RE: [Sipping] Question regarding reliable provisional responseretransmission

[xupeili <xupeili at huawei.com>]

Hi:

In my understanding, 

(1) retransmission of provisional response is to extent the 
Uac`s time out for the transaction.
 
(2) the SDP in different reliable 1xx is logically independent,
furthermore it is not necessary to provide SDP in each reliable 1xx. 

-----Original Message-----
From: sipping-bounces at ietf.org [mailto:sipping-bounces at ietf.org] On
Behalf Of DarshanBildikar 70559
Sent: Wednesday, June 15, 2005 1:18 PM
To: sipping at ietf.org
Subject: [Sipping] Question regarding reliable provisional
responseretransmission

The SIP RFC says that 

"A proxy has the option of canceling a transaction when there is a gap
of 3 minutes between responses in a transaction.  To prevent
cancellation, the UAS MUST send a non-100 provisional response at every
minute, to handle the possibility of lost provisional responses"

Assume a B2BUA has generated a request on behalf of a caller. When the
callee responds with a 180 Ringing message (with SDP) the B2BUA
negotiates the callee to the caller (who might be connected to a media
server, for example) so that a Ring back tone can be played or an IVR
session ensues. 

My queries are as follows

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" !

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?

Any help is appreciated.

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_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use sip-implementors at cs.columbia.edu for questions on current sip
Use sip at ietf.org for new developments of core SIP