Subject: [P2PSIP] P2PP and lost responses

From: "Beck01, Wolfgang" <[email-masked]>
Date: Fri, 20 Jul 2007 10:18:44 +0200

I'm sure I'm missing something, but the transaction mechanism
seems somewhat broken to me. 

In recursive mode, a peer should respond with '100 Trying'
thus preventing request retransmissions. Now, if the
final response is lost, the request originator can't do
anything until the whole transaction times out. 

We have the  same mechanism in SIP, but get away with it
most of the time. '200 OK' responses carrying important
information are usually part of an INVITE transaction,
where this problem does not occur. A lost '200 OK' response
in a MESSAGE transaction is less critical, as the important part of the
transaction -- delivery of the text -- has succeeded. 

In P2PP, responses do carry important information. Retrying
a whole transaction just to retransmit a lost response seems
not very efficient.

solutions?
1. mandate reliable transport for recursive request handling
2. PRACK for P2PP

Wolfgang

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