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Versions: (draft-jounay-pwe3-p2mp-pw-requirements) 00 01 02 03 04 05 09 10 RFC 7338

Network Working Group                                    F. Jounay (Ed.)
Internet Draft                                                  P. Niger
Category: Informational Track                             France Telecom
Expires: March 2009
                                                               Y. Kamite
L. Martini                                            NTT Communications
Cisco
                                                               S. Delord
R. Aggarwal                                                       Uecomm
Juniper Networks
                                                                 L. Wang
M. Bocci                                                         Telenor
M. Vigoureux
Alcatel-Lucent                                                  G. Heron
                                                                      BT
L. Jin
Nokia Siemens                                          September 4, 2008


            Requirements for Point-to-Multipoint Pseudowire

              draft-ietf-pwe3-p2mp-pw-requirements-00.txt

Status of this Memo

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   This Internet-Draft will expire on March 2, 2009.






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Abstract

   This document presents a set of requirements for providing an
   unidirectional Point-to-Multipoint PWE3 (Pseudowire Emulation Edge to
   Edge) emulation. The requirements identified in this document are
   related to architecture, signaling and maintenance aspects of a
   Point-to-Multipoint PW operation. They are proposed as guidelines for
   the standardization of such mechanisms. Among other potential
   applications Point-to-Multipoint PWs SHOULD be used to optimize the
   support of multicast services as defined in the Layer 2 Virtual
   Private Network working group.

Conventions used in this document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].


Table of Contents


   1. Introduction....................................................3
   1.1. Problem Statement.............................................3
   1.2. Scope of the document.........................................4
   2. Definition......................................................4
   2.1. Acronyms......................................................4
   2.2. Terminology...................................................4
   3. P2MP SS-PW Requirements.........................................5
   3.1. P2MP SS-PW Reference Model....................................5
   3.2. P2MP SS-PW Underlying Layer...................................7
   3.3. P2MP SS-PW Signaling Requirements.............................7
   3.3.1. PW type mismatch............................................7
   3.3.2. Interface Parameters sub-TLV................................7
   3.3.3. Leaf Grafting/Pruning.......................................8
   3.4. Failure Reporting and Processing..............................8
   3.5. Protection and Restoration....................................9
   3.6. Scalability...................................................9
   3.7. Order of Magnitude............................................9
   4. P2MP MS-PW Requirements........................................10
   4.1. P2MP MS-PW Pseudowire Reference Model........................10
   4.2. P2MP SS-PW Underlying Layer..................................11
   4.3. P2MP MS-PW Signaling Requirements............................12
   4.3.1. Dynamically Instantiated P2MP MS-PW........................12
   4.3.2. P2MP MS-PW Setup Mechanisms................................12
   4.3.3. PW type mismatch...........................................12
   4.3.4. Interface Parameters sub-TLV...............................12
   4.3.5. Leaf Grafting/Pruning......................................12
   4.3.6. Explicit Routing...........................................13
   4.4. Failure Reporting............................................13
   4.5. Protection and Restoration...................................14

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   4.6. Scalability..................................................14
   4.7. Order of Magnitude...........................................14
   5. Manageability considerations...................................14
   6. Backward Compatibility.........................................15
   7. Security Considerations........................................15
   8. IANA Considerations............................................15
   9. Acknowledgments................................................15
   10. References....................................................16
   10.1. Normative References........................................16
   10.2. Informative References......................................16
   Authors' Addresses................................................17
   Intellectual Property and Copyright Statements....................18

1. Introduction

1.1. Problem Statement

   As defined in the PWE3 WG charter, a Pseudowire (PW) emulates a
   point-to-point bidirectional link over an IP/MPLS network, and
   provides a single service which is perceived by its user as an
   unshared link or circuit of the chosen service. A Pseudowire is used
   to transport non IP traffic (e.g. Ethernet, TDM, ATM, and FR) in an
   IP/MPLS-based PSN (Packet Switched Network). PWE3 operates "edge to
   edge" to provide the required connectivity between the two endpoints
   of the PW.

