Subject: Re: [mobile-ip] Some Analysis

From: Erik Nordmark <[email-masked]>
Date: Wed, 2 May 2001 10:23:46 +0200 (CEST)

Jim,

Your analysis concludes with 
> But this is not possible by the inequalities in Equation 1 above.
> 
> Thus, the signalling latency in the hierarchical case will always
> be better.

Assuming my brain has some remaining amount of logic processing,
I think there is another possibility. Equation (1) is when you claim
it makes sense to deploy an hierarchical scheme.
Thus what I've think you've shown is that when it makes sense to
deploy the hierarchical scheme (per your constraints) it does better
than the non-hiearchical scheme. But that, depending on how you defined
(1), might be a tautology - if (1) is defined (which it seems to be)
to capture the case when an hierarchical scheme does well then
I'm not surprised that you can show that it does well.

Thus for this avenue of reasoning to be fruitful I think it needs to
be done without the assumptions you call "deploying X only makes sense if".
So something more akin to 
 given a topolgy for a network and some movement patterns that might be
 known in advance, try to first optimally place the LMMs (and presumably
 the placement is different for hierarchical vs. non) and then compute
 the handoff delay etc.

I think it would be useful to have a single example toplogy to stare at
and do some guestimates to get a feel for the differences.
An example of such a toplogy would be capture the fact that there are
ranges of delay (a lot larger between metro areas than inside metro areas, and
presumably likewise at a granularity smaller then a metro).

Does anybody have some insight they can share on what this looks in
practice?

  Erik

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From: James Kempf <[email-masked]>
Date: Wed, 2 May 2001 09:30:42 -0700 (PDT)

Hi Erik,

>I'm not surprised that you can show that it does well.

Right, the point I was trying to make was, given that it makes sense
to deploy a hierarchical scheme (it might not always, basically
network engineering is always needed), would not having that capability
negatively impact performance.

		jak