One document matched: draft-ietf-nsis-fw-05.txt
Differences from draft-ietf-nsis-fw-04.txt
Network Working Group
Internet Draft R. Hancock (editor)
Siemens/Roke Manor Research
I. Freytsis
Cetacean Networks
G. Karagiannis
University of Twente/Ericsson
J. Loughney
Nokia
S. Van den Bosch
Alcatel
Document: draft-ietf-nsis-fw-05.txt
Expires: April 2004 October 2003
Next Steps in Signaling: Framework
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
The Next Steps in Signaling working group is considering protocols
for signaling information about a data flow along its path in the
network. Based on existing work on signaling requirements, this
document proposes an architectural framework for such signaling
protocols.
This document provides a model for the network entities that take
part in such signaling, and the relationship between signaling and
the rest of network operation. We decompose the overall signaling
protocol suite into a generic (lower) layer, with a separate upper
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layers for each specific signaling application. An initial proposal
for the split between these layers is given, describing the overall
functionality of the lower layer, and discussing the ways that upper
layer behavior can be adapted to specific signaling application
requirements.
This framework also considers the general interactions between
signaling and other network layer functions, specifically routing,
mobility, and address translators. The different events that impact
signaling operation are described, along with how their handling
should be divided between the generic and application-specific
layers. Finally, an example signaling application (for Quality of
Service) is described in more detail.
Table of Contents
1 Introduction ...................................................3
1.1 Definition of the Signaling Problem ......................3
1.2 Scope and Structure of the NSIS Framework ................4
2 Terminology ....................................................5
3 Overview of Signaling Scenarios and Protocol Structure .........6
3.1 Fundamental Signaling Concepts ...........................6
3.1.1 Simple Network and Signaling Topology ..................6
3.1.2 Path-Coupled and Path-Decoupled Signaling ..............7
3.1.3 Signaling to Hosts, Networks and Proxies ...............8
3.1.4 Signaling Messages and Network Control State ..........10
3.1.5 Data Flows and Sessions ...............................10
3.2 Layer Model for the Protocol Suite ......................11
3.2.1 Layer Model Overview ..................................11
3.2.2 Layer Split Concept ...................................12
3.2.3 Bypassing Intermediate Nodes ..........................13
3.2.4 Core NTLP Functionality ...............................15
3.2.5 State Management Functionality ........................15
3.2.6 Path De-Coupled Operation .............................16
3.3 Signaling Application Properties ........................17
3.3.1 Sender/Receiver Orientation ...........................17
3.3.2 Uni- and Bi-Directional Operation .....................18
3.3.3 Heterogeneous Operation ...............................19
3.3.4 Aggregation ...........................................19
3.3.5 Peer-Peer and End-End Relationships ...................20
3.3.6 Acknowledgements and Notifications ....................20
3.3.7 Security and Other AAA Issues .........................21
4 The NSIS Transport Layer Protocol .............................21
4.1 Internal Protocol Components ............................22
4.2 Addressing ..............................................22
4.3 Classical Transport Functions ...........................23
4.4 Lower Layer Interfaces ..................................25
4.5 Upper Layer Services ....................................25
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4.6 Identity Elements .......................................26
4.6.1 Flow Identification ...................................26
4.6.2 Session Identification ................................27
4.6.3 Signaling Application Identification ..................27
4.7 Security Properties .....................................28
5 Interactions with Other Protocols .............................28
5.1 IP Routing Interactions .................................28
5.1.1 Load Sharing and Policy-Based Forwarding ..............29
5.1.2 Route Changes .........................................29
5.2 Mobility and Multihoming Interactions ...................31
5.3 Interactions with NATs ..................................33
5.4 Interactions with IP Tunneling ..........................34
6 Signaling Applications ........................................35
6.1 Signaling for Quality of Service ........................35
6.1.1 Protocol Message Semantics ............................36
6.1.2 State Management ......................................36
6.1.3 Route Changes and QoS Reservations ....................37
6.1.4 Resource Management Interactions ......................38
6.2 Other Signaling Applications ............................39
7 Security Considerations .......................................40
Normative References.............................................41
Informative References...........................................41
Acknowledgments..................................................43
Authors' Addresses...............................................44
Intellectual Property Considerations.............................44
Full Copyright Statement.........................................45
1 Introduction
1.1 Definition of the Signaling Problem
The Next Steps in Signaling (NSIS) working group is considering
protocols for signaling information about a data flow along its path
in the network.
It is assumed that the path taken by the data flow is already
determined by network configuration and routing protocols,
independent of the signaling itself; that is, signaling to set up the
routes themselves is not considered. Instead, the signaling simply
interacts with nodes along the data flow path. Additional
simplifications are that the actual signaling messages pass directly
through these nodes themselves (i.e. the 'path-coupled' case, see
section 3.1.2) and that only unicast data flows are considered.
The signaling problem in this sense is very similar to that addressed
by RSVP. However, there are two generalizations. Firstly, the
intention is that components of the NSIS protocol suite will be
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usable in different parts of the Internet, for different needs,
without requiring a complete end-to-end deployment (in particular,
the signaling protocol messages may not need to run all the way
between the data flow endpoints).
Secondly, the signaling is intended for more purposes than just QoS
(resource reservation). The basic mechanism to achieve this
flexibility is to divide the signaling protocol stack into two
layers: a generic (lower) layer, and an upper layer specific to each
signaling application. The scope of NSIS work is to define both the
generic protocol, and initially upper layers suitable for QoS
signaling (similar to the corresponding functionality in RSVP) and
middlebox signaling. Further applications may be considered later.
1.2 Scope and Structure of the NSIS Framework
The underlying requirements for signaling in the context of NSIS are
defined in [1] and a separate security threats document [2]; other
related requirements can be found in [3] and [4]. This framework does
not replace or update these requirements. Discussions about lessons
to be learned from existing signaling and resource management
protocols are contained in separate analysis documents [5], [6].
The role of this framework is to explain how NSIS signaling should
work within the broader networking context, and to describe the
overall structure of the protocol suite itself. Therefore, it
discusses important protocol considerations, such as routing,
mobility, security, and interactions with network 'resource'
management (in the broadest sense).
The basic context for NSIS protocols is given in section 3. Section
3.1 describes the fundamental elements of NSIS protocol operation in
comparison to RSVP [7]; in particular, section 3.1.3 describes more
general signaling scenarios, and 3.1.4 defines a broader class of
signaling applications for which the NSIS protocols should be useful.
The two-layer protocol architecture that supports this generality is
described in section 3.2, and section 3.3 gives examples of the ways
in which particular signaling application properties can be
accommodated within signaling layer protocol behavior.
The overall functionality required from the lower (generic) protocol
layer is described in section 4. This is not intended to define the
detailed design of the protocol or even design options, although some
are described as examples. It describes the interfaces between this
lower layer protocol and the IP layer (below) and signaling
application protocols (above), including the identifier elements that
appear on these interfaces (section 4.6). Following this, section 5
describes how signaling applications that use the NSIS protocols can
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interact sensibly with network layer operations, specifically routing
(and re-routing), IP mobility, and network address translation.
Section 6 describes particular signaling applications. The example of
signaling for QoS (comparable to core RSVP QoS signaling
functionality) is given in detail in section 6.1, which describes
both the signaling application specific protocol and example modes of
interaction with network resource management and other deployment
aspects. However, note that these examples are included only as
background and for explanation; it is not intended to define an over-
arching architecture for carrying out resource management in the
Internet. Further possible signaling applications are outlined in
section 6.2.
2 Terminology
Classifier - an entity which selects packets based on their contents
according to defined rules.
[Data] flow - a stream of packets from sender to receiver which is a
distinguishable subset of a packet stream. Each flow is distinguished
by some flow identifier (see section 4.6.1).
Edge node - an (NSIS-capable) node on the boundary of some
administrative domain.
Interior nodes - the set of (NSIS-capable) nodes which form an
administrative domain, excluding the edge nodes.
NSIS Entity (NE) - the function within a node which implements an
NSIS protocol. In the case of path-coupled signaling, the NE will
always be on the data path.
NSIS Signaling Layer Protocol (NSLP) - generic term for an NSIS
protocol component that supports a specific signaling application.
See also section 3.2.1.
NSIS Transport Layer Protocol (NTLP) - placeholder name for the NSIS
protocol component that will support lower layer (signaling
application independent) functions. See also section 3.2.1.
Path-coupled signaling - a mode of signaling where the signaling
messages follow a path that is tied to the data messages.
Path-decoupled signaling - signaling for state manipulation related
to data flows, but only loosely coupled to the data path, e.g. at the
AS level.
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Peer discovery - the act of locating and/or selecting which NSIS peer
to carry out signaling exchanges with for a specific data flow.
Peer relationship - signaling relationship between two adjacent NSIS
entities (i.e. NEs with no other NEs between them).
Receiver - the node in the network which is receiving the data
packets in a flow.
Sender - the node in the network which is sending the data packets in
a flow.
Session - application layer flow of information for which some
network control state information is to be manipulated or monitored
(see section 4.6.2).
Signaling application - the purpose of the NSIS signaling: a service
could be QoS management, firewall control, and so on. Totally
distinct from any specific user application.
3 Overview of Signaling Scenarios and Protocol Structure
3.1 Fundamental Signaling Concepts
3.1.1 Simple Network and Signaling Topology
The NSIS suite of protocols is envisioned to support various
signaling applications that need to install and/or manipulate state
in the network. This state is related to a data flow and is installed
and maintained on the NSIS Entities (NEs) along the data flow path
through the network; not every node has to contain an NE. The basic
protocol concepts do not depend on the signaling application, but the
details of operation and the information carried do. This section
discusses the basic entities involved with signaling as well as
interfaces between them.
Two NSIS entities that communicate directly are said to be in a 'peer
relationship'. This concept might loosely be described as an 'NSIS
hop'; however, there is no implication that it corresponds to a
single IP hop. Either or both NEs might store some state information
about the other, but there is no assumption that they necessarily
establish a long-term signaling connection between themselves.
It is common to consider a network as composed of various domains,
e.g. for administrative or routing purposes, and the operation of
signaling protocols may be influenced by these domain boundaries.
However, it seems there is no reason to expect that an 'NSIS domain'
should exactly overlap with an IP domain (AS, area) but it is likely
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that its boundaries would consist of boundaries (segments) of one or
several IP domains.
