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.
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?
tim
________________________________
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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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