Procedures for Communication between Stateful Path Computation Elements

The Path Computation Element (PCE) Communication Protocol (PCEP) provides mechanisms for PCEs to perform path computation in response to a Path Computation Client (PCC) request. The Stateful PCE extensions allow stateful control of Multi-Protocol Label Switching (MPLS) Traffic Engineering (TE) and Generalized Multi-Protocol Label Switching (GMPLS) Label Switched Paths (LSPs) using PCEP. A Path Computation Client (PCC) can synchronize LSP state information to a Stateful Path Computation Element (PCE). A PCC can have multiple PCEP sessions towards multiple PCEs. In some use cases, inter-PCE stateful communication can bring additional resiliency in the design, for instance, when some PCC-PCE session fails. This document describes the procedures to allow stateful communication between PCEs for various use cases, and also the procedures to prevent computational loops.