Technical Summary
This document presents an applicability of existing MPLS protection
mechanisms, both local and end-to-end, to Multi-Protocol Label
Switching Transport Profile (MPLS-TP) in ring topologies. This
document does not propose any new mechanisms or protocols.
Protection on rings offers a number of opportunities for optimization
as the protection choices are starkly limited (all traffic traveling
one way around a ring can only be switched to travel the other way on
the ring), but also suffers from some complications caused by the
limitations of the topology.
Requirements for MPLS-TP protection especially for protection in ring
topologies are discussed in "Requirements of an MPLS Transport
Profile" (RFC 5654) and "MPLS Transport Profile (MPLS-TP)
Survivability Framework" (RFC 6372). This document shows how MPLS-TP
linear protection as defined in RFC 6378 can be applied to single
ring topologies, discusses how most of the requirements are met, and
describes scenarios in which the function provided by applying linear
protection in a ring topology falls short of some of the
requirements.
Working Group Summary
This document was the subject of considerable debate in the MPLS
working group. There was some concern about whether this work
prohibited or devalued the development of specialised protection
techniques for deployment in ring topologies.
The document was re-worked to make it clear that it is basically
an applicability statement showing how linear protection defined
in RFC 6378 can be applied to ring topologies, what function can
be achieved, and what issues remain. It was made clear to the
working group that specialist ring protection techniques were still
in scope for the working group provided that they demonstrate
improvements over the application of linear protection, and provided
they can interwork with general protection in the wider MPLS-TP
network.
A second WG last call was held and the document gained consensus.
Please see RFC editor note for a commentary on the number of
front-page authors.
Document Quality
This an informational document, it describes how the technologies
defined in earlier RFCs can be applied to ring topologies.
The document has been reviewed needed, the working
group last call was brought to the attention of SG15 in
ITU-T.
Personnel
Loa Andersson (loa@pi.nu) is the document shepherd
Adrian Farrel (Adrian@olddog.co.uk) is the Responsible AD
RFC Editor Note
Please allow an exception to the normal front-page limit so
that all eight named authors can be present. The WG chair/
shepherd explains it as follows:
> Early 2010 we had 5 or 6 different drafts addressing "mpls-tp-
> ring-protection" from one aspect or another. Most of these
> drafts had 2 or maybe 3 different authors.
>
> The WG chairs took an initiative to discuss the possibilities to
> merge all drafts into one. The discussion was partially
> successful, and all draft but one, were merged into a single
> document. Texts from all drafts were merged into draft-
> weingarten-mpls-tp-ring-protection (later to be adopted as
> the working group draft draft-ietf-mpls-tp-ring-protection.
>
> The number of authors on the first page reflect text
> contributions made to the drafts that were merged.
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You may rename and reposition Section 1.4 according to your style guide.
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If (and only if) you consider it necessary, you may consider some of the text as Tables and apply captions as follows...
In Section 3.1 on page 19 "Table x : Backup LSPs for Node Protection"
In Section 3.1.1 on page 20 "Table x : Nodes Traversed by Protection: LSPs"
In Section 3.1.1 on page 21 "Table x : Bandwidth Utilization on Links During Protection"
In Section 3.2.2 on page 25 "Table x : Context Specific Labels for Connected LSPs"