This module defines configuration and operational state data relating to Path Computation Element Protocol (PCEP) for communications between a network element (router) acting as PCC and a PCE server, according to RFC4655 definitions:
-PCC: Path Computation Client; any client application requesting a path computation to be performed by a Path Computation Element.
-PCE: Path Computation Element; an entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints.
Also according to RFC4655, a PCE can be either stateful or stateless. In the former case, there is a strict synchronization between the PCE and not only the network states (in term of topology and resource information), but also the set of computed paths and reserved resources in use in the network. Conversely, stateless PCEs do not have to remember any computed path and each set of request(s) is processed independently of each other. For example, stateless PCEs may compute paths based on current TED information, which could be out of sync with actual network state given other recent PCE-computed paths changes.
On the other hand, RFC8051 defines for Stateful PCE two modes of operation:
-Passive Stateful PCE: a PCE that uses LSP state information learned from PCCs to optimize path computations. It does not actively update LSP state. A PCC maintains synchronization with the PCE.
-Active Stateful PCE: a PCE that may issue recommendations to the network. For example, an Active Stateful PCE may use the Delegation mechanism to update.
LSP parameters in those PCCs that delegate control over their LSPs to the PCE.
The type of PCEP capability supported which is advertised in the Open message when a PCEP session is established. It could be: - Stateless PCEs: A PCE that do not have to remember any computed path and each set of request(s) is processed independently of each other(RFC4655). - Passive Stateful PCE: a PCE that uses LSP state information learned from PCCs to optimize path computations, but it does not actively update LSP state(RFC8051). - Active Stateful PCE: a PCE that may issue recommendations to the network by using the Delegation mechanism to update LSP parameters in those PCCs that delegate control over their LSPs to the PCE (RFC8051).
The LSP path can be delegated to PCE, locally controled by PCC or only report information state to the PCE.