[Serusers] Forking Proxy

Klaus Darilion klaus.mailinglists at pernau.at
Thu Apr 1 09:44:17 CEST 2004


UA1 behaves wrong - per RFC 3261 the dialog will be established by the 
200 OK message (not by 180), therefore the to-tag from the 200 OK must 
be used.

It makes no sense to deal with such wrong implementations in the SIP proxy.

Which client is UA1?

Klaus

Jason Penton wrote:
> Hi All 
> 
> I have a question about the CORRECT operation of UA when making a call via a
> forking proxy:
> 
> Lets say UA1 calls 7000 at sip.com and user 7000 at sip.com is available at UA2
> and UA3 i.e. the
> Proxy forks the request.
> 
> 	UA1				Forking				UA2
> UA3
> 					Proxxy	
> 1	|------INVITE---------->|					|
> |			
> 2	|				|--------INVITE-------------->|
> |
> 3	|
> |---------------------------INVITE------------->|
> 4	|				|<---RINGING(totag=1234)------|
> |	
> 5	|<---RINGING(totag=1234)|					|
> |
> 6	|
> |<------------------RINGING(totag=5768)---------|
> 7	|<---RINGING(totag=5678)|					|
> |
> 	|				|
> |			|
> 	|				|
> |			|
> 	
> 					NOW UA3 WILL ANSWER
> 
> 	|				|<----------------200 OK
> (totag=5678)-----------|
> 8	|<-200 OK (totag=5678)--|					|
> |
> 9	|---ACK (totag=1234)--->|					|
> |
> 10	|				|------------------ACK
> (totag=1234)------------>|
> 	
> 	AT THIS STAGE UA 3 IGNORES THE ACK AS IT DOES NOT CORRESPOND TO
> ORIGINATING 200 OK AND THE
> 	CALL IS NOT SETUP
> 
> * UA1 is using the to-tag of the first 180 RINGING it received (frame 5) no
> matter what the to-tag in the 
>   200 OK is
> * My question here is: who is in the wrong???? The proxy or UA1? 
> * Should the proxy change the to-tag of the ACK before forewarding it to
> UA3???
> 
> 
> Any help/guidance would be much appreciated
> Jason Penton
> Rhodes University 
> Grahamstown
> South Africa
> 
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> 




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