One document matched: draft-ietf-pwe3-requirements-05.txt
Differences from draft-ietf-pwe3-requirements-04.txt
Internet Draft XiPeng Xiao
Document: draft-ietf-pwe3-requirements-05.txt Riverstone Networks
Expires: September 2003
Danny McPherson
TCB
Prayson Pate
Overture Networks
Editors
Requirements for Pseudo-Wire Emulation Edge-to-Edge (PWE3)
draft-ietf-pwe3-requirements-05.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document describes base requirements for the Pseudo-Wire
Emulation Edge to Edge Working Group (PWE3 WG). It provides
guidelines for other working group documents that will define
mechanisms for providing pseudo-wire emulation of Ethernet, ATM, and
Frame Relay. Requirements for pseudo-wire emulation of TDM (i.e.
"synchronous bit streams at rates defined by ITU G.702") are defined
in another document. It should be noted that the PWE3 WG standardizes
mechanisms that can be used to provide PWE3 services, but not the
services themselves.
Internet Draft draft-ietf-pwe3-requirements-05 Mar. 2003
Co-Authors
The following are co-authors of this document:
Vijay Gill AOL Time Warner, Inc.
Kireeti Kompella Juniper Networks, Inc.
Thomas D. Nadeau Cisco Systems
Craig White Level 3 Communications, LLC.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
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Table of Contents
1 Terminology .................................................. 4
2 Introduction ................................................. 4
2.1 What Are Pseudo Wires? ..................................... 4
2.2 Background and Motivation .................................. 5
2.3 Current Network Architecture ............................... 5
2.4 PWE3 as a Path to Convergence .............................. 6
2.5 Suitable Applications for PWE3 ............................. 6
2.6 Summary .................................................... 7
3 Reference Model of PWE3 ...................................... 7
4 Packet Processing ............................................ 8
4.1 Encapsulation .............................................. 8
4.2 Frame Ordering ............................................. 9
4.3 Frame Duplication .......................................... 9
4.4 Fragmentation .............................................. 9
4.5 Consideration of Per-PSN Packet Overhead ................... 9
5 Maintenance of Emulated Services ............................. 10
5.1 Setup and Teardown of Pseudo-Wires ......................... 10
5.2 Handling Maintenance Message of the Native Services ........ 10
5.3 PE-generated Maintenance Messages .......................... 11
6 Management of Emulated Services .............................. 13
6.1 MIBs ....................................................... 13
6.2 General MIB Requirements ................................... 13
6.3 Configuration and Provisioning ............................. 13
6.4 Performance Monitoring ..................................... 13
6.5 Fault Management and Notifications ......................... 14
6.6 Pseudo-Wire Connection Verification and Traceroute ........ 14
7 Faithfulness of Emulated Services ............................ 14
7.1 Characteristics of an Emulated Service ..................... 14
7.2 Service Quality of Emulated Services ....................... 15
8 Non-Requirements ............................................. 15
9 Quality of Service (QoS) Considerations ...................... 16
10 Inter-domain Issues ......................................... 16
11 Security Considerations ..................................... 17
12 Acknowledgments ............................................. 17
13 References .................................................. 17
14 Authors' Addresses .......................................... 18
15 Full Copyright Section ...................................... 20
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1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALLNOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
Some terms used throughout this document are listed below.
Attachment Circuit (AC)
The circuit or virtual circuit attaching a CE to a
PE.
Customer Edge A device where one end of a service originates
and/or terminates. The CE is not aware that it is
using an emulated service rather than a native
service.
Packet Switched Network
A network using IP or MPLS as the mechanism for
packet forwarding
Provider Edge A device that provides PWE3 to a CE.
Pseudo Wire A mechanism that carries the essential elements of
an emulated circuit from one PE to one or more
other PEs over a PSN.
Pseudo Wire Emulation Edge to Edge
A mechanism that emulates the essential attributes
of a service (such as a T1 leased line or Frame
Relay) over a PSN.
Pseudo Wire PDU A PDU sent on the PW that contains all of the data
and control information necessary to emulate the
desired service.
PSN Tunnel A tunnel across a PSN inside which one or more PWs
can be carried.
2. Introduction
2.1. What Are Pseudo Wires?
Pseudo Wire Emulation Edge-to-Edge (PWE3) is a mechanism that
emulates the essential attributes of a service over a Packet Switched
Network (PSN). The required functions of PWs include encapsulating
service-specific PDUs arriving at an ingress port, and carrying them
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across a path or tunnel, managing their timing and order, and any
other operations required to emulate the behavior and characteristics
of the service as faithfully as possible.
