PCEP - SDN Control Plane Protocol

Path Computation Element Communication Protocol (PCEP) is defined as a protocol that can work between two devices, one forwarding using Traffic Engineering (Router) while the other performing all of the computations for determining the traffic engineering paths (SDN Controller). It is defined in Request For Comment (RFC) 4655 and as per RFC device running a Traffic-Engineering (TE) protocol known as Path Computation Client (PCC). The device which does all the computation is referred to as a Path Computation Element (PCE), and naturally the protocol between the PCE and PCC takes up the name PCEP.

Traditionally, the routers perform their own computations and exchange information between each other for that purpose. In the PCEP model, the router (acting as a PCC) does the forwarding and label imposition, disposition, etc. but it leaves the entire computation and path decision-making process to the PCE. If there are multiple PCEs working collectively, PCEP may also be used as a communication protocol between them. To learn the Link State Database (LSDB) information from the network, the PCE device could establish a passive IGP relationship with the devices and share the entire traffic engineering database. This approach is limited to single area only as one area doesn’t have the link state information of other area.

PCEP is designed around SDN use-case for traffic engineering. So it applies to RSVP-TE, Generalized MPLS (GMPLS)–based TE, and more recently to Segment Routing TE (SR-TE). The role of the PCEP, PCC, and PCE remains the same in all these cases. For example, the PCC can request the PCE to perform path computations with specific constraints, and the PCE can respond back suggesting the possible paths that meet the required constraints.

PCC requires support only in the edge network. As contrast to OPEN Flow, PCEP is easy to manage, deploy and troubleshoot in any large ISP network.

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