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RE: on NAT-PT

Hi Juha,

Thanks for the references.
- IMS is an extensive concept; when saying that IMS is "exclusively IPv6", it is a valid statement for all elements that are connected to the IMS / considered to be a part of the IMS. Both signalling and user data traffic
belong to the IMS. E.g. the connections between two IMS UEs belong to the IMS. Connections can only be IPv6, not IPv4 and not IPv4 & IPv6 simultaneously.
I don't understand why the IMS being "exclusively IPv6" would prevent two
IMS-capable UEs from opening IPv4 PDP contexts and connecting to each other
for non-IMS services.  I'm not even sure how you could prevent this, as
an IMS-capable UE has no real way of knowing whether the remote service
that it is trying to access is/isn't hosted on another IMS-capable UE.

It seems very likely that, regardless of the capabilities of the handset,
some folks will want to use IPv4-only devices behind the handset (IPv4-only
palm pilots, laptops, etc.) for some time.  Even after IPv6 is available on
most laptops, palm pilots, etc. they may still need/want to run IPv4-only
applications.  I can't understand how it would be in the best interests of
3GPP, IPv6 or anyone else to prevent two people who buy very high-end
IMS-capable phones from making an IPv4 connection between their two phones
to run an IPv4-only application...
- The user has to activate an IPv6 PDP context to access IMS and registrate to the P-CSCF (i.e. registrate to the IMS SIP server) using an IPv6 address.
Right, this is clear.  The IMS-capable UE will have to use IPv6 to access
SIP and other IMS services.  IMS connections to regular Internet SIP services
(which may be IPv4-only) will be done through a proxy.  So, the IPv6 <-> IPv4
conversion can also be handled by that proxy.  Are there other services that
are part of IMS that need to be proxied?
- E.g. tunneling traffic (IPv4 in IPv6) through the IMS and IPv4 connection from the IMS UE to the IPv4 correspondent node is not a feasible solution for IMS scenario 1.

However, the (3GPP Release 5) UE can use IPv4 (type of PDP contexts) to access other services than IMS, e.g. web browsing, MMS, e-mail...
When you say that tunneling (IPv4 in IPv6) is not feasible, is that just a
dogmatic position (based on the dogma that IMS is IPv6-only), or is there
a technical reason why you couldn't tunnel IPv4 over the IPv6-only parts of
the IMS infrastructure?

As far as handsets go, I think it is fine that they have to use IPv6 to
access IMS services, as those services are IPv6-only.  As long as they can
use IPv4 to access non-IMS services, I don't see where the need for NAT-PT
comes in.

I've just printed out the latest 3GPP scenario/analysis documents, and I'll
read them again...  But, I'm still not convinced that NAT-PT is really
needed in this situation, and I'd like to see a clearer technical analysis
of why less damaging alternatives (dual-stack, possibly combined with IPv4
in IPv6 tunnels) would not work.

Margaret





The latest version of the 23.221 specification can be found here:
ftp://ftp.3gpp.org/specs/latest/Rel-5/23_series/23221-570.zip

Best Regards,
                -Juha W.-

-----Original Message-----
From: ext Margaret Wasserman [mailto:mrw@windriver.com]
Sent: 20 January, 2003 18:00
To: BELOEIL Luc FTRD/DMI/CAE
Cc: Erik Nordmark; itojun@iijlab.net; v6ops@ops.ietf.org
Subject: RE: on NAT-PT


At 04:51 PM 1/20/2003 +0100, BELOEIL Luc FTRD/DMI/CAE wrote:
>Hi all,
>
> >
> > The proxy alternative may make sense for the 3GPP IMS case, as this
> > is a special case where only certain services are required to be
> > IPv6-only.  IMS-capable handsets may still be capable of opening
> > IPv4 PDP contexts for communication with non-IMS IPv4 nodes and
> > services.
> >
>I've proposed that solution for months but it seems that current 3GPP
>specifications do not allow such a solution.

My understanding is that the IMS subsystem is specified to be IPv6-only,
which will require that some services are only available on IPv6 (i.e.
the 3GPP version of SIP).  This may also result in some parts of the
3GPP infrastructure (routers and equivalent) being IPv6-only.

While a handset can be IMS-capable, I don't think that an IMS-capable
handset is required to be IPv6-only.  An IMS handset could still be
capable of establishing IPv4 PDP contexts, and using IPv4 to access
the Internet and/or non-IMS 3GPP networks and services...

Could someone correct me if I'm wrong, and please cite relevant parts
of the 3GPP standards?

Margaret