From the customer perspective, the PW is perceived as an unshared
link or circuit of the chosen service. However, there may be
deficiencies that impede some applications from being carried on a
PW. These limitations should be fully described in the appropriate
service-specific documents and Applicability Statements.
2.2. Background and Motivation
The following sections give some background on where networks are
today and why they are changing. It also talks about the motivation
to provide converged networks while continuing to support existing
services. Finally it discusses how PWs can be a solution for this
dilemma.
2.3. Current Network Architecture
2.3.1. Multiple Networks
For any given service provider delivering multiple services, the
current infrastructure usually consists of parallel or "overlay"
networks. Each of these networks implements a specific service, such
as Frame Relay, Internet access, etc. This is expensive, both in
terms of capital expense and operational costs. Furthermore, the
presence of multiple networks complicates planning. Service providers
wind up asking themselves these questions:
- Which of my networks do I build out?
- How many fibers do I need for each network?
- How do I efficiently manage multiple networks?
A converged network helps service providers answer these questions in
a consistent and economical fashion.
2.3.2. Transition to a Packet-Optimized Converged Network
In order to maximize return on their assets and minimize their
operating costs, service providers often look to consolidate the
delivery of multiple service types onto a single networking
technology.
As packet traffic takes up a larger and larger portion of the
available network bandwidth, it becomes increasingly useful to
optimize public networks for the Internet Protocol. However, many
service providers are confronting several obstacles in engineering
packet-optimized networks. Although Internet traffic is the fastest
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growing traffic segment, it does not generate the highest revenue per
bit. For example, Frame Relay traffic currently generates higher
revenue per bit than native IP services do. Private line TDM
services still generate even more revenue per bit than does Frame
Relay. In addition, there is a tremendous amount of legacy equipment
deployed within public networks that does not communicate using the
Internet Protocol. Service providers continue to utilize non-IP
equipment to deploy a variety of services, and see a need to
interconnect this legacy equipment over their IP-optimized core
networks.
2.4. PWE3 as a Path to Convergence
How do service providers realize the capital and operational benefits
of a new packet-based infrastructure, while leveraging the existing
equipment and also protecting the large revenue stream associated
with this equipment? How do they move from mature Frame Relay or ATM
networks, while still being able to provide these lucrative services?
One possibility is the emulation of circuits or services via PWs.
Circuit emulation over ATM and interworking of Frame Relay and ATM
have already been standardized. Emulation allows existing services to
be carried across the new infrastructure, and thus enables the
interworking of disparate networks.
Implemented correctly, PWE3 can provide a means for supporting
today's services over a new network.
2.5. Suitable Applications for PWE3
What makes an application suitable (or not) for PWE3 emulation? When
considering PWs as a means of providing an application, the following
questions must be considered:
- Is the application sufficiently deployed to warrant emulation?
- Is there interest on the part of service providers in providing an
emulation for the given application?
- Is there interest on the part of equipment manufacturers in
providing products for the emulation of a given application?
- Are the complexities and limitations of providing an emulation
worth the savings in capital and operational expenses?
If the answer to all four questions is "yes", then the application is
likely to be a good candidate for PWE3. Otherwise, there may not be
sufficient overlap between the customers, service providers,
equipment manufacturers and technology to warrant providing such an
emulation.
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2.6. Summary
To maximize the return on their assets and minimize their operational
costs, many service providers are looking to consolidate the delivery
of multiple service offerings and traffic types onto a single IP-
optimized network.
In order to create this next-generation converged network, standard
methods must be developed to emulate existing telecommunications
formats such as Ethernet, Frame Relay, and ATM over IP-optimized core
networks. This document describes requirements for accomplishing
this goal.
