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Versions: 00 01 02 03 04 RFC 4461

Network Working Group                              Seisho Yasukawa (NTT)
Internet Draft                                                    Editor
Category: Informational
Expiration Date: May 2005                                  December 2004

           Signaling Requirements for Point to Multipoint
                    Traffic Engineered MPLS LSPs
           <draft-ietf-mpls-p2mp-sig-requirement-00.txt>

Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   or will be disclosed, and any of which I become aware will be
   disclosed, in accordance with RFC 3668.

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Abstract

   This document presents a set of requirements for the establishment
   and maintenance of Point-to-Multipoint (P2MP) Traffic Engineered (TE)
   Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs).

   There is no intent to specify solution specific details nor
   application specific requirements in this document.

   It is intended that the requirements presented in this document are
   not limited to the requirements of packet switched networks, but also
   encompass the requirements of L2SC, TDM, lambda and port switching
   networks managed by Generalized MPLS (GMPLS) protocols. Protocol
   solutions developed to meet the requirements set out in this document
   must attempt to be equally applicable to MPLS and GMPLS.


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   Table of Contents

   1. Introduction .................................................. 03
   2. Definitions ................................................... 06
      2.1 Acronyms .................................................. 06
      2.2 Terminology ............................................... 06
      2.2.1 Terminology for Partial LSPs ............................ 07
      2.3 Conventions ............................................... 09
   3. Problem Statement ............................................. 09
      3.1 Motivation ................................................ 09
      3.2. Requirements Overview .................................... 09
   4. Detailed requirements for P2MP TE extensions .................. 11
      4.1 P2MP LSP tunnels .......................................... 11
      4.2 P2MP explicit routing ..................................... 12
      4.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes . 13
      4.4 P2MP TE LSP establishment, teardown, and modification
          mechanisms ................................................ 14
      4.5 Fragmentation ............................................. 14
      4.6 Failure Reporting and Error Recovery ...................... 15
      4.7 Record route of P2MP TE LSP tunnels ....................... 16
      4.8 Call Admission Control (CAC) and QoS Control mechanism
          of P2MP TE LSPs ........................................... 16
      4.9 Variation of LSP Parameters ............................... 17
      4.10 Re-optimization of P2MP TE LSPs .......................... 17
      4.11 Tree Remerge ............................................. 18
      4.12 Data Duplication ......................................... 19
      4.13 IPv4/IPv6 support ........................................ 19
      4.14 P2MP MPLS Label .......................................... 19
      4.15 Routing advertisement of P2MP capability ................. 19
      4.16 Multi-Area/AS LSP ........................................ 20
      4.17 Multi-access LANs ........................................ 20
      4.18 P2MP MPLS OAM ............................................ 21
      4.19 Scalability .............................................. 21
      4.19.1 Absolute Limits ........................................ 22
      4.20 Backwards Compatibility .................................. 23
      4.21 GMPLS .................................................... 24
      4.22 Requirements for Hierarchical P2MP TE LSPs ............... 25
      4.23 P2MP Crankback routing ................................... 25
   5. Security Considerations ....................................... 25
   6. Acknowledgements .............................................. 25
   7. References .................................................... 26
      7.1 Normative References ...................................... 26
      7.2 Informational References .................................. 26
   8. Editor's Address .............................................. 28
   9. Authors' Addresses ............................................ 28
   10. Intellectual Property Consideration .......................... 29
   11. Full Copyright Statement ..................................... 30


Yasukawa, et. al.                                               [Page 2]

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1. Introduction

   Existing MPLS Traffic Engineering (MPLS-TE) allows for strict QoS
   guarantees, resources optimization, and fast failure recovery, but is
   limited to point-to-point (P2P) applications. Requirements have been
   expressed for the provision of services over point-to-multipoint
   (P2MP) traffic engineered tunnels and this clearly motivates
   enhancements of the base MPLS-TE tool box in order to support P2MP
   MPLS-TE LSPs.

   [RFC2702] specifies requirements for traffic engineering over MPLS.
   It describes traffic engineering in some detail, and those
   definitions and objectives are equally applicable to traffic
   engineering in a point-to-multipoint service environment. They are
   not repeated here, but it is assumed that the reader is fully
   familiar with them.

   [RFC2702] also explains how MPLS is particularly suited to traffic
   engineering, and presents the following eight reason.

      1. Explicit label switched paths which are not constrained by
         the destination based forwarding paradigm can be easily created
         through manual administrative action or through automated
         action by the underlying protocols.
      2. LSPs can potentially be efficiently maintained.
      3. Traffic trunks can be instantiated and mapped onto LSPs.
      4. A set of attributes can be associated with traffic trunks
         which modulate their behavioral characteristics.
      5. A set of attributes can be associated with resources which
         constrain the placement of LSPs and traffic trunks across
         them.
      6. MPLS allows for both traffic aggregation and disaggregation
         whereas classical destination only based IP forwarding
         permits only aggregation.
      7. It is relatively easy to integrate a "constraint-based routing"
         framework with MPLS.
      8. A good implementation of MPLS can offer significantly lower
         overhead than competing alternatives for Traffic Engineering.

   These points are equally applicable to point-to-multipoint
   traffic engineering. Points 1. and 7. are particularly important.

   That is, the traffic flow for a point-to-multipoint LSP is not
   constrained to the path or paths that it would follow during
   multicast routing or shortest path destination-based routing, but
   can be explicitly controlled through manual or automated action.



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   Further, the explicit paths that are used may be computed using
   algorithms based on a variety of constraints to produce all manner of
   tree shapes. For example, an explicit path may be cost-based
   [STEINER], shortest path, QoS-based, or may use some fair-cost QoS
   algorithm.

   [RFC2702] also describes the functional capabilities required to
   fully support Traffic Engineering over MPLS in large networks.

     1. A set of attributes associated with traffic trunks which
        collectively specify their behavioral characteristics.

     2. A set of attributes associated with resources which constrain
        the placement of traffic trunks through them. These can also be
        viewed as topology attribute constraints.

