Subject: [mpls] Fw: [Gen-art] Marked-up copy of draft-ietf-mpls-p2mp-sig-requirement-03 (fwd)

From: "Adrian Farrel" <[email-masked]>
Date: Wed, 30 Nov 2005 19:41:14 -0000

I didn't notice a copy of this added to the MPLS archive, so here it is.

These are Harald's detailed comments in addition to the high-level points
already discussed.

Seisho and I have been working on responses which will show up soon.

Cheers,
Adrian
---------- Forwarded Message ----------
Date: 22. november 2005 16:10 +0100
From: Harald Tveit Alvestrand <[email-masked]>
To: [email-masked], [email-masked], Bill Fenner
<[email-masked]>, Alex Zinin <[email-masked]>, [email-masked],
[email-masked]
Cc: INVALID_ADDRESS
Subject: [Gen-art] Marked-up copy of
draft-ietf-mpls-p2mp-sig-requirement-03

I'm sending this to the editor, the WG chairs, the ADs and the gen-art
list
(for archiving). Feel free to circulate further.
Most of the comments are "make this clearer, please", or "I can't see that
this adds anything - suggest deleting". The main technical comments are
repeats from my other message.

Comments are marked with HTA:

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

            Signaling Requirements for Point to Multipoint
                     Traffic Engineered MPLS LSPs

            <draft-ietf-mpls-p2mp-sig-requirement-03.txt>

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

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.

   The requirements presented in this document are
   not limited to the requirements of packet switched networks, but also
   encompass the requirements of Layer two Switching (L2SC), Time
   Division Multiplexing (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.

HTA: The last para reads oddly. I'd start it:

   The requirements presented in this document cover provisioning of the
   P2MP service on packet switched networks, Layer Two Switching.....

S. Yasukawa (Ed.)                                               [Page 1]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   Table of Contents

   1. Introduction ................................................... 3
      1.1 Non-Objectives ............................................. 5
   2. Definitions .................................................... 6
      2.1 Acronyms ................................................... 6
      2.2 Terminology ................................................ 6
         2.2.1 Terminology for Partial LSPs .......................... 7
      2.3 Conventions ................................................ 8
   3. Problem Statement .............................................. 8
      3.1 Motivation ................................................. 8
      3.2. Requirements Overview ..................................... 9
   4. Detailed requirements for P2MP TE extensions .................. 11
      4.1 P2MP LSP  ................................................. 11
      4.2 P2MP explicit routing ..................................... 11
      4.3 Explicit Path Loose Hops and Widely Scoped Abstract Nodes . 12
      4.4 P2MP TE LSP establishment, teardown, and modification
          mechanisms ................................................ 13
      4.5 Fragmentation ............................................. 14
      4.6 Failure Reporting and Error Recovery ...................... 14
      4.7 Record route of P2MP TE LSP  .............................. 15
      4.8 Call Admission Control (CAC) and QoS Control mechanism
          of P2MP TE LSPs ........................................... 16
      4.9 Variation of LSP Parameters ............................... 16
      4.10 Re-optimization of P2MP TE LSPs .......................... 16
      4.11 Tree Remerge ............................................. 17
      4.12 Data Duplication ......................................... 18
      4.13 IPv4/IPv6 support ........................................ 19
      4.14 P2MP MPLS Label .......................................... 19
      4.15 Routing advertisement of P2MP capability ................. 19
      4.16 Multi-access LANs ........................................ 20
      4.17 P2MP MPLS OAM ............................................ 20
      4.18 Scalability .............................................. 20
         4.18.1 Absolute Limits ..................................... 21
      4.19 Backwards Compatibility .................................. 23
      4.20 GMPLS .................................................... 23
      4.21 P2MP Crankback routing ................................... 24
   5. Security Considerations ....................................... 24
   6. IANA Considerations ........................................... 25
   7. Acknowledgements .............................................. 25
   8. References .................................................... 25
      8.1 Normative References ...................................... 25
      8.2 Informational References .................................. 26
   9. Editor's Address .............................................. 27
   10. Authors' Addresses ........................................... 27
   11. Intellectual Property Consideration .......................... 28
   12. Full Copyright Statement ..................................... 29

S. Yasukawa (Ed.)                                               [Page 2]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

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 point-to-multipoint (P2MP)
   services using traffic engineered LSPs and this clearly motivates
   enhancements of the base MPLS-TE tool box in order to support P2MP
   MPLS-TE LSPs.