Figure 1 shows a diagram of nearly the simplest possible signaling
configuration. A single data flow is running from an application in
the sender to the receiver via routers R1, R2 and R3. Each host and
two of the routers contain NEs which exchange signaling messages -
possibly in both directions - about the flow. This scenario is
essentially the same as that considered by RSVP for QoS signaling;
the main difference is that we make no assumptions here about the
particular sequence of signaling messages that will be invoked.
Sender Receiver
+-----------+ +----+ +----+ +----+ +-----------+
|Application|----->| R1 |----->| R2 |----->| R3 |----->|Application|
| +--+ | |+--+| |+--+| +----+ | +--+ |
| |NE|====|======||NE||======||NE||==================|===|NE| |
| +--+ | |+--+| |+--+| | +--+ |
+-----------+ +----+ +----+ +-----------+
+--+
|NE| = NSIS ==== = Signaling ---> = Data flow messages
+--+ Entity Messages (unidirectional)
Figure 1: Simple Signaling and Data Flows
3.1.2 Path-Coupled and Path-Decoupled Signaling
We can consider two basic paradigms for resource reservation
signaling, which we refer to as "path-coupled" and "path-decoupled".
In the path-coupled case, signaling messages are routed only through
nodes (NEs) that are in the data path. They do not have to reach all
the nodes on the data path (for example, there could be proxies
distinct from the sender and receiver as described in section 3.1.3,
or intermediate signaling-unaware nodes); and between adjacent NEs,
the route taken by signaling and data might diverge. The path-coupled
case can be supported by various addressing styles, with messages
either explicitly addressed to the neighbor on-path NE, or addressed
identically to the data packets but also with the router alert option
(see [8] and [9]) and intercepted. These cases are considered in
section 4.2. In the second case, some network configurations may
split the signaling and data paths (see section 5.1.1); this is
considered an error case for path-coupled signaling.
In the path-decoupled case, signaling messages are routed to nodes
(NEs) which are not assumed to be on the data path, but which are
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(presumably) aware of it. Signaling messages will always be directly
addressed to the neighbor NE, and the signaling endpoints may have no
relation at all with the ultimate data sender or receiver. The
implications of path-decoupled operation for the NSIS protocols are
considered briefly in section 3.2.6; however, the initial goal of
NSIS and this framework is to concentrate mainly on the path-coupled
case.
3.1.3 Signaling to Hosts, Networks and Proxies
There are different possible triggers for the signaling protocols.
Amongst them are user applications (that are using NSIS signaling
services), other signaling applications, network management actions,
some network events, and so on. The variety of possible triggers
requires that the signaling can be initiated and terminated in the
different parts of the network - hosts, domain boundary nodes (edge
nodes) or interior domain nodes.
The NSIS protocol suite extends the RSVP model to consider this wider
variety of possible signaling exchanges. As well as the basic end-to-
end model already described, examples such as end-to-edge and edge-
to-edge can be considered. The edge-to-edge case might involve the
edge nodes communicating directly, as well as via the interior nodes.
While the end-to-edge (host-to-network) scenario requires only intra-
domain signaling, the other cases might need inter-domain NSIS
signaling as well if the signaling endpoints (hosts or network edges)
are connected to different domains. Depending on the trust relation
between concatenated NSIS domains the edge-to-edge scenario might
cover single domain or multiple concatenated NSIS domains. The latter
case assumes the existence of trust relations between domains.
In some cases it is desired to be able to initiate and/or terminate
NSIS signaling not from the end host that sends/receives the data
flow, but from the some other entities in the network that can be
called signaling proxies. There could be various reasons for this:
signaling on behalf of the end hosts that are not NSIS-aware,
consolidation of the customer accounting (authentication,
authorization) in respect to consumed application and transport
resources, security considerations, limitation of the physical
connection between host and network and so on. This configuration can
be considered as a kind of "proxy on the data path", see Figure 2.
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Proxy1 Proxy2
+------+ +----+ +----+ +----+ +----+ +--------+
|Sender|-...->|Appl|---->| R |-.->| R |--->|Appl|-...->|Receiver|
| | |+--+| |+--+| |+--+| +----+ | |
+------+ ||NE||=====||NE||=.==||NE||====||NE|| +--------+
|+--+| |+--+| |+--+| |+--+|
+----+ +----+ +----+ +----+
+--+
|NE| = NSIS ==== = Signaling ---> = Data flow messages
+--+ Entity Messages (unidirectional)
Appl = signaling application
Figure 2: "On path" NSIS proxy
This configuration presents 2 specific challenges for the signaling:
*) A proxy that terminates signaling on behalf of the NSIS-unaware
host (or part of the network) should be able to make determination
that it is a last NSIS aware node along the path.
*) Where a proxy initiates NSIS signaling on behalf of the NSIS
unaware host, interworking with some other "local" technology might
be required, for example to provide QoS reservation from proxy to the
end host in the case of QoS signaling application.
+------+ +----+ +----+ +----+ +-----------+
|Sender|----->| PA |----->| R2 |----->| R3 | ---->| Receiver |
| | |+--+| |+--+| +----+ | +--+ |
+------+ ||NE||======||NE||==================|===|NE| |
|+--+| |+--+| | +--+ |
+-..-+ +----+ +-----------+
..
..
+-..-+
|Appl|
+----+
Appl = signaling PA = Proxy for signaling
application application
Figure 3: "Off path" NSIS proxy
Another possible configuration, shown in Figure 3, is where an NE can
send and receive signaling information to a remote processor. The
NSIS protocols may or may not be suitable for this remote
interaction, but in any case it is not currently part of the NSIS
problem. This configuration is supported by considering the NE as a
proxy at the signaling application level. This is a natural
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implementation approach for some policy control and centralized
control architectures, see also section 6.1.4.
3.1.4 Signaling Messages and Network Control State
The distinguishing features of the signaling supported by the NSIS
protocols are that it is related to specific flows (rather than to
network operation in general), and that it involves nodes in the
network (rather than running transparently between the end hosts).
Therefore, each signaling application (upper layer) protocol must
carry per-flow information for the aspects of network-internal
operation interesting to that signaling application. An example for
the case of an RSVP-like QoS signaling application would be state
data representing resource reservations. However, more generally, the
per-flow information might be related to some other control function
in routers and middleboxes along the path. Indeed, the signaling
might simply be used to gather per-flow information, without
modifying network operation at all.
We call this information generically 'network control state'.
Signaling messages may install, modify, refresh, or simply read this
state from network elements for particular data flows. Usually a
network element will also manage this information at the per-flow
level, although coarser-grained ('per-class') state management is
also possible.
3.1.5 Data Flows and Sessions
Formally, a data flow is a (unidirectional) sequence of packets
between the same endpoints which all follow a unique path through the
network (determined by IP routing and other network configuration). A
flow is defined by a packet classifier (in the simplest cases, just
the destination address and topological origin are needed). In
general we assume that when discussing only the data flow path, we
only need to consider 'simple' fixed classifiers (e.g. IPv4 5-tuple
or equivalent).
A session is an application layer concept for a (unidirectional) flow
of information between two endpoints, for which some network state is
to be allocated or monitored. (Note that this use of the term
'session' is not identical to the usage in RSVP. It is closer to the
session concept of, for example, the Session Initiation Protocol.)
The simplest service provided by NSIS signaling protocols is
management of network control state at the level of a specific flow,
as described in the previous subsection. In particular, it should be
possible to monitor routing updates as they change the path taken by
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a flow and, for example, update network state appropriately. This is
no different from the case for RSVP (local path repair). Where there
is a 1:1 flow:session relationship, this is all that is required.
However, for some more complex scenarios (especially mobility and
multihoming related ones, see [1] and the mobility discussion of [5])
it is desirable to update the flow:session mapping during the session
lifetime. For example, a new flow can be added, and the old one
deleted (and maybe in that order, for a 'make-before-break'
handover), effectively transferring the network control state between
data flows to keep it associated with the same session. Such updates
are best managed by the end systems (generally, systems which
understand the flow:session mapping and are aware of the packet
classifier change). To enable this, it must be possible to relate
signaling messages to sessions as well as data flows. A session
identifier (section 4.6.2) is one component of the solution.
3.2 Layer Model for the Protocol Suite
3.2.1 Layer Model Overview
In order to achieve a modular solution for the NSIS requirements, the
NSIS protocol suite will be structured in 2 layers:
*) a 'signaling transport' layer, responsible for moving signaling
messages around, which should be independent of any particular
signaling application; and
*) a 'signaling application' layer, which contains functionality
such as message formats and sequences, specific to a particular
signaling application.
For the purpose of this document, we use the term 'NSIS Transport
Layer Protocol' (NTLP) to refer to the component that will be used in
the transport layer. We also use the term 'NSIS Signaling Layer
Protocol' (NSLP) to refer generically to any protocol within the
signaling application layer; in the end, there will be several NSLPs,
largely independent of each other. These relationships are
illustrated in Figure 4. Note that the NTLP may or may not have an
interesting internal structure (e.g. including existing transport
protocols) but that is not relevant at this level of description.
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^ +-----------------+
| | NSIS Signaling |
| | Layer Protocol |
NSIS | +----------------| for middleboxes |
Signaling | | NSIS Signaling | +-----------------+
Layer | | Layer Protocol +--------| NSIS Signaling |
| | for QoS | | Layer Protocol |
| +-----------------+ | for ... |
V +-----------------+
=============================================
NSIS ^ +--------------------------------+
Transport | | NSIS Transport Layer Protocol |
Layer V +--------------------------------+
=============================================
+--------------------------------+
. IP and lower layers .
. .
Figure 4: NSIS Protocol Components
Note that not every generic function has to be located in the NTLP.
Another option would be to have re-usable components within the
signaling application layer. Functionality within the NTLP should be
restricted to that which interacts strongly with other transport and
lower layer operations.
3.2.2 Layer Split Concept
This section describes the basic concepts underlying the
functionality of the NTLP. Firstly, we make a working assumption that
the protocol mechanisms of the NTLP operate only between adjacent NEs
(informally, the NTLP is a 'hop-by-hop' protocol), whereas any larger
scope issues (including e2e aspects) are left to the upper layers.
