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Internet Draft                                               XiPeng Xiao
Document: draft-ietf-pwe3-requirements-01.txt              Photuris Inc.
Expires: January 2002                                    Danny McPherson
                                                          Amber Networks
                                                            Prayson Pate
                                                 Overture Networks, Inc.
                                                             Craig White
                                            Level 3 Communications, LLC.
                                                        Kireeti Kompella
                                                  Juniper Networks, Inc.
                                                              Vijay Gill
                                          Metromedia Fiber Network, Inc.
                                                        Thomas D. Nadeau
                                                     Cisco Systems, Inc.

       Requirements for Pseudo-Wre Emulation Edge-to-Edge (PWE3)
                  draft-ietf-pwe3-requirements-01.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
   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
   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 generic requirements for Pseudo-Wire
   Emulation Edge to Edge (PWE3). It provides guidelines for other
   working group documents that will define mechanisms for providing
   pseudo-wire emulation of specific services such as Ethernet, ATM,
   Frame Relay, TDM, and MPLS. It should be noted that the PWE3 Working
   Group (PWE3 WG) standardizes mechanisms that can be used to provide
   PWE3 services, but not the services themselves.











Internet Draft      draft-ietf-pwe3-requirements-01           July, 2001


Copyright Notice

   Copyright (C) The Internet Society (2001). All Rights Reserved.












































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                             Table of Contents

   1 Introduction .................................................    4
   1.1 Reference Model of PWE3 ....................................    4
   1.2 Terminology ................................................    5
   2 PDU Encapsulation ............................................    6
   2.1 Conveyance of Necessary L2/L1 Header Information ...........    7
   2.2 PDU Length .................................................    7
   2.3 Encapsulation of Control Messages of the Native  Services
        ...........................................................    7
   2.4 Support for Circuit Multiplexing ...........................    7
   2.5 Packet Ordering ............................................    7
   2.6 Packet Duplication .........................................    7
   3 Carrying the PW PDUs over a Packet-Switched Network ..........    8
   3.1 Setup of Pseudo-Wires ......................................    8
   3.2 Pseudo-Wire MTU ............................................    8
   3.3 Carrying Control Messages of the Native Services ...........    8
   3.4 PSN Tunnel Header Overhead .................................    9
   4 Faithfulness of Emulated Services ............................    9
   4.1 Characteristics of an Emulated Service .....................    9
   4.2 Service Quality of Emulated Services .......................   10
   5 Maintenance of Emulated Services .............................   10
   5.1 Keep-alive .................................................   10
   5.2 Status Monitoring ..........................................   10
   5.3 Notification of Status Changes .............................   11
   5.3.1 Up/Down Notification .....................................   11
   5.3.2 Misconnection and Payload Mistype ........................   11
   5.3.3 Packet Loss, Corruption, and Out-of-order Delivery .......   11
   5.3.4 Other Status Notification ................................   11
   5.3.5 Collective Status Notification ...........................   11
   5.4 Clock Recovery .............................................   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 Traceroute .....................................   13
   7 Scalability ..................................................   13
   8 Other Generic Requirements ...................................   14
   8.1 RFC 2914 Conformance .......................................   14
   9 Non-Requirements .............................................   14
   10 Quality of Service (QoS) Considerations .....................   15
   11 Inter-domain Pseudo-Wires ...................................   15
   12 Security Considerations .....................................   15
   12.1  Security  Considerations  for   the   Signaling/Control
        Channel ...................................................   15
   12.2 Security Considerations for the PW PDUs ...................   15
   13 Deployment Considerations ...................................   16
   14 Acknowledgments .............................................   16
   15 References ..................................................   16
   16 Authors' Addresses ..........................................   17

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   17 Full Copyright Section ......................................   19





















































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1.  Introduction

1.1.  Reference Model of PWE3

   To provide pseudo-wire emulation (PWE), two pseudo-wire end-services
   (PWESs) of the same type are first configured between each customer
   edge (CE) device and the corresponding provider edge (PE) device (See
   Figure 1).  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 TDM circuit, or
     - an MPLS LSP.
   A connection is then set up between the two PEs to connect these two
   PWESs. This connection is called a pseudo-wire (PW) in the PWE3
   context. 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 the PW is set up, layer-2 (e.g. Ethernet, ATM,
   Frame Relay and MPLS) or layer-1 (e.g. SONET/SDH) PDUs from a PWES
   are encapsulated at the PW ingress. The encapsulated PDUs are then
   sent over the PW to the egress, where L2 or L1 headers are re-
   constructed and the resulted frames are forwarded in their native
   format to the other CE.

                    |<------- 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

   This document does not assume that a particular type of PWs is used.
   Instead, it describes generic requirements that apply to all PWs, for
   all services including Ethernet, ATM, Frame Relay, TDM and MPLS.

