BGP LS and PCE

‘For … MPLS and Generalized MPLS (GMPLS), most existing traffic engineering solutions work in a single routing domain. These solutions do not work when a route from the ingress node to the egress node leaves the routing area or AS of the ingress node. In such cases, the path computation problem becomes complicated because of the unavailability of the complete routing information throughout the network.’[1]

Network topology information is available in IGPs[2], but their scalability, performance and security limitations make it difficult extracting and using this information. BGP LS (link-state distribution using BGP[3]) is designed to overcome these limitations – “describes a mechanism by which link-state and TE[4] information can be collected from networks and shared with external components using the BGP routing protocol.”[5]

“Path computation in large, multi-domain, multi-region, or multi-layer networks is complex and may require special computational components and cooperation between the different network domains.”[6] Path Computation Element (PCE)-based model addresses this problem space.

Stateful PCE is well described in IETF draft[7]: “The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform path computations in response to Path Computation Clients (PCCs) requests. Although PCEP explicitly makes no assumptions regarding the information available to the PCE, it also makes no provisions for PCE control of timing and sequence of path computations within and across PCEP sessions.  This document describes a set of extensions to PCEP to enable stateful control of MPLS-TE and GMPLS LSPs via PCEP.”

BGP LS and (stateful) PCE-based models should be supported by key network devices, all related SDN controllers and path optimization applications.