HTA: English unhappy. Are you trying to say "This document defines
requiremnets" or "Some people have expressed requirements, therefore this
document tries to specify some"?

HTA: This would be an appropriate place to define what you mean by a P2MP
service - what I said in my other note that I was missing.
Note that huge chunks of this document use the term "tree" liberally - but
in section 4.11 you talk about "tree remerge" - which makes the tree be
not
a tree. This is confusing; if you assume a tree-shaped pattern, with no
merges, you should say so up front; if not, you should avoid the term
"tree".

   [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.

HTA: Not all definitions of 2702 are appropriate for P2MP. For instance,
atomic establishment of bidirectional traffic trunks are not. I'd stick
with "definitions" and drop "objectives".

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

HTA: You might want to refer to section 3.0 of [RFC2702] - since the
formatting in 2702 is messed up, it's hard to find it.....

      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. Note that
   point 3. implies that the concept of a point-to-multipoint traffic
   trunk is defined and is supported (or mapped onto) P2MP LSPs.
HTA: Supported or mapped onto? I think it wiser to stick to "mapped onto"
only.

   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.

   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

S. Yasukawa (Ed.)                                               [Page 3]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   [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.

   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.

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

   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.

HTA: Same comment as in abstract.

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

   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 mechanisms.

   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.

HTA: These three paragraphs add no information - neither make requirements
nor make the problem easier to understand. Suggest removing.

   This requirements document assumes the following conditions for P2MP
   MPLS TE LSP establishment and maintenance:

   o 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. Although replication is a data plane issue, it is the
     responsibility of the control plane (acting in conjunction with the
     path computation component) to install LSPs in the network such
     that replication can be performed efficiently. Note that the notion
     of "efficient" replication is relative and may have different
     meanings depending on the objectives (see section 4.2).

S. Yasukawa (Ed.)                                               [Page 4]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

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

   o Tunnel endpoints of P2MP TE LSP will be modified by adding/removing
     egress LSRs to/from an existing P2MP TE LSP. It is assumed that the
HTA: English - "Tunnel endpoints" is different from "receivers" how?
I can't see the difference between the first bullet and the first sentence
of this bullet. Don't repeat if you can avoid it....
     rate of change of leaves of a P2MP service (that is, the rate at
     which new egress LSRs join, or old egress LSRs are pruned) is "not
     so high" because P2MP TE LSPs are assumed to be utilized for TE
     applications. This issue is discussed at greater length in section
     4.18.1.
HTA: Since "TE applications" is undefined, this adds no information. I'd
stick a number in here (10 join/leaves per day) and leave it at that.

   o A P2MP TE LSP will be protected by fast error recovery mechanisms
HTA: "will be" or "may be"? I think "may be" is right(er).
     to minimize disconnection of a P2MP service. And a set of
     attributes of the P2MP TE LSP (e.g. bandwidth etc) will be modified
     by some mechanism (e.g. Make-before-break etc) to accommodate
     attribute changes to the P2MP service.
HTA: I can't parse the sentence above, even though I think I know what it
says. Please rewrite.
     These issues are discussed
     in section 4.6 and 4.10.

   It is this document's objective that a solution compliant to the
   requirements equips and operates these P2MP TE capabilities in a
   scalable fashion.
HTA: This sentence says nothing. Remove?

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.

   The following are non-objectives of this document.
HTA: I don't understand this section. A "non-objective" may be understood
in multiple ways:
- This document places no requirement on the following things
- This document doesn't care whether or not these things occur in a
solution
- This document doesn't describe the details for the following things
I think it would be simpler if this section said "This document does not
specify any requirements for the following functions". In that case, the
"algorithms" point does not fit, and should be dropped.