3. Reference Model of PWE3
A pseudo-wire (PW) is a connection between two provider edge (PE)
devices which connects two attachment circuits (ACs). In this
document, An AC is either:
- an Ethernet link or a 802.1Q link between two ports, or
- an ATM VCC or VPC, or
- a Frame Relay VC
between a customer edge (CE) device and a PE (See Figure 1).
|<------- Pseudo Wire ------>|
| |
| |<-- PSN Tunnel -->| |
PW V V V V PW
End Service+----+ +----+ End Service
+-----+ | | PE1|==================| PE2| | +-----+
| |----------|............PW1.............|----------| |
| CE1 | | | | | | | | CE2 |
| |----------|............PW2.............|----------| |
+-----+ ^ | | |==================| | | +-----+
^ | +----+ +----+ ^
| | Provider Edge 1 Provider Edge 2 |
| | |
| Attachment Circuit |
| |
|<-------------- Emulated Service ---------------->|
Customer Customer
Edge 1 Edge 2
Figure 1: PWE3 Reference Model
During the setup of a PW, the two PEs will be configured or will
automatically exchange information about the service to be emulated
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so that later they know how to process packets coming from the other
end. After a PW is set up between two PEs, frames received by one PE
from an AC are encapsulated and sent over the PW to the remote PE,
where native frames are re-constructed and forwarded to the other CE.
For a detailed PWE3 architecture overview, readers should refer to
the PWE3 architecture document [PWE3_ARCH].
This document does not assume that a particular type of PWs (e.g.
[L2TPv3] sessions or [MPLS] LSPs) is used. Instead, it describes
generic requirements that apply to all PWs, for all services
including Ethernet, ATM, and Frame Relay.
4. Packet Processing
This section describes data plane requirements for PWE3.
4.1. Encapsulation
Every PE MUST provide encapsulation mechanism for PDUs from a PWES.
It should be noted that the PDUs to be encapsulated may or may not
contain L2 header information. This is service specific. Every PWE3
service MUST specify what the PDU is.
A PW header consists of all the header fields in a PW PDU that are
used by the PW egress to determine how to process the PDU. The PSN
tunnel header is not considered as part of the PW header.
Specific requirements on PDU encapsulation are listed below.
4.1.1. Conveyance of Necessary L2 Header Information
The egress of a PW needs some information, e.g. which native service
the PW PDUs belong to, and possibly some L2 header information, in
order to know how to process the PDUs received. A PWE3 encapsulation
approach MUST provide some mechanism for conveying such information
from the PW ingress to the egress. It should be noted that not all
such information must be carried in the PW header of the PW PDUs.
Some information (e.g. service type of a PW) can be stored as state
information at the egress during PW setup.
4.1.2. Support of Variable Length PDUs
A PWE3 approach MUST accommodate variable length PDUs, if variable
length PDUs are allowed by the native service. For example, a PWE3
approach for Frame Relay MUST accommodate variable length frames.
4.1.3. Support of Multiplexing and Demultiplexing
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If a service in its native form is capable of grouping multiple
circuits into a "trunk", e.g. multiple ATM VCCs in a VPC or multiple
Ethernet 802.1Q interfaces in a port, some mechanism SHOULD be
provided so that a single PW can be used to connect two end-trunks.
From encapsulation perspective, sufficient information MUST be
carried so that the egress of the PW can demultiplex individual
circuits from the PW.
4.2. Frame Ordering
When packets carrying the PW PDUs traverse a PW, they may arrive at
the egress out of order. For some services, the frames (either
control frames only or both control and data frames) must be
delivered in order. For such services, some mechanism MUST be
provided for ensuring in-order delivery. Providing a sequence number
in the PW header for each packet is one possible approach to detect
out-of-order frames. Mechanisms for re-ordering frames may be
provided by Native Service Processing (NSP) [PWE3_ARCH] but are out
of scope of PWE3.
4.3. Frame Duplication
In rare cases, packets traversing a PW may be duplicated. For some
services, frame duplication is not allowed. For such services some
mechanism MUST be provided to ensure that duplicated frames will not
be delivered. The mechanism may or may not be the same as the
mechanism used to ensure in-order frame delivery.
4.4. Fragmentation
If the combined size of the L2 payload and its associated PWE3 and
PSN headers exceeds the PSN path MTU, the L2 payload may need to be
fragmented (Alternatively the L2 frame may be dropped). For certain
native service, fragmentation may also be needed to maintain a
control frame's relative position to the data frames (e.g. an ATM PM
cell's relative position). In general, fragmentation has a
performance impact. It is therefore desirable to avoid fragmentation
if possible. However, for different services, the need for
fragmentation can be different. When there is potential need for
fragmentation, each service-specific PWE3 document MUST specify
whether to fragment the frame in question or to drop it. If an
emulated service chooses to drop the frame, the consequence MUST be
specified in its applicability statement.
