Subject: [MOBILE-IP] Beacons (was: Re: [MOBILE-IP] handover)

From: James Kempf <[email-masked]>
Date: Wed, 26 Apr 2000 10:39:03 -0700

>Everything else in your note can remain true and might be easier
>to implement if beacons are available on a timely basis.  If beacons
>are not available, perhaps there wouldn't be any signal on which to
>base a measurement!  If a mobile node has to solicit a beacon, then
>there is the danger that many mobile nodes will do solicitations
<at the same time, causing collisions and so on.

Agreed. I can see a place for beacons, especially at L2. I have
more of a problem with them at L3, though I suppose they
are useful for propagating FA addresses without requiring the
mobile to solicit, for some L2s like 802.11 which do cell switching
at L2 and tell the L3 software about it later.

>Anyway, my main point is that there are tradeoffs that have
>to be considered.  Probably for some cellular designs, beacons
>are better than for others.

Agreed.

>I disagree on this point. In telecom infrastructures administered by
>few big companies, the nkowledge about network topology may be a very
>useful thing for network initiated handoffs.
>

The point I was trying to make is that network elements, like FAs,
are in a better position to know about network topology than
mobile nodes because the wireless ISP will have set up the network
and configured it that way. Especially if the mobile node is a small Internet
appliance or a mobile phone, the moble node may not have enough
memory for doing everything that is needed to do fast handoff
of real time media streams. The mobile node may also
lack the right authentication, especially when it moves to
a foreign network, and for it to get the authentication is yet
another step in the handoff process that can slow things down.

If the network makes the decision about handoff (in conjunction with
radio quality information from the mobile node, of course), then it can set up
QoS and other network resources beforehand, and the handoff process
can be much faster. Also, authentication for network resource management can
be arranged beforehand.

>I assume that in the future mobile ip world, there are so many
>networks offering access to the network that it is impossible to
>administer theri knowledge about each others topology to assist
>network initiated handoffs.
>

Perhaps this isn't a good example, but the interaction between
something like PBXs and the PSTN shows that it is possible
to have local area and wide area co-operate. Something similar
would be needed to do handoff between CDMA and 802.11.

>Furthermore, I really like the idea of MN being able to decide about
>the handoff. It brings some freedom to the MN, and doesn't add
>complexity to the network, which makes the network faster/more robust.
>

If the mobile node is a full featured laptop, there may be more
room for sophisticated processing to do handoff. But if it's an
Internet appliance or a mobile phone, it may not have enough
processing power. Even in the laptop case, there may be billing
and security considerations that would favor having the network
do the handoff.

                jak