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Re: [Sip] 199 Open Issue: UAS sending 199

Title: 199 Open Issue: UAS sending 199
Christer,
 
Sorry, when I said "mis-interpret what they see as forking" I meant to refer to serial forking, which is of course a form of forking.  So there's no mis-interpretation (except mine!). 
 
But anyway the thought was that by providing a way to explicitly release an early media stream the 199 could enable a "middle box" (SBC) that today blocks serial forking, to support it.  This is one of the use cases Hadriel mentioned.
 
tim
 
 
 

From: Christer Holmberg [mailto:christer.holmberg at ericsson.com]
Sent: Tuesday, November 18, 2008 4:14 PM
To: Dwight, Timothy M (Tim); IETF SIP List
Subject: RE: [Sip] 199 Open Issue: UAS sending 199

Hi Tim,
 
>My opinion is that 199 shouldn't be restricted to cases involving forking, since some of its utility lies in  
>mitigating the behavior of middle boxes that mis-interpret what they see as forking. 
 
I am not sure I understand. Could you please clarify?
 
>Is it possible to define a simpler version of alternative #4, giving general guidance as to when a 199 may be issued  
>and being prescriptive about what the recipient is to do upon its receipt? 
 
Personally I think it would be very difficult to come up with something general and useful.
 
Regards,
 
Christer
 
 
 

From: sip-bounces at ietf.org [mailto:sip-bounces at ietf.org] On Behalf Of Christer Holmberg
Sent: Tuesday, November 18, 2008 1:17 PM
To: IETF SIP List
Subject: [Sip] 199 Open Issue: UAS sending 199


Hi,

The main open issue in the 199 draft at the moment is when a UAS sends 199 - IF a UAS sends 199.

The alternative proposals I have at the moment are described below (can also be found in the slides I was supposed to present yesterday).


1.      UAS never sends 199:

In this case only forking proxies/B2BUA would send 199.



2.      UAS always sends 199:

The issue with this alternative is that 199 would be sent even if no forking has occurred - which can be assumed to be the case in a large percentage of all calls.

3.      UAS sends 199 if forking proxy does not support 199:

With this alternative the forking proxy would have to insert an indicator that it supports 199.

Also, the UAS may not know whether it is the forking proxy closest to the UAS that has inserted the indicator. This may not be a big issues, since I assume in most forking cases there will only be one forking proxy in the signalling path.




4.      UAS sends 199 once procedures have reached a certain state

With this alternative 199 would not be sent until certain actions have taken place on an early dialog

Example: preconditions have been indicated as met
Example: SDP answer has been sent

The issue is that one would always have to specify at what point of different procedures 199 would be sengt.



5.      UAC and UAS negotiate sending of 199 once the early dialog has been established:

With this alternative that UAC would tell the UAS that forking has occurred (could this be useful information also for non-199 procedures?), and that it wants 199 to be sent.

The issues with this alternative is that it may require additional signalling (unless PRACK/UPDATE won't be sent for other reasons) to inform the UAS that forking has occurred.

Other alternatives?

NOTE: Robert S also raised an issue on what Require: 199 means. But, I think that outcome of that issue may depend on what way forward we choose for the issue in this mail.

Regards,

Christer 

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