The way in which the NTLP works can be described as follows: When a
signaling message is ready to be sent from one NE, it is given to the
NTLP along with information about what flow it is for; it is then up
to the NTLP to get it to the next NE along the path (up- or down-
stream), where it is received and the responsibility of the NTLP
ends. Note that there is no assumption here about how the messages
are actually addressed (this is a protocol design issue, and the
options are outlined in section 4.2). The key point is that the NTLP
for a given NE does not use any knowledge about addresses,
capabilities, or status of any NEs other than its direct peers.
The NTLP in the receiving NE either forwards the message directly,
or, if there is an appropriate signaling application locally, passes
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it upwards for further processing; the signaling application can then
generate another message to be sent via the NTLP. In this way, larger
scope (including end-to-end) message delivery is achieved.
This definition relates to NTLP operation. It does not restrict the
ability of an NSLP to send messages by other means. For example, an
NE in the middle or end of the signaling path could send a message
directly to the other end as a notification of or acknowledgement for
some signaling application event. However, the issues in sending such
messages (endpoint discovery, security, NAT traversal and so on) are
so different from the direct peer-peer case that there is no benefit
in extending the NTLP to include such non-local functionality;
instead, an NSLP which requires such messages and wants to avoid
traversing the path of NEs should use some other existing transport
protocol - for example, UDP or DCCP would be a good match for many of
the scenarios that have been proposed. Acknowledgements and
notifications of this type are considered further in section 3.3.6.
One motivation for restricting the NTLP to only peer-relationship
scope is that if there are any options or variants in design approach
- or, worse, in basic functionality - it is easier to manage the
resulting complexity if it only impacts direct peers rather than
potentially the whole Internet.
3.2.3 Bypassing Intermediate Nodes
Because the NSIS problem includes multiple signaling applications, it
is very likely that a particular NSLP will only be implemented on a
subset of the NSIS-aware nodes on a path, as shown in Figure 5. In
addition, a node inside an aggregation region will still wish to
ignore signaling messages which are per-flow, even if they are for a
signaling application which the node is able to process in general.
+------+ +------+ +------+ +------+
| NE | | NE | | NE | | NE |
|+----+| | | |+----+| |+----+|
||NSLP|| | | ||NSLP|| ||NSLP||
|| 1 || | | || 2 || || 1 ||
|+----+| | | |+----+| |+----+|
| || | | | | | | || |
|+----+| |+----+| |+----+| |+----+|
====||NTLP||====||NTLP||====||NTLP||====||NTLP||====
|+----+| |+----+| |+----+| |+----+|
+------+ +------+ +------+ +------+
Figure 5: Signaling with Heterogeneous NSLPs
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Where signaling messages traverse such NSIS-aware intermediate nodes,
it is desirable to process them at the lowest level possible (in
particular, on the fastest path). In order to offer a non-trivial
message transfer service (in terms of security, reliability and so
on) to the peer NSLP nodes, it is important that NTLP at intermediate
nodes is as transparent as possible, that is, it carries out minimal
processing. In addition, if intermediate nodes have to do slow-path
processing of all NSIS messages, this eliminates many of the scaling
benefits of aggregation, unless tunneling is used.
Considering first the case of messages sent with the router alert
option, there are two complementary methods to achieve this bypassing
of intermediate NEs:
*) At the IP layer, a set of protocol numbers can be used, or a range
of values in the router alert option. In this way, messages can be
marked with an implied granularity, and routers can choose to apply
further slow-path processing only to configured subsets of messages.
This is the method used in [10] to distinguish per-flow and per-
aggregate signaling.
*) The NTLP could process the message but determine that there was no
local signaling application it was relevant to. At this stage, the
message can be returned unchanged to the IP layer for normal
forwarding; the intermediate NE has effectively chosen to be
transparent to the message in question.
In both cases, the existence of the intermediate NE is totally hidden
from the NSLP nodes. If later stages of the signaling use directly
addressed messages (e.g. for reverse routing), they will not involved
the intermediate NE at all, except perhaps as a normal router.
There may be cases where the intermediate NE would like to do some
restricted protocol processing, for example:
*) Translating addresses in message payloads (compare section 4.6.1);
note this would have to be done to messages passing both directions
through a node.
*) Updating signaling application payloads with local status
information (e.g. path property measurement inside a domain).
If this can be done without fully terminating the NSIS protocols,
this would allow a more lightweight implementation of the
intermediate NE, and a more direct 'end-to-end' NTLP association
between the peer NSLPs where the signaling application is fully
processed. On the other hand, this is only possible with a limited
class of possible NTLP designs, and makes it harder for the NTLP to
offer a security service (since messages have to be partially
protected). The feasibility of this approach will be evaluated during
the NTLP design.
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3.2.4 Core NTLP Functionality
This section describes the basic functionality to be supported by the
NTLP. Note that the overall signaling solution will always be the
result of joint NSLP and NTLP operation; for example, we can always
assume that an NSLP is operating above the NTLP and taking care of
end-to-end issues (e.g. recovery of messages after restarts).
Therefore, NTLP functionality is essentially just efficient upstream
and downstream peer-peer message delivery, in a wide variety of
network scenarios. Message delivery includes the act of locating
and/or selecting which NTLP peer to carry out signaling exchanges
with for a specific data flow. This discovery might be an active
process (using specific signaling packets) or a passive process (a
side effect of using a particular addressing mode). In addition, it
appears that the NTLP can sensibly carry out many of the functions of
enabling signaling messages to pass through middleboxes, since this
is closely related to the problem of routing the signaling messages
in the first place. Further details about NTLP functionality are
contained in sections 3.2.5 and 4.3.
3.2.5 State Management Functionality
Internet signaling requires the existence and management of state
within the network for several reasons. This section describes how
state management functionality is split across the NSIS layers. (Note
that how the NTLP internal state is managed is a matter for its
design and indeed implementation.)
1. Conceptually, the NTLP provides a uniform message delivery
service. It is unaware of the difference in state semantics between
different types of signaling application message (e.g. whether a
message changes or just refreshes signaling application state, or
even has nothing to with signaling application state at all).
2. An NTLP instance processes and if necessary forwards all signaling
application messages "immediately". (It might offer different service
classes, but these would be distinguished e.g. by reliability or
priority, not state aspects.) This means that the NTLP does not know
explicit timer or message sequence information for the signaling
application; and that signaling application messages pass immediately
through an NSLP-unaware node (their timing cannot be jittered there,
nor can messages be stored up to be re-sent on a new paths in case of
a later re-routing event).
3. Within any node, it is an implementation decision whether to
generate/jitter/filter refreshes either separately within each
signaling application that needs this functionality, or to integrate
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it with the NTLP implementation as a generic "soft-state management
toolbox"; the choice doesn't affect the NTLP specification at all.
Implementations might piggy-back NTLP soft-state refresh information
(if the NTLP works this way) on signaling application messages, or
even combine soft-state management between layers. The state machines
of the NTLP and NSLPs remain logically independent, but an
implementation is free to allow them to interact to reduce the load
on the network to the same level as would be achieved by a monolithic
model.
4. It may be helpful for signaling applications to receive state-
management related 'triggers' from the NTLP, that a peer has failed
or become available ("down/up notifications"). These triggers would
be about adjacent NTLP peers, rather than signaling application
peers. We can consider this as another case of route change
detection/notification (which the NTLP is also allowed to do anyway).
However, apart from generating such triggers, the NTLP takes no
action itself on such events, other than to ensure that subsequent
signaling messages are correctly routed.
5. The existence of these triggers doesn't replace NSLP refreshes as
the mechanism for maintaining liveness at the signaling application
level. In this sense, up/down notifications are advisories which
allow faster reaction to events in the network, but shouldn't be
built into NSLP semantics. (This is essentially the same distinction
- with the same rationale - as SNMP makes between traps and normal
message exchanges.)
3.2.6 Path De-Coupled Operation
Path-decoupled signaling is defined as signaling for state
installation along the data path, without the restriction of passing
only through nodes that are located on the data path. Signaling
messages can be routed to nodes off the data path, but which are
(presumably) aware of it. This allows a looser coupling between
signaling and data plane nodes, e.g. at the autonomous system level.
The main advantages of path-decoupled signaling are ease of
deployment and support of additional functionality. The ease of
deployment comes from a restriction of the number of impacted nodes
in case of deployment and/or upgrade of an NSLP. It would allow, for
instance, deploying a solution without upgrading any of the routers
in the data plane. Additional functionality that can be supported
includes the use of off-path proxies to support authorization or
accounting architectures.
There are potentially significant differences in the way that the two
signaling paradigms should be analyzed. Using a single centralized
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off-path NE may increase the requirements in terms of message
handling; on the other hand, path-decoupled signaling is equally
applicable to distributed off-path entities. Failure recovery
scenarios need to be analyzed differently because fate-sharing
between data and control plane can no longer be assumed. Furthermore,
the interpretation of sender/receiver orientation becomes less
natural. With the local operation of NTLP, the impact of path-
decoupled signaling on the routing of signaling messages is
presumably restricted to the problem of peer determination. The
assumption that the off-path NSIS nodes are loosely tied to the data
path suggests, however, that peer determination can still be based on
L3 routing information. This means that a path-decoupled signaling
solution could be implemented using a lower layer protocol presenting
the same service interface to NSLPs as the path-coupled NTLP. A new
message transport protocol (possibly derived from the path-coupled
NTLP) would be needed, but NSLP specifications and the inter-layer
interaction would be unchanged from the path-coupled case.
3.3 Signaling Application Properties
It is clear that many signaling applications will require specific
protocol behavior in their NSLP. This section outlines some of the
options for NSLP behavior; further work on selecting from these
options would depend on detailed analysis of the signaling
application in question.
3.3.1 Sender/Receiver Orientation
In some signaling applications, a node at one end of the data flow
takes responsibility for requesting special treatment - such as a
resource reservation - from the network. Which end may depend on the
signaling application, or characteristics of the network deployment.
A sender-initiated approach is when the sender of the data flow
requests and maintains the treatment for that flow. In a receiver-
initiated approach the receiver of the data flow requests and
maintains the treatment for that flow. The NTLP itself has no freedom
in this area: next NTLP peers have to be discovered in the sender to
receiver direction, but after that time the default assumption is
that signaling is possible both upstream and downstream (unless
possibly a signaling application specifically indicates this is not
required). This implies that backward routing state must be
maintained by the NTLP or that backward routing information must be
available in the signaling message.
