[Pce] Re: draft-ietf-pce-pcecp-interarea-reqs-03.txt
"Adrian Farrel" <adrian@olddog.co.uk> Sat, 28 October 2006 11:30 UTC
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From: Adrian Farrel <adrian@olddog.co.uk>
To: Jean-Louis Le Roux <jeanlouis.leroux@orange-ft.com>
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Subject: [Pce] Re: draft-ietf-pce-pcecp-interarea-reqs-03.txt
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Hi, Hot on the heals of JP's comment, here are my thoughts on this draft. None of the issues is sufficiently large to warrant a respin before WG last call, but if you have time over the next two weeks it would be nice for people to have a clean copy to review immediately after San Diego. Thanks, Adrian Minor === Section 3 It is expected that a solution for a PCECP satisfies these requirements. What do we mean here exactly? I think that we mean... Any PCECP solution MUST satisfy the requirements of [RFC4657] and MUST either satisfy the requirements specified in this document of MUST be readily extensible to satisfy these requirements. --- Section 5.1 I think you need to require a failure reason that says "can't compute intra-area path to destination" --- Section 5.2 Hence the response message MUST support the inclusion of the identifiers of the crossed areas and MUST allow identifying the corresponding path segments. Can you add a few words to clarify? What you are asking for is that the returned path be segmented and marked so that it is possible to tell which pieces of the path lie within which area? --- Section 5.4 Need to clarify the intent of the list of preferred PCEs. Is there a requirement that only these PCEs will be used? Is there a requirement that all of these PCEs will be tried before any other is tried? Is there a linkage between the preferred PCEs and the IGP areas? although these questions do not impact on the bits and bytes of the protocol extensions that would be defined, they do change how the protocol procedure extensions will be defined, so you must say something here. --- Section 5.6 I think that for completeness and to ensure that the protocol meets your requirements, you should provide a table of all of the options that you wish to be able to signal. --- Section 5.6 The response message MUST allow indicating the level of diversity of a set of computed loose paths. There is something implicit in this sentence. You are saying that the level of diversity provided may be different from the level of diversity requested (if it was not different, you would not need to provide an indication of the actual diversity). I think this means that the diversity request can be exactly a request, not a demand. So you need to clarify. Does the path computation request message have "desired diversity" and "required diversity" constraints as separate fields? --- Section 5.7 There is a mention of AS-crossing. Is that in scope? --- Section 5.7 How is the second bullet different from the first paragraph of section 5.1? --- Do you need to add the ability to list areas that are to be explicitly excluded form the path? --- Section 6 I think you are adding requirements for a few extra things to be visible/manageable through the MIB modules. Which things? Which MIB modules? --- Nits ==== Title The RFC Editor is still not ready to accept that MPLS and GMPLS are well-known terms, so the title needs to change to... Path Computation Element Communication Protocol (PCECP) Specific Requirements for Inter-Area Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering --- Abstract You need to expand the following acronyms in the abstract... IGP TE LSP LSR --- Abstract OLD In a multi-area network, topology visibility remains local to a given area, and a head-end LSR cannot compute alone an inter-area shortest constrained path. NEW In a multi-area network, topology visibility remains local to a given area, and a head-end LSR cannot compute an inter-area shortest constrained path. --- Abstract I think you should add a sentence to explain where PCECP fits in. For example... One key application of the Path Computation Element (PCE) based architecture is the computation of inter-area TE-LSP paths. ** The PCE Communication Protocol (PCECP) is used to communicate computation requests from PCE clients to PCE servers and to return computed paths in responses.