Subject: [Pce] PathRequests with same RqId

From: "Fabien VERHAEGHE" <[email-masked]>
Date: Tue, 9 Oct 2007 15:38:28 +0200

Hello,

I have a little concern with PCEP draft.

At the end of section 7.3.1 it is said:

"If no path computation reply is received from the PCE, and the PCC wishes
to resend its

   request, the same Request-ID-number MUST be used."

I'm not sure what is the purpose here. Is it a kind of retransmission
process in case no reply is received

after N seconds or is it to offer the possibility to the PCC to change the
Path Computation constraints?

(Actually I guess the intent is the first one, but the draft does not forbid
the second case explicitly).

In the latter case I think there is a collision case to handle here if the
PCC resends the request at the same time

the PCE sends the reply for the first request.

The PCC cannot know if the reply is for the first request or the second one.

In the first case the 2 PathRequests are identical so the problem is less
important except that the PCC may receive 2 responses

(that may not be identical).

Another problem is that if the PathRequest belongs to an SVEC and if there
is a collision between a resent PathRequest

and the PathReply, the PCE may not remember the SVEC (since it already
replied) so the second received PathReply result

would not have been performed synchronously with other PathRequests of the
SVEC. 

Wouldn't it be preferable to forbid the reuse of a request id? If a PCC
wants to resend a PathRequest it can

send a Cancel Request Notification followed by a new PathRequest with a new
Id. It seems more straight forward and robust to me.

Actually I'm not sure I get the advantage of reusing the same request Id.

Best regards

Fabien

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