The sender and receiver initiated approaches have several differences
in their operational characteristics. The main ones are as follows:
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*) In a receiver-initiated approach, the signaling messages traveling
from the receiver to the sender must be backward routed such that
they follow exactly the same path as was followed by the signaling
messages belonging to the same flow traveling from the sender to the
receiver. In a sender-initiated approach, provided acknowledgements
and notifications can be securely delivered to the sending node,
backward routing is not necessary, and nodes do not have to maintain
backward routing state.
*) In a sender-initiated approach, a mobile node can initiate a
reservation for its outgoing flows as soon as it has moved to another
roaming subnetwork. In a receiver-initiated approach, a mobile node
has to inform the receiver about its handover, thus allowing the
receiver to initiate a reservation for these flows. For incoming
flows, the reverse argument applies.
*) In general, setup and modification will be fastest if the node
responsible for authorizing these actions can initiate them directly
within the NSLP. A mismatch between authorizing and initiating NEs
will cause additional message exchanges either in the NSLP or in a
protocol executed prior to NSIS invocation. Depending on how the
authorization for a particular signaling application is done, this
may favor either sender or receiver initiated signaling. Note that
this may complicate modifications of network control state for
existing flows.
*) Where the signaling is looking for the last (nearest to receiver)
NE on the data path, receiver oriented signaling is most efficient;
sender orientation would be possible, but take more messages.
*) In either case, the initiator can generally be informed faster
about reservation failures than the remote end.
3.3.2 Uni- and Bi-Directional Operation
For some signaling applications and scenarios, signaling may only be
considered for a unidirectional data flow. However, in other cases,
there may be interesting relationships between the signaling for the
two flows of a bi-directional session; an example is QoS for a voice
call. Note that the path in the two directions may differ due to
asymmetric routing. In the basic case, bi-directional signaling can
simply use a separate instance of the same signaling mechanism in
each direction.
In constrained topologies where parts of the route are symmetric, it
may be possible to use a more unified approach to bi-directional
signaling, e.g. carrying the two signaling directions in common
messages. This optimization might be used for example to make mobile
QoS signaling more efficient.
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In either case, the correlation of the signaling for the two flow
directions is carried out in the NSLP. The NTLP would simply be
enabled to bundle the messages together.
3.3.3 Heterogeneous Operation
It is likely that the appropriate way to describe the state NSIS is
signaling for will vary from one part of the network to another
(depending on signaling application). For example in the QoS case,
resource descriptions that are valid for inter-domain links will
probably be different from those useful for intra-domain operation
(and the latter will differ from one domain to another).
One way to address this issue is to consider the state description
used within the NSLP as carried in globally-understood objects and
locally-understood objects. The local objects are only applicable for
intra-domain signaling, while the global objects are mainly used in
inter-domain signaling. Note that the local objects are still part of
the protocol but are inserted, used and removed by one single domain.
The purpose of this division is to provide additional flexibility in
defining the objects carried by the NSLP such that only the objects
applicable in a particular setting are used. One approach for
reflecting the distinction is that local objects could be put into
separate local messages that are initiated and terminated within one
single domain; an alternative is that they could be "stacked" within
the NSLP messages that are used anyway for inter-domain signaling.
3.3.4 Aggregation
It is a well known problem that per-flow signaling in large-scale
networks present scaling challenges because of the large number of
flows that may traverse individual nodes.
The possibilities for aggregation at the level of the NTLP are quite
limited; the primary scaling approach for path-coupled signaling is
for a signaling application to group flows together and perform
signaling for the aggregate, rather than for the flows individually.
The aggregate may be created in a number of ways: for example, the
individual flows may be sent down a tunnel, or given a common DSCP
marking. The aggregation and deaggregation points perform per flow
signaling, but nodes within the aggregation region should only be
forced to process signaling messages for the aggregate, somehow
ignoring the per-flow signaling (see section 3.2.3).
Individual NSLPs will need to specify what aggregation means in their
context, and how it should be performed. For example, in the QoS
context it is possible to add together the resources specified in a
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number of separate reservations. In the case of other applications,
such as signaling to NATs and firewalls, the feasibility (and even
the meaning) of aggregation is less clear.
3.3.5 Peer-Peer and End-End Relationships
The assumption in this framework is that the NTLP will operate
'locally', that is, just over the scope of a single peer
relationship. End-to-end operation is built up by concatenating these
relationships. Non-local operation (if any) will take place in NSLPs.
The peering relations may also have an impact on the required amount
of state at each NSIS entity. When direct interaction with remote
peers is not allowed, it may be required to keep track of the path
that a message has followed through the network. This can be achieved
by keeping per-flow state at the NSIS entities or by maintaining a
record route object in the messages.
3.3.6 Acknowledgements and Notifications
We are assuming that the NTLP provides a simple message transfer
service, and any acknowledgements or notifications it generates are
handled purely internally (and apply within the scope of a single
NTLP peer relationship).
However, we expect that some signaling applications will require
acknowledgements regarding the failure/success of state installation
along the data path, and this will be an NSLP function.
Acknowledgements can be sent along the sequence of NTLP peer
relationships towards the signaling initiator, which relieves the
requirements on the security associations that need to be maintained
by NEs and can allow NAT traversal in both directions. (If this
direction is towards the sender, it implies maintaining reverse
routing state in the NTLP). In certain circumstances (e.g. trusted
domains), an optimization can be to send acknowledgements directly to
the signaling initiator outside the NTLP (see section 3.2.2).
The semantics of the acknowledgement messages are of particular
importance. An NE sending a message could assume responsibility for
the entire downstream chain of NEs, indicating for instance the
availability of reserved resources for the entire downstream path.
Alternatively, the message could have a more local meaning,
indicating for instance that a certain failure or degradation
occurred at a particular point in the network.
Notifications differ from acknowledgements because they are not
(necessarily) generated in response to other signaling messages. This
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means that it may not be obvious to determine where the notification
should be sent. Other than that, the same considerations apply as for
acknowledgements. One useful distinction to make would be to
differentiate between notifications that trigger a signaling action
and others that don't. The security requirements for the latter are
less stringent, which means they could be sent directly to the NE
they are destined for (provided this NE can be determined).
3.3.7 Security and Other AAA Issues
In some cases it will be possible to achieve the necessary level of
signaling security by using basic 'channel security' mechanisms [11]
at the level of the NTLP, and the possibilities are described in
section 4.7. In other cases, signaling applications may have specific
security requirements, in which case they are free to invoke their
own authentication and key exchange mechanisms and apply 'object
security' to specific fields within the NSLP messages.
In addition to authentication, the authorisation (to manipulate
network control state) has to be considered as functionality above
the NTLP level, since it will be entirely application specific.
Indeed, authorisation decisions may be handed off to a third party in
the protocol (e.g. for QoS, the resource management function as
described in section 6.1.4). Many different authorisation models are
possible, and the variations impact:
*) what message flows take place - for example, whether authorisation
information is carried along with a control state modification
request, or is sent in the reverse direction in response to it;
*) what administrative relationships are required - for example,
whether authorisation takes place only between peer signaling
applications, or over longer distances.
Because the NTLP operates only between adjacent peers, and places no
constraints on the direction or order in which signaling applications
can send messages, these authorisation aspects are left open to be
defined by each NSLP. Further background discussion of this issue is
contained in [12].
4 The NSIS Transport Layer Protocol
This section describes the overall functionality required from the
NTLP. It mentions possible protocol components within the NTLP layer
and the different possible addressing modes that can be utilized, as
well as the assumed transport and state management functionality. The
interfaces between NTLP and the layers above and below it are
identified, with a description of the identity elements that appear
on these interfaces.
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It is not the intention of this discussion to design the NTLP or even
to enumerate design options, although some are included as examples.
The goal is to provide a general discussion of required functionality
and to highlight some of the issues associated with this.
4.1 Internal Protocol Components
The NTLP includes all functionality below the signaling application
layer and above the IP layer. The functionality that is required
within the NTLP is outlined in section 3.2.4, with some more details
in sections 3.2.5 and 4.3.
Some NTLP functionality could be provided via components operating as
sublayers within the NTLP design. For example, if specific transport
capabilities are required, such as congestion avoidance,
retransmission, security and so on, then existing protocols, such as
TCP+TLS or DCCP+IPsec, could be incorporated into the NTLP. This
possibility is not required or excluded by this framework.
If peer-peer addressing (section 4.2) is used for some messages, then
active next-peer discovery functionality will be required within the
NTLP to support the explicit addressing of these messages. This could
use message exchanges for dynamic peer discovery as a sublayer within
the NTLP; there could also be an interface to external mechanisms to
carry out this function.
==================== ===========================
^ +------------------+ +-------------------------+
| | | | NSIS Specific Functions |
| | | | .............|
NSIS | | Monolithic | |+----------+. Peer .|
Transport | | Protocol | || Existing |. Discovery .|
Layer | | | || Protocol |. Aspects .|
| | | |+----------+.............|
V +------------------+ +-------------------------+
==================== ===========================
Figure 6: Options for NTLP Structure
4.2 Addressing
There are two ways to address a signaling message being transmitted
between NTLP peers:
*) peer-peer, where the message is addressed to a neighboring NSIS
entity that is known to be closer to the destination NE.
*) end-to-end, where the message is addressed to the flow
destination directly, and intercepted by an intervening NE.
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With peer-peer addressing, an NE will determine the address of the
next NE based on the payload of the message (and potentially on the
previous NE). This requires the address of the destination NE to be
derivable from the information present in the payload, either by
using some local routing table or through participation in active
peer discovery message exchanges. Peer-peer addressing inherently
supports tunneling of messages between NEs, and is equally applicable
to the path-coupled and path-decoupled cases.
In the case of end-to-end addressing, the message is addressed to the
data flow receiver, and (some of) the NEs along the data path
intercept the messages. The routing of the messages should follow
exactly the same path as the associated data flow (but see section
5.1.1 on this point). Note that securing messages sent this way
raises some interesting security issues (these are discussed in [2]).