   The P2MP topology mentioned in [VPMS REQ] and required to provide
   P2MP L2VPN services can be achieved via a P2MP PW. The use of PW
   becomes necessary for some P2MP services requiring specific
   encapsulation capabilities. This could be achieved using a set of
   point to point PWs, with traffic replication on the PE, but faces
   obvious bandwidth limitation issues, as traffic is carried multiple
   time on shared links.

   This document defines the use of a Point-to-Multipoint PW (P2MP PW).
   A Point-to-Multipoint (P2MP) Pseudowire (PW) is a mechanism that
   emulates the essential attributes of a unidirectional P2MP
   Telecommunications service such as P2MP ATM over PSN. One of the
   applicabilities of a P2MP PW is to deliver a non-IP multicast service
   that carries multicast frames from a multicast source to one or more
   multicast receivers. The required functions of P2MP PWs include
   encapsulating service-specific PDUs arriving at an ingress Attachment
   Circuit (AC), and carrying them across a tunnel to one or more egress
   ACs, managing their timing and order, and any other operations
   required to emulate the behavior and characteristics of the service
   as faithfully as possible.

   P2MP PWs extend the PWE3 architecture [RFC3985] to offer a P2MP
   Telecommunications service. They follow the PWE3 architecture as
   described in [RFC3985] with modifications as outlined in this
   document. One notable difference between point-to-point (P2P) PWs as
   outlined in [RFC3985] and P2MP PWs is that the former emulate a

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   bidirectional service whereas the latter emulate a unidirectional
   service.

   This document aims at defining the associated requirements related to
   the P2MP PW operation (e.g. setup and maintenance, protection,
   scalability, etc).
   It is intended that solutions that specify procedures and protocols
   or extensions to existing protocols for the signaling of P2MP
   Pseudowire satisfy these requirements.


1.2. Scope of the document

   The document describes the P2MP PW Reference Model architectures and
   outlines specific signaling requirements for the set up and
   maintenance of a P2MP PW. The requirements are divided into two
   parts, i.e. those applicable in a Single-Segment topology and those
   applicable in a Multi-Segment topology. For other aspects of P2MP PW
   implementation like packet processing, maintenance, etc, the document
   refers to [RFC3916].

   Some P2MP PW requirements are derived from the signaling requirements
   for P2MP Traffic-Engineered MPLS Label Switched Paths [RFC4461].


2. Definition

2.1. Acronyms

   P2P: Point-to-Point

   P2MP: Point-to-Multipoint

   PW: Pseudowire

   SS-PW: Single-Segment Pseudowire

   MS-PW: Multi-Segment Pseudowire

2.2. Terminology

   This document uses terminology described in [MS-PW REQ], [MS-PW
   ARCH], [SEG PW].

   It also introduces additional terms needed in the context of
   unidirectional P2MP PW.

   P2MP PW, (also referred as PW Tree)

   Point-to-Multipoint Pseudowire. A PW attached to a source used to
   distribute L1/L2 format traffic to a set of one or more receivers (or
   leaves). The P2MP PW is unidirectional.

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   P2MP SS-PW

   Point-to-Multipoint Single-Segment Pseudowire. A single segment P2MP
   PW set up between the PE attached to the source and the PEs attached
   to the receivers. The P2MP SS-PW relies on a P2MP LSP as PSN tunnel.

   P2MP MS-PW

   Point-to-Multipoint Multi-Segment Pseudowire. A multi-segment P2MP PW
   represents an End-to-End PW segmented by means of S-PEs which are in
   charge of switching the PW label. Each segment can rely on either
   P2P LSP or a P2MP LSP as PSN tunnel.

   Ingress PE

   P2MP PW Ingress Provider Edge. Router attached to a Customer
   Equipment (traffic source) via an Attachment Circuit (AC). In a MS-PW
   architecture the term used is Ingress T-PE.

   Egress PE

   P2MP PW Egress Provider Edge. Router attached to a set of on or more
   Customer Equipments (traffic receivers or leaves) via a set of one or
   more Attachment Circuits (AC). In a MS-PW architecture the term used
   is Egress T-PE.

   Branch S-PE

   The branch S-PE is only defined and required in the context of MS-PW.
   The branch S-PE has one upstream PW segment and one or several
   downstream PW segments.



