Subject: [Sipping] Question regarding reliable provisional response retransmission

From: DarshanBildikar 70559 <[email-masked]>
Date: Wed, 15 Jun 2005 10:18:05 +0500

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.

******************************************************************************************
 This email and its attachments contain confidential information from HUAWEI, which is intended only for the person or entity whose address is listed above. Any use of the information contained herein in any way (including, but not limited to, total or partial disclosure, reproduction, or dissemination) by persons other than the intended recipient(s) is prohibited. If you receive this e-mail in error, please notify the sender by phone or email immediately and delete it!
 *****************************************************************************************

_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use [email-masked] for questions on current sip
Use [email-masked] for new developments of core SIP

---

From: xupeili <[email-masked]>
Date: Wed, 15 Jun 2005 17:38:49 +0800

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: [email-masked] [mailto:[email-masked]] On
Behalf Of DarshanBildikar 70559
Sent: Wednesday, June 15, 2005 1:18 PM
To: [email-masked]
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. 

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.

************************************************************************
******************
 This email and its attachments contain confidential information from
HUAWEI, which is intended only for the person or entity whose address is
listed above. Any use of the information contained herein in any way
(including, but not limited to, total or partial disclosure,
reproduction, or dissemination) by persons other than the intended
recipient(s) is prohibited. If you receive this e-mail in error, please
notify the sender by phone or email immediately and delete it!
 
************************************************************************
*****************

---

From: Dean Willis <[email-masked]>
Date: Wed, 15 Jun 2005 13:39:19 -0500

On Jun 15, 2005, at 12:18 AM, DarshanBildikar 70559 wrote:
> 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