Path Computation Element Communication Protocol (PCEP) extension to advertise the PCE Controlled Identifier Space

The Path Computation Element Communication Protocol (PCEP) provides a mechanism for the Path Computation Elements (PCEs) to perform path computations in response to Path Computation Clients (PCCs) requests. The Stateful PCE extensions allow stateful control of Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) Label Switched Paths (LSPs) using PCEP. Furthermore, PCE can be used for computing paths in the SR networks. Stateful PCE provides active control of MPLS-TE LSPs via PCEP, for a model where the PCC delegates control over one or more locally configured LSPs to the PCE. Further, stateful PCE could also create and remove PCE-initiated LSPs by itself. A PCE-based Central Controller (PCECC) simplify the processing of a distributed control plane by integrating with elements of Software-Defined Networking (SDN). In some use cases, such as PCECC provisioning or Binding Segment Identifier (SID) for Segment Routing (SR) allocation, there are requirements for a stateful PCE to make allocation of labels, SIDs, etc. These use cases require PCE to be aware of various identifier spaces from where to make allocations on behalf of a PCC. This document defines a generic mechanism by which a PCC can inform the PCE of the identifier space set aside for the PCE control via PCEP. The identifier could be an MPLS label, a SID, or any other identifier that can be allocated and managed by the PCE.