     3. A "constraint-based routing" framework which is used to select
        paths for traffic trunks subject to constraints imposed by
        items 1) and 2) above. The constraint-based routing framework
        does not have to be part of MPLS. However, the two need to be
        tightly integrated together.

   These basic requirements should also be supported by P2MP traffic
   engineering.

   This document presents a set of requirements for
   Point-to-Multipoint(P2MP) Traffic Engineering (TE) extensions to
   Multiprotocol Label Switching (MPLS). It specifies functional
   requirements for solutions to deliver P2MP TE LSPs.

   It is intended that solutions that specify procedures for P2MP TE LSP
   setup satisfy these requirements. There is no intent to specify
   solution specific details nor application specific requirements in
   this document.

   It is intended that the requirements presented in this document are
   not limited to the requirements of packet switched networks, but
   also encompass the requirements of TDM, lambda and port switching
   networks managed by Generalized MPLS (GMPLS) protocols. Protocol
   solutions developed to meet the requirements set out in this
   document must attempt to be equally applicable to MPLS and GMPLS.

   Existing MPLS TE mechanisms such as [RFC3209] do not support P2MP TE
   LSPs so new mechanisms must be developed. This should be achieved
   with maximum re-use of existing MPLS protocols.



Yasukawa, et. al.                                               [Page 4]

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   Note that there is a separation between routing and signaling in
   MPLS TE. In particular, the path of the MPLS TE LSP is determined by
   performing a constraint-based computation (such as CSPF) on a traffic
   engineering database (TED). The contents of the TED may be collected
   through a variety of mechanism - extensions to the IGPs are a
   popular mechanism for P2P MPLS TE.

   This document focuses on requirements for establishing and
   maintaining P2MP MPLS TE LSPs through signaling protocols; and
   routing protocols are out of scope. No assumptions are made about how
   the TED used as the basis for path computations for P2MP LSPs is
   formed.

   A P2MP TE LSP will be set up with TE constraints and will allow
   efficient packet or data replication at various branching points in
   the network. Note that the notion of "efficient" packet replication
   is relative and may have different meanings depending on the
   objectives (see section 4.2).

   P2MP TE LSP setup mechanisms MUST include the ability to add/remove
   receivers to/from an existing P2MP TE LSP.

 1.1 Non-Objectives

   For clarity, this section lists some items that are out of scope of
   this document.

   It is assumed that some information elements describing the P2MP TE
   LSP are known to the ingress LSR prior to LSP establishment.
   For example, the ingress LSRs knows the IP addresses that identify
   the egress LSRs of the P2MP TE LSP. The mechanisms by which the
   ingress LSR obtains this information is outside the scope of P2MP TE
   signaling and so is not included in this document. Other documents
   may complete the description of this function by providing
   automated, protocol-based ways of passing this information to the
   ingress LSR.








Yasukawa, et. al.                                               [Page 5]

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   - Non-TE LSPs (such as per-hop, routing-based LSPs).
   - Discovery of egress leaves for a P2MP LSP

   - Hierarchical P2MP LSPs
   - OAM for P2MP LSPs
   - Inter-area and inter-AS P2MP TE LSPs

   - Applicability of P2MP MPLS TE LSPs to service scenarios
   - Specific application or application requirements

   - Algorithms for computing P2MP distribution trees

   - Multipoint-to-point LSPs
   - Multipoint-to-multipoint LSPs

   - Routing protocols
   - Construction of the traffic engineering database
   - Distirbution of the information used to construct the traffic
     engineering database

2. Definitions

2.1 Acronyms

   P2P:

      Point-to-point

   P2MP:

      Point-to-multipoint

2.2 Terminology

   The reader is assumed to be familiar with the terminology in
   [RFC3031] and [RFC3209].

   P2MP TE LSP:

      A traffic engineered label switched path that has one unique
      ingress LSR (also referred to as the root) and one or more
      egress LSRs (also referred to as the leaf).

   P2MP tree:

      The ordered set of LSRs and links that comprise the path of a
      P2MP TE LSP from its ingress LSR to all of its egress LSRs.


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   ingress LSR:

      The LSR that is responsible for initiating the signaling
      messages that set up the P2MP TE LSP.

   egress LSR:

      One of potentially many destinations of the P2MP TE LSP.
      Egress LSRs may also be referred to as leaf nodes or leaves.

   bud LSR:

     An LSR that is an egress, but also has one or more directly
     connected downstream LSRs.

   branch LSR:

      An LSR that has more than one directly connected downstream LSR.

   graft LSR:

      An LSR that is already a member of the P2MP tree and is in
      process of signaling a new sub-P2MP tree.

   prune LSR:

      An LSR that is a member of the P2MP tree and is in
      process of tearing down an existing sub-P2MP tree.

   P2MP-ID (Pid):

      A unique identifier of a P2MP TE LSP, that is constant for the
      whole LSP regardless of the number of branches and/or leaves.

2.2.1 Terminology for Partial LSPs

   It is convenient to sub-divide P2MP trees for functional and
   representational reasons. A tree may be divided in two dimensions:

   - A division may be made along the length of the tree. For example,
     the tree may be split into two components each running from the
     ingress LSR to a discrete set of egress LSRs
   - A tree may be divided at a branch LSR (or any transit LSR) to
     produce a component of the tree that runs from the branch (or
     transit) LSR to all downstream egress LSRs.



Yasukawa, et. al.                                               [Page 7]

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   These two methods of splitting the P2MP tree can be combined, so it
   is useful to introduce some terminology to allow the partitioned
   trees to be clearly described.

   Use the following designations:
     Source (ingress) LSR - S
     Leaf (egress) LSR - L
     Branch LSR - B
     Transit LSR - X

   Define three terms:

     Sub-LSP
       A component of the P2MP LSP that runs from one LSR to another
       without (or ignoring) any branches.

     Sub-tree
       A component of the P2MP LSP that runs from one LSR to more than
       one other LSR by branching.

     Tree
       A component of the P2MP LSP that runs from one LSR to all
       downstream LSRs.

   Using these new concepts we can define any combination or split of
   the P2MP tree. For example:

     S2L sub-LSP
       The path from the source to one specific leaf.

     S2L sub-tree
       The path from the source to a set of leaves.

