[SIPForum-discussion] The process sequence

Vivek Batra Vivek.Batra at matrixtelesol.com
Fri Jun 19 07:33:31 UTC 2009

Number of scnerios exist where 183 Session Progress is sent prior to 180
E.g., in VoIP-GSM Gateway, when VoIP end recieves incoming INVITE, gateway
first sends 183 Ringing to alert the caller that call has been progressed
and on reciept of Ringing Alert from GSM network, gateway sends 180 Ringing
to caller which indicates caller that called device is not ringing. 
However, it is upto caller device how to handle the 180 Ringing recieved
after 183 Session Progress.
Meanwhile, Linksys ATA provides 'Sticky 183' flag which indicates whether
180 Ringing should be handled or not if recieved after 183 Session Progress.
Best Regards,
Vivek Batra


From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of Mark R Lindsey
Sent: Friday, June 19, 2009 1:49 AM
To: Mike Jiang
Cc: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] The process sequence

Most devices that send both 180 and 183 for one transaction send them in
that order: first 180, then 183. There's no temporal coupling between 180
and 183: they can occur in either order. (AFAIK.)

But beware if you use 183 with SDP, then start streaming RTP to the calling
endpoint, and then send a 180 to the UAC, you may get odd results (such as
overlapped ringback).  

On Jun 18, 2009, at 1:35 PM, Mike Jiang wrote:

Hi All,
      One quick question: I was wondering if the Ringing (180) is always
occurring ahead of the Session Progress (183).
      In my case, the 183 response always happened before the 180 happened.


      Mike J.

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