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Internet Draft                                               XiPeng Xiao
Document: draft-ietf-pwe3-requirements-04.txt        Riverstone Networks
Expires: June 2003
                                                         Danny McPherson

                                                            Prayson Pate
                                                       Overture Networks


       Requirements for Pseudo-Wire Emulation Edge-to-Edge (PWE3)

                          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
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at


   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,
   Frame Relay, raw HDLC, and MPLS. 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-04            Dec. 2002


   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 ....................................................    6
   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 Segmentation and Reassembly ................................    9
   4.5 Handling Control Messages of the Native Services ...........    9
   4.6 Consideration of Per-PSN Packet Overhead ...................   10
   5 Maintenance of Emulated Services .............................   10
   5.1 Setup and Teardown of Pseudo-Wires .........................   10
   5.2 Status Monitoring ..........................................   10
   5.3 Notification of Status Changes .............................   11
   5.4 Keep-alive .................................................   12
   6 Management of Emulated Services ..............................   12
   6.1 MIBs .......................................................   12
   6.2 General MIB Requirements ...................................   12
   6.3 Configuration and Provisioning .............................   13
   6.4 Performance Monitoring .....................................   13
   6.5 Fault Management and Notifications .........................   13
   6.6  Pseudo-Wire Connection Verification and Traceroute ........   13
   7 Faithfulness of Emulated Services ............................   13
   7.1 Characteristics of an Emulated Service .....................   14
   7.2 Service Quality of Emulated Services .......................   14
   8 Non-Requirements .............................................   14
   9 Quality of Service (QoS) Considerations ......................   15
   10 Inter-domain Issues .........................................   16
   11 Security Considerations .....................................   16
   12 Acknowledgments .............................................   16
   13 References ..................................................   16
   14 Authors' Addresses ..........................................   17
   15 Full Copyright Section ......................................   19

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1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALLNOT",
   document are to be interpreted as described in RFC 2119.

   Some terms used throughout this document are listed below.

   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

   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 service 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
   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.

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   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

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

   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
   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

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   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

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

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.

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   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 pseudo-wire end-services (PWESs). In this
   document, A PWES is either:
     - an Ethernet link or a VLAN link between two ports, or
     - an ATM VC or VP, or
     - a Frame Relay VC, or
     - a raw HDLC circuit, or
     - an MPLS LSP
   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     |
         |                                                  |
         |<-------------- 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
   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 a PWES 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].

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   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, Frame Relay, raw HDLC and MPLS.

4.  Packet Processing

   This section describes forwarding plane requirements for PWE3.

4.1.  Encapsulation

   Every PE MUST provide service interfaces for encapsulating PDUs from
   the PWESs.  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

   If a service in its native form is capable of grouping multiple
   circuits into a "trunk", e.g. multiple ATM VCs in a VP or multiple
   Ethernet VLANs 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.

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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.

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.  Segmentation and Reassembly

   It is desirable to avoid packet Segmentation and Reassembly (SAR).
   One way to do thus is to ensure that the combined size of the payload
   and its associated PWE3 and PSN headers do not exceed the PSN path

   If SAR cannot be completely avoided, at a PW ingress, if the length
   of a packet resulted from encapsulation exceeds the PSN path MTU, the
   PDU MAY be dropped. In this case, the management plane of the ingress
   PE MAY be notified. Alternatively, a segmentation mechanism MAY be
   defined and used. At a PW egress, if the length of a L2 frame that is
   restored from a PW PDU exceeds the MTU of destination PWES, it MUST
   be dropped. In this case, the management plane of the egress PE MAY
   be notified.

4.5.  Handling Control Messages of the Native Services

   Some native services use control messages for maintaining the
   circuits. These control messages may be in-band, e.g. Ethernet flow
   control or ATM performance management, or out-of-band, e.g. the
   signaling VC of an ATM VP.

   It is desirable that the PEs participate as little as possible in the
   signaling and maintenance of the native services. However, it is up
   to each specific PWE3 approach to specify what the PEs MUST do in
   this regard.  For an emulated service, it is possible that some
   control messages (e.g. OAM) are processed at the PEs while others
   (e.g. keep-alive) are passed through transparently like data messages
   to the remote CE.  If control messages are passed through, it MAY be
   desirable to provide higher reliability for them. The mechanisms for
   providing the high reliability NEED NOT be defined in the PWE3 WG.

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4.6.  Consideration of Per-PSN Packet Overhead

   For ATM emulation, if each packet carries one cell, the PSN tunnel
   header overhead is relatively large. In order to reduce overhead,
   multiple cells MAY be concatenated before a PSN tunnel header is
   added. Each encapsulated cell still carries its own PW header so that
   the egress of the PW knows how to process it. However, the benefit of
   concatenating multiple cells for header efficiency should be weighed
   against the resulting increase in delay, jitter and the larger
   penalty incurred by packet loss. In some cases, it may be appropriate
   to perform silence suppression or other compression.

5.  Maintenance of Emulated Services

   This section describes control plane requirements for PWE3.

5.1.  Setup and Teardown of Pseudo-Wires

   A PW must be set up before an emulated service can be established,
   and must be torn down when an emulated service 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 signaling (i.e. setup or teardown) of
   a PWES, 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. 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.

