Subject: Re: [MOBILE-IP] handover

From: James Kempf <[email-masked]>
Date: Thu, 27 Apr 2000 09:33:15 -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 anyone is proposing that the mobile play no role in
handoff. In the case where there are two interfaces, it may even
be necessary to get the user involved, because there may be
issues of pricing and accessability. The user may not have
an account with the provider on the other interface, for example,
or may want to know how much it will cost to transfer to the other
medium.

>
>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).
>

And you want to do this with how much memory? :-)

Seriously, one of the key reasons for having the network take a more
active role in handoff is to enable wireless Internet devices
that are relatively cheap and require little processing power.
Low end cell phones currently have about 256K of application memory,
and supporting full featured handover on them may require more.
Conventional wisdom is that memory is cheap and getting cheaper, but
it's not free and I think there will always be a place on the low
end for interesting applications.

>    - soft-handover support in CDMA systems
>While adjusting the arrival times of the wavefronts from multiple base
>stations can't easily be done by the mobile, the mobile can invoke
>IP simulcasting from multiple base stations and then as long as at
>least one copy of a packet makes it to the mobile it will not loose
>any data and thus can achieve a soft-handoff.
>
>

I don't think soft handoff is a good candidate for replacing with
IP mobility. Hopefully, there will be a ID forthcoming shortly that
explains why.

                jak