Subject: [Sip] Bis-05 question: re-invite

From: "Shan Lu" <[email-masked]>
Date: Mon, 29 Oct 2001 18:15:12 -0500

Hi all,

Section 14.1, line 1937, "If a UAS generates a 2xx and never receives an
ACK, it SHOULD generate a re-invite with an offer equal to last session
description sent to peer."

I think this creates unnecessary burden on the UA and doesn't achieve
much. If the re-invite is to change codecs, then the UAS would have to
reserve DSP resources before it sends 200 ok. Now with this requirement,
the UAS has to keep the resource reserved for the duration of currect
invite transaction (31 s) plus potentially another 31 s for the
re-invite that it generates. If you have any confidence in the
invite-200-ack retransmission scheme, the UAS should consider the UAC
down upon seven 200 oks and no ACK. Let's consider the case where the
connection from UA1 to UA2 goes down after the intitial re-invite. UA2
does not receive ACK for this re-invite. So UA2 generates its own
re-invite. UA1 responds with 200 OK but never received by UA2. So next
UA1 would re-invite. It's just a mess.

Furthermore, if the initial re-invite has no sdp, what is the benefit of
having UAS resend its sdp offer? That is equivalent to having the UAC
resend the re-invite upon no response.
BTW, I believe section 14 should describe what happens when re-invite
does not generate any response -- terminate the call.

Shan Lu
sentitO Networks

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