[SIPForum-discussion] IMS call: Answer just when 180 is sent out
sreekant nair
sreekant_nair at yahoo.com
Tue Aug 21 16:26:39 UTC 2007
Hi Gopalarathnam,
I think RFC 3262 (section 3 in particular) should help you out. See a small excerpt below.
The UAS MAY send a final response to the initial request before
having received PRACKs for all unacknowledged reliable provisional
responses, unless the final response is 2xx and any of the
unacknowledged reliable provisional responses contained a session
description. In that case, it MUST NOT send a final response until
those provisional responses are acknowledged. If the UAS does send a
final response when reliable responses are still unacknowledged, it
SHOULD NOT continue to retransmit the unacknowledged reliable
provisional responses, but it MUST be prepared to process PRACK
requests for those outstanding responses. A UAS MUST NOT send new
reliable provisional responses (as opposed to retransmissions of
unacknowledged ones) after sending a final response to a request.To depicting your scenario
Invite (SDP)------>
<------- 100 Trying
<------- 180 (SDP)
<------- 200 Ok for Invite (No SDP)
From the above excerpt it is clear that the above scenario is invalid(assuming that the
REQUIRE header was included saying 100Rel). The only final that can be sent without waiting
for PRACK are NON-200OK final responses. If the final response is a 200OK we have to wait
for PRACK for earlier 18Xs(see earlier paragraphs).
However had the 18X not contained an SDP, the 200OK must contain the answer SDP and so can be sent I believe.
Regards
Sreekant Nair
----- Original Message ----
From: Gopalarathnam Sambasivan <s.gopalarathnam at gmail.com>
To: discussion at sipforum.org; imsclub at googlegroups.com
Sent: Tuesday, August 21, 2007 9:33:57 AM
Subject: [SIPForum-discussion] IMS call: Answer just when 180 is sent out
Hello All,
Just after the moment 180 ringing is sent in a scenario with require and supported 100rel, state to be waiting for PRACK
If terminating side answers the call (200 OK), what will happen? what is the expected behaviour?
What about SDP negotiation with PRACK in this case?
Please tell me the sections of RFC/TS which describes this scenario.
Thanks in Advance.
Best Regards,
Gopalarathnam.
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