The channel and DLCI are attached as meta-
data for other use (classifiers, for example.)
The current definition does not specify what to do if the Frame
Relay type information is not IP.
Packets arriving on input ports arrive with the Laser Channel and
Frame Relay DLCI as meta-data. As such, a single input port could
have been used. With the structure that is defined (which parallels
the output structure), the selection of channel and DLCI could be
restricted by the arriving input port group (LMI vs. data) and port
index. As an alternative LFB design, the structures could require a
1-1 relationship between DLCI and LFB port, in which case no meta-
data would be needed. This would however be quite complex and
noisy. The intermediate level of structure here allows parallelism
between input and output, without requiring excessive ports.
Yang, et al. Expires April 2007 [Page 107]
Internet Draft ForCES FE Model October 2006
8.1.2. Setting up a DLCI
When a CE chooses to establish a DLCI on a specific laser channel,
it sends a SET request directed to this LFB. The request might look
like
T = SET-OPERATION
T = PATH-DATA
Path: flags = first-avail, length = 4, path = 2, channel, 4
DataRaw: DLCI, Enable(1), false, out-idx
Which would establish the DLCI as enabled, with traffic going to a
specific element of the output port group DatatoFE. (The CE would
ensure that output port is connected to the right place before
issuing this request.
The response to the operation would include the actual index
assigned to this Frame Relay circuit. This table is structured to
use separate internal indices and DLCIs. An alternative design
could have used the DLCI as index, trading off complexities.
One could also imagine that the FE has an LMI LFB. Such an LFB
would be connected to the LMItoFE and LMIfromFE port groups. It
would process LMI information. It might be the LFBs job to set up
the frame relay circuits. The LMI LFB would have an alias entry
that points to the Frame Relay circuits table it manages, so that it
can manipulate those entities.
8.1.3. Error Handling
The LFB will receive invalid packets over the wire. Many of these
will simply result in incrementing counters. The LFB designer might
also specify some error rate measures. This puts more work on the
FE, but allows for more meaningful alarms.
There may be some error conditions that should cause parts of the
packet to be sent to the CE. The error itself is not something that
can cause an event in the LFB. There are two ways this can be
handled.
One way is to define a specific field to count the error, and a
field in the LFB to hold the required portion of the packet. The
field could be defined to hold the portion of the packet from the
most recent error. One could then define an event that occurs
whenever the error count changes, and declare that reporting the
event includes the LFB field with the packet portion. For rare but
extremely critical errors, this is an effective solution. It
ensures reliable delivery of the notification. And it allows the CE
to control if it wants the notification. (Use of the event variance
Yang, et al. Expires April 2007 [Page 108]
Internet Draft ForCES FE Model October 2006
property would suppress multiple notifications. It would suppress
them even if they were many hours apart, so the CE is unlikely to
use that.)
Another approach is for the LFB to have a port that connects to a
redirect sink. The LFB would attach the laser channel, the DLCI,
and the error indication as meta-data, and ship the packet to the
CE.
Other aspects of error handling are discussed under events below.
8.2. LFB Attributes
This LFB is defined to have two top level attributes. One reflects
the administrative state of the LFB. This allows the CE to disable
the LFB completely.
The other attribute is the table of information about the laser
channels. It is a variable sized array. Each array entry contains
an identifier for what laser frequency this entry is associated
with, whether that frequency is operational, the power of the laser
at that frequency, and a table of information about frame relay
circuits on this frequency. There is no administrative status since
a CE can disable an entry simply by removing it. (Frequency and
laser power of a non-operational channel are not particularly
useful. Knowledge about what frequencies can be supported would be
a table in the capabilities section.)
The Frame Relay circuit information contains the DLCI, the
operational circuit status, whether this circuit is to be treated as
carrying LMI information, and which port in the output port group of
the LFB traffic is to be sent to. As mentioned above, the circuit
index could, in some designs, be combined with the DLCI.
