The ability to compute shortest constrained Traffic Engineering Label
Switched Paths (TE LSPs) in Multiprotocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) networks across multiple domains has been
identified as a key requirement for point-to-point (P2P) and point-
to-multipoint (P2MP) scenarios. Backward-Recursive Path Computation
(BRPC) [RFC5441] defines Virtual Shortest Path Tree (VSPT) as a
default de-facto data structure for path reply message in inter-
As Path Computation Element (PCE) will get used in newer scenarios
like inter-domain, protection, P2MP etc. As well as PCE is being
explored to be used in Cross Stratrum Optimization (CSO) environment
(see [CSO-PCE]) as well as in [ABNO]. Limiting PCE communication
Protocol (PCEP) to just one data structure limits the usage of PCEP.
Its important to keep PCEP generic enough to use differnt data
structure and apply different algorithms.
This document defines extensions to the PCEP to allow multiple data
structures. Extensions are defined for PCE to indicate the set of
Data Structure (DS) it supports; also Path Computation Client (PCC)
or PCE can indicate in a path computation request the required DS,
and a PCE can report in a path computation reply the Data Structure
that was used in the path reply message.