4.5. Consideration of Per-PSN Packet Overhead
When the L2 PDU size is small, in order to reduce PSN tunnel header
overhead, multiple PDUs MAY be concatenated before a PSN tunnel
header is added. Each encapsulated PDU still carries its own PW
header so that the egress PE knows how to process it. However, the
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benefit of concatenating multiple PDUs for header efficiency should
be weighed against the resulting increase in delay, jitter and the
larger penalty incurred by packet loss.
5. Maintenance of Emulated Services
This section describes maintenance requirements for PWE3.
5.1. Setup and Teardown of Pseudo-Wires
A PW must be set up before an emulated circuit can be established,
and must be torn down when an emulated circuit is no longer needed.
Setup and teardown of a PW can be triggered by a CLI command from the
management plane of a PE, or by Setup/Teardown of an AC (e.g., an ATM
SVC), or by an auto-discovery mechanism.
Every PWE3 approach MUST define some setup mechanism for establishing
the PWs. During the setup process, the PEs need to exchange some
information (e.g. to learn each other's capability). The setup
mechanism MUST enable the PEs to exchange all necessary information.
For example, both endpoints must agree on methods for encapsulating
PDUs and handling frame ordering. Which signaling protocol to use and
what information to exchange are service specific. Every PWE3
approach MUST specify them. Manual configuration of PWs can be
considered as a special kind of signaling and is allowed.
If a native circuit is bi-directional, the corresponding emulated
circuit can be signaled "Up" only when the associated PW and PSN
tunnels in both directions are functional.
5.2. Handling Maintenance Message of the Native Services
Some native services have mechanisms for maintenance purpose, e.g.
ATM OAM and FR LMI. Such maintenance messages can be in-band (i.e.
mixed with data messages in the same AC) or out-of-band (i.e. sent in
a dedicated control circuit). For such services, all in-band
maintenance messages related to a circuit SHOULD be transported in-
band just like data messages through the corresponding PW to the
remote CE. In other words, no translation is needed at the PEs for
in-band maintenance messages. In addition, it MAY be desirable to
provide higher reliability for maintenance messages. The mechanisms
for providing high reliability NEED NOT be defined in the PWE3 WG.
Out-of-band maintenance messages between a CE and a PE may relate to
multiple ACs between the CE and the PE. They need to be processed at
the local PE and possibly at the remote PE as well. If a native
service has some out-of-band maintenance messages, the corresponding
emulated service MUST specify how to process such messages at the
PEs.
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For PWE maintenance purpose, maintenance mechanisms of the native
service SHOULD be used whenever appropriate, as opposed to inventing
new maintenance mechanisms.
5.3. PE-generated Maintenance Messages
A PE needs to generate some maintenance messages under two
circumstances for an emulated service. Such circumstances are
triggered either:
1. by maintenance messages of the native service; or
2. by some events such as an "Up/Down" status change of the PW or
the local AC.
In circumstance #1, when a PE receives an out-of-band maintenance
message from the local CE, for each relevant emulated circuit, the PE
may need to translate the out-of-band maintenance message into an
appropriate in-band maintenance message of the native service and
send it via the PW to the remote CE. For example, if the ACs between
a CE and a PE are some ATM VCCs, and a F4 AIS is received by the PE
from the CE, the PE may need to translate that F4 AIS into a F5 AIS
for each VCC and send it to the remote CE. Alternatively, for each
relevant emulated circuit, the PE may generate a PWE-specific
maintenance message to the remote PE, e.g. a label withdrawal
message. Sometimes, multiple such maintenance messages can be
grouped together; this is further discussed in the "collective status
notification" paragraph later. When the remote PE receives such a
PWE-specific maintenance message, it may need to generate a
maintenance message of the native service and send it to the attached
CE.
In circumstance #2, the reason the PEs need to generate some
maintenance messages under some events is because the existence of a
PW between two CEs reduces the CEs' maintenance capability if the PEs
do nothing. This is illustrated in the following example. If two CEs
are directly connected by a physical wire, a native service (e.g.
ATM) can use notifications of the lower layer (e.g. the physical link
layer) to assist its maintenance. For example, the ATM PVC can be
signaled "Down" if the physical wire fails. However, consider the
following scenario.