8.3. Capabilities
The capability information for this LFB includes whether the
underlying interface is operational, how many frequencies are
supported, and how many total circuits, across all channels, are
permitted. The maximum number for a given laser channel can be
determined from the properties of the FrameRelayCircuits table. A
GET-Properties on path 2.channel.4 will give the CE the properties
of the array which include the number of entries used, the first
available entry, and the maximum number of entries permitted.
8.4. Events
This LFB is defined to be able to generate several events that the
CE may be interested in. There are events to report changes in
Yang, et al. Expires April 2007 [Page 109]
Internet Draft ForCES FE Model October 2006
operational state of frequencies, and the creation and deletion of
frequency entries. There is an event for changes in status of
individual frame relay circuits. So an event notification of
61.5.3.11 would indicate that there had been a circuit status change
on subscript 11 of the circuit table in subscript 3 of the frequency
table. The event report would include the new status of the circuit
and the DLCI of the circuit. Arguably, the DLCI is redundant, since
the CE presumably knows the DLCI based on the circuit index. It is
included here to show including two pieces of information in an
event report.
As described above, the event declaration defines the event target,
the event condition, and the event report content. The event
properties indicate whether the CE is subscribed to the event, the
specific threshold for the event, and any filter conditions for the
event.
Another event shown is a laser power problem. This event is
generated whenever the laser falls below the specified threshold.
Thus, a CE can register for the event of laser power loss on all
circuits. It would do this by:
T = SET-Properties
Path-TLV: flags=0, length = 2, path = 61.4
Path-TLV: flags = property-field, length = 1, path = 2
Content = 1 (register)
Path-TLV: flags = property-field, length = 1, path = 3
Content = 15 (threshold)
This would set the registration for the event on all entries in the
table. It would also set the threshold for the event, causing
reporting if the power falls below 15. (Presumably, the CE knows
what the scale is for power, and has chosen 15 as a meaningful
problem level.)
If a laser oscillates in power near the 15 mark, one could get a lot
of notifications. (If it flips back and forth between 9 and 10,
each flip down will generate an event.) Suppose that the CE decides
to suppress this oscillation somewhat on laser channel 5. It can do
this by setting the variance property on that event. The request
would look like:
T = SET-Properties
Path-TLV: flags=0, length = 3, path = 61.4.5
Path-TLV: flags = property-field, length = 1, path = 4
Content = 2 (hysteresis)
Setting the hysteresis to 2 suppress a lot of spurious
notifications. When the level first falls below 10, a notification
Yang, et al. Expires April 2007 [Page 110]
Internet Draft ForCES FE Model October 2006
is generated. If the power level increases to 10 or 11, and then
falls back below 10, an event will not be generated. The power has
to recover to at least 12 and fall back below 10 to generate another
event. Once common cause of this form of oscillation is when the
actual value is right near the border. If it is really 9.5, tiny
changes might flip it back and forth between 9 and 10. A variance
level of 1 will suppress this sort of condition. Many other events
have oscillations that are somewhat wider, so larger variance
settings can be used with those.
9. IANA Considerations
This model creates the need for unique class names and numeric class
identifiers. To meet that goal, IANA will maintain a registry of
LFB Class names, corresponding class identifiers, and the document
which defines the LFB Class. The registry policy is simply first
come first served with regard to LFB Class names. With regard to
LFB Class identifiers, identifiers less than 65536 are reserved for
assignment by RFCs. Identifiers above 65536 are available for
assignment on a first come, first served basis. Registry entries
must be documented in a stable, publicly available form.
The LFBLibrary element and all of its sub-elements are defined in
the following namespace:
http://ietf.org/forces/1.0/lfbmodel
[Editor’s Note: A registry template registry name, and other parts
required for a new IANA registry are still needed here.]
10. Authors Emeritus
The following are the authors who were instrumental in the creation
of earlier releases of this document.
Lily Yang, Intel Corp.
Ram Gopal, Nokia Research Center
Alan DeKok, Infoblox, Inc.