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   This document is not an introductory document. For an architecture
   overview of PWE3, readers should refer to the PWE3 framework document
   [PATE].

1.2.  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.

   Below are the definitions for the terms used throughout the document.

   Packet Switched Network
                         A Packet Switched Network (PSN) is a network
                         using IP, MPLS or L2TP as the unit of
                         switching.

   Pseudo Wire Emulation Edge to Edge
                         Pseudo Wire Emulation Edge to Edge (PWE3) is a
                         mechanism that emulates the essential
                         attributes of a service (such as a T1 leased
                         line or Frame Relay) over a PSN.

   Customer Edge         A Customer Edge (CE) is a device where one end
                         of an emulated service originates and
                         terminates. The CE is not aware that it is
                         using an emulated service rather than a "real"
                         service.

   Provider Edge         A Provider Edge (PE) is a device that provides
                         PWE3 to a CE.

   Pseudo Wire           A Pseudo Wire (PW) is a connection between two
                         PEs carried over a PSN. The PE provides the
                         adaptation between the CE and the PW.

   Pseudo Wire PDU       A Pseudo Wire PDU (PW PDU) is a PDU sent on the
                         PW that contains all of the data and control
                         information necessary to provide the desired
                         service.

   PSN Tunnel            A PSN Tunnel is a tunnel inside which multiple
                         PWs can be nested so that they are transparent
                         to core network devices.

   Path-oriented PW      A Path-oriented PW is a PW for which the
                         network devices of the underlying PSN must

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                         maintain state information.

   Non-path-oriented PW  A Non-path-oriented PW is a PW for which the
                         network devices of the underlying PSN need not
                         maintain state information.

   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. In general, since not all
                         functions may be supported in one or other of
                         the networks, the translation of PCI may be
                         partial or non-existent. However, this should
                         not result in any loss of user data since the
                         payload is not affected by PCI conversion at
                         the service interworking IWF.

   Network Interworking  In Network Interworking, the PCI (Protocol
                         Control Information) of the protocol and the
                         payload information used in two similar
                         networks are transferred transparently by an
                         IWF of the PE across the PSN. Typically the IWF
                         of the PE encapsulates the information which is
                         transmitted by means of an adaptation function
                         and transfers it transparently to the other
                         network.

2.  PDU Encapsulation

   Every PE MUST provide service interfaces to use common service-
   specific techniques for encapsulating PDUs from the PWESs.  It should
   be noted that the PDUs to be encapsulated may or may not contain L2
   or L1 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 header
   that is used for sending the PW PDUs from the PW ingress to the
   egress (e.g. the tunnel label in [MARTINI2]) is not considered as
   part of the PW header.  It is called PSN tunnel header.

   Specific requirements on PDU encapsulation for a PWE3 approach are
   listed below.


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2.1.  Conveyance of Necessary L2/L1 Header Information

   The egress of a PW needs some information, e.g. which native service
   the PW PDUs belong to, and possibly some L2 or L1 header information,
   in order to know how to process the PDUs received.  A PWE3 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.

2.2.  PDU Length

   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.

2.3.  Encapsulation of Control Messages of the Native Services

   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 need to do in
   this regard.

2.4.  Support for Circuit Multiplexing

   If a service in its native form is capable of grouping multiple
   circuits into a "trunk", e.g. an ATM VP, some mechanism SHOULD be
   provided so that a single PW can be used to connect two end-trunks.
   From encapsulation perspective, the encapsulation header MUST carry
   sufficient information, e.g. VCI of each cell, so that the egress of
   the PW can demultiplex individual circuits from the PW.

2.5.  Packet Ordering

   When packets carrying the PW PDUs traverse a PW, they may arrive at
   the egress out of order. For some services, the PW PDUs 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.

2.6.  Packet Duplication

   In rare cases, packets traversing a PW may be duplicated.  For some
   services, packet duplication is not allowed. For such services some
   mechanism MUST be provided to ensure that duplicated packets will not
   be delivered. The mechanism may or may not be the same as the
   mechanism used to ensure in-order packet delivery.

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3.  Carrying the PW PDUs over a Packet-Switched Network

   This section describes requirements on how to send packets carrying
   the PW PDUs over a packet-switched network (PSN) that provides PWE3
   services.

