Subject: [Sipping] Comment on ISUP to SIP mapping draft 3

From: Romel Khan <[email-masked]>
Date: Thu, 4 Oct 2001 14:26:00 -0400

In section 12 of the draft, it states:
"Circuit Reservation Message (CRM) and Circuit Reservation Acknowledgment
(CRA) as part of its interworking procedures - although a SIP gateway should
not ever receive these messages, if it does receive such a message there is
no appropriate SIP action to be taken (the recommended behavior is sending a
REL in response to the CRM)"

Why should SIP Gateway (GW) never receive this message? Unless I am missing
something, this statement is blocking the following scenario which CAN
HAPPEN: A SIP GW can connect to an Access Tandem (AT) switch of an ILEC (e,g
Verizon) using SS7. The ILEC AT can connect to one of its end office (EO)
using MF inband. So if a caller connected to the EO makes a call that gets
routed to the SIP GW, then the AT will SEND CRM to the SIP GW. The right
behavior for the SIP GW should be to send CRA (according to the procedure of
ANSI T1.113) back and then wait for the IAM, and not to send a REL.

Please Look at Figure 11 A/T1.113.4 - "Successful call using circuit
reservation procedure" in ANSI T1.113 (1995). Then replace the Interexchange
Carrier Exchange (IXC) with the SIP GW, and you have the above scenario.

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