   - 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

S. Yasukawa (Ed.)                                               [Page 5]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   - Multipoint-to-point LSPs
   - Multipoint-to-multipoint LSPs
   - Routing protocols
   - Construction of the traffic engineering database
   - Distribution 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].

   The following terms are defined for use in the context of TE LSPs
   only.
HTA: you mean "P2MP TE LSPs", not any TE LSPs, I think.

   P2MP tree:

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

   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.
HTA: Is there a distinction between the term "egress" and "egress LSR"?
The
terms are used somewhat inconsistently.

   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.

S. Yasukawa (Ed.)                                               [Page 6]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   graft LSR:

      An LSR that is already a member of the P2MP tree and is in
      process of signaling a new sub-P2MP tree.
HTA: I don't understand the term "signaling a new sub-P2MP tree". Do you
mean "signaling LSRs that are not currently members of the P2MP tree in
order to add a new subtree to the P2MP tree"?
Note - the term is not used in this document.

   prune LSR:

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

HTA: Also not clear.

   P2MP-ID (P2ID):

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

HTA: The term "receiver" is used, but does not appear to be defined.

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

HTA: This is unclear. Does the ingress LSR become a member of one
division,
or both?

   - 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.

HTA: This is also unclear. Is the tree divided at the link, or is the LSR
it's divided at become part of both subsections?

   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
HTA: The definition of X2X below seems to indicate that by "transit", you
mean that a transit LSR does not branch the tree. This is, however, not
stated anywhere.
     All - A
     Partial (i.e. not all) - P

   Define a new term:

     Sub-LSP

       A segment of a P2MP TE LSP that runs from one of the LSP's LSRs
       to one or more of its other LSRs.

S. Yasukawa (Ed.)                                               [Page 7]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   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.

     S2PL sub-LSP
       The path from the source to a set of leaves.

     B2AL sub-LSP
       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.
HTA: If true, it means that the X constrains the 2 to be only X LSRs.
That's not described anywhere.

     Note that the S2AL sub-LSP is equivalent to the P2MP LSP.

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
HTA: The sentence above parses badly - I can't tell which level of
subparagraph the various commas belong to. Rewrite?
   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.
HTA: I think the proper term is "when defining mechanisms", not "to define
mechanisms".

S. Yasukawa (Ed.)                                               [Page 8]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

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.

HTA: The paragraph above repeats material from the introduction. Remove?

   A P2MP TE LSP path will be computed taking into account various
   constraints such as bandwidth, affinities, required level of
   protection and so on.
HTA: I dislike passive voice. Do you mean "The traffic engineering
solution
will be used to compute a P2MP path ..."?
   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.

   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
HTA: Would like to say "all the applicable TE LSP.." - see comment about
the establishment of bidirectional tunnels earlier.
   already defined for P2P TE LSP. Further, when new TE LSP procedures
   are developed for P2P TE LSPs equivalent or identical procedures
   SHOULD be developed for P2MP TE LSPs.
HTA: I think there's a comma before "equivalent". Without it, the sentence
is hard to parse.

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

S. Yasukawa (Ed.)                                               [Page 9]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   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.

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

      a) A P2MP tree which satisfies various constraints is
         pre-determined and supplied to ingress I-LSR1.
HTA: A description of a P2MP tree is supplied.. the tree itself is
established....

         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.
HTA: Delete "Note that" in the last sentence. You don't want to have
requirements language (SHOULD) inside a "Note that" sentence.

         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 B2L sub-LSP from
         LSR2 to E-LSR5 is grafted onto the P2MP TE LSP. LSR2 becomes a
         branch LSR.

HTA: It's unclear to me whether the requirements want to say anything
about
who does this - is it envisioned that R5 expresses the interest to either
S1 or I-LSR1, and that I-LSR1 initiates the change, or is it envisioned
that R5 can express interest straigtht to LSR2 or E-LSR5, without
involving
S1 or I-LSR1 in the process? The model in this document seems to tend
towards the first alternative, but the language does not rule out the
second - which I find highly confusing.

