3GPP analysis

[suresh.leroy@alcatel.be]

Hello,

After reading section 4.2 'IMS to IPv4 node' of
[draft-ietf-v6ops-3gpp-analysis-01.txt] I have a few small questions on
how this would work in practice.

1) If the destination is an IPv4 node registered to a dual stack SIP
server, is the interworking  then by default handled outside the IMS
operator's network or are there ways to keep the control whithin the IMS
operator's network.

2) How is the SIP-ALG added in the path for outgoing SIP calls (assuming
the SIP-ALG is only in the path when needed). Is it a configuration in
the S-CSCF, e.g. if DNS resolve only returns a IPv4 address then forward
SIP messages to SIP-ALG, SIP-ALG then resends again the same DNS query
to find the next 'IPv4' hop.

3) For incomming SIP sessions how is decided if the call should go to
the I-CSCF or the SIP-ALG. Is this done based on DNS information in the
IMS operator network, IPv6 address corresponding to I-CSCF, IPv4 address
to SIP-ALG.
This would result in external IPv6 SIP server sending their messages to
the I-CSCF and IPv4 servers forwarding SIP to the SIP-ALG.
How about external SIP server that are dual stack, where does it forward
SIP messages to.

Wouldn't it be easier if the ALG functionality for IMS would be
integrated in the I-CSCF or S-CSCF although there was heavy resistance
for this in 3GPP.

My apologies if these questions were already addressed in the past.

Regards,
    Suresh