Re: [Sip] NOTIFY on call transfer procedure

Section 6 of RFC3515 calls out why REFER is constructed this way.

The root cause is the fixed length of any SIP non-INVITE transaction.
The approach you sketch won't work as provisional responses to 
non-INVITE requests do _not_ lengthen the transaction.

If you want a more detailed description, look at
http://www.ietf.org/internet-drafts/draft-sparks-sip-nit-problems-00.txt
and
http://www.ietf.org/internet-drafts/draft-sparks-sip-nit-actions-00.txt

RjS

On Thu, 2004-05-06 at 23:55, Thomas Ackermann wrote:
> Hi all,
> 
> can anybody tell me why the transfer procedure needs NOTIFY message
> with application/sipfrag message body?
> 
> Why not simply keep the REFER transaction open by sending:
>  - a provisional response instead of the 202/Accepted and
>  - a final 200/OK response instead of NOTIFY(200 OK) ?
> Just like the INVITE transaction with all its intermediate responses.
> 
> Or even more simple:
> The Transferee sends the BYE by itself instead of asking the Transferor
> to terminate the call?
> 
> Do you know the reason why the NOTIFY transaction has been added to
> call transfer procedure?
> 
> Thanks for your help,
> Thomas
> 
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