Subject: [SIP] Question regarding CSEQ processing with PRACK...

From: "Venkatesh Venkataramanan" <[email-masked]>
Date: Mon, 12 Feb 2001 10:30:57 -0800

All:

I needed some clarification on the usage of CSEQ with PRACK's. The draft
says that the CSEQ number in PRACK MUST be higher than the last transaction
CSEQ number (INVITE or otherwise). So, for example, say, an UAC sends out an
INVITE with CSEQ 1, it receives a 180 ringing, it issues a PRACK with CSEQ
2. 

The question I had is should these CSEQ's be preserved after the INVITE
transaction has ended? Meaning, in the above example, say the PRACK,
generates a 200 OK by the UAS for the same, followed by an ACK for the
INVITE(when the called party answers), the UAC issues an ACK with CSEQ 1
INVITE to complete the 3 way handshake. At a later point of time, say, the
user hungup, which causes the UAC to issue a BYE, should the CSEQ field be
constructed with a sequence number, higher than the last PRACK it sent
out(or received in case of far end disconnects) or the last INVITE it sent
out(or received)? Please elaborate.

Thanks.
Venkatesh

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