Hi Bhagat,
Regarding your query, the offer/answer model prohibits
any unreliable 1xx to contain SDP information. Any answer
to an offer can only be given in a *reliable* response to
the message (In case of an offer in the INVITE, this is
either a reliable provisional or a 200 OK response). I
think you are referring to normal provisional responses
as being reliable since its a loss-less environment. But,
it may so happen that the peer may not be ready for
understading SDP from non-reliable provisional responses,
as its not expected there.
That said, there are 2 scenarios :
a) INVITE contained SDP:
The UAS cannot send 2 different answers to the offer.
The first reliable provisional response contained the
answer, a second one cannot change the answer (!)
b) INVITE did not contain SDP:
The UAS sends an offer in its response. However, there
can be only one outstanding SDP offer at any time from
the UAS. So, the first reliable provisional response
contained the offer which must be responded to by the UAC.
Another offer cannot anyways be made till that time as
the UAC sends a PRACK (or an ACK) with the answer.
Hence, the scenario you mentioned cannot be held good for
SDP in particular at least.
The second part of the question was regarding whether the
same provisional response code can be used with different
application information (I understand you mean different
application headers here)... again, I believe this is not
normally done in a SIP-SIP call. (Others may correct me
if I'm incorrect... or if some other scenario desires this)
Isn't it easier to look for more application data if you
know the response is different in some way from the previous
response; rather than find out looking at the entire message
to see if there's any new information? Though, I believe,
if you are implementing peers on both ends (UAC and UAS) of
the call, nothing in the spec stops you from doing the
scenario you mentioned (for application data, that is :)
Regards,
Siddharth.
-------------------
Siddharth Toshniwal @ Hughes Software Systems
Bangalore, India.
http://www.hssworld.com
"Janarthanan, Bhagatram" <[EMAIL PROTECTED]> on 07/09/2002
06:11:12 AM
To: [EMAIL PROTECTED]
cc: (bcc: Siddharth J Toshniwal/HSSBLR)
Subject: [Sip-implementors] 1xx responses to INVITE
Hi ,
In a loss-less environment, where UAs is not using reliable 1xx messages,
is
it valid for the UaS to send two 1xx response with the same response code,
but with different sdp/appln information.
For eg, is the following allowed ?
----INV------------>
<---182--appln-part1---
<---182--appln-part2---
Thanks
Bhagat
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