Subject: [Speermint] draft-hancock-sip-interconnect-guideline - offerless INVITE requests

From: "Elwell, John" <[email-masked]>
Date: Fri, 31 Jul 2009 14:00:34 +0100

One of the points mentioned during this afternoon's presentation was
restricting the scope to basic 2-way call establishment **not** using
3PCC, which implies no support for offerless INVITE requests. I tried to
make a comment via Jabber, but it was not taken to the mic.

This would be an unacceptable limitation of the scope. Enterprises make
substantial use of 3PCC techniques, including third party call
establishment. This necessitates an offerless INVITE request to one of
the parties.

For example, I use my web browser to establish a call to you. The device
I wish to use is my cellphone, so it sends an offerless INVITE request
to, which will be routed to a PSTN gateway. The PSTN gateway returns an
SDP offer that can be used in the INVITE request towards you (who might
also be reachable via a PSTN gateway, or directly via SIP). If the
initial offerless INVITE request is carried inter-domain before reaching
the PSTN gateway, it needs to get through.

Note that this concern applies not just to enterprise-to-enterprise (if
the scope of the document were to be extended to include this), but to
any interconnect interface.

John