3.1.  Setup of Pseudo-Wires

   A PW is a tunnel that connects two PWESs. After the L2/L1 PDUs of a
   service are encapsulated, they must be sent over the PW to the other
   PWES.

   Every PWE3 approach MUST define some signaling mechanism for setting
   up the PWs. During the setup process, the PEs need to exchange some
   information (e.g. learn each other's capability).  The signaling
   mechanism MUST enable the PEs to exchange all necessary information.
   For example, both endpoints must agree on an encapsulation method. As
   another example, in order to support circuit multiplexing using ATM
   VPs, both PEs must agree on using the VCIs in the PW PDUs to
   demultiplex individual VCs from the VP at the PW egress.  Which
   signaling protocol to use and what information to exchange are
   service specific. Every PWE3 approach MUST specify these.  Manual
   configuration can be considered as a special kind of signaling and is
   explicitly allowed.

   IP tunnels [MPLSINIP], sessions in a [L2TP] tunnel, or [MPLS] LSPs
   can all be used as PWs. Selection of a particular type of PWs is
   carrier-dependent and is outside scope of the PWE3 WG.

3.2.  Pseudo-Wire MTU

   A PW MUST be able to be configured with an PW_MTU. One way to do this
   is to set the PW_MTU to (PW_Path_MTU - PW_header -
   PSN_tunnel_header). At a PW ingress, if a packet's length exceeds the
   PW_MTU, it MAY be dropped. In this case, the management plane of the
   ingress PE MAY be notified. Alternatively, a fragmentation mechanism
   MAY be defined and used. At a PW egress, if the length of a L2/L1
   frame that is restored from a PW PDU exceeds the MTU of destination
   PWES, it MAY be dropped. In this case, the management plane of the
   egress PE MAY be notified. Alternatively, a fragmentation mechanism
   MAY be defined and used.

3.3.  Carrying 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.  If such control messages are lost,
   functionality of the services will be significantly affected.

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   Therefore, it can be desirable to provide higher reliability for
   carrying control messages. What mechanisms to use and how to use
   those mechanisms for providing higher reliability are outside scope
   of the PWE3 WG.

3.4.  PSN Tunnel Header Overhead

   In order to reduce PSN tunnel header overhead, multiple PDUs MAY be
   concatenated before a PSN tunnel header is added. Each PDU still
   carries its own PW header so that the egress of the PW knows how to
   process it. However, the benefit of concatenating multiple PDUs for
   header efficiency should be weighed against the resulting larger
   penalty incurred by packet loss.


4.  Faithfulness of Emulated Services

   An emulated service SHOULD be as similar to the native service as
   possible, but it is not REQUIRED that they should be identical. The
   applicability statement of a PWE3 service MUST report any limitations
   of the emulated service.  All limitations between an emulated service
   and the corresponding native service can be classified as either
   functional or non-functional.  Functional limitations are those that
   cause some features of the native service to become disabled in the
   emulated one. For example, if an emulated Ethernet service introduces
   some difference that can cause the Spanning Tree Protocol (STP) to
   malfunction, such a difference will be classified as a functional
   difference.  Other differences are non-functional.  For examples,
   differences in service quality between an emulated service and the
   native one are non-functional.

   Some basic requirements on faithfulness of an emulated service are
   described below.

4.1.  Characteristics of an Emulated Service

   Functionally, two CEs that are connected by an emulated service
   SHOULD appear directly connected by a native 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 service.

   2) The two endpoints of emulated service #1 and the two endpoints of
      emulated service #2 may be connected to the same PE at each end,
      respectively. As a result, the PWs of these two emulated services
      may share the same physical paths between the two PEs.  But from

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      the CEs' perspective, each emulated service MUST appear as
      unshared, that is, a CE MUST NOT be aware of existence of other
      CEs or other emulated services.

   3) If an emulated service 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 service, it MUST be possible to be established over an
      emulated service as well. Spanning Tree Protocol (STP) is not
      considered as a routing protocol and requirements on support/non-
      support of STP is outside scope of this document.

   5) The TTL fields of the PW PDUs, if exist, MUST not be changed
      inside an emulated service.

4.2.  Service Quality of Emulated Services

   It is RECOMMENDED but not REQUIRED that an emulated service provide
   as high service quality as the native service.  However, 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.

5.  Maintenance of Emulated Services

   Every PWE3 approach MUST provide mechanisms for maintaining the
   working condition of an emulated service.

5.1.  Keep-alive

   If a native service has keep-alive mechanism, the corresponding
   emulated service MUST define a similar mechanism for keep-alive.

