Subject: [Sipping] SIP-T signaling to manage bilateral agreements

From: "Chaney, Charles" <[email-masked]>
Date: Mon, 29 Apr 2002 09:01:06 -0400

It's likely this has come up before but I can't seem to locate any
information on it:
 
From the information in <draft-ietf-sipping-isup-01> and RFC 3204, there is
no mention for including the circuit identification code from the ISUP
header in the SIP message body or the encapsulated ISUP since the
encapsulation starts at the message type code. In the PSTN the circuit code
is part of the ISUP message header and its handling is fully standardized.
It is used to not only identify the involved circuit or connection but also
allows assignment of specific handling by the source and destination network
nodes via bilateral agreements. These circuits are typically grouped
together in ranges, a.k.a., Trunk Groups and assigned special handling
properties. For there to be any form of interoperability between networks
(e.g., SIP bridging) support for this is fundamental. 
 
While there are some options that could be considered, the support must be
agreed (as a standard?) since multi-vendors are likely involved. Some
examples that one might consider for signaling the bilateral agreement
requirements:
 
- Dedicated SIP Call-Id allocation algorithms, known by the involved
signaling nodes.
 
- MG SDP (e.g., RTP address and port number) assignment and bilateral
knowledge about this allocation in involved call partner MGC assignments,
SDP.  
 
- Static assignment at the transport level, e.g., UDP port number could be
associated with a grouping of these circuits if UDP is used. Other transport
support would require further investigation.
 
- None of the above are proposals at this time, they are only meant to be
examples to further the discussion. Maybe there are others?

Regards,
Chuck Chaney