Subject: Re: Multiple Levels of LMM agents (was: RE: [mobile-ip] Revised L ocalized Mobility Management Requirement s)

From: James Kempf <[email-masked]>
Date: Tue, 24 Apr 2001 15:46:11 -0700 (PDT)

Hi Phil,

>
>Oh, yes.  We had talked about this on the CT list just today.  Lets say I am a
>LMM pool hosting router.  We know that due to just the physics of proximity 
with
>other LMM pool hosting routers that any given host will almost always hand off
>exclusively with a certain set of "regular neighbors".  A security association 
(sort
>of a security web) is formed apriori with the regular neighbors so that secure
>tunnels are in place between all regular neighbors.  This makes the context
>transfer very fast, i.e. no dependency on building a secure tunnel before 
transfering
>it.  This allows the virtual LMM to simply walk through the pre-approved
>web of routers that it is authorized for.  If make-before-break is desired that
>can be added for seamlessness.

There is, of course, one problem here. The LMM agent doesn't necessarily have to 
be at the access router, in fact, many deployment situations would instead have 
it at the border router for purposes of reducing the frequency of globally
visible CoA changes. Otherwise, there is no benefit for the mobile node.

		jak

---

From: "Phil Neumiller" <[email-masked]>
Date: Tue, 24 Apr 2001 17:51:39 -0500

Hi James,

Some comments below.
----- Original Message -----
From: "James Kempf" <[email-masked]>
To: <[email-masked]>

> visible CoA changes. Otherwise, there is no benefit for the mobile node.

That seems odd to me James.  I guess I would not classify it as a "local"
method then?  Eitherway, there is no loss of generality here, exact same
technique can apply to border routers, why not?

---

From: Arthur Ross <[email-masked]>
Date: Thu, 26 Apr 2001 17:31:10 -0700

>visible CoA changes. Otherwise, there is no benefit for the mobile node.

Pardon me for showing up to this LMM party a day late & a dollar short -
had other distractions, and the volume of stuff on this thread has been so
large that it's been a bit challenging to keep up.

Seems to me that there is a basic issue that has slipped under the radar,
in the realm of "Where does IP meets radio physics?"

Most of this LMM discussion presupposes that the attachment points come one
at a time, and that there is a CoA change propagated as a result of MN
movement, the CoA associated with the old attachment link being replaced
with that of a new link.

That's too much of a simplification, depending on the nature of the air
interface in question.

The attachment points may be multiple and simultaneous, with time-varying
performance that will exhibit high raw error rates. From a comm-theoretic
standpoint, you will almost always do better in bad link conditions if the
network can use whatever transceiver resources are available, i.e. listen
from multiple transceivers & diversity combine them in the network;
transmit from multiple transceivers & diversity combine them in the MN.
This is what "soft handoff" in the CDMA air interfaces is all about.

This leads to the need to distinguish between the addresses of the access
transceivers (which may or may not be one-to-one with access routers), and
physical radio comm link addresses (spreading code, or whatever). The
physical addresses may be MN-permanent, BTS-permanent, dynamically
assigned, or something as yet to be defined. That is a question in itself.

I firmly believe that the IP nature of the network should extend down as
close to the ether as possible, meaning that those transceivers (BTS's, in
"big wireless" parlance), should be the lowest level in the LMM heirarchy,
however it is structured. But if you insist on that as a requirement, and
further require that, within broad limits, any air interface be
supportable, there is a problem. The nature of the air interface intrudes
into the lower layers of LMM. The routing problem is complicated by having
to deliver & collect to/from multiple places. That first level access
(border?) router will, in practice, wind up being a
"router/distributer/combiner", i.e. NOT universal and air interface
independent.

I think we need to keep in mind, when writing this stuff, that distinction
between MN permanent IPv6 addresses, CoA's, and radio addresses, .

   -- ahmr

---

From: "Phil Neumiller" <[email-masked]>
Date: Thu, 26 Apr 2001 21:02:29 -0500

Arthur,

Please take a look at the OBAST paper at http://federalmobility.com/.  I think this
will explain how to do this with CDMA macro-diversity selection.  The paper
describes a way to put macro-diversity into a BTS thus allowing BTSs, SDUs,
and RNCs to all be co-located at the edge of the network and function peer-to
peer.  What I have been describing in digestable chunks to the MIP list is
essentially OBAST.  Others have called it MIPv6, some have called it
MIPv4 fast handoff, but none of those address the CDMA issues (and therefore
3G issues) that you have brought up, except for OBAST.

Thanks,

Phil

---

From: Karann Chew <[email-masked]>
Date: Fri, 27 Apr 2001 19:44:31 +0100 (BST)

Could somebody please give me a pointer to the file/draft which describes
these "L ocalized Mobility Management Requirement s"?

Many thanks.

	Karann

++++++++++++++++++++++++++++++++++++++++++
Karann Chew   
Mobile Communications Research Group
Centre for Communication Systems Research
University of Surrey
Guildford
Surrey GU2 7XH
United Kingdom
Tel: +44 (0) 1483-879488
Fax: +44 (0) 1483-876011
++++++++++++++++++++++++++++++++++++++++++