> A UA cannot send a BYE for a call until it has received an ACK for
>      the initial INVITE.  This was allowed in RFC 2543 but leads to a
>      potential race condition.

Probably that should read

A UA cannot send a BYE for a call until it has received an ACK for
the initial INVITE or *server transaction has timed out*.  This was
allowed in RFC 2543 but leads to a potential race condition.

This is appropriately indicated below (RFC 3261)

13.3.1.4 The INVITE is Accepted

   If the server retransmits the 2xx response for 64*T1 seconds without
   receiving an ACK, the dialog is confirmed, but the session SHOULD be
   terminated.  This is accomplished with a BYE, as described in Section
   15.

15 Terminating a Session

   However, the callee's UA MUST NOT send a BYE on a confirmed dialog
   until it has received an ACK for its 2xx response or until the server
   transaction times out.

On Wed, Jan 13, 2010 at 3:46 PM,  <[email protected]> wrote:
> Thanks for the reply.
>
> But the in the RFC (28.1 Major Functional Changes) it is mentioned that:
>
> A UA cannot send a BYE for a call until it has received an ACK for
>      the initial INVITE.  This was allowed in RFC 2543 but leads to a
>      potential race condition.
>
>
> Please let me know the correct behavior in this case.
>
> Thanks and regards,
> Sunil
>
> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Iñaki 
> Baz Castillo
> Sent: Wednesday, January 13, 2010 3:42 PM
> To: [email protected]
> Subject: Re: [Sip-implementors] INVITE Transaction
>
> El Miércoles, 13 de Enero de 2010, [email protected] escribió:
>> Hi,
>>
>> I have one doubt in this.
>> If ACK is not properly sent by the UAC, how will the call be terminated?
>
>> Will the UAC send a CANCEL
>
> How can now the UAC that its ACK didn't arrive to the UAS? just by inspecting
> the arrival of new 200 responses (same response) which means that the UAS
> didn't receive the ACK (or the proper ACK).
>
>
>> or will the other end send a BYE to terminate
>>  the call?
>
> The SIP dialog is creted with the INVITE and 200, regardless of the
> presence/abscense of the ACK, so the call must be terminated with a BYE (from
> the caller or called).
> A CANCEL from UAC is not valid as the INVITE was already accepted.
>
> --
> Iñaki Baz Castillo <[email protected]>
>
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