Subject: RE: [mobile-ip] Draft Agenda for MIP WG @ IETF54

From: Singh Ajoy-ASINGH1 <[email-masked]>
Date: Mon, 24 Jun 2002 11:56:09 -0500

Hello Masatak-san,
Sorry for jumping in the middle.
Please find my in-line reply. 
regards,
ajoy 

-----Original Message-----
From: Masataka Ohta [mailto:[email-masked]]
Sent: Monday, June 24, 2002 11:08 AM
To: James Kempf
Cc: [email-masked]; [email-masked]
Subject: Re: [mobile-ip] Draft Agenda for MIP WG @ IETF54

jak;

> > Which particular layer 2 technology, are you saying, is necessary
> > to support smooth handover with two receivers?
> >
> > There is none and it works with any layer 2 technologies.

> I'm sorry, Ohta-san, but it does not. It does not work with cdma2000 and
> it does not work with wCDMA. If you think this is so, then please point
> to the paragraphs in the spec that say it will. These protocols are
> designed to use soft handover with a single Rake receiver on the mobile
> station. They are not designed to use two receivers.

Huh?

W.r.t CDMA, I stated in my draft that:

:   Note that a CDMA based wireless transceiver can simultaneously use
:   two access points with different code without additional RF modules.

What are you trying to deny?

Ajoy-> CDMA does not provide multiple simultaneous IP 
accesses. In soft-handoff, a terminal sends multiple copies of same 
radio frame to the selector via different base stations. 
The selector chooses the best frame from the multiple copies
of the received frame. 
 
Can you please point to the paragraphs in the spec that say it will
need multiple RF modules?

> These protocols are
> designed to use soft handover

As is stated in RFC 1958,

:   2.3 It is also generally felt that end-to-end functions can best be
:   realised by end-to-end protocols.

:   To quote from [Saltzer], "The function in question can completely and
:   correctly be implemented only with the knowledge and help of the
:   application standing at the endpoints of the communication system.
:   Therefore, providing that questioned function as a feature of the
:   communication system itself is not possible. (Sometimes an incomplete
:   version of the function provided by the communication system may be
:   useful as a performance enhancement.")

that some link layer has link specific functionality (such as link
soft handover of some CDMA link layer) may be useful as a incomplete
performance enchancement (though, in general, performance rather
degrades), it is merely allowed as an exception.

Ajoy-> Could you please elaborate how soft-handoff degrades the performance?

IP layer solutions can ignore that some link protocol is designed
to use soft handover.

Ajoy-> I guess IP layer solution must not assume that a 
terminal will always have multiple transmitters/receivers.
This may work in your case, but will not work in most of the cases
where no such provision is available.  

That CDMA has an imcomplete L2 function does not mean we should
not have a complete version at L3.

Ajoy-> What do you mean? Could you please elaborate?

						Masataka Ohta

---

From: Masataka Ohta <[email-masked]>
Date: Wed, 26 Jun 2002 00:58:26 +0859 ()

ajoy;

> Please find my in-line reply. 

You are welcome.

> accesses.

Nor WLAN does, because of interference.

But, terminals on the Internet tolerate some packet losses.

Moreover, as is written in RFC1958:

:   (Sometimes an incomplete
:   version of the function provided by the communication system may be
:   useful as a performance enhancement.")

just as WLAN, a CDMA link layer may deploy CSMA/CA or something
like that to reduce probability of packet losses.

> In soft-handoff, a terminal sends multiple copies of same 

If you are using phone, it is two way streaming communication so that
it is OK to asume you have something to send frequently enough.

However, if you are receiving voice, music or video stream, there
is nothing for the terminal to send so frequently.

Of course, terminals without data can generate beacon frames, but,
it is a waste of bandwidth.

> Ajoy-> Could you please elaborate how soft-handoff degrades the performance?

It is a generic statement not necessarily applicable to soft-handoff
of your CDMA.

However, see above.

> terminal will always have multiple transmitters/receivers.

Just as an IP layer solution assume that a terminal has
at least one transmitters/receivers, it can assume that
a terminal has more than one transmitters/receivers.

For example, ICMP redirect assumes that a default router has
multiple interfaces.

It has nothing to do with whether the solution is at IP or
other layer.

> where no such provision is available.  

Assume that a network with no such provision as selector is
available, which is the Internet today.

If base stations are connected by a private IP network, you can
put selectors whereever you wish. But, it is not the case with the
Internet.

According to your explanation:

> In soft-handoff, a terminal sends multiple copies of same 

you assume IP packets to the selector is sent via different base
stations.

Then, you are assuming that link layer between the selector
and the base stations has special L2 header with signal
quality information.

You also assume terminals have something to send frequently to the
selector.

That is, your soft-handover is an imcomplete L2 function.

						Masataka Ohta