Subject: [Sipping] Optional optimisation for SIP overlap to ISUP en-bloc (Overlap WG LC)

From: "Chris Hogg" <[email-masked]>
Date: Wed, 12 Jun 2002 09:53:27 +0100

Hi all,

Apologies for the lateness of this proposal in the WGLC.

I have a comment on draft-ietf-sipping-overlap00.txt. In section 4.1
"Receiving subsequent INVITEs" I would like to propose an optional
enhancement for the case of a SIP overlap to ISUP en-bloc call where the
gateway has the ability to identify whether or not it has received enough
digits.  The enhancement is fully specified by adding one line of text
(marked [CH]) to the paragraph in section 4.1.

4.1 Receiving subsequent INVITEs

   An egress gateway does not have any means to know whether SIP
   overlap signalling is being used or not. So, upon reception of an
   INVITE, the gateway generates an IAM following the procedures
   described in [3].

   If a gateway receives a subsequent INVITE with the same Call-ID and
   From tag as the previous one and an updated Request-URI, a SAM
   should be generated as opposed to a new IAM. Upon reception of a
   subsequent INVITE, the INVITE received previously is answered with
   490 Request Updated.

   If the gateway is attached to the PSTN in an area where en-bloc
   signalling is used, a REL for the previous IAM and a new IAM should
   be generated.  

[CH] "As an option, if the gateway can determine that there are too few
digits received in the INVITE for the call to be routed "en-bloc" to the
ISUP network then the gateway shall respond with a 484 Address Incomplete."
[CH]

Comments?

Thanks

Chris Hogg
Nortel Networks