Subject: RE: Cellular host requirements, 01 & next steps

From: "Soininen Jonne (NET/MtView)" <[email-masked]>
Date: Thu, 4 Oct 2001 10:29:58 -0500

Hi Mattias and Alexandru,

as Mattias states it is important that GGSN does not have to do DAD.
Thus, the same method is used as with PPPv6. In addition, there is
nothing in the mobile that could reliably be used as the interface
identifier. Especially, as the mobile can actually have many PDP
Contexts open with different IP Addresses.

Cheers,

Jonne.
-----Original Message-----
From: ext Mattias Pettersson [mailto:[email-masked]]
Sent: Thursday, October 04, 2001 7:39 AM
To: alexandru.petrescu
Cc: Delecki Andrew-Y10658; 'Jari Arkko'; [email-masked]
Subject: Re: Cellular host requirements, 01 & next steps

Alexandru Petrescu wrote:
> 
> > Appendix A of the draft, uses text from 3GPP TS 23.060, Clause
9.2.1.1
> > without any criticism.
> 
> The funniest thing of the 3GPP "stateless autoconf" is that GGSN
> provides the "unique interface identifier" (an equivalent of an
EUI-64)
> to the mobile as if the mobile would not know its own unique ID.

The reason for this, AFAIK, is to get rid of DAD on the GGSN side. If
the GGSN hands out IDs from a pool it can easily keep control of what
IDs are unused and DAD becomes a simple task.

On the other hand, if the GGSN was to do real DAD, it would have to scan
a probably *huge* address space to detect collisions, as the GGSN is the
only node that knows all the addresses used since the terminals never
talk directly to each other.

/Mattias

> 
> OTOH, I can understand this if 3GPP considers there'll be a sort
> of "tunnel" between mobile and GGSN, like in PPP.  But in that
> case they just can't state this is stateless autoconf.
> 
> Alex
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---

From: Alexandru Petrescu <[email-masked]>
Date: 05 Oct 2001 02:10:35 +0200

> as Mattias states it is important that GGSN does not have to do DAD.

Hi Jonne.  At first I thought I misunderstood what Mattias wrote; but
now that you re-state it, I really don't understand: is GGSN involved
when mobile does DAD?  Or I might have a totally different mental
model of it.

> Especially, as the mobile can actually have many PDP Contexts open
> with different IP Addresses.

Is there any effort somewhere that tries to "flatten" those underlying
channels into an entity that could present itself as a "shared" medium
to the above IP (and not channels; I understand channels lend
themselves to Point-to-Point approaches)?  Thanks for any info.  I
think it's that entity's address that could lead to a unique ID.

Again, in my understanding, the whole point of a node doing DAD is
that it doesn't have to obtain that address from a central server.
Automagic à la Apple.  Distributed.  But, if the mobile is required to
get something from a server and required not to do DAD, then why not
getting the whole address from the GGSN?

Alex