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] or
   [MPLSOAM], 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 if any, 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
   mechanism.

   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 similar mechanism for doing so.

5.3.2.  Misconnection and Payload Mistype

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

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.  Packet
   loss, corruption, and out-of-order delivery can be considered as
   "generalized bit error" of a 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

   Status of a group of emulated services may be affected identically by
   a single network incidence.  For example, when the physical link

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   between a CE and a PE fails, all the emulated services that go
   through that link will fail.  It is likely that there exists a group
   of emulated services 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 services.  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 service with a group
   ID when the PW for that emulated service is set up. Multiple emulated
   services can then be grouped by associating them with identical group
   ID. In status notification, that group ID can be used to refer all
   the emulated services in that group.

5.4.  Clock Recovery

   For some services, the PEs need to maintain some kind of timing
   relationship (e.g. synchronization). The corresponding PWE3 services
   MUST provide some mechanism to support that. If time stamps need to
   be carried across the PSN, [RTP] MUST be used.

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
   ifTable.


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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 Traceroute

   It can be desirable to know the exact path of a PW, especially for
   troubleshooting purpose. A PW emulation service MUST support PW
   traceroute. One tunnel traceroute approach is defined in [BONICA].

7.  Scalability

   Scalability requirements for PWE3 are described below.

   - Only PEs should be aware of existence of PWs and PWE3 services.
     Core network devices SHOULD NOT be exposed to a large number of
     PWs.

     PWs can be path-oriented or non-path-oriented. For path-oriented
     PWs, core network devices must maintain state information for them.
     If a large number of path-oriented PWs are used, core network
     devices will have to maintain a large amount of state information.
     In order to avoid scalability problem, PSN tunnels between PEs can
     be introduced. PWs from the same ingress to the same egress are
     nested inside the PSN tunnel that is from that ingress to that
     egress. By creating such a tunnel hierarchy, individual PWs are
     transparent to the core devices.  If a specific PWE3 approach uses
     path-oriented PWs, PSN tunnels SHOULD be used to improve

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     scalability.  However, a PSN tunnel is not part of any PW.
     Signaling of PSN tunnels NEED NOT be defined in the PWE3 approach
     itself. As an example, if LSPs are used as PWs in a PWE3 approach,
     they can be nested inside a tunnel LSP from the PW ingress to the
     PW egress.  The tunnel LSPs can be signaled by any mechanism
     defined in [MPLS].

   - Circuit multiplexing: circuit multiplexing SHOULD be supported.

   - Collective status notification: collective status notification
     SHOULD be supported.

8.  Other Generic Requirements

8.1.  RFC 2914 Conformance

   [RFC2914] describes the need for congestion control in the Internet,
   and discusses what constitute correct congestion control. Any PWE3
   approach MUST conform to RFC 2914 and be TCP-friendly in its response
   to congestion. The applicability document of a PWE3 approach MUST
   provide a statement on RFC 2914 conformance.

9.  Non-Requirements

   Some non-requirements are mentioned in various sections of this
   document. Those work items are outside scope of the PWE3 WG.  The
   non-requirements are listed below:

   - Service interworking;

   - Point-to-multipoint or multipoint-to-multipoint PWs;

   - Selection of a particular type of PWs;

   - Striving 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;

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

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     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;

10.  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 the 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, e.g. what fields in the
   original L2 or L1 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
   .1P field to EXP field, is out of scope.

11.  Inter-domain Pseudo-Wires

   The PWE3 WG will determine the requirements for having a PW pass
   across an administrative boundary.  An edge could be a native hand-
   off or hand-off to a further PW.  The working group may analyze
   requirements for both security and performance for the inter-
   administration technology. This topic is for further study.

12.  Security Considerations

12.1.  Security Considerations for the Signaling/Control Channel

   If a signaling/control channel is used in a PWE3 approach, some
   security mechanism MUST be provided to ensure integrity of the
   information transmitted across the signaling/control channel.

12.2.  Security Considerations for the PW PDUs

   Providing security for the PW PDUs is outside scope of the PWE3 WG.

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Internet Draft      draft-ietf-pwe3-requirements-01           July, 2001

13.  Deployment Considerations

   Transition from using separate networks for TDM, ATM, Frame Relay and
   IP services to using a single network for multiple services requires
   careful planning and execution.  This is an important topic for
   further study.

14.  Acknowledgments

   Some requirements specified in this document were originally
   articulated in a number of documents including [MARTINI1],
   [MARTINI2], [CES], and [SFBS].  The authors would like to acknowledge
   authors of those documents. The authors would also like to
   acknowledge the input and comments from Eric Rosen, Tricci So and Ron
   Cohen.

