Subject: [Sipping] Queries about draft-petrie-sipping-xfer-issues-00.txt

From: "David R. Oran" <[email-masked]>
Date: Wed, 22 Oct 2003 08:02:25 -0400

Some initial comments and queries on 
draft-petrie-sipping-xfer-issues-00.txt. In most cases I think there are 
easier fixes than the ones you suggest in the document.

1. Isn't your "Consultative Transfer to Lost Target" exactly the sort of 
problem GRUU fixes? If TT' returns a GRUU in the 200OK contact of the 
Invite, the TC just puts this GRUU in the Refer-with-replaces to the TE, 
and the TE->TT' Invite is guaranteed to go to the right place.

2. For "Consultative Call Prompting" and other similar advisory notices 
about the purpose of a call, just like for email, isn't the "Subject:" 
header exactly what's called for?

3. For "Consultative Turned Blind Double Ring" I think we could easily give 
the right hint by putting a "Reason: replacement dialog coming" in the 
reason header of the CANCEL. This is exactly the sort of thing the reason 
header was created for.

4. "Coerce Gateway Hairpins" is the first of these scenarios for which 
reasonably obvious use of existing protocol features doesn't seem to hold a 
solution. I have a suggestion though, which might have wider applicability, 
and now that we have GRUUs may be just the ticket. Define a new header 
field called "Dialog Affinity: <gruu>". The semantics would be for the 
proxy in the destination user's domain to attempt if possible to route the 
request to the same UA (in this case gateway) as is indicated by the 
corresponding Contact: address of the referenced GRUU. Finer granularity to 
the trunk level could be achieved if the subject gateway manufactured GRUUs 
which contained grid values identifying the appropriate trunk.

5. For "Consultative Turned Blind Gateway Glare" I don't see how we could 
ever fix that, given the inherent glare scenarios present on the PSTN due 
to the single TDM channel mapping property of calls. The entire SIP 
architecture exploits the ability to have parallel and overlapping dialogs 
to the same destination.

Dave.

------------------------
David R. Oran
Cisco Systems
7 Ladyslipper Lane
Acton, MA 01720
Office: +1 978 264 2048
VoIP: +1 408 571 4576
Email: [email-masked]

_______________________________________________
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