3. P2MP SS-PW Requirements

3.1. P2MP SS-PW Reference Model

   A unidirectional P2MP SS-PW provides a Point-to-Multipoint
   connectivity from an Ingress PE connected to a traffic source to at
   least two Egress PEs connected to traffic receivers. The PW endpoints
   connect the PW to its attachment circuits (AC). As for a P2P PW, an
   AC can be a Frame Relay DLC, an ATM VP/VC, an Ethernet port, a VLAN,
   a HDLC link on a physical interface.


   Figure 1 describes the P2MP SS-PW reference model which is derived
   from [RFC3985] to support P2MP emulated services.




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                  |<-----------P2MP SS-PW------------>|
          Native  |                                   |  Native
         Service  |    |<----P2MP PSN tunnel --->|    |  Service
          (AC)    V    V                         V    V   (AC)
            |     +----+         +-----+         +----+     |
            |     |PE1 |         |  P  |=========|PE2 |AC3  |     +----+
            |     |    |         |   ......PW1.......>|---------->|CE3 |
            |     |    |         |   . |=========|    |     |     +----+
            |     |    |         |   . |         +----+     |
            |     |    |=========|   . |                    |
            |     |    |         |   . |         +----+     |
   +----+   | AC1 |    |         |   . |=========|PE3 |AC4  |     +----+
   |CE1 |-------->|........PW1.............PW1.......>|---------->|CE4 |
   +----+   |     |    |         |   . |=========|    |     |     +----+
            |     |    |         |   . |         +----+     |
   +----+   |AC2  |    |=========|   . |                    |
   | CE2|<--------|    |         |   . |         +----+AC5  |     +----+
   +----+   |     |    |         |   . |=========|PE4 |---------->|CE5 |
            |     |    |         |   ......PW1.......>|     |     +----+
            |     |    |         |     |=========|    |AC6  |     +----+
            |     |    |         |     |         |    |---------->| CE6|
            |     +----+         +-----+         +----+     |     +----+

                    Figure 1 P2MP SS-PW Reference Model

   This architecture applies to the case where a P2MP PSN tunnel extends
   between edge nodes of a single PSN domain to transport a
   unidirectional P2MP PW with endpoints at these edge nodes.
   In this model a single copy of each PW packet is sent over the P2MP
   PSN tunnel and is received by all Egress PEs due to the P2MP nature
   of the PSN tunnel. P Router is joining P2MP PSN tunnel operation but
   is free from signaling of P2MP PW. P2MP PW operation is associated
   with PE1, PE2, PE3 and PE4.
   An AC attached to P2MP PW MUST be configured as "sender" or
   "receiver" not both.  Any AC is associated with the role of either
   sending side (Tx) or receiving side (Rx) from the view of CE.  Thus
   every AC deals with unidirectional traffic. In Figure 1, AC1 is
   configured as sending sides while AC2, AC3, AC4, AC5 and AC6 are as
   receiving sides.

   Referring to Figure 1, CE2, CE5 and CE6 MAY want to receive multicast
   traffic from CE1. P2MP SS-PW (and P2MP MS-PW outlined in section 4)
   solution MUST support such an operational case where one or more ACs
   are connected to the same PE and local replication is needed. A PE
   providing P2MP PW MUST support the following functions:
   - Ingress PE  MUST support traffic replication over its directly
   connected ACs toward receiver CEs if necessary, in addition to PSN
   transport.
   - Egress PE MUST support traffic replication over its directly
   connected ACs toward receiver CEs if necessary.


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3.2. P2MP SS-PW Underlying Layer

   The P2MP SS-PW implies an underlying P2MP PSN tunnel. Figure 2 gives
   an example of P2MP SS-PW topology relying on a P2MP LSP. The PW tree
   is composed of one Ingress PE (i1) and several Egress PEs (e1, e2,
   e3, e4).

   The P2MP PSN MAY be signaled with P2MP RSVP-TE [RFC4875] or MLDP
   [MLDP].

                                    i1
                                     /
                                    / \
                                   /   \
                                  /     \
                                 /\      \
                                /  \      \
                               /    \      \
                              /      \    / \
                             e1      e2  e3 e4

         Figure 2 Example of P2MP Underlying Layer for P2MP SS-PW


   The P2MP PW MUST be supported over only one P2MP PSN tunnel. This
   P2MP PSN tunnel MUST be able to serve more than one P2MP PW.



