[SIPForum-discussion] UAC - INVITE Transaction Timeout Timer

sreekant nair sreekant_nair at yahoo.com
Thu Jun 18 20:11:07 UTC 2009

Thanks for the info Mark.

We are dealing with a non reliable link between UAC and UAS. We were testing how the client should behave in the case mentioned below. The proxy behavior you mentioned is clear, but what we specifically wanted to know was - What should the UAC(client) that initiated the INVITE do to gracefully terminate and prevent it from being a hung/zombie transaction.

Thanks anyways. 

From: Mark R Lindsey <lindsey at e-c-group.com>
To: sreekant nair <sreekant_nair at yahoo.com>
Cc: discussion at sipforum.org
Sent: Thursday, June 18, 2009 2:42:33 PM
Subject: Re: [SIPForum-discussion] UAC - INVITE Transaction Timeout Timer

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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