S. Yasukawa (Ed.)                                              [Page 10]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

4. Detailed requirements for P2MP TE extensions

4.1 P2MP LSP

   The P2MP TE extensions MUST be applicable to the signaling of LSPs
   for different switching types. For example, it MUST be possible to
   signal a P2MP TE LSP in any switching medium being packet or
   non-packet based (including frame, cell, TDM, lambda, 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.

   In order to scale to a large number of branches, P2MP TE LSPs SHOULD
   be identified by a unique identifier (the P2MP ID or P2ID) 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.

HTA: Suggest deleting the last sentence. It adds nothing, and confuses.

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 2 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 2 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

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   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 2). 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.

   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
   (that is, abstract nodes that are not simple [RFC3209]) 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.

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   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 and where policies along the path (such
   as at domain boundaries) support full specification.

   In all cases, the egress nodes of the P2MP TE LSP must be fully
   specified either individually or through some collective identifier.
   Without this information, it is impossible to know to where the TE
   LSP should be routed.

   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
   protocol mechanisms for the ingress LSR of the P2MP TE LSP to learn
   the full P2MP tree. Note that this information may not always be
   obtainable owing to policy considerations, but where part of the path
   remains confidential it MUST be reported through aggregation (for
   example, using an AS number).

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 manner that is at least scalable in a
   linear way. This MUST include both the existence of very many LSPs at
   once, and the existence of very many destinations for a single P2MP
   LSP.
HTA: "scalable in a linear way" is an awkward phrase. No suggested
rephrase.

   In addition to P2MP TE LSP establishment and teardown mechanism, it
   SHOULD implement partial P2MP tree modification mechanism.
HTA: The document varies between "support" and "implement". I suggest
sticking with "support". Also, it should be "a partial" since "mechanism"
is singular.

   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.
HTA: Suggest "that are not along the path" instead of "except along the
path". Also, capitalize MUST NOT - and "MUST NOT disrupt traffic" is
better
than "MUST not be traffic disruptive".

   There is no assumption that the explicitly routed P2MP LSP remains on
   an optimal path after several grafts and prunes have occurred. In
   this context, scalable refers to the signaling process for the P2MP
   TE LSP. The TE nature of the LSP allows that re-optimization may take
   place from time to time to restore the optimality of the LSP.

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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 of
   protocol messages and it is RECOMMENDED to rely on some protocol
   procedures specific to the signaling solution.

   In the event that fragmented IP packets containing protocol messages
   are received, it is NOT RECOMMENDED that they are reassembled at the
   receiving LSR.

HTA: This section is extremely strange, in that it seems to warn against a
particular choice in a particular solution - not stating the requirement
at
all. I'd suggest just saying

The solution MUST allow the establishing of large P2MP LSPs (with a large
number of LSRs and recipients being identified). Note that the set of
identified LSRs can grow at transit nodes.

and leave the packet sizes out of it entirely.

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
   [RFC4090] 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 [RFC4090] 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 [RFC4090], this requirement is limited to the
   subset of the solution space that applies to packet switched networks
   only.

   Note that the requirements expressed in this document are general to
   all MPLS TE P2MP signaling, and any solution that meets them will
   therefore be general. Specific applications may have additional
   requirements, or may want to relax some requirements stated in this

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   document. This may lead to variations in the solution.

   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.

   If the ingress is informed of the failure of delivery to fewer than
   all of the egress nodes this 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.

   When all egress nodes downstream of a branch node have become
   disconnected from the P2MP tree, and the some branch node is unable
HTA: "the some branch" does not parse.
   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 (that is, a
   bud). 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. An upstream LSR or
   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 4.21.

4.7 Record route of P2MP TE LSP

   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 [RFC4090]. A
   network operator uses this information to manage P2MP TE LSPs.
   Therefore the P2MP TE solution MUST support a mechanism which can
   collect and update P2MP tree topology information after P2MP LSP
   establishment and modification process.

   It is RECOMMENDED that the information is collected in a data format
   which allows easy recognition of the P2MP tree topology.

   The solution MUST support mechanisms for the recording of both
   outgoing interfaces and node-ids.

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   The solution MUST gracefully handle scaling issues concerned with the
   collection of P2MP tree information including the case where the
   collected information is too large to be carried in a single protocol
   message.

