Subject: [Sip] Forking INVITE SIP message - regarding

From: Raj <[email-masked]>
Date: Tue, 28 Nov 2006 09:17:02 -0800 (PST)

Hello,
   
  Consider the following situation.
   
              Adam wants to call Bob, let’s say that Bob is registered at three locations, that is, at home, at head office and at his branch office. Hence, when Adam makes a call, INVITE request is forked by the proxy and it reaches all the three destinations. Hence, three 200 OK SIP response will be sent back to Adam. 
   
              Consider the situation, when Bob’s friends answer the call at all the three locations at the same time, what will happen? Either three media channel will be established between them or which two will be discarded.
   
              Can anyone please clear this?
   
  With regards
  Raj.

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From: Paul Kyzivat <[email-masked]>
Date: Tue, 28 Nov 2006 12:39:56 -0500

>               Can anyone please clear this?

While all three locations may ring at once, its unlikely that all three 
with answer at exactly the same time. As long as one answers first be a 
second of so, the proxy will cancel the others and they won't send a 200 
response.

Its only when multiple phones are answered in the small time window 
where they can't be canceled that you get multiple 200 replies. If that 
happens, its up to Adam's UA to decide what to do. While it *could* 
conference them all together, a common strategy is simply to send a BYE 
to all except the first.

	Paul