     B2L tree
       The path from a branch LSR to all downstream leaves.

     X2X sub-LSP
       A component of the P2MP LSP that is a simple path with
       no branches.






Yasukawa, et. al.                                               [Page 8]

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2.3 Conventions

   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].

3. Problem Statement

3.1 Motivation

   As described in section 1, Traffic Engineering and Constraint Based
   Routing, including Call Admission Control(CAC), explicit source
   routing and bandwidth reservation, are required to enable efficient
   resource usage and strict QoS guarantees. Such mechanisms also make
   it possible to provide services across a congested network where
   conventional "shortest path first" forwarding paradigms would fail.

   Existing MPLS TE mechanisms [RFC3209] and GMPLS TE mechanisms
   [RFC3473] only provide support for P2P TE LSPs. While it is possible
   to provide P2MP TE services using P2P TE LSPs, any such approach is
   potentially suboptimal since it may result in data replication at
   the ingress LSR, or in duplicate data traffic within the network.

   Hence, to provide P2MP MPLS TE services in a fully efficient manner
   it is necessary to specify specific requirements. These requirements
   can then be used to define mechanisms for the use of existing
   protocols and/or extensions to existing protocols and/or new
   protocols.

3.2. Requirements Overview

   This document states basic requirements for the setup of P2MP TE
   LSPs. The requirements apply to the signaling techniques only, and no
   assumptions are made about which routing protocols are run within the
   network, nor about how the information that is used to construct the
   Traffic Engineering Database (TED) is distributed. These factors are
   out of the scope of this document.

   A P2MP TE LSP path will be computed taking into account various
   constraints such as bandwidth, affinities, required level of
   protection and so on. The solution MUST allow for the computation
   of P2MP TE LSP paths satisfying constraints with the objective of
   supporting various optimization criteria such as delays, bandwidth
   consumption in the network, or any other combinations. This is likely
   to require the presence of a TED, as well as the ability to signal
   the explicit path of an LSP.


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   A desired requirement is also to maximize the re-use of existing
   MPLS TE techniques and protocols where doing so does not adversely
   impact the function, simplicity or scalability of the solution.

   This document does not restrict the choice of signaling protocol
   used to set up a P2MP TE LSP, but it should be noted that [RFC3468]
   states
     ... the consensus reached by the Multiprotocol Label Switching
   (MPLS) Working Group within the IETF to focus its efforts on
   "Resource Reservation Protocol (RSVP)-TE: Extensions to RSVP for
   Label-Switched Paths (LSP) Tunnels" (RFC 3209) as the MPLS signaling
   protocol for traffic engineering applications...

   The P2MP TE LSP setup mechanism MUST include the ability to
   add/remove egress LSRs to/from an existing P2MP TE LSP and MUST
   allow for the support of all the TE LSP management procedures
   already defined for P2P TE LSP such as the non disruptive rerouting
   (the so called "Make before break" procedure).

   The computation of P2MP TE trees is implementation dependent and is
   beyond the scope of the solutions that are built with this document
   as a guideline.

   Consider the following figure.

                         Source 1 (S1)
                               |
                             I-LSR1
                             |   |
                             |   |
            R2----E-LSR3--LSR1   LSR2---E-LSR2--Receiver 1 (R1)
                             |   :
                  R3----E-LSR4   E-LSR5
                             |   :
                             |   :
                            R4   R5

                           Figure 1

   Figure 1 shows a single ingress (I-LSR1), and four egresses(E-LSR2,
   E-LSR3, E-LSR4 and E-LSR5). I-LSR1 is attached to a traffic source
   that is generating traffic for a P2MP application.
   Receivers R1, R2, R3 and R4 are attached to E-LSR2, E-LSR3 and
   E-LSR4.



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   The following are the objectives of P2MP LSP establishment and use.

      a) A P2MP TE LSP tree which satisfies various constraints is
         pre-determined and supplied to ingress I-LSR1.

         Note that no assumption is made on whether the tree is
         provided to I-LSR1 or computed by I-LSR1. Note that the
         solution SHOULD also allow for the support of partial path by
         means of loose routing.

         Typical constraints are bandwidth requirements, resource class
         affinities, fast rerouting, preemption, to mention a few of
         them. There should not be any restriction on the possibility
         to support the set of constraints already defined for point to
         point TE LSPs. A new constraint may specify which LSRs should
         be used as branch points for the P2MP LSR in order to take
         into account some LSR capabilities or network constraints.

      b) A P2MP TE LSP is set up from I-LSR1 to E-LSR2, E-LSR3 and
         E-LSR4 using the tree information.

      c) In this case, the branch LSR1 should replicate incoming
         packets or data and send them to E-LSR3 and E-LSR4.

      d) If a new receiver (R5) expresses an interest in receiving
         traffic, a new tree is determined and a sub-P2MP tree from
         LSR2 to E-LSR5 is grafted onto the P2MP tree. LSR2 becomes a
         branch LSR.

4. Detailed requirements for P2MP TE extensions

4.1 P2MP LSP tunnels

   The P2MP TE extensions MUST be applicable to the signaling of LSPs
   of different traffic types. For example, it MUST be possible to
   signal a P2MP TE LSP to carry any kind of payload being packet or
   non-packet based (including frame, cell, TDM un/structured, etc.)

   As with P2P MPLS technology [RFC3031], traffic is classified with a
   FEC in this extension. All packets which belong to a particular FEC
   and which travel from a particular node MUST follow the same P2MP
   tree.




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   In order to scale to a large number of branches, P2MP TE LSPs SHOULD
   be identified by a unique identifier (the P2MP ID or Pid) that is
   constant for the whole LSP regardless of the number of branches
   and/or leaves. Therefore, the identification of the P2MP session by
   its destination addresses is not adequate.

4.2 P2MP explicit routing

   Various optimizations in P2MP tree formation need to be applied to
   meet various QoS requirements and operational constraints.

   Some P2MP applications may request a bandwidth guaranteed P2MP tree
   which satisfies end-to-end delay requirements. And some operators
   may want to set up a cost minimum P2MP tree by specifying branch
   LSRs explicitly.