+-----+ Phy-link +----+ +----+ Phy-link +-----+
| CE1 |----------| PE1|......PW......|PE2 |----------| CE2 |
+-----+ +----+ +----+ +-----+
If the PW between PE1 and PE2 fails, CE1 and CE2 will not receive
physical link-failure notification. As a result, they cannot declare
failure of the emulated circuit in a timely fashion, which will in
turn affect higher layer applications. Therefore, when the PW fails,
PE1 and PE2 need to generate some maintenance messages to notify the
client layer on CE1 and CE2 that use the PW as a server layer. (In
this case, the client layer is the emulated service). Similarly, if
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the physical link between PE1-CE1 fails, PE1 needs to generate some
maintenance message(s) so that the client layer at CE2 will be
notified. PE2 may be involved in this process.
In the rare case when a physical wire between two CEs incurs many bit
errors, the physical link can be declared "Down" and the client layer
at the CEs be notified. Similarly, a PW can incur packet loss,
corruption, and out-of-order delivery. These can be considered as
"generalized bit error". Upon detection of excessive "generalized bit
error", a PE may need to take some maintenance actions so that the
client layer at the CEs is notified.
To summarize the requirements for circumstance #2: PWE MUST provide
to an emulated circuit the server-layer (i.e. lower-layer)
maintenance assistance that a native circuit would receive from a
physical wire.
Overall, the need for PE-generated maintenance messages is different
for different services. Every emulated service MUST specify:
* what PE-generated maintenance messages are needed,
* when they are needed, and
* how to generate and process them at the PEs.
Furthermore, if a PE needs to generate and send a maintenance message
to a CE, the PE MUST use a maintenance message of the native service.
This is essential in keeping the emulated service transparent to the
CEs.
In specifying "when PE-generated maintenance messages are needed",
some monitoring mechanisms are needed for detecting the triggering
events. (Some of such events are briefly discussed above). Such
mechanisms NEED NOT be defined in the PWE3 WG. A service-specific-
PWE-definition document MAY cite some status monitoring mechanisms
defined elsewhere, e.g. [LSPPING].
Status of a group of emulated circuits may be affected identically by
a single incidence. For example, when the physical link between a CE
and a PE fails, all the emulated circuits that go through that link
will fail. It is likely that there exists a group of emulated
circuits which all terminate at a remote CE. (There can be multiple
such CEs). Therefore, it is desirable that a single maintenance
message be used to notify failure of the whole group of emulated
circuits. A PWE3 approach MAY provide some mechanism for notifying
status changes of a group of emulated circuits. One possible
approach is to associate each emulated circuit with a group ID while
setting up the PW for that emulated circuit. Multiple emulated
circuits can then be grouped by associating them with an identical
group ID. In the maintenance message, that group ID can be used to
refer to all the emulated circuits in that group. This is called
"collective status notification".
The requirements stated in this section comply with the ITU-T
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maintenance philosophy (client layer/server layer concept) for
telecommunications networks [G805].
6. Management of Emulated Services
Each PWE3 approach SHOULD provide some mechanisms for network
operators to manage the emulated service. These mechanisms can be in
the forms described below.
6.1. MIBs
SNMP MIBs [SMIV2] MUST be provided for managing each emulated circuit
as well as pseudo-wire in general. These MIBs SHOULD be created with
the following requirements.
6.2. General MIB Requirements
New MIBs MUST augment or extend where appropriate, existing tables as
defined in other existing service-specific MIBs for existing services
such as MPLS or L2TP. For example, the ifTable as defined in the
Interface MIB [IFMIB] MUST be augmented to provide counts of out-of-
order packets. A second example is the extension of the MPLS-TE-MIB
[TEMIB] when emulating circuit services over MPLS. Rather than
redefining the tunnelTable so that PWES can utilize MPLS tunnels, for
example, entries in this table MUST instead be extended to add
additional PWES-specific objects. Doing so facilitates a natural
extension of those objects defined in the existing MIBs in terms of
management, as well as leveraging existing agent implementations.
Interfaces implementing a PWES MUST appear as an interface in the
ifTable.
6.3. Configuration and Provisioning
MIB Tables MUST be designed to facilitate configuration and
provisioning of the PWES.
The MIB(s) MUST facilitate intra-PSN configuration and monitoring of
PWES connections.
6.4. Performance Monitoring
MIBs MUST collect statistics for performance and fault management.
MIBs MUST provide a description of how existing counters are used for
PW emulation and SHOULD not replicate existing MIB counters.
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6.5. Fault Management and Notifications
Notifications SHOULD be defined where appropriate to notify the
network operators of any interesting situations, including faults
detected in the PWES.