It is not possible at this stage to mandate one addressing mode or
the other. Indeed, each is necessary for some aspects of NTLP
operation: in particular, initial discovery of the next downstream
peer will usually require end-to-end addressing, whereas reverse
routing will always require peer-peer addressing. For other message
types, the choice is a matter of protocol design. The mode used is
not visible to the NSLP, and the information needed in each case is
available from the flow identifier (section 4.6.1) or locally stored
NTLP state.
4.3 Classical Transport Functions
The NSIS signaling protocols are responsible for transporting
(signaling) data around the network; in general, this requires
functionality such as congestion management, reliability, and so on.
This section discusses how much of this functionality should be
provided within the NTLP. It appears that this doesn't affect the
basic way in which the NSLP/NTLP layers relate to each other (e.g. in
terms of the semantics of the inter-layer interaction); it is much
more a question of the overall performance/complexity tradeoff
implied by placing certain functions within each layer.
Note that, following the discussion at the end of section 3.2.3,
there may be cases where intermediate nodes wish to modify messages
in transit even though they do not perform full signaling application
processing. In this case, not all of the following functionality
would be invoked at every intermediate node.
The following functionality is assumed to lie within the NTLP:
1. Bundling together of small messages (comparable to [13]) can be
provided locally by the NTLP as an option if desired; it doesn't
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affect the operation of the network elsewhere. The NTLP should
always support unbundling, to avoid the cost of negotiating the
feature as an option. (The related function of refresh
summarization - where objects in a refresh message are replaced
with a reference to a previous message identifier - is left to
NSLPs which can then do this in a way tuned to the state
management requirements of the signaling application. Additional
transparent compression functionality could be added to the NTLP
design later as a local option.) Note that end-to-end addressed
messages for different flows cannot be bundled safely unless the
next node on the outgoing interface is known to be NSIS-aware.
2. Message fragmentation should be provided by the NTLP when needed.
For NSLPs that generate large messages, it will be necessary to
fragment them efficiently within the network, where the use of IP
fragmentation may lead to reduced reliability and be incompatible
with some addressing schemes. To avoid imposing the cost of
reassembly on intermediate nodes, the fragmentation scheme used
should allow for the independent forwarding of individual
fragments towards a node hosting an interested NSLP.
3. There can be significant benefits for signaling applications if
state-changing messages are delivered reliably (as introduced in
[13] for RSVP; see also the more general analysis of [14]). This
does not change any assumption about the use of soft-state by
NSLPs to manage signaling application state, and leaves the
responsibility for detecting and recovering from application
layer error conditions in the NSLP. However, it means that such
functionality does not need to be tuned to handle fast recovery
from message loss due to congestion or corruption in the lower
layers, and also means that the NTLP can prevent the
amplification of message loss rates caused by fragmentation.
Reliable delivery functionality is invoked by the NSLP on a
message-by-message basis and is always optional to use.
4. The NTLP should not allow signaling messages to cause congestion
in the network (i.e. at the IP layer). Congestion could be caused
by retransmission of lost signaling packets or by upper layer
actions (e.g. a flood of signaling updates to recover from a
route change). In some cases it may be possible to engineer the
network to ensure that signaling cannot overload it; in other
cases, the NTLP would have to detect congestion and adapt the
rate at which it allows signaling messages to be transmitted.
Principles of congestion control in Internet protocols are given
in [15]. The NTLP may or may not be able to detect overload in
the control plane itself (e.g. an NSLP-aware node several NTLP-
hops away which cannot keep up with the incoming message rate)
and indicate this as a flow-control condition to local signaling
applications. However, for both the congestion and overload
cases, it is up to the signaling applications themselves to adapt
their behavior accordingly.
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4.4 Lower Layer Interfaces
The NTLP interacts with 'lower layers' of the protocol stack for the
purposes of sending and receiving signaling messages. This framework
places the lower boundary of the NTLP at the IP layer. The interface
to the lower layer is therefore very simple:
*) The NTLP sends raw IP packets
*) The NTLP receives raw IP packets. In the case of peer-peer
addressing, they have been addressed directly to it. In the case of
end-to-end addressing, this will be achieved by intercepting packets
that have been marked in some special way (by special protocol number
or by some option interpreted within the IP layer, such as the router
alert option).
*) The NTLP receives indications from the IP layer regarding route
changes and similar events (see section 5.1).
For correct message routing, the NTLP needs to have some information
about link and IP layer configuration of the local networking stack.
In general, it needs to know how to select the outgoing interface for
a signaling message, where this must match the interface that will be
used by the corresponding flow. This might be as simple as just
allowing the IP layer to handle the message using its own routing
table. There is no intention to do something different from IP
routing (for end-to-end addressed messages); however, some hosts
allow applications to bypass routing for their data flows, and the
NTLP processing must account for this. Further network layer
information would be needed to handled scoped addresses (if such
things ever will exist).
Configuration of lower layer operation to handle flows in particular
ways is handled by the signaling application.
4.5 Upper Layer Services
The NTLP offers transport layer services to higher layer signaling
applications for two purposes: sending and receiving signaling
messages, and exchanging control and feedback information.
For sending and receiving messages, two basic control primitives are
required:
*) Send Message, to allow the signaling application to pass data to
the NTLP for transport.
*) Receive Message, to allow the NTLP to pass received data to the
signaling application.
The NTLP and signaling application may also want to exchange other
control information, such as:
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*) Signaling application registration/de-registration, so that
particular signaling application instances can register their
presence with the transport layer. This may also require some
identifier to be agreed between the NTLP and signaling application to
allow support the exchange of further control information and to
allow the de-multiplexing of incoming data.
*) NTLP configuration, allowing signaling applications to indicate
what optional NTLP features they want to use, and to configure NTLP
operation, such as controlling what transport layer state should be
maintained.
*) Error messages, to allow the NTLP to indicate error conditions to
the signaling application and vice versa.
*) Feedback information, such as route change indications so that the
signaling application can decide what action to take.
4.6 Identity Elements
4.6.1 Flow Identification
The flow identification is a method of identifying a flow in a unique
way. All packets associated with the same flow will be identified by
the same flow identifier. The key aspect of the flow identifier is
to provide enough information such that the signaling flow receives
the same treatment along the data path as that actual data itself,
i.e. consistent behavior is applied to the signaling and data flows
by a NAT or policy-based forwarding engine.
Information that could be used in flow identification may include:
*) source IP address;
*) destination IP address;
*) protocol identifier and higher layer (port) addressing;
*) flow label (typical for IPv6);
*) SPI field for IPsec encapsulated data;
*) DSCP/TOS field
It is assumed that wildcarding on these identifiers is not needed
(further analysis may be required).
We've assumed here that the flow identification is not hidden within
the NSLP, but is explicitly part of the NTLP. The justification for
this is that it might be valuable to be able to do NSIS processing
even at a node which was unaware of the specific signaling
application (see section 3.2.3): an example scenario would be
messages passing through an addressing boundary where the flow
identification had to be re-written.
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4.6.2 Session Identification
There are circumstances where it is important to be able to refer to
signaling application state independently of the underlying flow.
For example, if the address of one of the flow endpoints changes due
to a mobility event, it is desirable to be able to change the flow
identifier without having to install a completely new reservation.
The session identifier provides a method to correlate the signaling
about the different flows with the same network control state.
The session identifier is essentially a signaling application
concept, since it is only used in non-trivial state management
actions that are application specific. However, we assume here that
it should be visible within the NTLP. This enables it to be used to
control NTLP behavior, for example, by controlling how the transport
layer should forward packets belonging to this session (as opposed to
this signaling application). In addition, the session identifier can
be used by the NTLP to demultiplex received signaling messages
between multiple instances of the same signaling application, if such
an operational scenario is supported (see section 4.6.3 for more
information on signaling application identification).
To be useful for mobility support, the session identifier should be
globally unique, and it should not be modified end-to-end. It is well
known that it is practically impossible to generate identifiers in a
way which guarantees this property; however, using a large random
number makes it highly likely. In any case, the NTLP ascribes no
valuable semantics to the identifier (such as 'session ownership');
this problem is left to the signaling application, which may be able
to secure it to use for this purpose.
4.6.3 Signaling Application Identification
Since the NTLP can be used to support several NSLP types, there is a
need to identify which type a particular signaling message exchange
is being used for. This is to support:
*) processing of incoming messages - the NTLP should be able to
demultiplex these towards the appropriate signaling applications;
*) processing of general messages at an NSIS aware intermediate node
- if the node does not handle the specific signaling application, it
should be able to make a forwarding decision without having to parse
upper layer information.
No position is taken on the form of the signaling application
identifier, or even the structure of the signaling application
'space' - free-standing applications, potentially overlapping groups
of capabilities, etc. These details should not influence the rest of
NTLP design.
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4.7 Security Properties
It is assumed that the only security service required within NTLP is
channel security. Channel security requires a security association to
be established between the signaling endpoints, which is carried out
via some authentication and key management exchange. This
functionality could be provided by reusing a standard protocol.
In order to protect a particular signaling exchange, the NSIS entity
needs to select the security association that it has in place with
the next NSIS entity that will be receiving the signaling message.
The ease of doing this depends on the addressing model in use by the
NTLP (see section 4.2).
Channel security can provide many different types of protection to
signaling exchanges, including integrity and replay protection and
encryption. It is not clear which of these is required at the NTLP
layer, although most channel security mechanisms support them all.
Channel security can also be applied to the signaling messages with
differing granularity, i.e. all or parts of the signaling message may
be protected. For example, if the flow is traversing a NAT, only the
parts of the message that do not need to be processed by the NAT
should be protected (alternatively, if the NAT takes part in NTLP
security procedures, it only needs to be given access to the message
fields containing addresses, often just the flow id). It is an open
question as to which parts of the NTLP messages need protecting, and
what type of protection should be applied to each.
5 Interactions with Other Protocols
5.1 IP Routing Interactions
The NTLP is responsible for determining the next node to be visited
by the signaling protocol. For path-coupled signaling, this next node
should be one that will be visited by the data flow. In practice,
this peer discovery will be approximate, as any node could use any
feature of the peer discovery packet to route it differently from the
corresponding data flow packets. Divergence between data and
signaling path can occur due to load sharing or load balancing
(section 5.1.1). An example specific to the case of QoS is given in
section 6.1.1. Route changes cause a temporary divergence between the
data path and the path on which signaling state has been installed.
