3-way handshake needed because 1xx responses stop retries of INVITE.  However, 
the ACK can also contain things such as an answer SDP.

> -----Original Message-----
> From: [email protected] [mailto:sip-
> [email protected]] On Behalf Of Vineet Menon
> Sent: Monday, February 06, 2012 11:56 AM
> To: [email protected]
> Subject: [Sip-implementors] Significance of ACK in SIP
> 
> Hi,
> 
> I was wondering what is the significance of ACK in SIP?
> 
> I mean can't the caller UA just send the media instead of the ACK
> message?
> This feature is present in H.323 too, so it might have some
> significance!
> Its just that im not able to get it....
> 
> 
> Regards,
> 
> Vineet Menon


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