3.3. P2MP SS-PW Signaling Requirements

3.3.1. PW type mismatch

   As for P2P PW, the ACs configured at Ingress PE and Egress PEs of a
   P2MP PW MUST be of the same PW type [RFC4446]. In case of a different
   type, the passive PE (Ingress or Egress PE, depending on the
   signaling process) MUST support mechanisms to reject attempts to
   establish the P2MP PW.

3.3.2. Interface Parameters sub-TLV

   Some interface parameters [RFC4446] related to the AC capability have
   been defined according to the PW type and are signaled during the PW
   setup from the Egress PE to the Ingress PE.
   This mechanism used for the P2P PW setup SHOULD be enhanced for P2MP
   PW setup so as to ascertain that AC at the Egress PE is capable to
   support traffic coming from AC at the Ingress PE.
   Note that the signaling of such parameters is not mandatory and can
   also be configured statically at PW endpoints.



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   When the interface parameters are signaled, the Ingress PE SHOULD
   take the decision to accept or not an Egress PE in the PW tree based
   on the interface parameters advertised by the Egress PE. For that
   purpose the Ingress PE MUST be configured with a threshold value of
   the advertised interface parameters. E.g. for some interface
   parameters (e.g. MTU size (Ethernet), number max of concatenated ATM
   cells, etc), the parameters advertised by the Egress PE MUST be at
   least superior or equal to those configured at the Ingress PE. For
   other like CEP/TDM Payload bytes (TDM), the value MUST match exactly
   at the Ingress and Egress PEs.

   Note that when using an Ethernet P2MP PW with the Tag mode, the
   interface parameter VLAN requested MUST be disabled, since a given
   Egress PE requesting a VLAN marking at the Ingress PE will impose
   this value to all Egress PEs belonging to the PW tree.

   Note that a translation (VPI/VCI or VLAN service delimiter) SHOULD be
   enabled only at the Egress PE.


3.3.3. Leaf Grafting/Pruning

   Once the PW tree is setup, the solution MUST allow the addition or
   removal of a leaf, or a subset of leaves to/from the existing tree,
   without any impact on the PW tree (data and control planes) for the
   remaining leaves.
   The addition or removal of a leaf SHOULD also lead to the P2MP PSN
   tunnel update accordingly. This MAY cause P2MP PSN tunnel to add or
   remove the corresponding leaf.


3.4. Failure Reporting and Processing

   Since the underlying layer has an End-to-End P2MP topology between
   the Ingress PE and the Egress PEs, the failure reporting and
   processing procedures are implemented only on the edge nodes.

   Failure events MAY cause one or more Egress PEs and associated leaves
   to become detached from the PW tree. These events MUST be reported to
   the Ingress PE, using appropriate out-band OAM messages.
   The solution SHOULD allow the Ingress PE to be informed of Egress PEs
   and associated leaves failure for management purposes.

   Based on these failure notifications the solution MUST allow the
   Ingress PE to update the remaining leaves of the PW tree.

   - A solution MUST support in-band OAM mechanism to detect failures:
   unidirectional point-to-multipoint traffic failure. This SHOULD be
   realized by enhancing existing unicast PW methods, such as VCCV for
   seamless and familiar operation.



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   - In case of failure, it SHOULD correctly report which leaf PEs are
   affected. This SHOULD be realized by enhancing existing PW methods,
   such as LDP Notification for seamless and familiar operation. The
   notification message SHOULD include the type of fault (P2MP PW, AC or
   PSN tunnel).

   - A solution MAY support OAM message mapping at PE if failure happens
   i.e., mapping between AC service OAM and P2MP PW OAM. (This needs
   more discussion)



3.5. Protection and Restoration

   It is assumed that if recovery procedures are required the P2MP PSN
   tunnel will support standard MPLS-based recovery techniques
   (typically based on RSVP-TE). In that case a mechanism SHOULD be
   implemented to avoid race conditions between recovery at the PSN
   level and recovery at the PW level.


