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

[Sam]

Such scenario often comes,

When the call is picked up by party B, but there is no ACK for the 200OK ,
there should be ACK coming from part A,
As per the timers the party B will resend 200 OK until the timer expires and
the call will auto disconnect terminating the transaction.

Regards
Sam

On Mon, Aug 16, 2010 at 9:17 AM, sachin garg <sachingarg2k1 at gmail.com>wrote:

> @Ranganathan:
> I understood what you said but what if the OK gets lost i.e no ACK is
> received by B party. The transaction layer will resend the OK (as per the
> timers). But B party has already picked up the phone. So, the dead air could
> be heard by B party for a very small duration of time.Or is it so that
> unless and until ACK is received the user agent will not try to play the
> media and hence no question of dead air?
>
> regards
>
> On Fri, Aug 13, 2010 at 10:37 PM, M. Ranganathan <mranga at gmail.com> wrote:
>
>> 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
>>
>
>
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