Subject: Re: [MOBILE-IP] IPv6 handover document

From: James Kempf <[email-masked]>
Date: Fri, 18 Aug 2000 09:33:34 -0700

Hi Chip,

>One of the changes which needs to occur is that WLAN manufacturers
>have to start designing their systems to support mobile clients,
>rather than the current model of simply eliminating the wire. If you
>really want to support mobility, you gain an enormous amount by having
>this second receive channel -- since then you can look for new access
>points. We also pointed out in an early paper that this means that you
>can also use a dedicated spreading code to send from an access point
>to a particular mobile (or group) or mobiles - while still using the
>first channel for two way communication. As the access point alone
>controls this 2nd channel you can have very highly efficient use of
>the channel and thus burst large amounts of data.
>

The problem is that wideband spectrum is *extremely* expensive. The
auctions that just completed in Germany resulted in licenses that
costed more that $9 billion per license. At that cost, the operators
are highly motivated to squeeze as much revenue as possible out
of each MHz. Perhaps if the radio protocol were designed correctly
the amount of actual housekeeping traffic on the second channel could be
limited, but, still, any use of spectrum for any housekeeping rather than
revenue bearing traffic is likely to meet with strong resistence. I think
that radio protocols which maximize the amount of revenue producing data per MHz
of spectrum used are more likely to interest operators.

                jak

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From: Gerald Maguire <[email-masked]>
Date: Fri, 18 Aug 2000 18:59:33 +0200

"Hesham Soliman (EPA)" <[email-masked]> ask about
WLAN and CDMA terminals.

Thus my response was largely directed to the WLAN and CDMA markets,
in the WLAN case these systems primarily use licensed equipment
rather than license spectrum -- so it is manufacturing costs which
is the major issue not the license fee for allocated spectrum.

Many existing CDMA cellular systems do in fact use spectrum for
"house keeping" - witness the pilot channel used by Qualcomm's systems.

As I noted, if you just wanted to indicate the presence of an
access point (i.e., offer service) -- you need very very little
bandwidth for this channel, so in the case of CDMA you can use long
codes and therefore you present little interference to the revenue
producing use of your spectrum.

In defense of this other traffic, it should be noted that even in GSM
systems each operator uses a control channel which has in most cases
very little traffic going over it {this is why it is possible to carry
some amount of SMS messages on this channel}. Of course it is possible
to have too much traffic for this channel and thus prevent the full
utilization of the other channels which an operator has licensed, but
I think this illustrates the problems of having fixed assignments of
traffic types to specific channels and the resulting limited ability
to multiple (which is not a problem which IP based systems should
have).

It should also be noted that for many cellular operators there is an
advantage of having mobiles able to find a more local means of getting
serivce as this removes traffic which has to contend for the larger
cell. Of course there are some practical difficulties as some
operators have these more local systems under one part of the
organization and the cellular group under another. This results in
some cases in suboptimal service to the customer. But in general the
customer always wins when they can get more local coverage as this
in general requires less power for a given amount of data transfer.

I think that we are starting to see operators who are recognizing that
even when they have licensed spectrum, that providing the service(s)
which are necessary to get and keep a large number of customers is a
much better business metric than simply maximizing $/MHz/year.

I think that one of the very important contributions of mobile IP is
to help operators and others to maximize service to customers/users
across whatever physical and link layer infrastructures are available.

Chip