[OpenSIPS-Users] Transfer issue

[Bogdan-Andrei Iancu]

Hi Iñaki,

Iñaki Baz Castillo wrote:
> El Sábado, 24 de Octubre de 2009, Bogdan-Andrei Iancu escribió:
>   
>> So you actually can have a highly scalable signalling B2BUA - the 
>> opensips module could be used to locally (on opensips) interpret the 
>> REFER and do the call transfer, totally transparent to the other party.
>>     
>
> Hi Bogdan, even if that sounds look let me be the "bad boy" ;)
>   
OK, let;s play good-cops and bad-cops to get the best of it ;)
> - What about the implicit NOTIFY during the REFER transaction?
>   
B2BU will take care of the entire transfer signalling (sending the 
NOTIFY with the state of the transfer)
> - What about if parallel forking occurs during REFER transaction?
>   
from b2bua, there are 2 distinct calls : (1) one already established, 
between B2B and transferred party and (2) a new one from the b2b to the 
transferee party - The b2b will finally wait for a 200 OK, so there is 
no risk if the new call is doing any kind of forking (like no UA is 
affected by the forking done by a proxy)
> A more complex case:
>
> - A is speaking with P (PSTN provider).
> - A sends a REFER (Refer-To: B).
> - OpenSIPS handles the REFERa and generates an INVITE to B.
>   - Which codecs does it use?
>   
    none :) - the re-INVITEs in b2bua are done with INVITEs without SDP, 
so that the SDPs are directly exchanged between end parties.
> - B sends 180 during 10 seconds.
> - Before B answers or declines the call, P sends a re-INVITE to A.
>   - What does then happen? note that a re-INVITE shouldn't take place
>     in middle of a REFER transaction (but P kwnos *nothing* about
>     the REFER transaction since OpenSIPS b2bua handled it!).
>   
This is good question - and mainly because of how should be done and not 
because you cannot do it.
Depends how you do the transfer scenario in B2BUA:
    (1) once you received the REFER from A, the b2bua can hung up the P 
leg (unattended transfer)
    (2) if P leg is still kept and B2B receives a re-INVITE from there, 
it should deny it...what is the proper SIP response ? hmmm:D
> Like this I can imagine hundreds of real cases in which, personally, I expect 
> b2bua module wouldn't behave correctly. 
>   
I agree that a b2bua is more complex than a proxy, but I guess the idea 
is to identify all these buggy cases and fix them.

Thanks and Regards,
Bogdan


-- 
Bogdan-Andrei Iancu
www.voice-system.ro