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Re: [osip-dev] Extend call ringing

From: Carl Bevil
Subject: Re: [osip-dev] Extend call ringing
Date: Mon, 29 Apr 2013 08:12:30 -0700 (PDT)


I'm not Aymeric, but I might be able to help with this.  I briefly checked the RFC, but didn't do a comprehensive search (so there may be more to the story; please feel free to check my facts).

As far as I know, you cannot send a re-INVITE until a SIP dialog has been established.  Until you receive a final response for your initial INVITE (and you have sent an ACK), you are not in a dialog.  From RFC 3261, section 14:

An INVITE request sent within an
   existing dialog is known as a re-INVITE.

Prior to dialog establishment, you would be sending a retransmission of the INVITE.  Once you receive a provisional response (such as a 100 Trying or 180 Ringing), you are not supposed to send any retransmissions.  From section

After receiving a 1xx response, any retransmissions cease altogether, and
   the client waits for further responses.

Also, I think retransmitting with altered/added headers would be incorrect.

Good luck,


From: Sithara Santharam <address@hidden>
To: Aymeric Moizard <address@hidden>
Cc: "address@hidden" <address@hidden>
Sent: Monday, April 29, 2013 4:12 AM
Subject: Re: [osip-dev] Extend call ringing

Hi Aymeric, thanks for the reply.
One follow-up question: 

When A called B (no expires header) and B is still ringing, can a new re-invite from A be sent to B? Will the re-invite (with expires header) be processed by B and ringing can be extended?


On Fri, Apr 26, 2013 at 5:39 PM, Aymeric Moizard <address@hidden> wrote:

From rfc3261:

      1. If the request is an INVITE that contains an Expires header
         field, the UAS core sets a timer for the number of seconds
         indicated in the header field value.  When the timer fires, the
         invitation is considered to be expired.  If the invitation
         expires before the UAS has generated a final response, a 487
         (Request Terminated) response SHOULD be generated.

Many sip app won't look at this parameter... But this is the standard way to ask
for a long ringer duration. I think even if this parameter exists, UAS is not requested
to accept the expires duration anyway.


2013/4/26 Sithara Santharam <address@hidden>
Please assume the scenario where A calls B. B keeps ringing without answering. B is pre-configured to ring for 20 seconds before dropping an unanswered call. So after 20 seconds B drops call.

I would like to know if there is a way in which the caller A can extend the call by sending re-invite so that B keeps ringing for another period. If so, is there a particular format/parameters for the re-invite? 

[This scenario becomes more meaningful in case when there is an Auto-attendant in between, but let us assume direct call from A to B for now.]

Can anyone please tell me if this is possible.


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