The occurrence, detection and impact of route changes is described in
section 5.1.2. A description of this issue in the context of QoS is
given in section 6.1.2.
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5.1.1 Load Sharing and Policy-Based Forwarding
Load sharing or load balancing is a network optimization technique
that exploits the existence of multiple paths to the same destination
in order to obtain benefits in terms of protection, resource
efficiency or network stability. The significance of load sharing in
the context of NSIS is that, if the load sharing mechanism in use
will forward packets on any basis other than the destination address,
routing of signaling messages using end-to-end addressing does not
guarantee that the messages will follow the data path. Policy-based
forwarding for data packets - where the outgoing link is selected
based on policy information about fields additional to the packet
destination address - has the same impact. Signaling and data packets
may diverge because of both of these techniques.
Load balancing techniques have been proposed for a number of routing
protocols, such as OSPF equal cost paths [16] and others. Typically,
based on the load reported from a particular path, load balancing
determines which fraction of the data to direct to that path.
Incoming packets are subject to a (source, destination address) hash
computation, and effective load sharing is accomplished by means of
adjusting the hash thresholds.
If signaling packets are given source and destination addresses
identical to data packets, signaling and data packets may still
diverge because of layer 4 load-balancing (based on protocol or port
number). Such techniques would also cause ICMP errors to be
misdirected to the source of the data because of the source address
spoofing. If signaling packets are made identical in the complete
five-tuple, divergence may still occur because of the presence of
router alert options. In this case, the same ICMP misdirection
applies. Additionally, it becomes difficult for the end systems to
distinguish between data and signaling packets. Finally, QoS routing
techniques may base the routing decision on any field in the packet
header (e.g. DSCP, ...).
Many load-balancing implementations use the first n bytes of the
packet header (including SA, DA and protocol) in the hash function.
In this case, the general considerations above regarding SA/DA or
five-tuple based forwarding continue to apply.
5.1.2 Route Changes
In a connectionless network, each packet is independently routed
based on its header information. Whenever a better route towards the
destination becomes available, this route is installed in the
forwarding table and will be used for all subsequent (data and
signaling) packets. This can cause a divergence between the path
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along which state has been installed and the path along which
forwarding will actually take place. (The problem of route changes is
reduced if route pinning is performed. Route pinning refers to the
independence of the path taken by certain data packets from
reachability changes caused by routing updates from an Interior
Gateway Protocol (OSPF, IS-IS) or an Exterior Gateway Protocol (BGP).
Nothing about NSIS signaling prevents route pinning being used as a
network engineering technique, provided it is done in a way which
preserves the common routing of signaling and data. However, even if
route pinning is used, it cannot be depended on to prevent all route
changes (for example in the case of link failures).
Handling route changes requires the presence of three processes in
the signaling protocol:
1. route change detection
2. installation of state on the new path
3. removal of state on the old path
Many route change detection methods can be used, some needing
explicit protocol support and some of which are implementation-
internal. They differ in their speed of reaction and the types of
change they can detect. In rough order of increasing applicability,
they can be summarized as:
a) monitoring changes in local interface state
b) monitoring topology changes in a link-state routing protocol
c) inference from changes in data packet TTL
d) inference from loss of packet stream in a flow-aware router
e) inference from changes in signaling packet TTL
f) changed route of an end-to-end addressed signaling packet
g) changed route of a specific end-to-end addressed probe packet
These methods can be categorized as being based on network monitoring
(method a-b), based on data packet monitoring (method c-d) and based
on monitoring signaling protocol messages (method e-g); method f is
the baseline method of RSVP. Methods contingent on monitoring
signaling messages become less effective as soft state refresh rates
are reduced.
When a route change has been detected, it is important that state is
installed as quickly as possible along the new path. It is not
guaranteed that the new path will be able to provide the same
characteristics that were available on the old path. In order to be
able to avoid duplicate state installation or, worse, rejection of
the signaling message because of previously installed state, it is
important to be able to recognize the new signaling message as
belonging to an existing session. In this respect, we distinguish
between route changes with associated change of the flow
identification (e.g. in case of a mobility event when the IP source
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might change) and route changes without change of the flow
identification (e.g. in case of a link failure along the path). The
former case requires an identifier independent from the flow
identification, i.e. the session identifier (section 4.6.2). Mobility
issues are discussed in more detail in section 5.2.
When state has been installed along the new path, the existing state
on the old path needs to be removed. With the soft-state principle,
this will happen automatically because of the lack of refresh
messages. Depending on the refresh timer, however, it may be required
to tear down this state much faster (e.g. because it is tied to an
accounting record). In that case, the teardown message needs to be
able to distinguish between the new path and the old path.
In some environments, it is desired to provide connectivity and per
flow or per class state management with high-availability
characteristics, i.e. with rapid transparent recovery even in the
presence of route changes. This may need interactions with protocols
which are used to manage the routing in this case, such as VRRP [17].
Our basic assumption about such interactions is that the NTLP would
be responsible for detecting the route change and ensuring that
signaling messages were re-routed appropriately along with data
traffic; but that the further state re-synchronization (including
failover between 'main' and 'standby' nodes in the high availability
case) would be the responsibility of the signaling application and
its NSLP, possibly triggered by the NTLP.
5.2 Mobility and Multihoming Interactions
The issues associated with mobility and multihoming are a
generalization of the basic route change case of the previous
section. As well as the fact that packets for a given session are no
longer traveling over a single topological path, the following extra
considerations arise:
1) The use of IP-layer mobility and multihoming means that more than
one IP source or destination address will be associated with a single
session. The same applies if application layer solutions (e.g. SIP-
based approaches) are used.
2) Mobile IP and associated protocols use some special encapsulations
for some segments of the data path.
3) The double route may persist for some time in the network (e.g. in
the case of a 'make-before-break' handover being done by a multihomed
host).
4) Conversely, the re-routing may be rapid and routine (unlike
network internal route changes), increasing the importance of rapid
state release on old paths.
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The interactions between mobility and signaling have been extensively
analyzed in recent years, primarily in the context of RSVP and Mobile
IP interaction (e.g. the mobility discussion of [5]), but also in the
context of other types of network (e.g. [18]); a general review of
the fundamental interactions is given in [19], which provides further
details on many of the subjects considered in this section.
We are assuming that the signaling will refer to 'outer' IP headers
when defining the flows it is controlling. There two main reasons for
this. The first is that the data plane will usually be unable to work
in terms of anything else when implementing per-flow treatment (e.g.
we cannot expect a router will analyse inner headers to decide how to
schedule packets). The second reason is that we are implicitly
relying on the security provided by the network infrastructure to
ensure that the correct packets are given the special treatment being
signaled for, and this is built on the relationship between packet
source and destination addresses and network topology (this is
essentially the same approach that is used as the basis of route
optimization security in Mobile IPv6 [20]). The consequence of this
assumption is that we see the packet streams to (or from) different
addresses as different flows, and where a flow is carried inside a
tunnel this is seen as a different flow again. The encapsulation
issues (point (2) above) are therefore to be handled the same way as
other tunneling cases (section 5.4).
The most critical aspect is therefore the fact that multiple flows
are being used, and the signaling for them needs to be correlated
together. This is the intended role of the session identifier (see
section 4.6.2, which also describes some of the security requirements
for such an identifier). Although the session identifier is visible
at the NTLP, it is the signaling application which is responsible for
performing the correlation (and doing so securely). The NTLP
responsibility is limited to delivering the signaling messages for
each flow between the correct signaling application peers. The
locations at which the correlation takes place are the end system and
the signaling application aware node in the network where the flows
meet (this node is generally referred to as the "crossover router";
it can be anywhere in the network).
Although much work has been done in the past on finding the crossover
router directly from information held in particular mobility
signaling protocols, the initial focus of NSIS work should be to have
a solution which is not tightly bound to any single mobility
approach. In other words, it should be possible to determine the
crossover router based on NSIS signaling. (This doesn't rule out the
possibility that some implementations may be able to do this
discovery faster, e.g. by being tightly integrated with local
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mobility management protocols; this is directly comparable to
spotting route changes in fixed networks by being routing aware.)
Note that the crossover router discovery may involve end-to-end
signaling exchanges (especially for flows towards the mobile or
multihomed node) which raises a latency concern; on the other hand,
end to end signaling will have been necessary in any case, both at
the application level (to communicate changed addresses) and also to
update packet classifiers along the path. It is a matter for further
analysis to decide how these exchanges could be combined or carried
out in parallel.
On the shared part of the path, signaling is needed at least to
update the packet classifiers to include the new flow, although if
correlation with the existing flow is possible it should be possible
to bypass any policy or admission control processing. State
installation on the new path (and possibly release on the old one)
are also required. Which entity (one of the end hosts or the
crossover router) controls all these procedures depends on which
entities are authorised to carry out network state manipulations, so
this is therefore a matter of signaling application and NSLP design.
The approach may depend on the sender/receiver orientation of the
original signaling (see section 3.3.1). In addition, in the mobility
case, the old path may no longer be directly accessible to the mobile
node; inter-access-router communication may be required to release
state in these circumstances.
The frequency of handovers in some network types encourages the
consideration of fast handover support protocols, for selection of
the optimal access router to hand over to (for example, [21]), and
transfer of state information to avoid having to regenerate it in the
new access router after handover (for example, [22]). Both these
procedures could have strong interactions with signaling protocols,
the former because a selection criterion might be what network
control state could be supported on the path through the new access
router, the latter because signaling application state or NTLP/NSLP
protocol state may be a candidate for context transfer.
5.3 Interactions with NATs
Because at least some messages will almost inevitably contain
addresses and possibly higher layer information as payload, we must
consider the interaction with address translation devices (NATs).
These considerations apply both to 'traditional' NATs of various
types (as defined in [23]) as well as some IPv4/v6 transition
mechanisms such as SIIT [24].
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In the simplest case of an NSIS unaware NAT in the path, payloads
will be uncorrected and signaling will refer to the flow incorrectly.
Applications could attempt to use STUN [25] or similar techniques to
detect and recover from the presence of the NAT. Even then, NSIS
protocols would have to use a well known encapsulation (TCP/UDP/ICMP)
to avoid being dropped by more cautious low-end NAT devices.