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.

   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

   Certain parameters (such as priority and bandwidth) are associated
   with an LSP. The parameters are installed by the signaling exchanges
   associated with establishing and maintaining the LSP.

   Any solution MUST NOT allow for variance of these parameters within
   a single P2MP LSP. 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 of a
     single P2MP LSP.

   Variation of parameters may be allowed so long as it applies to the
   whole LSP from ingress to all egresses.

HTA: The term "variation of parameters" is unclear to me.
This paragraph seems to say MUST NOT do one definition (value differs in
different parts of the tree) and MAY do another definition (value changes
for a whole tree over time). Using the same term for both is not a good
idea; stating the last sentence as "Changing the parameters for the whole
tree may be supported; the change applies to the whole tree from ingress
to
all egresses" avoids this.

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

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   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.
HTA: is this a requirement or not? I think the document says the same
thing
if this paragraph is deleted.

   The solution SHOULD allow for make-before-break re-optimization of
   any subdivision of the P2MP LSP (S2PL sub-LSP, S2X sub-LSP, S2L
   sub-LSP, X2AL sub-LSP, B2PL sub-LSP, X2AL sub-LSP, or B2AL tree).
   Further it SHOULD do so minimizing the signaling impact on the rest
   of the P2MP LSP, and without affecting the ability of the management
   plane to manage the LSP.

   The solution SHOULD also provide the ability for the ingress LSR to
   have a strict control on the re-optimization process. The ingress
HTA: control on -> control of
   LSR SHOULD be able to limit all re-optimization to be
   source-initiated.

   Where sub-LSP re-optimization is allowed by the ingress LSR, such
   re-optimization MAY be initiated by a downstream LSR that is the
   root of the sub-LSP that is to be re-optimized. Sub-LSP
   re-optimization initiated by a downstream LSR MUST be carried out
   with the same regard to minimizing the hit on active traffic as
HTA: hit on -> impact on (or) disruption of
   was described above for other re-optimization.

4.11 Tree Remerge

HTA: The term "remerge" is confusing. "Merging of tree branches"?

   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).
HTA: Section 4.5 doesn't say that..... suggest deleting this paragraph.

   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).

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   The solution MUST support the case where of multiple signaling
   messages for the same P2MP LSP are received at a single transit LSR
   and refer to the same upstream interface. In this case the result of
   the protocol procedures SHOULD be a single data flow on the upstream
   interface.

HTA: The more interesting question is whether there's a single data flow
on
the downstream interfaces - I think the answer is "yes".

   The solution SHOULD support the case where multiple signaling
   messages for the same P2MP LSP are received at a single transit LSR
   and refer to different upstream interfaces, and where each signaling
   message results in the use of different downstream interfaces. This
   case represents data flows that cross at the LSR but which do not
   merge.

   The solution MAY support the case where multiple signaling messages
   for the same P2MP LSP are received at a single transit LSR and refer
   to different upstream interfaces, and where the downstream interfaces
   are shared across the received signaling messages. This case
   represents the merging of data flows. A solution that supports this
   case MUST ensure that data is not replicated on the downstream
   interfaces.
HTA: The more interesting case here is where the two data streams from
upstream are almost, but not completely, identical - for instance,
exhibiting different patterns of packet loss or signal bit errors.
The other interesting case is where the set of recipients is overlapping,
but not identical.
I suspect that this will become the source of headaches.

   An alternative to supporting this last case is for the signaling
   protocol to indicate an error such that the merge may be resolved by
   the upstream LSRs.
HTA: And I think it's a preferred alternative.....

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 small-scale packet duplication
HTA: small-scale = duplicate all packets in a short interval, or duplicate
occasional packets at random? Different problems....
   should be a benign (if inefficient) situation, certain existing and
HTA: benign -> harmless
   deployed applications will not tolerate packet duplication. Long-term
HTA: term "Long-term" is not the best one....
   packet duplication is, at best, a waste of network and processing
   resources, and at worst may cause congestion and the inability to
   process the data correctly.

