Re: [Sipping] Question regarding reliable provisional response retransmission

[Dean Willis <dean.willis at softarmor.com>]

On Jun 15, 2005, at 12:18 AM, DarshanBildikar 70559 wrote:
> 1) RFC 3262 states that reliable provisional responses are to be 
> retransmitted every two and a half minutes. Why is this really 
> required since the response is after all "reliable" !

Because in addition to being reliable, they're still "provisional", and 
we need a state recovery mechanism to deal with state recovery in the 
cases where a transaction fails after a reliable provisional is 
exchanged.

> 2) Should the retransmitted provisional response always contain the 
> same SDP? i.e. Should I only consider the first SDP and ignore SDP's 
> in subsequent messages?

Well, it would be terribly rude to change your offer in midstream, as 
there is a race conditional where an answer might be "in flight" as the 
new offer is being transmitted, so if the repsonse in question 
contained SDP, repeats should contain the same.

It's not clear to me that one actually has to repeat the SAME 
reliable-provisional response sequence in order to maintain the 
transaction in the final-pending state. It would seem to suffice to 
send another reliable provisional (perhaps a 180) without SDP.

Others may think differently.


Question: Shouldn't this really be on the sip-implementors list?

--
Dean


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