[SIPForum-discussion] Why three way handshake for INVITE?

[M. Ranganathan]

The delay is caused by the human picking up the phone ( that is when
the OK gets sent ).  The ACK indicates to the UAS that the OK was
actually seen by the UAC, thereby allowing the UAS to set up a media
stream. If not for the ACK , you could have a situation where the OK
is lost and the human picking up could hear dead air.  INVITE
transactions are long running and expensive to set up - hence the
three way handshake. This does not apply to other kinds of
transactions.


On Fri, Aug 13, 2010 at 12:05 AM, sachin garg <sachingarg2k1 at gmail.com> wrote:
> Hi,
>
> I was curious to know that why SIP (RFC3261) mandates a 3 way handshake for
> INVITE only.
> The extract (RFC 3261 section 17.1) says "
>
> The long delays expected for
>
>
>    sending a response argue for a three-way handshake"
>
>
> I can understand about the need of session parameters negotiation but what
> is the rationale behind the delay?
>
> regards
>
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-- 
M. Ranganathan