A simple 'NSIS-aware' NAT would require flow identification
information to be in the clear and not integrity protected. An
alternative conceptual approach is to consider the NAT functionality
being part of message processing itself, in which case the
translating node can take part natively in any NSIS protocol security
mechanisms. Depending on NSIS protocol layering, it would be possible
for this processing to be done in an NSIS entity which was otherwise
ignorant of any particular signaling applications. This is the
motivation for including basic flow identification information in the
NTLP (section 4.6.1).
Note that all of this discussion is independent of the use of a
specific NSLP for general control of NATs (and firewalls). This is
considered in section 6.2.
5.4 Interactions with IP Tunneling
Tunneling is used in the Internet for a number of reasons such as
flow aggregation, IPv4/6 transition mechanisms, mobile IP, virtual
private networking, and so on. An NSIS solution must continue to work
in the presence of these techniques, i.e. the presence of the tunnel
should not cause problems for end-to-end signaling, and it should
also be possible to use NSIS signaling to control the treatment of
the packets carrying the tunneled data.
It is assumed that the NSIS approach will be similar to that of [26],
where the signaling for the end-to-end data flow is tunneled along
with that data flow, and is invisible to nodes along the path of the
tunnel (other than the endpoints). This provides backwards
compatibility with networks where the tunnel endpoints do not support
the NSIS protocols. We assume that NEs will not unwrap tunnel
encapsulations to find and process tunneled signaling messages.
To signal for the packets carrying the tunneled data, the tunnel is
considered as a new data flow in its own right, and NSIS signaling is
applied recursively to it. This requires signaling support in at
least one tunnel endpoint. In some cases (where the signaling
initiator is at the opposite end of the data flow from the tunnel
initiator - i.e. in the case of receiver initiated signaling), there
needs to be the ability to provide a binding between the original
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flow identification and that for the tunneled flow. It is left open
here whether this should be an NTLP or an NSLP function.
6 Signaling Applications
This section gives an overview of NSLPs for particular signaling
applications. The assumption is that the NSLP uses the generic
functionality of the NTLP given earlier; this section describes
specific aspects of NSLP operation. It is intended to clarify by
simple examples how NSLPs fit into the framework. It does not replace
or even form part of the formal NSLP protocol specifications; in
particular, initial designs are being developed for NSLPs for
resource reservation [27] and middlebox communication [28].
6.1 Signaling for Quality of Service
In the case of signaling for QoS, all the basic NSIS concepts of
section 3.1 apply. In addition, there is an assumed directionality of
the signaling process, in that one end of the signaling flow takes
responsibility for actually requesting the resource. This leads to
the following definitions:
*) QoS NSIS Initiator (QNI): the signaling entity which makes the
resource request, usually as a result of user application request.
*) QoS NSIS Responder (QNR): the signaling entity that acts as the
endpoint for the signaling and can optionally interact with
applications as well.
*) QoS NSIS Forwarder (QNF): the signaling entity between a QNI and
QNR which propagates NSIS signaling further through the network.
Each of these entities will interact with a resource management
function (RMF) which actually allocates network resources (router
buffers, interface bandwidth and so on).
Note that there is no constraint on which end of the signaling flow
should take the QNI role: with respect to the data flow direction it
could be at the sending or receiving end.
Note the continued assumption is that the NTLP works with standard
(i.e. best-effort) layer 3 routing. There are, however, several
proposals for the introduction of QoS awareness in routing protocols.
All of these essentially lead to the existence of multiple paths
(with different QoS) towards the same destination. As such, they also
contain an inherent risk for a divergence between control plane and
data plane, similar to the load sharing case. Clearly, any QoS NSLP
needs to be able to handle this type of routing, although, provided
the NTLP continues to deliver signaling messages correctly, the
impact on the QoS NSLP protocol design itself should be limited.
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6.1.1 Protocol Message Semantics
The QoS NSLP will include a set of messages to carry out resource
reservations along the signaling path. A possible set of message
semantics for the QoS NSLP is shown below. Note that the 'direction'
column in the table below only indicates the 'orientation' of the
message. Messages can be originated and absorbed at QNF nodes as well
as the QNI or QNR; an example might be QNFs at the edge of a domain
exchanging messages to set up resources for a flow across a it. Note
that it is left open if the responder can release or modify a
reservation, during or after setup. This seems mainly a matter of
assumptions about authorization, and the possibilities might depend
on resource type specifics.
The table also explicitly includes a refresh operation. This does
nothing to a reservation except extend its lifetime, and is one
possible state management mechanism (see next section).
+-----------+---------+------------------------------------------+
| Operation |Direction| Semantics |
+-----------+---------+------------------------------------------+
| Request | I-->R | Create a new reservation for a flow |
+-----------+---------+------------------------------------------+
| Modify | I-->R | Modify an existing reservation |
| |(&R-->I?)| |
+-----------+---------+------------------------------------------+
| Release | I-->R | Delete (tear down) an |
| |(&R-->I?)| existing reservation |
+-----------+---------+------------------------------------------+
| Accept/ | R-->I | Confirm (possibly modified?) or reject a |
| Reject | | reservation request |
+-----------+---------+------------------------------------------+
| Notify | I-->R & | Report an event detected within the |
| | R-->I | network |
+-----------+---------+------------------------------------------+
| Refresh | I-->R | State management (see section 6.1.2) |
+-----------+---------+------------------------------------------+
6.1.2 State Management
The prime purpose of NSIS is to manage state information along the
path taken by a data flow. The issues regarding state management
within the NTLP (state related to message transport) are described in
section 4. The QoS NSLP will typically have to handle additional
state related to the desired resource reservation to be made.
There two critical issues to be considered in building a robust NSLP
to handle this problem:
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*) The protocol must be scalable. It should allow minimization of the
resource reservation state storage demands that it implies for
intermediate nodes; in particular, storage of state per 'micro' flow
is likely to be impossible except at the very edge of the network. A
QoS signaling application might require per flow or lower granularity
state; examples of each for the case of QoS would be IntServ [29] or
RMD [30] (per 'class' state) respectively.
*) The protocol must be robust against failure and other conditions,
which imply that the stored resource reservation state has to be
moved or removed.
For resource reservations, soft state management is typically used as
a general robustness mechanism. According to the discussion of
section 3.2.5, the soft state protocol mechanisms are built into the
NSLP for the specific signaling application that needs them; the NTLP
sees this simply as a sequence of (presumably identical) messages.
6.1.3 Route Changes and QoS Reservations
In this section, we will explore the expected interaction between
resource signaling and routing updates (the precise source of routing
updates does not matter). The normal operation of the NSIS protocol
will lead to the situation depicted in Figure 7, where the reserved
resources match the data path.
reserved +-----+ reserved +-----+
=========>| QNF |===========>| QNF |
+-----+ +-----+
--------------------------------------->
data path
Figure 7: Normal NSIS protocol operation
A route change can occur while such a reservation is in place. The
route change will be installed immediately and any data will be
forwarded on the new path. This situation is depicted Figure 8.
Resource reservation on the new path will only be started once the
next control message is routed along the new path. This means that
there is a certain time interval during which resources are not
reserved on (part of) the data path. To minimize this time interval
several techniques could be considered. As an example, RSVP [7] has
the concept of local repair, where the router may be triggered by a
route change. In that case the RSVP node can start sending PATH
messages directly after the route has been changed. Note that this
option may not be available if no per-flow state is kept in the NF.
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Route update
|
v
reserved +-----+ reserved +-----+
=========>| QNF |===========>| QNF |
+-----+ +-----+
-------- ||
\ || +-----+
| ===========>| QNF |
| +-----+
+--------------------------->
data path
Figure 8: Route Change
It is not guaranteed that the new path will be able to provide the
same guarantees that were available on the old path. Therefore, in a
more desirable scenario, the QNF should wait until resources have
been reserved on the new path before installing the route change
(unless of course the old path no longer exists). The route change
procedure then consists of the following steps:
1. QNF receives a route announcement,
2. Refresh messages are forwarded along the current path,
3. A copy of the refresh message is re-marked as a request and sent
along the new path that was announced,
4. When the QNF has been acknowledged about the reservations on the
new path, the route will be installed and data will flow along it.
Another example related to route changes is denoted as severe
congestion and is explained in [30]. This solution adapts to a route
change, when a route change creates congestion on the new routed
path.
6.1.4 Resource Management Interactions
The QoS NSLP itself is not involved in any specific resource
allocation or management techniques. The definition of an NSLP for
resource reservation with Quality of Service, however, implies the
notion of admission control. For a QoS NSLP, the measure of signaling
success will be the ability to reserve resources from the total
resource pool that is provisioned in the network. We define the
function responsible for allocating this resource pool as the
Resource Management Function (RMF). The RMF is responsible for all
resource provisioning, monitoring and assurance functions in the
network.
A QoS NSLP will rely on the RMF to do resource management and to
provide inputs for admission control. In this model, the RMF acts as
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a server towards client NSLP(s). It is noted, however, that the RMF
may in turn use another NSLP instance to do the actual resource
provisioning in the network. In this case, the RMF acts as the
initiator (client) of an NSLP.
This essentially corresponds to a multi-level signaling paradigm,
with an 'upper' level handling internetworking QoS signaling,
possibly running end-to-end, and a 'lower' level handling the more
specialized intradomain QoS signaling, running between just the edges
of the network (see [10], [31], and [32] for a discussion of similar
architectures). Given that NSIS signaling is already supposed to be
able to support multiple instances of NSLPs for a given flow, and
limited scope (e.g. edge-to-edge) operation, it is not currently
clear that supporting the multi-level model leads to any new protocol
requirements for the QoS NSLP.
The RMF may or may not be co-located with a QNF (note that co-
location with a QNI/QNR can be handled logically as a combination
between QNF and QNI/QNR). To cater for both cases, we define a
(possibly logical) NF-RMF interface. Over this interface, information
may be provided from the RMF about monitoring, resource availability,
topology, and configuration. In the other direction, the interface
may be used to trigger requests for resource provisioning. One way to
formalize the interface between the QNF and the RMF is via a Service
Level Agreement (SLA). The SLA may be static or it may be dynamically
updated by means of a negotiation protocol. Such a protocol is
outside the scope of NSIS.
