Dear all, The use of PCReq/PCRep messages with the passive stateful PCE is well documented in draft-ietf-pce-stateful-pce-10. There is however no explicit procedures for using PCReq/PCRep with active stateful PCE.
There are cases where the router will not be able to compute the initial path for an LSP configured on the router. This can be for example a Segment Routing TE LSP which has a bandwidth requirement. In this case, the LSP will remain down until PCE computes a path for it. In such a case, the PCC must make a request to PCE for the computation of the initial path for the LSP. I can think of two different ways for achieving this but none of these are explicitly described in the draft: 1. The PCC starts with the passive stateful procedures and uses the PCReq/PCRep message to request the initial path for the LSP. If the PCE returns a path, then the PCC can delegate the LSP to the PCE in the subsequent PCRpt message after the LSP is instantiated on the PCC. From there on, the active stateful procedures with PCRpt/PCUpd messages can be followed until such time the LSP delegation is changed. This method seems appropriate and complete but it is not described in the draft. In other words, there is no statement that an active stateful PCE can operate in passive mode for a given LSP when delegation of the LSP has not been given to it. 2. The PCC starts in the active stateful mode and delegates the LSP, which is in down state, using the PCRpt message. In this case, the PCRpt is used to synchronize the state of the LSP with the PCE but also as an implicit way to request the initial LSP path computation. The issue though is that the PCRpt message is not an explicit path computation request and lacks the following: a. path request timeout: draft-ietf-pce-stateful-pce-10 does not describe a timer mechanism that a PCC might use to detect an initial path request timeout. From reading the draft, the PCE is not mandated to compute a path and send a PCUpd message in response to a PCRpt message even when the LSP is down. b. No path found by PCE: Even if one assumes that the PCE attempts a path computation within a reasonable time from receiving the PCRpt message, how will it communicate to PCC a failure to find a path for that LSP? c. Synchronous path computation: How can a PCC request synchronous path computation for a set of link/node/SRLG disjoint LSP paths? With PCReq/PCRep, this was possible via the SVEC object. I appreciate if you could provide comments on the above points. Regards, Mustapha.
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