Subject: Re: [MOBILE-IP] Cellular IP Source Code Distribution

From: Roberts Phil-QA3445 <[email-masked]>
Date: Fri, 19 Nov 1999 11:37:55 -0600

Charlie, Andrew,

        we do need to exercise care when describing these things.  I'm in a
cellular development organization and find myself clarifying these points
repeatedly.  From the cellular perspective it must be pointed out that in a
mobile-ip implementation where the client is on a mobile separated from the
foreign agent by a cellular link, the mobile-ip protocol cannot update its
location until a new air interface link has been established, so it is
necessarily slower than a system not using mobile ip.  From the mobile-ip
perspective, it must be emphasized that it doesn't take much to update the
location once this is done.

Phil

-----Original Message-----
From: Charles Perkins [mailto:[email-masked]]
Sent: Friday, November 19, 1999 11:09 AM
To: [email-masked]
Subject: Re: [MOBILE-IP] Cellular IP Source Code Distribution

Hello Andrew,

I have a bone to pick with you (and with others who have
made similar statements) ...

>                                   Mobile IP represents
> a simple and scalable global mobility solution but lacks
> support for fast handoff control and real-time
> location tracking  found in cellular networks today.

This statement, which I have heard from many people, is
not technically correct.  It would be better to say
that "Mobile IP does not _mandate_ fast handoff", and
that "Mobile IP allows wide latitude for the time granularity
of location tracking".  I hope you will agree that the
two formulations are essentially different.  The result
of your formulation is, I think, misleading to many
people.  Reading your formulation, people might think
that Mobile IP _inherently_ suffers from poor handoff
performance.  They might think that Mobile IP _inherently_
has poor real-time performance.  Both of these are false.

As an example, using eager cell switching (ECS), we managed to
make Mobile IP work with smooth handovers, losing _zero_
packets.  Depending upon the characteristics of the physical
medium, it's no problem, and follows naturally from RFC 2002
(with the appropriate interpretation to allow the use of ECS).

Any statement containing the words "real time" is, as you
well know, a red flag begging for clarification and delineation
of the desired real-time behavior.  As an example of how
Mobile IP enables very tight real-time behavior without any
changes to RFC 2002, suppose we have a good layer 2
protocol that supplies timely information about media
conditions.  This is permitted, of course, by RFC 2002 --
in fact, it is encouraged and the protocol was specifically
designed to support such layer 2 protocols.

Then getting Mobile IP to work in real time is just a matter
of system design.  It is possible (in fact likely) that managing
tunnel drivers to work well, and getting authentication to work
well, will need close attention in the system design.  But that
is not really a problem with RFC 2002.

Thus, I strongly request that you modify your advertisement for
Cellular IP to reflect these considerations about how it might
possibly be misleading to uninitiated observers.

> Cellular IP attempts to combine the strengths of both
> approaches without inheriting their weaknesses. Cellular IP
> provides micro-mobility support interworking
> with Mobile IP (which provides macro-mobility support).

This statement might imply that Mobile IP is inappropriate
for handling "micro-mobility".  I have seen no such evidence.
It is true that Mobile IP can be _replaced_ in some scenarios
by other protocols that may _already_ be doing the job of
Mobile IP in those scenarios.  I have not seen evidence to
indicate that those replacement protocols do a _better job_
than could be done by Mobile IP, except insofar as traversing
the Internet for interaction with the home agent can take too
long.  For reducing that delay, very simple modifications to
the Mobile IP registration request message are appropriate,
and all schemes posit the existence of a local agent that
has proxy registration authority to relieve the need for
delivering registration packets over the Internet.

Thus, I would replace "micro-mobility" management with
"localized registration" management, to more precisely
focus on the right problem.

Thanks for listening to my requests for clarification!

Regards, and have a great day!
Charlie P.