Re: [Sip] Constraints on MESSAGE responses

On Sep 7, 2005, at 5:36 AM, Cuda Alberto wrote:
> According to RFC 3428, paragraph 7, an UAS must send a final response
> immediately after receiving a MESSAGE request. What does "immediately"
> actually mean?
>

MESSAGE is a non-invite transaction, so the constraints from:
	draft-sparks-sip-nit-problems-02.txt
and
	draft-sparks-sip-nit-actions-03.txt
apply. Note that both of these documents are approved and in the RFC 
editor queue.

Clearly you need to respond before the retransmit timer occurs. That 
retransmit timer can be delayed by a 100-class provisional response, so 
if the final response requires some "pending" time, then one should 
send a 100 within the first retransmit window (but not before timer E 
lapses if a non-reliable transport is used).

This is more completely spelled out in action 1 of the nit-actions 
draft:

    A SIP element MUST NOT send any provisional response with a
    Status-Code other than 100 to a non-INVITE request.

    A SIP element MUST NOT respond to a non-INVITE request with a
    Status-Code of 100 over any unreliable transport, such as UDP, before
    the amount of time it takes a client transaction's Timer E to be
    reset to T2.

    A SIP element MAY respond to a non-INVITE request with a Status-Code
    of 100 over a reliable transport at any time.

    Without regard to transport, a SIP element MUST respond to a
    non-INVITE request with a Status-Code of 100 if it has not otherwise
    responded after the amount of time it takes a client transaction's
    Timer E to be reset to T2.

--
Dean

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