[SIPForum-discussion] UAC - INVITE Transaction Timeout Timer

srinivas.banda at wipro.com srinivas.banda at wipro.com
Fri Jun 19 18:00:18 UTC 2009

This Session-Expires timer will be started only for the confirmed
In your case still the call is not established and it is in ringing
state..so u can't rely on the session expires header.


From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of sreekant nair
Sent: Friday, June 19, 2009 9:45 AM
To: Tomasz Zieleniewski
Cc: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] UAC - INVITE Transaction Timeout

Thanks Tomasz,

Rely on the user to hang up thereby sending a CANCEL to the far end -
interesting. So does your statement imply that on receiving a
provisional response, we must STOP TIMER B? 

A related query - Any idea how the "session-expires" header works in
conjunction with this scenario? The client I use supports this header
and uses a default value of 1800 seconds. Does that mean the SIP stack
starts another timer for 30mins and hypothetically if the user never
ends the call, should this tear down the transaction? Or is this timer
only started for Confirmed Dialogs?

Thanks again. 


From: Tomasz Zieleniewski <tzieleniewski at gmail.com>
To: sreekant nair <sreekant_nair at yahoo.com>
Cc: discussion at sipforum.org
Sent: Friday, June 19, 2009 8:50:50 AM
Subject: Re: [SIPForum-discussion] UAC - INVITE Transaction Timeout


Timer B is only relevant while transaction is in the initial "calling"
It is used both for reliable and unreliable transports.
When transaction moves to "proceeding" state as it receives 
a provisional response, it is completely up to UAC what to do then.
You can compare it to the situation when You call someone 
and You hear never ending ringing in the phone.
Probably You will eventually give up and hang up.
The same thing happens here, UAC hang up by sending
a CANCEL which cancels the transaction.

Kind regards,
- Tomasz Zieleniewski  

2009/6/18 sreekant nair <sreekant_nair at yahoo.com>

	Hi Everyone,
	Have a query regarding Timers. 
	If a client sends an INVITE and receives a provisional response
but does NOT get a Final Response, is there a Timer that clears up the
	RFC3261 specifies Timer B as the INVITE Transaction Timeout
Timer. However in the state transition diagram, there is no mention of
whether Timer B is stopped,restarted on moving from the "CALLING" state
to the "PROCEEDING" state on receiving a 1xx message. These are my
specific queries:

	1.	If while in "PROCEEDING" state no final response is
received, what happens? 
	2.	Is it implied that Timer B is only stopped/canceled on
receiving a final response? 
	3.	What happens when Timer B fires? Should the client send
a CANCEL or just kill the transaction?

	Thanks for any inputs in this regard.
	Sreekant Nair

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