Subject: Re: [MOBILE-IP] handover

From: James Kempf <[email-masked]>
Date: Thu, 27 Apr 2000 08:37:05 -0700

Chip:

>However, this is not necessarily true. To begin with, only the mobile
>really knows what it can hear/sense, the infrastructure only know what
>it is told by the mobile or what it can _infer_ from listening. If a
>mobile has multiple interfaces, it may or may not have a way to tell
>the infrastructure about these interfaces -- but it can certainly make
>a local decision of which interface it wishes to use. Unless this
>mobile node (or another mobile node which visited earlier) tells a
>given infrastructure system about the existance of another
>infrastructure which could be able to this mobile how can the various
>infrastructures know about each other. For example, there is no method
>of telling the IEEE 802.11 network access point that at this moment my
>notebook happens to have a better access via an IrDA link than it does
>via the the 802.11 access point that is on the same desk. But this is
>easily handled at L3, but making the route via the IrDA interface
>preferable to the link via the 802.11 interface. But should I set a
>glass of tea in the way of the IR link, the notebook can easily use
>the radio link.
>

I don't think that anybody is proposing that the mobile node have
no say in handoff at all. In the case of multiple interfaces,
it may also be the case that the user needs to get involved, because
changing from one interface to another may have billing consequences,
or even accessability consequences, since the user may have an
account with the provider on one interface but not on another.

>Load balancing can be done in distributed manner, the base stations
>only have to provide the appropriate information (such as current or
>future prices for service) and the mobiles can start moving out or
>moving in (depending on the pricing).
>
>Roaming is an issue of AAA and a mobile can make use of any
>infrastructure that will give it service -- so if any service provider
>wants to service the mobile it can (if the mobile decides to ask it
>for service).
>
>I think that the mobile is best equipped to do the WLAN to (2G or) 3G
>handover - the best part is that the 3G operator doesnot even have to
>know of the existance of the WLAN. Also by allowing applications in
>the mobile to be aware of the impending change from WLAN to WAN then
>they can do things, such as quickly finish the transfer of the file
>which is being moved, adapt their performance and data requirements,
>... . Note that mobile can notify the WAN via the WLAN that it is
>going to want service and thus the WAN system can start to allocate
>resource, do authorization, etc. all before the mobile arrives
>(perhaps using even lesss control channel capacity).
>

And you want to do this with how much memory in the mobile node? :-)

Seriously, one of the best reasons for allowing the network to
take a more active role in handoff is to enable the deployment
of wireless Internet appliances that have very little memory
and processing power, for sensing and other purposes. Conventional
wisdom is that "memory is cheap and getting cheaper" but it is
not free and so there will always be room on the low end. Cell phones
currently have about 256K of application accessable memory on the
low end, 51

---

From: Gerald Maguire <[email-masked]>
Date: Thu, 27 Apr 2000 17:48:31 +0200

I'm certainly aware that memory is not cheap (in either cost or power
consumption). The current devices which I'm working with have 1Mbyte SRAM
and 1Mbyte of FLASH (the next version will have a bit more memory
because the OSs are so fat). Thanks to processors such as the
StrongARM it is possible to have high peak performance for relatively
little power and then slow down the clock and/or shutdown subsystems
to reduce the power even more.

However, I am working with systems that do have more than one
interface and also have lots of sensors (light level, temperature,
humidity, 3 axis accelerometer, audio in/out, ... ); one of the goals
is to have the mobile have a much greater sense of their location and
context which can be used in handoff decisions, functions presented
to the user, etc.

So in summary I am interested in very low power internet applicances.

Chip