   In a non-packet environment data duplication 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.
HTA: I didn't understand that one...... perhaps delete?

   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:

   - SHOULD limit to bounded transitory conditions the cases where
     network bandwidth is wasted by the existence of duplicate delivery
     paths.

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   - MUST limit the cases where duplicate data is delivered to an
     application to bounded transitory conditions.

4.13 IPv4/IPv6 support

   Any P2MP TE solution MUST support IPv4 and IPv6 addressing.

4.14 P2MP MPLS Label

   A P2MP TE solution MUST allow the continued use of existing
   techniques to establish P2P LSPs (TE and otherwise) within the same
   network, and MUST allow the co-existence of P2P LSPs within the same
   network as P2MP TE LSPs.

   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.

4.15 Routing advertisement of P2MP capability

HTA: I find the term "routing" in the title confusing. Just "Advertising"
would be enough.

   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.

   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.

4.16 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.
HTA: discriminate the reception of -> select which data to receive

   The first option has a significant data plane 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

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   branch node to send a single copy of the data onto a multi-access
   network and reach multiple (adjacent) downstream nodes. The second
   option may have control plane scaling issues.

4.17 P2MP MPLS OAM

   The MPLS and GMPLS MIB modules will be enhanced to provide P2MP TE
   LSP management in line with whatever signaling solutions are
   developed.
HTA: This sentence seems out of place. Remove?
If not - reformulate as "A solution should specify extensions to the MPLS
and GMPLS MIB modules to provide...."

   In order to facilitate correct management, P2MP TE LSPs MUST have
   unique identifiers since otherwise it is impossible to determine
   which LSP is being managed.

   Further discussions of OAM are out of scope for this document.
   See [P2MP-OAM] for more details.

4.18 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 control plane operation (setup, maintenance,
   modification and teardown) MUST be considered.

   Key considerations MUST 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 additional data distributed in potential routing
     extensions.
   - the amount of additional control plane processing required in
     the network to detect whether an add/delete of a new branch is
     required, and in particular, the amount of processing in steady
     state when no add/delete is requested
   - 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.

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

4.18.1 Absolute Limits

   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 scaling bound is placed on the solution mechanism such that a
     P2MP TE LSP MUST reduce to similar scaling properties as a P2P LSP
     when the number of recipients reduces to one.
HTA: Is this a convoluted way of saying "Establishing a P2MP TE LSP to a
single recipient should cost approximately as much as establishing a P2P
LSP"? If not, I don't understand it....

     It is important to classify the issues of scaling within the
     context of Traffic Engineering. It is anticipated that the initial
     deployments of P2MP TE LSPs will be limited to a maximum of around
     a hundred recipients, but that medium term deployments may increase
     this to several hundred, and that future deployments may require
     significantly larger numbers.
HTA: Define "medium term"? A year? Five years?

     An acceptable upper bound for a solution, therefore, is one that
     scales linearly with the number of recipients. It is expected that
     solutions will scale better than linearly.

     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.
HTA: "branch point" is not well defined. Use "branch LSR"?

   - 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 LSP
     egresses may be expected to be lower than the rate of change of
     recipients in an IP multicast group.

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     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
     groups and so the dynamics of the P2MP LSP would be relatively
     small.

     Solutions MUST optimize around such relatively low rates of change
     and are NOT REQUIRED to optimize for significantly higher rates
     of change.
HTA: "optimize around" is not well defined, so it's dangerous to have a
MUST there. Suggest "work well with" instead.
"NOT REQUIRED" is a hard-to-parse use of RFC 2119 language (logically it
means the same as MAY). I suggest downcasing it.

   - 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
HTA: I don't think there should be a comma on the line above.
     in the recipients, because P2MP is used as a TE tool.

     The solution MUST follow this distinction.
HTA: Not clear that this has meaning. Suggest deleting the sentence.

4.19 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.

S. Yasukawa (Ed.)                                              [Page 22]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

4.20 GMPLS

   The requirement for P2MP services for non-packet switch interfaces
   is similar to that for Packet-Switch Capable (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.

   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:

HTA: The term "backward and forward compatible" is, IMHO, meaningless.
The long list of specific RSVP-TE constructs below is, IMHO,
inappropriate.