3.6. Scalability

   The solution SHOULD scale at least as well as linearly with an
   increase in the number of Egress PEs.


3.7. Order of Magnitude

   This section will be filled in a future version.

   Number of Egress PE, TAII per Egress PE, dynamicity (Leaf
   Grafting/Pruning) required, etc.




















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4. P2MP MS-PW Requirements

4.1. P2MP MS-PW Pseudowire Reference Model

   Figure 3 describes the P2MP MS-PW reference model which is derived
   from [MS-PW ARCH] to support P2MP emulated services.


                  |<-----------P2MP MS-PW------------>|
          Native  |                                   |  Native
         Service  |    |<-PSN1-->|     |<--PSN2->|    |  Service
          (AC)    V    V         V     V         V    V   (AC)
            |     +----+         +-----+         +----+     |
            |     |T-PE|         |S-PE |=========|T-PE|     |     +----+
            |     |  1 |         |   ......PW2.....>2 |---------->|CE2 |
            |     |    |         |   . |=========|    |     |     +----+
            |     |    |         |   . |         +----+     |
            |     |    |=========|   . |                    |
            |     |    |         |   . |         +----+     |
   +----+   |     |    |         |   . |=========|T-PE|     |     +----+
   |CE1 |-------->|........PW1......>......PW3.....>3.|---------->|CE3 |
   +----+   |     |    |         |   . |=========|    |     |     +----+
            |     |    |         |   . |         +----+     |
            |     |    |=========|   . |                    |
            |     |    |         |   . |         +----+     |
            |     |    |         |   . |=========|T-PE|     |     +----+
            |     |    |         |   . |     ......>4.|---------->|CE4 |
            |     |    |         |   . |     .   |    |     |     +----+
            |     |    |         |   ....PW4..   +----+     |
            |     |    |         |     |     .   +----+     |
            |     |    |         |     |     .   |T-PE|     |     +----+
            |     |    |         |     |     ......>5.|---------->|CE5 |
            |     |    |         |     |=========|    |     |     +----+
            |     +----+         +-----+         +----+     |

                    Figure 3 P2MP MS-PW Reference Model

   Figure 3 extends the P2MP SS-PW architecture of Figure 1 to a multi-
   segment configuration. In a P2P MS-PW configuration as described in
   [MS-PW REQ] the S-PE is responsible to switch a MS-PW from one input
   segment to only one output segment, based on the PW identifier. Here
   in a P2MP MS-PW configuration the S-PE is responsible to switch a MS-
   PW from one input segment to one or several output segments.

   Referring to Figure 3 T-PE1 is the Ingress T-PE and T-PE2, T-PE3, T-
   PE4 and T-PE5 are the Egress T-PEs. In the reference model, the
   Egress T-PEs are assumed to be located in the same PSN (PSN2), but it
   could be envisioned that each output PW is located in a different PSN
   (PSN2, PSN3, PSN4). The S-PE plays the role of branch S-PE since it
   is in charge of switching simultaneously the input PW1 segment to the
   output PW2, PW3, PW4 segments.


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   Note that a P2MP MS-PW MAY obviously transit through more than one S-
   PE along its path.

   Note that if the P2MP SS-PW case mandatory implies the use of P2MP
   PSN tunnel (underlying layer) between the edge nodes, the P2MP MS-PW
   does not imply such a requirement since each PW segment can be
   supported over a P2P PSN tunnel. However as we will see hereafter,
   the coexistence of both kind of PSN tunnel (P2P and P2MP) MUST be
   considered, as described in Figure 3 where the P2MP PW3 segment is
   supported over P2MP LSP.

4.2. P2MP SS-PW Underlying Layer

   Figure 4 describes an example of P2MP MS-PW topology relying on a
   combination of both P2P and P2MP LSPs as PSN tunnels. The PW tree is
   composed of one Ingress PE (i1) and several Egress PEs (e1, e2, e3,
   e4). The branch S-PEs are represented as b1, b2, b3, b4, b5. In that
   case the traffic replication along the path of the PW tree is
   performed at the PW level. For instance the branch S-PE b5 MUST
   replicate incoming packets or data received from b2 and send them to
   Egress T-PEs e3 and e4.