   The P2MP TE solution therefore MUST provide a means of establishing
   arbitrary P2MP trees under the control of an external tree
   computation process or path configuration process or dynamic tree
   computation process located on the ingress LSR. Figure 4 shows two
   typical examples.

               A                                      A
               |                                    /   \
               B                                   B     C
               |                                  / \   / \
               C                                 D   E  F   G
               |                                / \ / \/ \ / \
   D--E*-F*-G*-H*-I*-J*-K*--L                  H  I J KL M N  O

        Steiner P2MP tree                        SPF P2MP tree

                Figure 4 Examples of P2MP TE LSP topology

   One example is the Steiner P2MP tree (Cost minimum P2MP tree)
   [STEINER]. This P2MP tree is suitable for constructing a cost
   minimum P2MP tree so as to minimize the bandwidth consumption in
   the core. To realize this P2MP tree, several intermediate LSRs must
   be both MPLS data terminating LSRs and transit LSRs (LSRs E, F, G,
   H, I, J and K in the figure 4). This means that the LSRs must perform
   both label swapping and popping at the same time. Therefore, the P2MP
   TE solution MUST support a mechanism that can setup this kind of bud
   LSR between an ingress LSR and egress LSRs. Note that this includes
   constrained Steiner trees that allow for the computation of a minimal
   cost trees with some other constraints such as a bounded delay
   between the source and every receiver.


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   Another example is a CSPF (Constraint Shortest Path First) P2MP
   tree. By some metric (which can be set upon any specific criteria
   like the delay, bandwidth, a combination of those), one can
   calculate a shortest path P2MP tree. This P2MP tree is suitable for
   carrying real time traffic.

   The solution MUST allow the operator to make use of any tree
   computation technique. In the former case an efficient/optimal tree
   is defined as a minimal cost tree (Steiner tree) whereas in the
   later case it is defined as the tree that provides shortest path
   between the source and any receiver.

   To support explicit setup of any reasonable P2MP tree shape, a P2MP
   TE solution MUST support some form of explicit source-based control
   of the P2MP tree which can explicitly include particular LSRs as
   branch nodes. This can be used by the ingress LSR to setup the P2MP
   TE LSP.  For instance, a P2MP TE LSP can be simply represented as a
   whole tree or by its individual branches.

4.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes

   A P2MP tree is completely specified if all of the required branches
   and hops between a sender and leaf LSR are indicated.

   A P2MP tree is partially specified if only a subset of intermediate
   branches and hops are indicated. This may be achieved using loose
   hops in the explicit path, or using widely scoped abstract nodes
   such as IPv4 prefixes shorter than 32 bits, or AS numbers.
   A partially specified P2MP tree might be particularly useful in
   inter-area and inter-AS situations although P2MP requirements for
   inter-area and inter-AS are beyond the scope of this document.

   Protocol solutions SHOULD include a way to specify loose hops and
   widely scoped abstract nodes in the explicit source-based control
   of the P2MP tree as defined in the previous section. Where this
   support is provided, protocol solutions MUST allow downstream LSRs
   to apply further explicit control to the P2MP tree to resolve a
   partially specified tree into a (more) completely specified tree.

   Protocol solutions MUST allow the P2MP tree to be completely
   specified at the ingress where sufficient information exists to
   allow the full tree to be computed.

   In all cases, the egress nodes of the P2MP TE LSP must be fully
   specified.



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   In case of a tree being computed by some downstream LSRs (e.g. the
   case of hops specified as loose hops), the solution MUST provide
   the ability for the ingress LSR of the P2MP TE LSP to learn the full
   P2MP tree. Note that this requirement MAY be relaxed in some
   environments (e.g. Inter-AS) where confidentiality must be preserved.

4.4 P2MP TE LSP establishment, teardown, and modification mechanisms

   The P2MP TE solution MUST support establishment, maintenance and
   teardown of P2MP TE LSPs in a scalable manner. This MUST include
   both the existence of very many LSPs at once, and the existence of
   very many destinations for a single P2MP LSP.

   In addition to P2MP TE LSP establishment and teardown mechanism, it
   SHOULD implement partial P2MP tree modification mechanism.

   For the purpose of adding sub-P2MP TE LSPs to an existing P2MP TE
   LSP, the extensions SHOULD support a grafting mechanism. For the
   purpose of deleting a sub-P2MP TE LSPs from an existing P2MP TE LSP,
   the extensions SHOULD support a pruning mechanism.

   It is RECOMMENDED that these grafting and pruning operations do not
   cause any additional processing in nodes except along the path to
   the grafting and pruning node and its downstream nodes. Moreover,
   both grafting and pruning operations MUST not be traffic disruptive
   for the traffic currently forwarded along the P2MP tree.

4.5 Fragmentation

   The P2MP TE solution MUST handle the situation where a single
   protocol message cannot contain all of the information necessary to
   signal the establishment of the P2MP LSP. It MUST be possible to
   establish the LSP in these circumstances.

   This situation may arise in either of the following circumstances.
     a. The ingress LSR cannot signal the whole tree in a single
        message.
     b. The information in a message expands to be too large (or is
        discovered to be too large) at some transit node. This may
        occur because of some increase in the information that needs
        to be signaled or because of a reduction in the size of
        signaling message that is supported.

   The solution to these problems SHOULD NOT rely on IP fragmentation,
   it is RECOMMENDED to rely on some protocol procedures specific to
   the signaling solution.


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   It is NOT RECOMMENDED that fragmented protocol messages are
   re-combined at any downstream LSR.

4.6 Failure Reporting and Error Recovery

   Failure events may cause egress nodes or sub-P2MP LSPs to become
   detached from the P2MP TE LSP. These events MUST be reported
   upstream as for a P2P LSP.

   The solution SHOULD provide recovery techniques such as protection
   and restoration allowing recovery of any impacted sub-P2MP TE
   LSPs. In particular, a solution MUST provide fast protection
   mechanisms applicable to P2MP TE LSP similar to the solutions
   specified in [FRR] for P2P TE LSPs. Note also that no assumption is
   made on whether backup paths for P2MP TE LSPs should or should not
   be shared with P2P TE LSPs backup paths.