*** This document lists a detailed set of PCECP specific requirements for support of inter-area TE-LSP path computation. --- Abstract It complements generic requirements for a PCE Communication Protocol. s/generic/the generic/ --- Section 1 I suggest you remove this as the Gen Art reviewers keep objecting. You have section 12 anyway. --- Section 2 Add ERO --- Section 3 OLD The main challenge with inter-area MPLS-TE relies actually on path computation. NEW The main challenge with inter-area MPLS-TE lies in path computation. --- Section 3 OLD Indeed the head-end LSR cannot compute a constrained path across areas, as its topology visibility is limited to its own area. NEW Indeed the head-end LSR cannot compute an explicit path across areas, as its topology visibility is limited to its own area. --- Section 3 The generic requirements for a PCE Communication Protocol (PCECP), which allows a PCC to send path computation requests to a PCE and the PCE to sent path computation responses to a PCC, are set forth in [RFC4657]. s/sent/send/ --- Section 3 Note that PCE-based inter-area path computation may require a mechanism for an automatic PCE discovery across areas, which is out of the scope of this document. s/for an automatic/for automatic/ --- Section 4 OLD IGP hierarchy allows improving IGP scalability, by dividing the IGP domain into areas and limiting the flooding scope of topology information to area boundaries. A router in an area has full topology information for its own area but only reachability to destinations in other areas._ Thus, a head-end LSR cannot compute an end-to-end constrained path that traverses more than one IGP area. NEW IGP hierarchy enables improved IGP scalability by dividing the IGP domain into areas and limiting the flooding scope of topology information to within area boundaries. A router in an area has full topology information for its own area, but only information about reachability to destinations in other areas. Thus, a head-end LSR cannot compute an end-to-end path that crosses the boundary of its IGP area. --- Section 4 OLD A solution for computing inter-area TE-LSP path currently relies on a per domain path computation ([PD-COMP]). It is based on loose hop routing with an ERO expansion on each ABR. This can allow setting up a constrained path, but faces two major limitations: - This does not allow computing an optimal constrained path; - This may lead to several crankback signaling messages and hence delay the LSP setup, and also invoke possible alternate routing activities. NEW A current solution for computing inter-area TE-LSP path relies on a per domain path computation mechanism ([PD-COMP]). It is based on loose hop routing with an ERO expansion on each ABR. This allows an LSP to be set up following a contrained path, but faces two major limitations: - This does not guarantee the use of an optimal constrained path; - This may lead to several crankback signaling messages and hence delay the LSP setup, and may also invoke possible alternate routing activities. --- Section 4 OLD The PCE based architecture [RFC4655] is well suited to inter-area path computation, as it allows overcoming the path computation limitations resulting from the limited topology visibility, by introducing path computation entities with more topology visibility, or by allowing cooperation between path computation entities in each area. NEW The PCE based architecture [RFC4655] is well suited to inter-area path computation, as it allows the path computation limitations resulting from the limited topology visibility to be overcome by introducing path computation entities with more topology visibility, or by allowing cooperation between path computation entities in each area. --- Section 4 OLD - Single PCE computation: The path is computed by a single PCE that has topology visibility in all areas and can alone compute an end- to-end optimal constrained path. NEW - Single PCE computation: The path is computed by a single PCE that has topology visibility in all areas and can compute an end-to-end optimal constrained path on its own. --- Section 4 - Multiple PCE computation with inter-PCE communication: the path computation is distributed on multiple PCEs, which have partial topology visibility. They compute path segments in their areas of visibility and collaborate with each other so as to arrive at an end-to-end optimal constrained path. Such collaboration is ensured thanks to inter-PCE communication. s/communication: the/communication: The/ s/their areas/their domains/ --- Section 5.1 Missing paragraph break after first paragraph. --- Section 5.3 s/one ore more/one or more/ --- Section 5.4 Missing paragraph break between paras 2 and 3 --- Section 5.5 Missing paragraph break --- Sections 10.1 and 10.2 Some non-ASCII characters crept in thanks to MS smart-quotes. --- Section 10.2 [ID-RSVP] is not cited in the main text. --- Section 10.2 Missing reference for [METRIC] --- _______________________________________________ Pce mailing list Pce@lists.ietf.org https://www1.ietf.org/mailman/listinfo/pce
- [Pce] I-D ACTION:draft-ietf-pce-pcecp-interarea-r… Internet-Drafts
- RE: [Pce] I-D ACTION:draft-ietf-pce-pcecp-interar… LE ROUX Jean-Louis RD-CORE-LAN
- RE: [Pce] I-D ACTION:draft-ietf-pce-pcecp-interar… LE ROUX Jean-Louis RD-CORE-LAN
- [Pce] draft-ietf-pce-pcecp-interarea-reqs-03.txt JP Vasseur
- [Pce] Re: draft-ietf-pce-pcecp-interarea-reqs-03.… Adrian Farrel