   However giving the fact that some PW segments MAY be supported over a
   P2MP LSP, the traffic replication along the path of these PW segments
   can be performed as well at the underlying LSP level.

   Figure 4 describes the case where each segment is supported over a
   P2P LSP except for the b1-b3 and b1-b4 segments which are conveyed
   over a P2MP LSP on this section.



                                    i1
                                   /  \
                                 b1    b2
                                 /      \
                                /        \
                               /\         \
                              /  \         \
                             b3  b4         b5
                            /      \       / \
                          e1        e2   e3   e4


     Figure 4 Example of P2P and P2MP underlying Layer for P2MP MS-PW


   The P2MP PSN MAY be signaled with P2MP RSVP-TE [RFC4875] or MLDP
   [MLDP].




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4.3. P2MP MS-PW Signaling Requirements

4.3.1. Dynamically Instantiated P2MP MS-PW

   The PW tree could be statically configured at the T-PEs and each S-PE
   crossed. However it is RECOMMENDED that a solution provides the
   ability to dynamically setup a MS-PW tree, by allowing the MS-PW
   segments to be dynamically stitched.

   During the PW tree setup, a branch S-PE SHOULD be capable to inform
   the upstream PEs, including the Ingress T-PE that a set of Egress T-
   PEs and associated leaves are not reachable.


4.3.2. P2MP MS-PW Setup Mechanisms

   The requirements described in this section assume that dynamic setup
   of MS-PW segments allows the T-PE and S-PEs to dynamically signal MS-
   PW segments and stitch these segments in order to build the MS-PW
   tree.

   It is RECOMMENDED that the solution provides various optimization
   options in the P2MP MS-PW construction (Traffic-Engineered P2MP MS-
   PW).


4.3.3. PW type mismatch

   As described for P2MP SS-PW, the P2MP MS-PW requires ACs of the same
   PW type. Therefore the segments composing the P2MP MS-PW MUST be also
   of the same PW type [RFC4446]. The S-PE MAY only support switching
   PWs of the same PW type. In case of a different type, the passive PE
   (S-PE or T-PE) MUST support mechanisms to reject attempts to
   establish the P2MP MS-PW.


4.3.4. Interface Parameters sub-TLV

   The section 3.3.2 is also relevant to P2MP MS-PW. The Egress T-PE MAY
   signal its AC' interface parameters to the Ingress T-PE so as to make
   sure that AC at the Egress T-PE is capable to support traffic coming
   from AC at the Ingress T-PE. In the P2MP MS-PW case, S-PEs MUST
   propagate correctly this information up to the Ingress T-PE.


4.3.5. Leaf Grafting/Pruning

   Once the PW tree is setup, the solution MUST allow the addition or
   removal of a leaf, or a subset of leaves to/from the existing tree,
   without any impact on the PW tree (data and control planes) for the
   remaining leaves.


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4.3.6. Explicit Routing

   The P2MP MS-PW signaling solution MUST provide a means of
   establishing arbitrary P2MP MS-PW, according to pre-computed and
   configured S-PE paths as well as dynamically computed S-PE paths on
   the Ingress PE.

   To support setup of explicitly routed MS-PW tree, the signaling
   solution SHOULD support some source-based control that can explicitly
   define particular S-PE nodes as branch S-PEs for the PW tree.

   The solution SHOULD let possible Explicit Path Loose Hops (to be
   defined). Therefore the P2MP MS-PW MAY be partially specified with
   only a subset of intermediate branch S-PEs.


4.4. Failure Reporting

   The solution SHOULD rely on specific OAM mechanisms to detect a node
   (T-PE and S-PE) or segment failure of a PW tree. The solution SHOULD
   also support the ability to inform the Ingress T-PE of the failure as
   well as to indicate the identity of affected Egress T-PEs and
   associated leaves.

   Based on these failure notifications the solution MUST allow the
   Ingress T-PE to update the remaining Egress PEs and associated leaves
   of the PW tree.

   - A solution MUST support in-band OAM mechanism to detect failures:
   unidirectional point-to-multipoint traffic failure. This SHOULD be
   realized by enhancing existing unicast PW methods, such as VCCV for
   seamless and familiar operation.