   Note that the functions specified in [FRR] are currently specific to
   packet environments and do not apply to non-packet environments.
   Thus, while solutions MUST provide fast protection mechanisms
   similar to those specified in [FRR], this requirement is limited to
   the subset of the solution space that applies to packet switched
   networks only.

   Note that application-specific requirement documents may introduce
   even more stringent requirement, such as no packet loss, as a
   trade-off for the relaxation of other requirements, such as increased
   bandwidth consumption.

   The solution SHOULD also support the ability to meet other network
   recovery requirements such as bandwidth protection and bounded
   propagation delay increase along the backup path during failure.

   A P2MP TE solution MUST support P2MP fast protection mechanism to
   handle P2MP applications sensitive to traffic disruption.

   The report of the failure of delivery to fewer than all of the
   egress nodes SHOULD NOT cause automatic teardown of the P2MP TE LSP.
   That is, while some egress nodes remain connected to the P2MP tree
   it should be a matter of local policy at the ingress whether the
   P2MP LSP is retained.





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   When all egress nodes downstream of a branch node have become
   disconnected from the P2MP tree, and the some branch node is unable
   to restore connectivity to any of them by means of some recovery or
   protection mechanisms, the branch node MAY remove itself from the
   P2MP tree provided that it is not also an egress LSR. Since the
   faults that severed the various downstream egress nodes from the
   P2MP tree may be disparate, the branch node MUST report all such
   errors to its upstream neighbor. The ingress node can then decide
   to re-compute the path to those particular egress nodes, around the
   failure point.

   Solutions MAY include the facility for transit LSRs and particularly
   branch nodes to recompute sub-P2MP trees to restore them after
   failures. In the event of successful repair, error notifications
   SHOULD NOT be reported to upstream nodes, but the new paths are
   reported if route recording is in use. Crankback requirements are
   discussed in Section 4.23.

4.7 Record route of P2MP TE LSP tunnels

   Being able to identify the established topology of P2MP TE LSP is
   very important for various purposes such as management and operation
   of some local recovery mechanisms like Fast Reroute [FRR]. A network
   operator uses this information to manage P2MP TE LSPs. Therefore,
   topology information MUST be collected and updated after P2MP TE LSP
   establishment and modification process.

   The P2MP TE solution MUST support a mechanism which can collect and
   update P2MP tree topology information after P2MP LSP establishment
   and modification process. For example, the P2P MPLS TE mechanism of
   route recording could be extended and used if RSVP-TE was used as
   the P2MP signaling protocol.

   It is RECOMMENDED that the information is collected in a data format
   by which the sender node can recognize the P2MP tree topology
   without involving some complicated data calculation process.

   The solution MUST support the recording of both outgoing interfaces
   and node-id.

4.8 Call Admission Control (CAC) and QoS Control mechanism
    of P2MP TE LSPs

   P2MP TE LSPs may share network resource with P2P TE LSPs. Therefore
   it is important to use CAC and QoS in the same way as P2P TE LSPs
   for easy and scalable operation.


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   P2MP TE solutions MUST support both resource sharing and exclusive
   resource utilization to facilitate co-existence with other LSPs to
   the same destination(s).

   P2MP TE solution MUST be applicable to DiffServ-enabled networks
   that can provide consistent QoS control in P2MP LSP traffic.

   Any solution SHOULD also satisfy the DS-TE requirements [RFC3564]
   and interoperate smoothly with current P2P DS-TE protocol
   specifications.

   Note that this requirement document does not make any assumption on
   the type of bandwidth pool used for P2MP TE LSPs which can either be
   shared with P2P TE LSP or be dedicated for P2MP use.

4.9 Variation of LSP Parameters

   Various parameters to an LSP (such as priority, bandwidth, etc.) are
   signaled along each branch of the LSP.

   Any solution MUST NOT allow for variance of these parameters. That
   is,
   - no attributes set and signaled by the ingress of a P2MP LSP may be
     varied by downstream LSRs
   - there MUST be homogeneous QoS from the root to all leaves.

   THIS IS A PROVISIONAL REQUIREMENT STILL OPEN FOR DISCUSSION.

4.10 Re-optimization of P2MP TE LSPs

   The detection of a more optimal path (for example, one with a lower
   overall cost) is an example of a situation where P2MP TE LSP
   re-routing may be required. While re-routing is in progress, an
   important requirement is avoiding double bandwidth reservation
   (over the common parts between the old and new LSP) thorough the use
   of resource sharing.

   Make-before-break MUST be supported for a P2MP TE LSP to ensure that
   there is minimal traffic disruption when the P2MP TE LSP is
   re-routed.

   It is possible to achieve make-before-break that only applies to a
   sub-P2MP tree without impacting the data on all of the other parts
   of the P2MP tree.




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   The solution SHOULD allow for make-before-break re-optimization of
   any subdivision of the P2MP LSP (S2L sub-tree, S2X sub-LSP, S2L
   sub-LSP, X2L sub-tree, B2L sub-tree, X2L tree, or B2L tree) with no
   impact on the rest of the P2MP LSP (no label reallocation, no change
   in identifiers, etc.).

   The solution SHOULD also provide the ability for the ingress LSR to
   have a strict control on the re-optimization process.
   Such re-optimization MAY be initiated by the sub-tree root branch
   node (that is, the branch node MAY setup a new sub-tree, then splice
   traffic on the new subtree and delete the former sub-tree).

   THE REQUIREMENT FOR RE-OPTIMIZATION BY SUB-TREE ROOT BRANCH IS
   STILL OPEN FOR DISCUSSION

4.11 Tree Remerge

   It is possible for a single transit LSR to receive multiple
   signaling messages for the same P2MP LSP but for different
   sets of destinations. These messages may be received from the
   same or different upstream nodes and may need to be passed on
   to the same or different downstream nodes.

   This situation may arise as the result of the signaling solution
   definition or implementation options within the signaling
   solution. Further, it may happen during make-before-break
   reoptimization (section 4.10), or as a result of signaling
   message fragmentation (section 4.5).

