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List:       sip-implementors
Subject:    [Sip-implementors]  Re: [Sip] Why do we need 3-way handshake for INVITE transaction....
From:       Jonathan Rosenberg <jdrosen () dynamicsoft ! com>
Date:       2003-05-31 5:24:04
Message-ID: 3ED83C74.6060106 () dynamicsoft ! com
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Vishal Phirke wrote:
> I think the problem with the forking is, when an INVITE is forked and you
> actually want to setup multiple calls.
> In such a case application will send INVITE without SDP body and each 200
> OK will carry an offer in SDP to which application can respond via using
> ACK with separate media ports for each connection. If 3-way handshake is
> not supported, setting up multiple calls with one INVITE is not possible.

This is not the case. The INVITE can contain an offer, and if forked, 
you get multiple answers. The caller then gets media from multiple 
sources to the same port, which it can disambiguate using SSRC. If it 
wants to move each dialog to a different port, it can then do a 
re-invite if it wants to.

The reason the three way handshake is needed has everything to do with 
the long delays in responding to an invite.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Scientist                             Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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