Subject: [Pce] draft-lazzeri-pce-residual-bw - follow up

From: Daniele Ceccarelli <[email-masked]>
Date: Tue, 1 Aug 2017 15:06:22 +0000

Dear WG,

Just a follow up on the comments made against the residual bw draft:

(see minutes)

         3.1<https://tools.ietf.org/wg/pce/minutes?item=minutes-99-pce-00.html#section-3.1>. PCEP Extensions for Residual Bandwidth (Daniele Ceccarelli, 10 min)

          [45/120] draft-lazzeri-pce-residual-bw<http://tools.ietf.org/html?draft=draft-lazzeri-pce-residual-bw>

          Jon: Clarification question for Daniele - Is this applicable for only one

               source requesting the LSP, so that reporting residual BW can be used?

               What happens if multiple PCCs are setting up LSPs and consuming

               resources

               separately?

          Daniele Ceccarelli: We had considered single source (a single H-PCE),

          and in

                              case of multiple, some synchronization between

                              them. Scope

                              was a single source.

          Dhruv: Even if only single source node, the proposed mechanism will

          only work

                     if there is no other path computation requests asking for

                     the same

                     resource. It is possible there should be a timing issue,

                     i.e., the

                     residual resource should only be valid for a duration of time.

                     Shouldn't this be similar to delay metric, the delay at the

                     time of

                     path computation in a stateless PCRep message and receiving

                     delay

                     later via telemetry.

          Daniele: In the worst case, you cannot get any advantage, but it

          improves if

                   you are lucky.

          Dhruv: Agree.

We were thinking of addressing the "race condition" issue as follows:

  *   Apply the concept only to stateful requests
  *   Define a flag in the path computation request that allows registering for residual bandwidth updates (PCEP report). IN this way if the residual bw changes due to LSP setup (either by other HPCE or by any other mean) the H-PCE can receive a notification.
Please note:

  1.  This is applicable to black topologies
  2.  This is applicable also to white topologies in those cases where TE-topology updates do not include path level residual bw.
  3.  It is still possible to have a number of stateless path computation requests (used to e.g. define the domain sequence in multi-domain scenarios) but then register for updates only when a stateful request is issued.

Thanks a lot
Daniele + co-authors