There is no assumed restriction on the placement of the RMF. It may
be a centralized RMF per domain, several off-path distributed RMFs,
or an on-path RMF per router. The advantages and disadvantages of
both approaches are well-known. Centralization typically allows
decisions to be taken using more global information with more
efficient resource utilization as a result. It also facilitates
deployment or upgrade of policies. Distribution allows local decision
processes and rapid response to data path changes.
6.2 Other Signaling Applications
As well as the use for 'traditional' QoS signaling, it should be
possible to develop NSLPs for other signaling applications which
operate on different types of network control state. One specific
case is setting up flow-related state in middleboxes (firewalls,
NATs, and so on). Requirements for such communication are given in
[4]. Other examples include network monitoring and testing, and
tunnel endpoint discovery.
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7 Security Considerations
This document describes a framework for signaling protocols which
assumes a two-layer decomposition, with a common lower layer (NTLP)
supporting a family of signaling application specific upper layer
protocols (NSLPs). The overall security considerations for the
signaling therefore depend on the joint security properties assumed
or demanded for each layer.
Security for the NTLP is discussed in section 4.7. We have assumed
that the role of the NTLP will be to provide message protection over
the scope of a single peer relationship, between adjacent signaling
application entities (see section 3.2.3 for a discussion of the case
where these entities are separated by more than one NTLP hop). These
functions can most likely be provided by some kind of channel
security mechanism using an external key management mechanism based
on mutual authentication. In addition, the NTLP should be resilient
against denial of service attacks on the protocol itself.
Security for the NSLPs is entirely dependent on signaling application
requirements. In some cases, no additional protection may be required
compared to what is provided by the NTLP. In other cases, more
sophisticated object-level protection and the use of public key based
solutions may be required. In addition, the NSLP needs to consider
the authorisation requirements of the signaling application.
Authorisation is a complex topic, for which a very brief overview is
provided in section 3.3.7.
Another factor is that NTLP security mechanisms operate only locally,
whereas NSLP mechanisms may also need to operate over larger regions
(not just between adjacent peers) especially for authorisation
aspects; this complicates the analysis of basing signaling
application security on NTLP protection.
An additional concern for signaling applications is the session
identifier security issue (sections 4.6.2 and 5.2). The purpose of
this identifier is to decouple session identification (as a handle
for network control state) from session "location" (i.e. the data
flow endpoints). The identifier/locator distinction has been
extensively discussed in the user plane for end to end data flows,
and is known to lead to non-trivial security issues in binding the
two together again; our problem is the analogue in the control plane,
and is at least similarly complex, because of the need to involve
nodes in the interior of the network as well.
Further work on this and other security design will depend on a
refinement of the NSIS threats work begun in [2].
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Normative References
1 Brunner, M., "Requirements for Signaling Protocols", draft-ietf-
nsis-req-09.txt (work in progress), August 2003
2 Tschofenig, H. and D. Kroeselberg, "Security Threats for NSIS",
draft-ietf-nsis-threats-02.txt (work in progress), June 2003
3 Chaskar, H. (editor), " Requirements of a Quality of Service (QoS)
Solution for Mobile IP", RFC 3583, September 2003
4 Swale, R. P., Mart, P. A., Sijben, P., Brim, S. and M. Shore,
"Middlebox Communications (midcom) Protocol Requirements", RFC
3304, August 2002
Informative References
5 Manner, J., Fu, X. and P. Pan, "Analysis of Existing Quality of
Service Signaling Protocols", draft-ietf-nsis-signalling-analysis-
02.txt (work in progress), June 2003
6 Tschofenig, H., "RSVP Security Properties", draft-ietf-nsis-rsvp-
sec-properties-02.txt (work in progress), June 2003
7 Braden, R., Zhang, L., Berson, S., Herzog, S. and S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, September 1997
8 Katz, D., "IP Router Alert Option", RFC2113, February 1997
9 Partridge, C. and A. Jackson, "IPv6 Router Alert Option", RFC
2711, October 1999
10 Baker, F., Iturralde, C., Le Faucheur, F. and B. Davie,
"Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175,
September 2001
11 Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on
Security Considerations", BCP 72, RFC 3552, July 2003
12 Tschofenig, H., Buechli, M., Van den Bosch, S. and H. Schulzrinne,
"NSIS Authentication, Authorization and Accounting Issues", draft-
tschofenig-nsis-aaa-issues-01.txt (work in progress), March 2003
Hancock et al. Expires - April 2004 [Page 41]
Next Steps in Signaling: Framework October 2003
13 Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F. and S.
Molendini, "RSVP Refresh Overhead Reduction Extensions", RFC2961,
April 2001
14 Ji, P., Ge, Z., Kurose, J. and D. Townsley, "A Comparison of Hard-
State and Soft-State Signaling Protocols", Computer Communication
Review, Volume 33, Number 4, October 2003
15 Floyd, S., "Congestion Control Principles", BCP 41, RFC 2914,
September 2000
16 Apostolopoulos, G., Williams, D., Kamat, S., Guerin, R., Orda, A.
and T. Przygienda, "QoS Routing Mechanisms and OSPF Extensions",
RFC 2676, August 1999
17 Knight, S., Weaver, D., Whipple, D., Hinden, R., Mitzel, D., Hunt,
P., Higginson, P., Shand, M. and A. Lindem, "Virtual Router
Redundancy Protocol", RFC2338, April 1998
18 Heijenk, G., Karagiannis, G., Rexhepi, V. and L. Westberg,
"DiffServ Resource Management in IP-based Radio Access Networks",
Proceedings of 4th International Symposium on Wireless Personal
Multimedia Communications-WPMC'01, September 9 - 12, 2001
19 Manner, J., Lopez, A., Mihailovic, A., Velayos, H., Hepworth, E.
and Y. Khouaja, "Evaluation of Mobility and QoS Interaction",
Computer Networks, Volume 38, Issue 2, 5 February 2002, pp 137-163
20 Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in IPv6",
draft-ietf-mobileip-ipv6-24.txt (work in progress), June 2003
21 Trossen, D., Krishnamurthi, G., Chaskar, H. and J. Kempf, "Issues
in candidate access router discovery for seamless IP-level
handoffs", draft-ietf-seamoby-cardiscovery-issues-04.txt (work in
progress), October 2002
22 Kempf, J., "Problem Description: Reasons For Performing Context
Transfers Between Nodes in an IP Access Network", RFC3374,
September 2002
23 Srisuresh, P. and M. Holdrege, "IP Network Address Translator
(NAT) Terminology and Considerations", RFC2663, August 1999
24 Nordmark, E., "Stateless IP/ICMP Translation Algorithm (SIIT)",
RFC2765, February 2000
Hancock et al. Expires - April 2004 [Page 42]
Next Steps in Signaling: Framework October 2003
25 Rosenberg, J., Weinberger, J., Huitema, C. and R. Mahy, "STUN -
Simple Traversal of User Datagram Protocol (UDP) Through Network
Address Translators (NATs)", RFC3489, March 2003
26 Terzis, A., Krawczyk, J., Wroclawski, J. and L. Zhang, "RSVP
Operation Over IP Tunnels", RFC 2746, January 2000
27 Van den Bosch, S., Karagiannis, G. and A. McDonald, "NSLP for
Quality-of- -
Service Signaling", draft ietf-nsis-qos-nslp-00.txt
(work in progress), September 2003
28 Stiemerling, M., Tschofenig, H., Martin, M. and C. Aoun, "A
NAT/Firewall NSIS Signaling Layer Protocol (NSLP)", draft-ietf-
nsis-nslp-natfw-00 (work in progress), October 2003
29 Braden, R., Clark, D. and S. Shenker, "Integrated Services in the
Internet Architecture: an Overview", RFC 1633, June 1994
30 Westberg, L., Csaszar, A., Karagiannis, G., Marquetant, A.,
Partain, D., Pop, O., Rexhepi, V., Szabo, R. and A. Takacs,
"Resource Management in Diffserv (RMD): A Functionality and
Performance Behavior Overview", Seventh International Workshop on
Protocols for High-Speed networks - PfHSN 2002, 22 - 24 April 2002
31 Ferrari, D., Banerjea, A. and H. Zhang, "Network Support for
Multimedia - A Discussion of the Tenet Approach", Berkeley TR-92-
072, November 1992
32 Nichols, K., Jacobson, V. and L. Zhang, "A Two-bit Differentiated
Services Architecture for the Internet", RFC 2638, July 1999
Acknowledgments
The authors would like to thank Bob Braden, Maarten Buchli, Eleanor
Hepworth, Andrew McDonald, Melinda Shore and Hannes Tschofenig for
significant contributions in particular areas of this draft. In
addition, the authors would like to acknowledge Cedric Aoun, Attila
Bader, Anders Bergsten, Roland Bless, Marcus Brunner, Louise Burness,
Xiaoming Fu, Ruediger Geib, Danny Goderis, Cornelia Kappler, Sung
Hycuk Lee, Thanh Tra Luu, Mac McTiffin, Paulo Mendes, Hans De Neve,
Ping Pan, David Partain, Vlora Rexhepi, Henning Schulzrinne, Tom
Taylor, Michael Thomas, Daniel Warren, Michael Welzl, Lars Westberg,
and Lixia Zhang for insights and inputs during this and previous
framework activities.
Hancock et al. Expires - April 2004 [Page 43]
Next Steps in Signaling: Framework October 2003
Authors' Addresses
Robert Hancock (editor)
Roke Manor Research
Old Salisbury Lane
Romsey
Hampshire
SO51 0ZN
United Kingdom
email: robert.hancock@roke.co.uk
Ilya Freytsis
Cetacean Networks Inc.
100 Arboretum Drive
Portsmouth, NH 03801
USA
email: ifreytsis@cetacean.com
Georgios Karagiannis
University of Twente
P.O. BOX 217
7500 AE Enschede
The Netherlands
email: g.karagiannis@ewi.utwente.nl
John Loughney
Nokia Research Center
11-13 Italahdenkatu
00180 Helsinki
Finland
email: john.loughney@nokia.com
Sven Van den Bosch
Alcatel
Francis Wellesplein 1
B-2018 Antwerpen
Belgium
email: sven.van_den_bosch@alcatel.be
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Hancock et al. Expires - April 2004 [Page 44]
Next Steps in Signaling: Framework October 2003
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