[mpls] Tree Re-merge in P2MP MPLS-TE
Seisho Yasukawa <yasukawa.seisho@lab.ntt.co.jp> Thu, 10 February 2005 12:28 UTC
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Date: Thu, 10 Feb 2005 21:29:06 +0900
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From: Seisho Yasukawa <yasukawa.seisho@lab.ntt.co.jp>
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Subject: [mpls] Tree Re-merge in P2MP MPLS-TE
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Hi, One of the remaining unresolved issues in draft-ietf-mpls-p2mp-sig-requirement is how to handle a "re-merge" of the P2MP LSP. A re-merge is defined as the receipt of more than one signaling message at one LSR for the same LSP where the messages are intended to establish the LSP to different (possibly overlapping) sets of egresses. The issues that arise concern both control plane state and data plane traffic. On the upstream side there are two possibilities. 1. The messages refer to the same upstream data plane interface. 2. The messages refer to different upstream data plane interfaces. On the downstream side there are also two distinct possibilities. a. There is no overlap of data flows. That is, each incoming signaling message results in outgoing signaling message(s) that do not refer to common data plane interfaces. b. There is some "re-merge" of data flows such that outgoing signaling messages caused by the separate incoming messages refer to the same outgoing data plane interface. The issues are clearly: - a desire to reduce unnecessary control plane state - a requirement not to duplicate traffic to any egress - a desire not to duplicate traffic on any link. The text in the current draft states: 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. It seems to us that this final paragraph is too loose and propose to replace it as follows. 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. 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. 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. We would appreciate your input on this point. Regards, Seisho. _______________________________________________ mpls mailing list mpls@lists.ietf.org https://www1.ietf.org/mailman/listinfo/mpls
- [mpls] Tree Re-merge in P2MP MPLS-TE Seisho Yasukawa