Subject: RE: 3gpp-analysis-04: SIP/SDP transition [issue10]

From: <[email-masked]>
Date: Fri, 22 Aug 2003 15:29:38 +0300

Hi,

that's right. SIP/SDP transition scenarios still need more work and I think the generic SIP/SDP transition problem (mainly) belongs to SIP wg(s), not our wg. Anyway, main lines of a recommended "IMS interworking" mechanism should be written out in our document. 3GPP Analysis currently describes SIP ALG that modifies SIP/SDP, and no changes are needed in basic Rel5/Rel6 UEs. Draft-elmalki... describes a bit modified solution proposing some changes in the UEs, i.e. the UE needs to understand a new header to put the IPv4 address received into SDP using the ALT extension.

Cheers,
	-Juha-

-----Original Message-----
From: ext Pekka Savola [mailto:[email-masked]]
Sent: 25 July, 2003 06:20

The text in section 4.2 on IMS scenarios describes SIP/SDP transition
scenarios.  At least based on Karim El-Malki et al.'s work, it is not
apparent that ALG should/has to change the SIP messages and SDP payload.  
I thought the "architectural" approach would have been been different,
i.e., in principle, make the IPv6-only IMS aware of the payload
translation, a la RSIP.  In any case, the SIP/SDP transition scenarios
need to be fleshed out a bit more.

=====
    SIP and SDP transition has to be made in an SIP/SDP Application
    Level Gateway. The ALG has to change the IP addresses transported
    in the SIP messages and the SDP payload of those messages to the
    appropriate version. In addition, there has to be interoperability
    for DNS queries; see section 4.1 for details.