[Sip] draft-ietf-sip-refer-02

Hi,

I'm a bit confused about the way NOTIFY are used by the "referee" party.

referer              referee
 |====== SIP session ===|
 |--------REFER-------> |
 |<--------202--------- |----INVITE -->
 |                      |<---180------
        ... quite a long time ...
 |<------NOTIFY ------  |<---200------ 
 |----------200-------->|
 |---------- BYE ------>|

draft-ietf-sip-refer-02 states :
"3.5.3.1 Using NOTIFY
Once it is known whether the reference succeeded or failed, the UA receiving the REFER SHOULD notify the agent sending the refer using the NOTIFY mechanism [...]"

All the example flows I've seen around use the NOTIFY mechanism whenever a REFER is accepted. 

If I understand the "SHOULD" strength correctly, the referer can't know whether the referee will send a NOTIFY. So it can't know when to stop waiting for a NOTIFY and when to send a BYE. I think that's quite awkward. 

Besides, I understand that nothing prevents a referee to send NOTIFY on provisional responses (and not only on final responses). But the way the sentence is written : "whether the reference succeeded or failed" does not really take provisional responses into account. No example in draft-ietf-sip-cc-transfer-05.txt shows NOTIFY triggered by 1xx. If the referee INVITEs a human, the referer may have a very long time to wait before receiving a NOTIFY triggered by the 200 response to the INVITE.

Do people implement REFER without the NOTIFY mechanism ? If we can't change the SHOULD strength, could we have a way for the referee to indicate that it will send NOTIFY ? Could the wording in 3.5.3.1 include NOTIFY on provisional responses ?

Jean-Francois.
-- 

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[Sip] draft-ietf-sip-refer-02 - SHOULD strength when sending NOTIFY