RSVP Path computation request and reply messages
draft-vasseur-mpls-computation-rsvp-05

Abstract

This document describes extensions to RSVP-TE to support a new message type called a “Path computation” message. This message is to be used between an LSR and a Path Computation Element (PCE), which may be an LSR or a centralized path computation tool. An RSVP Path Computation Request message is used by the head-end LSR to send its request to the PCE. The PCE in turn sends an RSVP Path Computation Reply message containing either: - a positive reply, containing one or more paths, if the request can be satisfied. - a negative reply if no path obeying the requested constraints can be found. The PCE may also optionally suggest new constraint values for which one or several paths could be found. There are many situations where a PCE may be used. A typical example is in the context of Inter-area MPLS TE. A head-end LSR could request that a PCE compute one or more paths obeying a specified set of constraints for a TE LSP spanning multiple areas. The PCE could be a centralized path computation Element or an LSR such as an ABR or an ASBR. Another example is the use of a PCE to compute diversely routed paths between two end points. This may be useful in the context of MPLS TE LSP Path protection or GMPLS LSP Path protection. The computation of Multi-constraints paths requires intensive CPU resources, and may be yet another usage example. Lastly, those protocol extensions could be used as a “UNI” like protocol between a CE (Customer Edge equipment) and a PE (Provider Edge equipment) where the CE is not part of the PE’s IGP domain.

Authors

JP Vasseur

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