Subject: [mobile-ip] Agent Discovery during handover

From: "Tanis, Michael (Michael)" <[email-masked]>
Date: Thu, 12 Jul 2001 15:14:26 +0100

Hello all,

I am currently doing my MSc project in simulating the Agent Discovery
process in OPNET. There is a critical point where the MN is receiving
advertisements from two or more Agents. What should be the reaction of the
MN? Should it start registration according to the signal power received,
according to the Lifetime field or to the services offered ?

I would really appreciate it if someone could answer the question or point
me to the suitable document

Thanks in advance,   

--------------------------------
Michael Tanis

O Lucent Technologies UMTS-SAE
Optimus Building
Windmill Hill Business Park
Swindon
Wilts SN5 6PP  
United Kingdom

Work Tel: +44 1793 897856
Mobile  : +44 7779 032004
e-mail  : [email-masked]

---

From: Gerald Maguire <[email-masked]>
Date: Thu, 12 Jul 2001 16:32:45 +0200 (MET DST)

It is a complex policy decision which depends on the objectives of the
local node, the state of its communications, who the potential new
access point will server, the traffic which this access point is
currently service, the expected traffic that this mobile will add to
the access point, the time since the mobile last changed access point,
etc.

For example, if the mobile node was just recently using this access
point and has now switched to another access point - then you might
not want to switch back - so that you introduce some hysteresis.

For example, if the new access point is not likely to provide it with
the services that it wants, then there is no reason to register. (This
knowledge might come from an earlier visit or from another model node
who has passed htis information on to you.)

Another example, you currently have a streaming media connection via a
multicast tree, but you have not used Jiang Wu's pre-registration
approach to join the multicast tree of the new access point, then you
might want to delay registering until either you have pre-registered
or there is a lull in the streaming traffic or you are finished with
this application; then you might register with the new access point.

You might also be very cost sensitive, thus you might consider the
economic cost of staying with your current access point vs. switching.

...

As you can see, the decision to register or not can be a very complex
decision based on your policies, current state, expected future state,
... .

Chip

---

From: Pat Calhoun <[email-masked]>
Date: Thu, 12 Jul 2001 07:35:25 -0700

The Seamoby WG is working on defining handoff candidates discovery based
on certain characteristics or required features. In MIP, the fact that 
you've received an agent advertisement is sufficient.

So I suggest you send e-mail to the seamoby list.

Thanks,

PatC

---

From: Charlie Perkins <[email-masked]>
Date: Thu, 12 Jul 2001 08:54:46 -0700

Hello Michael,

As others have pointed out, it's not a trivial question.
And you are likely to get a diversity of opinions!

Chip's answer points out that it is at least as difficult
as choosing a route from among several alternatives.

But if we assume that all routes are equally preferable
except for wishing to minimize the number of registrations,
and assuming that no other information is available,
then there are two good strategies.

1) Pick the one with the best signal strength, making some
    allowance for hysteresis.

2) If signal strength is not available, then pick the newest
    beacon.  Don't switch back to old beacons unless the
    newer beacons stop working.

The latter strategy is called "Eager Cell Switching", and
it works better than "Lazy Cell Switching" because moving
bodies tend to continue moving (inertia) in the same
direction.

Regards,
Charlie P.