   It is even possible that it is necessary to construct distinct
   upstream branches in order to achieve the correct label choices
   in certain switching technologies managed by GMPLS (for example,
   photonic cross-connects where the selection of a particular
   lambda for the downstream branches is only available on different
   upstream switches).

   The solution MUST handle the case where multiple signaling
   messages for the same P2MP LSP are received at a single transit
   LSR with the end result of all receivers being added to the
   P2MP LSP.

   THIS REQUIREMENT IS STILL UNDER DISCUSSION





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4.12 Data Duplication

   Data duplication refers to the receipt by any recipient of duplicate
   instances of the data. In a packet environment this means the
   receipt of duplicate packets - although this should be a benign (if
   inefficient) situation, it may be catastrophic in certain existing
   and deployed applications. In a non-packet environment this means
   the duplication in time of some part of the signal that may lead to
   the replication of data or to the scrambling of data.

   Data duplication may legitimately arise in various scenarios
   including re-optimization of active LSPs as described in the
   previous section, and protection of LSPs. Thus, it is impractical to
   regulate against data duplication in this document.

   Instead, the solution MUST provide a mechanism to resolve, limit or
   avoid data duplication at either or both of:
   - the point at which the data path diverges
   - the point at which the data paths converge.

   THE EXTENT TO WHICH DATA DUPLICATION MAY BE TOLERATED (in time or in
   a count of bits or packets) IS FOR FURTHER STUDY.

4.13 IPv4/IPv6 support

   Any P2MP TE solution MUST be equally applicable to IPv4 and IPv6.

4.14 P2MP MPLS Label

   A P2MP TE solution MUST support establishment of both P2P and P2MP
   TE LSPs and MUST NOT impede the operation of P2P TE LSPs within the
   same network. A P2MP TE solution MUST be specified in such a way
   that it allows P2MP and P2P TE LSPs to be signaled on the same
   interface. Labels for P2MP TE LSPs and P2P TE LSPs MAY be assigned
   from shared or dedicated label space(s). Label space shareability is
   implementation specific.

4.15 Routing advertisement of P2MP capability

   Several high-level requirements have been identified to determine
   the capabilities of LSRs within a P2MP network. The aim of such
   information is to facilitate the computation of P2MP trees using TE
   constraints within a network that contains LSRs that do not all have
   the same capabilities levels with respect to P2MP signaling and data
   forwarding.



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   These capabilities include, but are not limited to:

   - the ability of an LSR to support branching.
   - the ability of an LSR to act as an egress and a branch for the
     same LSP.
   - the ability of an LSR to support P2MP MPLS-TE signaling.

   It is expected that it may be appropriate to gather this information
   through extensions to TE IGPs (see [RFC3630] and [IS-IS-TE]), but
   the precise requirements and mechanisms are out of the scope of this
   document. It is expected that a separate document will cover this
   requirement.

4.16 Multi-Area/AS LSP

   P2MP TE solutions SHOULD support multi-area/AS P2MP TE LSPs.

   The precise requirements in support of multi-area/AS P2MP TE LSPs is
   out of the scope of this document. It is expected that a separate
   document will cover this requirement.

4.17 Multi-access LANs

   P2MP MPLS TE may be used to traverse network segments that are
   provided by multi-access media such as Ethernet. In these cases, it
   is also possible that the entry point to the network segment is a
   branch point of the P2MP LSP.

   Two options clearly exist:

    - the branch point replicates the data and transmits multiple
      copies onto the segment
    - the branch point sends a single copy of the data to the segment
      and relies on the exit points to discriminate the reception of
      the data.

   The first option has a significant scaling issue since all
   replicated data must be sent through the same port and carried on
   the same segment. Thus, a solution SHOULD provide a mechanism for a
   branch node to send a single copy of the data onto a multi-access
   network and reach multiple (adjacent) downstream nodes.





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4.18 P2MP MPLS OAM

   Management of P2MP LSPs is as important as the management of P2P
   LSPs.

   The MPLS and GMPLS MIB modules MUST be enhanced to provide P2MP TE
   LSP management.

   In order to facilitate correct management, P2MP TE LSPs MUST have
   unique identifiers.

   OAM facilities will have special demands in P2MP environments
   especially within the context of tracing the paths and connectivity
   of P2MP TE LSPs. The precise requirements and mechanisms for OAM are
   out of the scope of this document. It is expected that a separate
   document will cover these requirements.

4.19 Scalability

   Scalability is a key requirement in P2MP MPLS systems. Solutions
   MUST be designed to scale well with an increase in the number of any
   of the following:

   - the number of recipients
   - the number of branch points
   - the number of branches.

   Both scalability of performance and operation MUST be considered.

   Key considerations SHOULD include:
   - the amount of refresh processing associated with maintaining
     a P2MP TE LSP.
   - the amount of protocol state that must be maintained by ingress
     and transit LSRs along a P2MP tree.
   - the number of protocol messages required to set up or tear down a
     P2MP LSP as a function of the number of egress LSRs.
   - the number of protocol messages required to repair a P2MP LSP
     after failure or perform make-before-break.
   - the amount of protocol information transmitted to manage
     a P2MP TE LSP (i.e. the message size).
   - the amount of potential routing extensions.
   - the amount of control plane processing required by the ingress,
     transit and egress LSRs to add/delete a branch LSP to/from an
     existing P2MP LSP.

   It is expected that the applicability of each solution will be
   evaluated with regards to the aforementioned scalability criteria.


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4.19.1 Absolute Limits

   THIS IS SECTION DESCRIBES PROVISIONAL REQUIREMENTS STILL OPEN FOR
   DISCUSSION.

   In order to achieve the best solution for the problem space it is
   helpful to clarify the boundaries for P2MP TE LSPs.

   - Number of recipients.
     A P2MP TE LSP MUST reduce to similar scaling properties as a P2P
     LSP when the number of recipients reduces to one.
     It is important to classify the problem as a Traffic Engineering
     problem. It is anticipated that the initial deployments of P2MP TE
     LSPs may be limited to only several hundred recipients, but also
     that future deployments may require significantly larger numbers.
     An acceptable solution, therefore, is one that scales linearly
     with the number of recipients.

