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Title : RSVP Path computation request and reply messages
Author(s) : J. Vasseur, et al.
Filename : draft-vasseur-mpls-computation-rsvp-05.txt
Pages : 31
Date : 2004-7-19
This document describes extensions to RSVP-TE to support a new
message type called a ôPath computationö 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 ôUNIö like protocol between a
CE (Customer Edge equipment) and a PE (Provider Edge equipment) where
the CE is not part of the PEÆs IGP domain.
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