Zsolt Haraszti, Clovis Solutions
11. Acknowledgments
Many of the colleagues in our companies and participants in the
ForCES mailing list have provided invaluable input into this work.
Yang, et al. Expires April 2007 [Page 111]
Internet Draft ForCES FE Model October 2006
12. Security Considerations
The FE model describes the representation and organization of data
sets and attributes in the FEs. The ForCES framework document [2]
provides a comprehensive security analysis for the overall ForCES
architecture. For example, the ForCES protocol entities must be
authenticated per the ForCES requirements before they can access the
information elements described in this document via ForCES. Access
to the information contained in the FE model is accomplished via the
ForCES protocol, which will be defined in separate documents, and
thus the security issues will be addressed there.
13. Normative References
[1] Khosravi, H. et al., "Requirements for Separation of IP Control
and Forwarding", RFC 3654, November 2003.
[2] Yang, L. et al., "Forwarding and Control Element Separation
(ForCES) Framework", RFC 3746, April 2004.
14. Informative References
[3] Bernet, Y. et al., "An Informal Management Model for Diffserv
Routers", RFC 3290, May 2002.
[4] Chan, K. et al., "Differentiated Services Quality of Service
Policy Information Base", RFC 3317, March 2003.
[5] Sahita, R. et al., "Framework Policy Information Base", RFC
3318, March 2003.
[6] Moore, B. et al., "Information Model for Describing Network
Device QoS Datapath Mechanisms", RFC 3670, January 2004.
[7] Snir, Y. et al., "Policy Framework QoS Information Model", RFC
3644, Nov 2003.
[8] Li, M. et al., "IPsec Policy Information Base", work in
progress, April 2004, <draft-ietf-ipsp-ipsecpib-10.txt>.
[9] Quittek, J. et Al., "Requirements for IP Flow Information
Export", RFC 3917, October 2004.
[10] Duffield, N., "A Framework for Packet Selection and Reporting",
work in progress, January 2005, <draft-ietf-psamp-framework-10.txt>.
Yang, et al. Expires April 2007 [Page 112]
Internet Draft ForCES FE Model October 2006
[11] Pras, A. and Schoenwaelder, J., RFC 3444 "On the Difference
between Information Models and Data Models", January 2003.
[12] Hollenbeck, S. et al., "Guidelines for the Use of Extensible
Markup Language (XML) within IETF Protocols", RFC 3470, January
2003.
[13] Thompson, H., Beech, D., Maloney, M. and N. Mendelsohn, "XML
Schema Part 1: Structures", W3C REC-xmlschema-1, May 2001,
<http://www.w3.org/TR/xmlschema-1/>.
[14] Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes", W3C
REC-xmlschema-2, May 2001, <http://www.w3.org/TR/xmlschema-2/>.
[15] Davis, M. and M. Suignard, "UNICODE Security Considerations",
July 2005,<http://www.unicode.org/reports/tr36/tr36-3.html>.
15. Authors' Addresses
Joel M. Halpern
Self
P.O. Box 6049
Leesburg, VA 20178
Phone: +1 703 371 3043
Email: jmh@joelhalpern.com
Ellen Deleganes
Intel Corp.
Mail Stop: CO5-156
15400 NW Greenbrier Parkway
Beaverton, OR 97006
Phone: +1 503 677-4996
Email: ellen.m.deleganes@intel.com
16. Intellectual Property Right
The authors are not aware of any intellectual property right issues
pertaining to this document.
17. Copyright Statement
"Copyright (C) The Internet Society (2006). This document is
subject to the rights, licenses and restrictions contained in BCP
78, and except as set forth therein, the authors retain all their
rights."
"This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
Yang, et al. Expires April 2007 [Page 113]
Internet Draft ForCES FE Model October 2006
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
Yang, et al. Expires April 2007 [Page 114]
| PAFTECH AB 2003-2026 | 2026-04-24 07:14:32 |