   - In case of failure, it SHOULD correctly report which leaf T-PEs and
   branch S-PEs are affected. This SHOULD be realized by enhancing
   existing unicast PW methods, such as LDP Notification for seamless
   and familiar operation. The notification message SHOULD include the
   type of fault (P2MP PW, AC or PSN tunnel).

   - A solution MAY support OAM message mapping at T-PE if failure
   happens i.e., mapping between AC service OAM and P2MP PW OAM. (Need
   more discussion: in particular, when upstream T-PE AC fails, it can
   be mapped to all downstream connection. Meanwhile downstream T-PE AC
   failure does not impose other T-PEs AC.)









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4.5. Protection and Restoration

   The solution SHOULD provide mechanisms to recover as fast as possible
   following a failure event. The fast protection/recovery is typically
   dedicated to P2MP applications sensitive to traffic disruption.

   Considering (i) a source-initiated PW tree setup and (ii) that a
   local repair (PSN-tunnel or PW segment-based) is not feasible after a
   failure event and that (iii) the PE upstream to the failure receives
   by means of OAM mechanisms a message indicating that a subset of
   Egress T-PEs are detached from the PW tree, the solution SHOULD allow
   the upstream PE to re-compute the path to those particular Egress T-
   PEs. If the upstream PE failed to compute an alternative path, the
   procedure SHOULD be propagated upstream until the Ingress-PE is
   reached.

   It is also assumed that recovery procedures can be implemented at the
   underlying P2P or P2MP LSP layer, using standard MPLS-based recovery
   techniques. These procedures could be used to provide faster recovery
   time in case of link or node failure affecting this layer.

   A mechanism SHOULD be implemented to avoid race conditions between
   recovery at the PSN level and recovery at the PW level.


4.6. Scalability

   In definition of solution for P2MP MS-PW a particular attention MUST
   dedicated to scalability.

   The solution MUST be designed to scale as well as linearly with an
   increase in the number of leaves, Egress T-PEs, branch S-PEs. The
   scalability issues MUST be addressed for the control plane (e.g.
   addressing of PW endpoints, number of signaling sessions, etc) and
   for data plane (e.g. duplication of PW segments, OAM mechanism, etc).


4.7. Order of Magnitude

   This section will be filled in a future version.

   Number of Egress T-PE per tree, TAII per Egress T-PE, S-PE crossed,
   replication supported per S-PE, dynamicity (Leaf Grafting/Pruning)
   required, etc.


5. Manageability considerations

   The solution SHOULD provide a simple provisioning procedure to build
   a P2MP SS-PW or a P2MP MS-PW.



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6. Backward Compatibility


   The solution SHOULD be completely backward compatible with
   the current PW standards. The solution SHOULD take into account the
   capability advertisement and negotiation procedures for the PEs
   implementing P2MP PW endpoints.

   Implementation of OAM mechanisms also implies the advertisement of PE
   capabilities to support specific OAM features. The solution MAY allow
   advertising P2MP PW OAM capabilities.


   A solution MUST NOT allow PW connection with non-compliant PEs.  It
   MUST have a mechanism to report an error for non-compliant PEs.  In
   this case, it SHOULD report which PE (S-PE and T-PEs) are not
   compliant.

   In some cases, upstream traffic is required from downstream CE to
   upstream CE.
   A solution SHOULD allow co-existing operation with point-to-point PW
   that provides upstream connection.
   In particular, it is expected to be allowed that the same ACs are
   shared between downstream and upstream direction. For downstream, a
   CE receives from its connected AC traffic originated by the ingress
   PE transported over a P2MP PW.  For upstream, the CE MAY also send
   over the same AC traffic destinated to the same remote PE transported
   over point-to-point PW.

7. Security Considerations

   This section will be added in a future version.

8. IANA Considerations

   This draft does not define any new protocol element, and hence does
   not require any IANA action.


9. Acknowledgments

   The authors thank the contributors of [RFC4461] since the structure
   and content of this document were, for some sections, largely
   inspired by [RFC4461].

   Many thanks to JL Le Roux and A. Cauvin for the discussions, comments
   and support.






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10. References

10.1. Normative References

[RFC2119]       Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, March 1997.

