[SIPForum-discussion] UAC - INVITE Transaction Timeout Timer

Shmulik Basan sbasan at 10levels.com
Fri Jun 19 22:23:16 UTC 2009



I don't think the below answer is accurate.


SIP defines two types of responses, provisional and final.

Final responses convey the result of the request processing, and are sent

Provisional responses provide information on the progress of the request
processing, but are not sent reliably in RFC 3261.

Both UAC & UAS will response with CANCEL after 32 Sec when there is no
additional provisional or final response.

The PRACK should provide the reliable answer to the un-reliable response.


Please refer to RFC 3262.



From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of Tomasz Zieleniewski
Sent: Friday, June 19, 2009 3:51 PM
To: sreekant nair
Cc: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] UAC - INVITE Transaction Timeout Timer



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 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:

1.	If while in "PROCEEDING" state no final response is received, what
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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