   - 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.

4.21 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-LSP around any failures or problems in the
   network.

S. Yasukawa (Ed.)                                              [Page 23]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

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.

HTA: I think this section needs more work. It doesn't say anything about
what the security requirements are for solutions in this space.

6. IANA Considerations

   This informational draft does not introduce any new encodings or code
   points. It requires no action from IANA.

7. Acknowledgements

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

   Thanks to Loa Andersson for his help resolving the final issues in
   this document.

8. References

8.1 Normative References

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

   [RFC2205]     Braden, R., Zhang, L., Berson, S., Herzog, S. and
                 S. Jamin, "Resource ReSerVation Protocol (RSVP) -
                 Version 1, Functional Specification", RFC 2205,
                 September 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.

S. Yasukawa (Ed.)                                              [Page 24]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   [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.

8.2 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.

   [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.

   [RFC4090]     P. Pan, G. Swallow, A. Atlas, "Fast Reroute Extensions
                 to RSVP-TE for LSP Tunnels", RFC 4090, May 2005.

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

S. Yasukawa (Ed.)                                              [Page 25]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   [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.

   [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, work in
                 progress.

   [LSP-HIER]    K. Kompella, Y. Rekhter, "LSP Hierarchy with
                 Generalized MPLS TE",
                 draft-ietf-mpls-lsp-hierarchy, work in progress.

   [P2MP-OAM]    S. Yasukawa, A. Farrel, D. King, and T. Nadeau, "OAM
                 Requirements for Point-to-Multipoint MPLS Networks",
                 draft-yasukawa-mpls-p2mp-oam-reqs, work in progress.

9. 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: [email-masked]

10. Authors' Addresses

   Dimitri Papadimitriou
   Alcatel
   Francis Wellensplein 1,
   B-2018 Antwerpen,
   Belgium
   Phone : +32 3 240 8491
   Email: [email-masked]

   JP Vasseur
   Cisco Systems, Inc.
   300 Beaver Brook Road
   Boxborough, MA 01719,
   USA
   Email: [email-masked]

S. Yasukawa (Ed.)                                              [Page 26]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   Yuji Kamite
   NTT Communications Corporation
   Tokyo Opera City Tower
   3-20-2 Nishi Shinjuku, Shinjuku-ku,
   Tokyo 163-1421,
   Japan
   Email: [email-masked]

   Rahul Aggarwal
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale, CA 94089
   Email: [email-masked]

   Alan Kullberg
   Motorola Computer Group
   120 Turnpike Rd.
   Southborough, MA 01772
   Email: [email-masked]

   Adrian Farrel
   Old Dog Consulting
   Phone: +44 (0) 1978 860944
   Email: [email-masked]

   Markus Jork
   Quarry Technologies
   8 New England Executive Park
   Burlington, MA 01803
   EMail: [email-masked]

   Andrew G. Malis
   Tellabs
   2730 Orchard Parkway
   San Jose, CA 95134
   Phone: +1 408 383 7223
   Email: [email-masked]

   Jean-Louis Le Roux
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   France
   Email: [email-masked]

11. Intellectual Property Consideration

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed
   to pertain to the implementation or use of the technology
   described in this document or the extent to which any license

S. Yasukawa (Ed.)                                              [Page 27]

Internet Draft draft-ietf-mpls-p2mp-sig-requirement-03.txt     June 2005

   under such rights might or might not be available; nor does it
   represent that it has made any independent effort to identify any
   such rights.  Information on the procedures with respect to rights
   in RFC documents can be found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use
   of such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository
   at http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention
   any copyrights, patents or patent applications, or other
   proprietary rights that may cover technology that may be required
   to implement this standard.  Please address the information to the
   IETF at [email-masked].

12. Full Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is
   subject to the rights, licenses and restrictions contained in BCP
   78, and except as set forth therein, the authors retain all their
   rights.

   This document and the information contained herein are provided
   on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
   THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
   ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
   PARTICULAR PURPOSE.

S. Yasukawa (Ed.)                                              [Page 28]

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