   Sessions in a L2TPv3 tunnel or MPLS LSPs can be used as PWs.
   Selection of a particular type of PWs is carrier-dependent and is
   outside scope of the PWE3 WG.

5.2.  Status Monitoring

   Some native services have mechanisms for status monitoring. For
   example, ATM supports OAM for this purpose.  For such services, the
   corresponding emulated services MUST specify how to perform status
   monitoring.  The mechanisms NEED NOT be defined in this WG. Some
   status monitoring mechanisms defined in other WGs, e.g. [LSPPING],
   may be leveraged.

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5.3.  Notification of Status Changes

5.3.1.  Up/Down Notification

   If a native service is bi-directional, the corresponding emulated
   service can only be signaled up when the associated PWs and PSN
   tunnels in both directions are functional.

   Because the two CEs of an emulated service are not adjacent, a
   failure may occur at a place such that one or both physical links
   between the CEs and PEs remain up. For example in Figure 1, if the
   physical link between CE1 and PE1 fails, the physical link between
   CE2 and PE2 will not be affected and will remain up. Unless CE2 is
   notified about the remote failure, it will continue to send traffic
   over the emulated service to CE1. Such traffic will be discarded at
   PE1.  Some native services have failure notification so that when the
   services fail, both CEs will be notified.  For such native services,
   the corresponding PWE3 service MUST provide a failure notification

   Similarly, if a native service has notification mechanism so that
   when a network failure is fixed, all the affected services will
   change status from "Down" to "Up", the corresponding emulated service
   MUST provide a mechanism for doing so.

5.3.2.  Misconnection and Payload Type Mismatch

   With PWE3, misconnection and payload type mismatch can occur. A PWE3
   approach MAY define some mechanism for detecting and handling
   misconnection and payload type mismatch.

5.3.3.  Packet Loss, Corruption, and Out-of-order Delivery

   A PW can incur packet loss, corruption, and out-of-order delivery.
   This can impact the working condition of an emulated service.  For
   some payload types, packet loss, corruption, and out-of-order
   delivery can be mapped to either a bit error burst, or loss of
   carrier on the PW. If a native service has some mechanism to deal
   with bit error, the corresponding PWE3 service SHOULD provide a
   similar mechanism.

5.3.4.  Other Status Notification

   A PWE3 approach MAY provide mechanism for other status notification,
   if any.

5.3.5.  Collective Status Notification

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   Status of a group of emulated circuits may be affected identically by
   a single network 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
   notification 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 when the PW for that emulated circuit is set up. Multiple emulated
   circuits can then be grouped by associating them with identical group
   ID. In status notification, that group ID can be used to refer to all
   the emulated circuits in that group.

5.4.  Keep-alive

   If a native service has keep-alive mechanism, the corresponding
   emulated service MUST have keep-alive support.  This can possibly be
   done by transparently transporting the native keep-alive messages
   across the PW. Alternatively, the keep-alive mechanism of the PW
   signaling protocol (e.g. L2TPv3), if it exists, can be utilized.

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 service
   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

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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.

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 it is NOT REQUIRED that they are 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.

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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 services 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.

   3) If an emulated circuit fails (either at one of the PWESs 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. In fact, different SPs can use the same PWE3 approach with
   different QoS mechanisms to provide the same emulated service with
   different service quality.

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:

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   - 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;

   - Striving to make the emulated services perfectly match their native

   - Defining mechanisms for signaling the PSN tunnels;

   - Defining how to perform traffic management on packets that carry PW

   - Providing security for the PW PDUs;

   - Providing any multicast service that is not native to the emulated

     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

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

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   guidelines for marking and differentiating, e.g. what fields in the
   original L2 headers should be used for determining the EXP/DSCP
   value. 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

   PWs are directly between the PW end-points.  Whether a PSN tunnel is
   inter-domain or not is transparent to PWE3.  Therefore, inter-domain
   issues caused by two PW end-points locating in different
   administrative domains are issues for PSN-tunnel setup protocols such
   as RSVP or LDP or L2TPv3, not for PWE3.

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 S. Bryant, R. Cohen,
   G. Heron, T. Johnson, A. Malis, L. Martini, E. Rosen, J. Rutemiller,
   T. So, Y. Stein and S. Vainshtein.

13.  References

[IFMIB]     K. McCloghrie, and F. Kastenholtz, "The Interfaces Group MIB
            using SMIv2", RFC 2233, Nov. 1997.

[L2TPv3]    J. Lau, M. Townsley, A. Valencia, G. Zorn, I. Goyret, G.
            Pall, A. Rubens, B. Palter, "Layer Two Tunneling Protocol
            (L2TPv3)", <draft-ietf-l2tpext-l2tp-base-04.txt>, work in
            progress, Nov. 2002.

[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-01.txt>, work in progress,
            Oct. 2002.

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[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.

[PWE3_ARCH] S. Bryant and P. Pate, et. al., "PWE3 Architecture",
            <draft-ietf-pwe3-arch-01.txt>, work in progress, Nov. 2002.

[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
   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

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   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

   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
   kind, provided that the above copyright notice and this paragraph are
   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
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

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