Objects defined to augment existing protocol-specific notifications
in order to add PWES functionality MUST explain how these
notifications are to be emitted.
6.6. Pseudo-Wire Connection Verification and Traceroute
For network management purpose, a connection verification mechanism
SHOULD be supported by PWs. Connection verification as well as other
alarming mechanisms can alert network operators that a PW has lost
its remote connection. It is sometimes desirable to know the exact
functional path of a PW for troubleshooting purpose, thus a
traceroute function capable of reporting the path taken by data
packets over the PW SHOULD be provided.
7. Faithfulness of Emulated Services
An emulated service SHOULD be as similar to the native service as
possible, but NOT REQUIRED to be identical. The applicability
statement of a PWE3 service MUST report limitations of the emulated
service.
Some basic requirements on faithfulness of an emulated service are
described below.
7.1. Characteristics of an Emulated Service
From the perspective of a CE, an emulated circuit is characterized as
an unshared link or circuit of the chosen service, although service
quality of the emulated service may be different from that of a
native one. Specifically, the following requirements MUST be met:
1) It MUST be possible to define type (e.g. Ethernet, which is
inherited from the native service), speed (e.g. 100Mbps), and MTU
size for an emulated circuit, if it is possible to do so for a
native circuit.
2) If the two endpoints CE1 and CE2 of emulated circuit #1 are
connected to PE1 and PE2, respectively, and CE3 and CE4 of
emulated circuit #2 are also connected to PE1 and PE2, then the
PWs of these two emulated circuits may share the same physical
paths between PE1 and PE2. But from each CE's perspective, its
emulated circuit MUST appear as unshared. For example, CE1/CE2
MUST NOT be aware of existence of emulated circuit #2 or CE3/CE4.
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3) If an emulated circuit fails (either at one of the ACs or in the
middle of the PW), both CEs MUST be notified in a timely manner,
if they will be notified in the native service. The definition of
"timeliness" is service-dependent.
4) If a routing protocol (e.g. IGP) adjacency can be established over
a native circuit, it MUST be possible to be established over an
emulated circuit as well.
7.2. Service Quality of Emulated Services
It is NOT REQUIRED that an emulated service provide the same service
quality as the native service. The PWE3 WG only defines mechanisms
for providing PW emulation, not the services themselves. What quality
to provide for a specific emulated service is a matter between a
service provider (SP) and its customers, and is outside scope of the
PWE3 WG.
8. Non-Requirements
Some non-requirements are mentioned in various sections of this
document. Those work items are outside scope of the PWE3 WG. They are
summarized below:
- Service interworking;
In Service Interworking, the IWF (Interworking Function) between
two dissimilar protocols (e.g., ATM & MPLS, Frame Relay & ATM, ATM
& IP, ATM & L2TP, etc.) terminates the protocol used in one network
and translates (i.e. maps) its Protocol Control Information (PCI)
to the PCI of the protocol used in other network for User, Control
and Management Plane functions to the extent possible.
- Selection of a particular type of PWs;
- To make the emulated services perfectly match their native
services;
- Defining mechanisms for signaling the PSN tunnels;
- Defining how to perform traffic management on packets that carry PW
PDUs;
- Providing security for the PW PDUs;
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- Providing any multicast service that is not native to the emulated
medium.
To illustrate this point, Ethernet transmission to a multicast
IEEE-48 address is considered in scope, while multicast services
like [MARS] that are implemented on top of the medium are out of
scope;
9. Quality of Service (QoS) Considerations
In this document, QoS means satisfactory service quality. It should
not be confused with QoS mechanisms such as Weighted Fair Queuing
(WFQ) or Random Early Detection (RED).
QoS is essential for ensuring that emulated services are similar (but
not necessarily identical) to their native forms. It is up to network
operators to decide how to provide QoS - They can choose to rely on
over-provisioning and/or deploy some QoS mechanisms.
In order to take advantage of QoS mechanisms defined in other working
groups, e.g. the traffic management schemes defined in DiffServ WG,
it is desirable that some mechanisms exists for differentiating the
packets resulted from PDU encapsulation. These mechanisms NEED NOT be
defined in the PWE3 approaches themselves. For example, if the
packets are MPLS or IP packets, their EXP or DSCP fields can be used
for marking and differentiating. A PWE3 approach MAY provide
guidelines for marking and differentiating. But the exact procedure
of how to perform marking and differentiating, e.g. specifying the
mapping function from Ethernet 802.1p field to EXP field, is out of
scope.