     Solutions that scale worse than linear (that is, exponential or
     polynomial) are not acceptable whatever the number of recipients
     they could support

   - Number of branch points.
     Solutions MUST support all possibilities from one extreme of a
     single branch point that forks to all leaves on a separate branch,
     to the greatest number of branch points which is (n-1) for n
     recipients. Assumptions MUST NOT be made in the solution regarding
     which topology is more common, and the solution MUST be designed
     to ensure scalability in all topologies.

   - Dynamics of P2MP tree.
     Recall that the mechanisms for determining which recipients should
     be added to an LSP, and for adding and removing recipients from
     that group are out of the scope of this document. Nevertheless, it
     is useful to understand the expected rates of arrival and
     departure of recipients since this can impact the selection of
     solution techniques.
     Again, it must be recalled that this document is limited to Traffic
     Engineering, and in this model the rate of change of recipients
     may be expected to be lower than in an IP multicast group.
     Although the absolute number of recipients coming and going is the
     important element for determining the scalability of a solution,
     it may be noted that a percentage may be a more comprehensible
     measure but that this is not as significant for LSPs with a small
     number of recipients.
     A working figure for an established P2MP TE LSP is less than 10%
     churn per day. That is, a relatively slow rate of churn.
     We could say that a P2MP LSP would be shared by multiple multicast


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     groups and dynamics of P2MP LSP would be relatively small.
     Considering applicability that P2MP LSP to use L2 multi-access
     path technology, we can consider stable P2MP L2 path even when we
     transfer IP multicast traffic over the path.

     Solutions MUST optimize around such relatively low rates of change
     and are NOT REQUIRED to optimize for significantly higher rates
     of change.

   - Rate of change within the network.
     It is also important to understand the scaling with regard to
     changes within the network. That is, one of the features of a
     P2MP TE LSP is that it can be robust or protected against network
     failures, and can be re-optimized to take advantage of newly
     available network resources.

     It is more important that a solution be optimized for scaling with
     respect to recovery and re-optimization of the LSP, than for change
     in the recipients, because P2MP is used as a TE tool.
     The solution MUST follow this distinction.

4.20 Backwards Compatibility

   It SHOULD be an aim of any P2MP solution to offer as much backward
   compatibility as possible. An ideal which is probably impossible to
   achieve would be to offer P2MP services across legacy MPLS networks
   without any change to any LSR in the network.

   If this ideal cannot be achieved, the aim SHOULD be to use legacy
   nodes as both transit non-branch LSRs and egress LSRs.

   It is a further requirement for the solution that any LSR that
   implements the solution SHALL NOT be prohibited by that act from
   supporting P2P TE LSPs using existing signaling mechanisms. That is,
   unless administratively prohibited, P2P TE LSPs MUST be supported
   through a P2MP network.

   Also, it is a requirement that P2MP TE LSPs MUST be able to co-exist
   with IP unicast and IP multicast networks.






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4.21 GMPLS

   The requirement for P2MP services for non-packet switch interfaces
   is similar to that for PSC interfaces. Therefore, it is a requirement
   that reasonable attempts must be made to make all the features/
   mechanisms (and protocol extensions) that will be defined to provide
   MPLS P2MP TE LSPs equally applicable to P2MP PSC and non-PSC TE-LSPs.
   If the requirements of non-PSC networks over-complicate the PSC
   solution a decision may be taken to separate the solutions. This
   decision must be taken in full consultation with the MPLS and CCAMP
   working groups.

   Solutions for MPLS P2MP TE-LSPs when applied to GMPLS P2MP PSC or
   non-PSC TE-LSPs MUST be backward and forward compatible with the
   other features of GMPLS including:

   - control and data plane separation (IF_ID RSVP_HOP and IF_ID
     ERROR_SPEC),
   - full support of numbered and unnumbered TE links (see [RFC 3477]
     and [GMPLS-ROUTE]),
   - use of the GENERALIZED_LABEL_REQUEST, the GENERALIZED_LABEL
     (C-Type 2 and 3), the SUGGESTED_LABEL and the RECOVERY_LABEL,
     in conjunction with the LABEL_SET and the ACCEPTABLE_LABEL_SET
     object,
   - processing of the ADMIN_STATUS object,
   - processing of the PROTECTION object,
   - support of Explicit Label Control,
   - processing of the Path_State_Removed Flag,
   - handling of Graceful Deletion procedures.
   - E2E and Segment Recovery procedures.
   - support of Graceful Restart

   In addition, since non-PSC TE-LSPs may have to be processed in
   environments where the "P2MP capability" could be limited, specific
   constraints may also apply during the P2MP TE Path computation.
   Being technology specific, these constraints are outside the scope
   of this document. However, technology independent constraints
   (i.e. constraints that are applicable independently of the LSP
   class) SHOULD be allowed during P2MP TE LSP message processing.
   It has to be emphasized that path computation and management
   techniques shall be as close as possible to those being used for
   PSC P2P TE LSPs and P2MP TE LSPs.





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4.22 Requirements for Hierarchical P2MP TE LSPs

   [LSP-HIER] defines concepts and procedures for P2P LSP hierarchy.

   The P2MP MPLS-TE solution SHOULD support the concept of region and
   region hierarchy (PSC1<PSC2<PSC3<PSC4<L2SC<TDM<LSC<FSC).

   Particularly it SHOULD allow a Region i P2MP TE LSP to be nested
   into a region j P2MP TE LSP or multiple region j P2P TE LSPs,
   providing that i<j.

   The precise requirements and mechanisms for this function are out of
   the scope of this document. It is expected that a separate document
   will cover these requirements.

4.23 P2MP Crankback routing

   P2MP solutions SHOULD support crankback requirements as defined in
   [CRANKBACK]. In particular, they SHOULD provide sufficient
   information to a branch LSR from downstream LSRs to allow the branch
   LSR to re-route a sub-tree around any failures or problems in the
   network.

5. Security Considerations

   This requirements document does not define any protocol extensions
   and does not, therefore, make any changes to any security models.

