[SIPForum-discussion] UAC - INVITE Transaction Timeout Timer

Mark R Lindsey lindsey at e-c-group.com
Thu Jun 18 18:42:33 UTC 2009

RFC3261 talks about this somewhat.

I believe this is the timer you seek: "A proxy has the option of  
canceling a transaction when there is a gap of 3 minutes between  
responses in a transaction. To prevent cancellation, the UAS MUST send  
a non-100 provisional response at every minute, to handle the  
possibility of lost provisional responses."

On Jun 18, 2009, at 10:20 AM, sreekant nair wrote:

> 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  
> transaction?
> 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:
> 	• If while in "PROCEEDING" state no final response is received,  
> what happens?
> 	• Is it implied that Timer B is only stopped/canceled on receiving  
> a final response?
> 	• What happens when Timer B fires? Should the client send a CANCEL  
> or just kill the transaction?
> Thanks for any inputs in this regard.
> Regards
> Sreekant Nair
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