[RFC3916]       McPherson, D.,Pate, P., Xiao, X., "Requirements for
                Pseudo-Wire Emulation Edge-to-Edge", September 2004

[RFC3985]       Bryant, S., Pate, P. "PWE3 Architecture", March 2005

[RFC4461]       Aggarwal, R., Farrel, A., Jork, M., Kamite, Y.,
                Kullberg, A., Le Roux, JL., Malis, A., Papadimitriou,
                D., Vasseur, JP., Yasukawa, S., "Signaling Requirements
                for P2MP TE MPLS LSPs",April 2006

[RFC4875]      Aggarwal, R., Papadimitriou, D., Yasukawa, S.,
                "Extensions to RSVP-TE for Point-to-Multipoint TE LSPs",
                MAY 2007

[RFC4446]      Martini, L. "IANA Allocations for Pseudowire Edge to
                Edge Emulation (PWE3)", April 2006

10.2. Informative References

[MS-PW REQ]      Bitar, N., Bocci, M., and Martini, L., "Requirements
                 for inter domain Pseudo-Wires", Internet Draft, draft-
                 ietf-pwe3-ms-pw-requirements-07.txt, June 2008


[MS-PW ARCH]     Bocci, M., and Bryant, S.,T., " An Architecture for
                 Multi-Segment Pseudo Wire Emulation Edge-to-Edge",
                 Internet Draft, draft-ietf-pwe3-ms-pw-arch-04.txt,
                 June 2008

[SEG PW]         Martini et al, "Segmented Pseudo Wire", Internet
                 Draft, draft-ietf-pwe3-segmented-pw-09.txt, July 2008


[MLDP]           Minei, I., Wijnands, I., Thomas, B., "Label
                 Distribution Protocol Extensions for Point-to-
                 Multipoint and Multipoint-to-Multipoint Label Switched
                 Paths", Internet Draft, draft-ietf-mpls-ldp-p2mp-05,
                 June 2008

[VPMS REQ]       Kamite, Y., Jounay, F. "Framework and Requirements for
                 Virtual Private Multicast Service (VPMS)", Internet
                 Draft, draft-kamite-l2vpn-vpms-frmwk-requirements-01,
                 July 2008



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Author's Addresses

   Frederic Jounay
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   FRANCE
   Email: frederic.jounay@orange-ftgroup.com

   Philippe Niger
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   FRANCE
   Email: philippe.niger@orange-ftgroup.com

   Yuji Kamite
   NTT Communications Corporation
   Tokyo Opera City Tower
   3-20-2 Nishi Shinjuku, Shinjuku-ku
   Tokyo  163-1421
   Japan
   Email: y.kamite@ntt.com

   Luca Martini
   Cisco Systems, Inc.
   9155 East Nichols Avenue, Suite 400
   Englewood, CO, 80112
   EMail: lmartini@cisco.com

   Giles Heron
   Tellabs
   Abbey Place
   24-28 Easton Street
   High Wycombe
   Bucks
   HP11 1NT
   UK
   EMail: giles.heron@tellabs.com

   Simon Delord
   Uecomm
   658 Church St
   Richmond, VIC, 3121, Australia
   E-mail: sdelord@uecomm.com.au

   Lei Wang
   Telenor
   Snaroyveien 30
   Fornebu 1331
   Norway
   Email: lei.wang@telenor.com

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   Rahul Aggarwal
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale, CA 94089
   Email: rahul@juniper.net


   Martin Vigoureux
   Alcatel-Lucent France
   Route de Villejust
   91620 Nozay
   FRANCE
   Email: martin.vigoureux@alcatel-lucent.fr

   Matthew Bocci
   Alcatel-Lucent Telecom Ltd,
   Voyager Place
   Shoppenhangers Road
   Maidenhead
   Berks, UK
   E-mail: matthew.bocci@alcatel-lucent.co.uk

   Lizhong JIN
   Nokia Siemens Networks
   Building 89, 1122 North QinZhou Road,
   Shanghai, 200211, P.R.China
   Email: lizhong.jin@nsn.com

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   Disclaimer of Validity

   This document and the information contained herein are provided on an
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