Hi All,

Need expert advice on below scenario, Consider the following call flow,

SIP Proxy          P2

---- (INVITE) ---->
<----- (100) ------
<- (183;100Rel) -
---- (PRACK) ---->
<-(200;PRACK) --

<- (183;100Rel) - (new TO Tag)
<- (183;100Rel) - (new TO Tag)
<- (183;100Rel) - (new TO Tag)

<- (200;INVITE) - (new TO Tag; not matching to above)
--- (ACK;200)---->

Two questions,

1. In a ISUP to SIP interoperability scenario, does SIP proxy need to PRACK
all the 183 received since the INVITE was forked by the next hope proxy P2?

2. Is it valid to send a 200|OK for INVITE with new To Tag, not matched to
any sent 183?

I go through the RFC3262, things and not much clear on this scenario.
relevant section of RFC,

3 UAS Behavior

...

   After the first reliable provisional response for a request has been
   acknowledged, the UAS MAY send additional reliable provisional
   responses.  The UAS MUST NOT send a second reliable provisional
   response until the first is acknowledged.  After the first, it is
   RECOMMENDED that the UAS not send an additional reliable provisional
   response until the previous is acknowledged.  The first reliable
   provisional response receives special treatment because it conveys
   the initial sequence number.  If additional reliable provisional
   responses were sent before the first was acknowledged, the UAS could
   not be certain these were received in order.


and

5 The Offer/Answer Model and PRACK

...

   If the UAS had placed a session description in any reliable
   provisional response that is unacknowledged when the INVITE is
   accepted, the UAS MUST delay sending the 2xx until the provisional
   response is acknowledged.  Otherwise, the reliability of the 1xx
   cannot be guaranteed, and reliability is needed for proper operation
   of the offer/answer exchange.



Thanks,
Aman
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