   It should be noted that P2MP signaling mechanisms built on P2P
   RSVP-TE signaling are likely to inherit all of the security
   techniques and problems associated with RSVP-TE. These problems may
   be exacerbated in P2MP situations where security relationships may
   need to maintained between an ingress and multiple egresses. Such
   issues are similar to security issues for IP multicast.

   It is a requirement that documents offering solutions for P2MP LSPs
   MUST have detailed security sections.

6. Acknowledgements

   The authors would like to thank George Swallow, Ichiro Inoue, Dean
   Cheng, Lou Berger and Eric Rosen for their review and suggestions.





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7. References

7.1 Normative References

   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2475]     Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
                 and W. Weiss,  "An Architecture for Differentiated
                 Services", RFC 2475, December 1998.

   [RFC2597]     Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
                 "Assured Forwarding PHB Group", RFC 2597, June 1999.

   [RFC2702]     D. Awduche, J. Malcolm, J. Agogbua, M. O'Dell, J.
                 McManus, "Requirements for Traffic Engineering Over
                 MPLS", RFC2702, September 1999.

   [RFC3031]     Rosen, E., Viswanathan, A. and R. Callon,
                 "Multiprotocol Label Switching Architecture", RFC 3031,
                 January 2001.

   [RFC3209]     Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
                 V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
                 Tunnels", RFC 3209, December 2001.

   [RFC3246]     Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le
                 Boudec, J.Y., Davari, S., Courtney, W., Firioiu, V. and
                 D. Stiliadis, "An Expedited Forwarding PHB (Per-Hop
                 Behavior)", RFC 3246, March 2002.

   [RFC3667]     Bradner, S., "IETF Rights in Contributions", BCP 78,
                 RFC 3667, February 2004.

   [RFC3668]     Bradner, S., Ed., "Intellectual Property Rights in IETF
                 Technology", BCP 79, RFC 3668, February 2004.

7.2 Informational References

   [RFC3471]     Berger, L., Editor, "Generalized Multi-Protocol Label
                 Switching (GMPLS) Signaling Functional Description",
                 RFC 3471, January 2003.

   [RFC3473]     Berger, L., Editor, "Generalized Multi-Protocol Label
                 Switching (GMPLS) Signaling - Resource ReserVation
                 Protocol-Traffic Engineering (RSVP-TE) Extensions",
                 RFC 3473, January 2003.


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Internet Draft draft-ietf-mpls-p2mp-sig-requirement-00.txt December 2004

   [RFC3477]     K. Kompella, Y. Rekhter, "Signalling Unnumbered Links
                 in Resource ReSerVation Protocol -Traffic Engineering
                 (RSVP-TE)", RFC3477, January 2003.

   [RFC3564]     F. Le Faucheur, W. Lai, "Requirements for Support of
                 Differentiated Services-aware MPLS Traffic
                 Engineering", RFC 3564, July 2003.

   [RFC3630]     D. Katz, D. Yeung, K. Kompella, "Traffic Engineering
                 Extensions to OSPF Version 2", RFC 3630, September
                 2003.

   [GMPLS-ROUTE] K. Kompella, Y. Rekhter,  Editor, "Routing Extensions
                 in Support of Generalized Multi-Protocol Label
                 Switching", draft-ietf-ccamp-gmpls-routing-09.txt,
                 October 2003.

   [STEINER]     H. Salama, et al., "Evaluation of Multicast Routing
                 Algorithm for Real-Time Communication on High-Speed
                 Networks," IEEE Journal on Selected Area in
                 Communications, pp.332-345, 1997.

   [FRR]         P. Pan, G. Swallow, A. Atlas, "Fast Reroute Extensions
                 to RSVP-TE for LSP Tunnels",
                 draft-ietf-mpls-rsvp-lsp-fastreroute-07.txt,
                 August 2004.

   [IS-IS-TE]    Henk Smit, Tony Li, "Intermediate System to
                 Intermediate System (IS-IS) Extensions for Traffic
                 Engineering (TE)", RFC 3784, June 2004.

   [CRANKBACK]   A. Farrel, A. Satyanarayana, A. Iwata, N. Fujita, G.
                 Ash, S. Marshall, "Crankback Signaling Extensions for
                 MPLS Signaling", draft-ietf-ccamp-crankback-03.txt,
                 July 2004.

   [LSP-HIER]    K. Kompella, Y. Rekhter, "LSP Hierarchy with
                 Generalized MPLS TE",
                 draft-ietf-mpls-lsp-hierarchy-08.txt, September 2002.






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8. Editor's Address

   Seisho Yasukawa
   NTT Corporation
   9-11, Midori-Cho 3-Chome
   Musashino-Shi, Tokyo 180-8585,
   Japan
   Phone: +81 422 59 4769
   Email: yasukawa.seisho@lab.ntt.co.jp

9. Authors' Addresses

   Dimitri Papadimitriou
   Alcatel
   Francis Wellensplein 1,
   B-2018 Antwerpen,
   Belgium
   Phone : +32 3 240 8491
   Email: dimitri.papadimitriou@alcatel.be

   JP Vasseur
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough, MA 01719,
   USA
   Email: jpv@cisco.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

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

   Alan Kullberg
   Motorola Computer Group
   120 Turnpike Rd.
   Southborough, MA 01772
   Email: alan.kullberg@motorola.com


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   Adrian Farrel
   Old Dog Consulting
   Phone: +44 (0) 1978 860944
   Email: adrian@olddog.co.uk

   Markus Jork
   Avici Systems
   101 Billerica Avenue
   N. Billerica, MA 01862
   Phone: +1 978 964 2142
   Email: mjork@avici.com

   Andrew G. Malis
   Tellabs
   2730 Orchard Parkway
   San Jose, CA 95134
   Phone: +1 408 383 7223
   Email: andy.malis@tellabs.com

   Jean-Louis Le Roux
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   France
   Email: jeanlouis.leroux@francetelecom.com

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   Copies of IPR disclosures made to the IETF Secretariat and any
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   at http://www.ietf.org/ipr.




Yasukawa, et. al.                                              [Page 29]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-00.txt December 2004

   The IETF invites any interested party to bring to its attention
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11. Full Copyright Statement

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Yasukawa, et. al.                                              [Page 30]
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