10. Inter-domain Issues
PWE is a matter between the PW end-points and is transparent to the
network devices between the PW end-points. Therefore, inter-domain
PWE is fundamentally similar to intra-domain PWE. As long as PW
end-points use the same PWE approach, they can communicate
effectively, regardless of whether they are in the same domain.
Security may become more important in the inter-domain case and some
security measure such as end-point authentication MAY be applied.
Inter-domain PSN tunnels are generally more difficult to set up, tear
down and maintain than intra-domain ones. For example, inter-domain
PSN tunnels cannot be set up using RSVP-TE. But that is an issue for
PSN tunneling protocols such as MPLS and L2TPv3 and is outside the
scope of PWE3.
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11. Security Considerations
The PW end-point, PW demultiplexing mechanism, and the payloads of
the native service can all be vulnerable to attack. PWE3 should
leverage security mechanisms provided by the PW Demultiplexer or PSN
Layers. Such mechanisms SHOULD protect PW end-point and PW
Demultiplexer mechanism from denial-of-service (DoS) attacks and
spoofing of the native data units. Controlling PSN access to the PW
end-point is generally effective against DoS attacks and spoofing,
and can be part of protection mechanism. Protection mechanisms
SHOULD also address the spoofing of tunneled PW data. The validation
of traffic addressed to the PW Demultiplexer end-point is paramount
in ensuring integrity of PW encapsulation. Security protocols such
as IPSec [RFC2401] can be used.
12. Acknowledgments
The authors would like to acknowledge input from M. Bocci, S. Bryant,
R. Cohen, N. Harrison, G. Heron, T. Johnson, A. Malis, L. Martini, E.
Rosen, J. Rutemiller, T. So, Y. Stein and S. Vainshtein.
13. References
[G805] "Generic Functional Architecture of Transport Networks",
ITU-T Recommendation G.805, 2000.
[IFMIB] K. McCloghrie, and F. Kastenholtz, "The Interfaces Group MIB
using SMIv2", RFC 2233, Nov. 1997.
[L2TPv3] J. Lau, M. Townsley, and I. Goyret, et. al., "Layer Two
Tunneling Protocol (Version 3)", <draft-ietf-l2tpext-l2tp-
base-07.txt>, work in progress, Feb. 2003.
[LSPPING] K. Kompella, P. Pan, N. Sheth, D. Cooper, G. Swallow, S.
Wadhwa, and R. Bonica, "Detecting Data Plane Liveliness in
MPLS", <draft-ietf-mpls-lsp-ping-02.txt>, work in progress,
Mar. 2003.
[MARS] G. Armitage, "Support for Multicast over UNI 3.0/3.1 based
ATM Networks", RFC2022, November 1996
[MPLS] E. Rosen, A. Viswanathan, and R. Callon, "Multiprotocol
Label Switching Architecture", RFC3031, January 2001
[TEMIB] C. Srinivasan, A. Viswanathan, and T. Nadeau, "MPLS Traffic
Engineering Management Information Base", <draft-ietf-mpls-
te-mib-09.txt>, work in progress, Nov. 2002.
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[PWE3_ARCH] S. Bryant and P. Pate, et. al., "PWE3 Architecture",
<draft-ietf-pwe3-arch-02.txt>, work in progress, Feb. 2003.
[RFC2401] S. Kent, R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, Nov. 1998.
[RTP] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications",
RFC1889, January 1996.
[SMIV2] J. Case, K. McCloghrie, M. Rose, and S. Waldbusser,
"Structure of Management Information for Version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC 1902,
January 1996.
14. Authors' Addresses
XiPeng Xiao
Riverstone Networks
5200 Great America Parkway
Santa Clara, CA 95054
Email: xxiao@riverstonenet.com
Danny McPherson
TCB.net
Email: danny@tcb.net
Prayson Pate
Overture Networks
P. O. Box 14864
RTP, NC, USA 27709
Email: prayson.pate@overturenetworks.com
Vijay Gill
AOL Time Warner
EMail: vijaygill9@aol.com
Kireeti Kompella
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
Email: kireeti@juniper.net
Thomas D. Nadeau
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
Email: tnadeau@cisco.com
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Craig White
Level 3 Communications, LLC.
1025 Eldorado Blvd.
Broomfield, CO, 80021
Email: Craig.White@Level3.com
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15. Full Copyright Section
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
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included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
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English.
The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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