15.  References

[BONICA]    R. Bonica, K. Kompella, and D. Meyer, "Tracing Requirements
            for Generic Tunnels", <draft-bonica-tunneltrace-01.txt>,
            work in progress, Feb. 2001.

[CES]       A. Malis et al, "SONET/SDH Circuit Emulation Service Over
            MPLS (CEM) Encapsulation" , work in progress, April 2001.

[GRE]       D. Farinacci, T. Li, S. Hanks, D. Meyer, P. Traina, "Generic
            Routing Encapsulation (GRE)", RFC2784, March 2000.

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

[L2TP]      W.M. Townsley, A. Valencia, A. Rubens, G. Singh Pall, G.
            Zorn, B. Palter, "Layer Two Tunneling Protocol (L2TP)", RFC
            2661, August 1999.

[LSPPING]   P. Pan, N. Sheth, and D. Cooper, "Detecting Data Plane
            Liveliness in RSVP-TE", <draft-pan-lsp-ping-00.txt>, work in
            progress, July 2001.

[MARS]      G. Armitage, "Support for Multicast over UNI 3.0/3.1 based
            ATM Networks", RFC2022, November 1996

[MARTINI1]  L. Martini et al, "Transport of Layer 2 Frames Over MPLS",
            <draft-martini-l2circuit-trans-MPLS-06.txt>, work in
            progress, May 2001.


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[MARTINI2]  L. Martini et al, "Encapsulation Methods for Transport of
            Layer 2 Frames Over MPLS", <draft-martini-l2circuit-encap-
            MPLS-02.txt>, work in progress, May 2001.

[MPLS]      E. Rosen, A. Viswanathan, and R. Callon, "Multiprotocol
            Label Switching Architecture", RFC3031, January 2001

[MPLSINIP]  P. Doolan, Y. Katsube, A. Malis, R. Wilder, T. Worster,
            "MPLS Label Stack Encapsulation in IP", <draft-worster-
            mpls-in-ip-04.txt>, work in progress, Feb. 2001.

[MPLSOAM]   N. Harrison, P. Willis, S. Davari, B. Mack-Crane, H. Ohta,
            "OAM Functionality for MPLS Networks", <draft-harrison-
            mpls-oam-00.txt>, work in progress, Feb. 2001.

[TEMIB]     C. Srinivasan, A. Viswanathan, and T. Nadeau, "MPLS Traffic
            Engineering Management Information Base Using SMIv2",
            <draft-ietf-mpls-te-mib-05.txt>, work in progress, November
            2000.

[PATE]      P. Pate, X. Xiao, T. So, C. White, and K. Kompella,
            "Framework for Pseudo-Wire Emulation Edge-to-Edge (PWE3)",
            <draft-pate-pwe3-framework-00.txt>, work in progress, May
            2001.

[RFC2914]   S.Floyd, "Congestion Control Principles", RFC 2914, Sept.
            2000.

[RTP]       H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson,
            "RTP: A Transport Protocol for Real-Time Applications",
            RFC1889, January 1996.

[SFBS]      B. St-Denis, D. Fedyk, A. Bhatnagar, A. Siddiqui, R.
            Hartani, and T. So, "Multi-service over MPLS", <draft-
            stdenis-ms-over-mpls-00.txt>, work in progress, Nov. 2000.

[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.

16.  Authors' Addresses

   XiPeng Xiao
   Photuris, Inc.
   2025 Stierlin Court
   Mountain View, CA 94043

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   Email: xxiao@photuris.com

   Danny McPherson
   Amber Networks, Inc.
   48664 Milmont Drive
   Fremont, CA 94538
   Email: danny@ambernetworks.com

   Prayson Pate
   Overture Networks
   P. O. Box 14864
   RTP, NC, USA 27709
   Email: prayson.pate@overturenetworks.com

   Craig White
   Level 3 Communications, LLC.
   1025 Eldorado Blvd.
   Broomfield, CO, 80021
   e-mail: Craig.White@Level3.com

   Kireeti Kompella
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089
   Email: kireeti@juniper.net

   Vijay Gill
   Metromedia Fiber Network Inc.
   8075 Leesburg Pike, Suite 300
   Vienna, VA  22182
   Email: vgill@mfnx.net

   Thomas D. Nadeau
   Cisco Systems, Inc.
   250 Apollo Drive
   Chelmsford, MA 01824
   Email: tnadeau@cisco.com















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17.  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
   English.

   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
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   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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