Subject: RE: [mobile-ip] Hierarchy and Low Latency Handoff

From: James Kempf <[email-masked]>
Date: Tue, 24 Apr 2001 16:37:48 -0700 (PDT)

Hi Hesham,

>	Either way, the main point here is that delays on the 
>	wire are completely insignificant compared to the 
>	delays over the air. This is a _proven_fact.
>

Not quite. I did a little experiment at IETF50 to see what signalling
delays would be for an intercontinental BU - about 160 ms RTT to Japan
and Europe. That is over half the RTT delay recommended by the ITU
before human perception notices a gap. I think transcontinental
times would be maybe half of this. 

If the network operator cannot deploy a hierarchy of LMM agents,
they may not be able to counter.

But I think you've missed my point. You maintain, as I understand it, that we 
shouldn't include hierarchy because there is no demonstrated need for it
at this time. We've been discussing this issue for some time, and I've
just come up with an interaction between low latency handoff and
hierarchy that could cause an interruption in real time traffic
in certain deployments. Arguable, but possible.

Do you honestly believe that this won't happen again? 

			jak
			
PS: On the issue of handoff smoothing, there is more that could be
said and I think there are other problems with bicasting in addition
to the ones identified in the low latency MIPv6 work. We have kept it
in the low latency IPv4 handover draft for now. This issue should
be discussed in a separate thread when the drafts are put up for
working group review, here is not the right place to talk about
it.

---

From: Erik Nordmark <[email-masked]>
Date: Thu, 26 Apr 2001 07:41:27 -0700 (PDT)

Jim,

> they may not be able to counter.

Why not. Each operator could solve the above by having an LMM agent
per continent. Or they could be more fine grain and have one per metropolitan
area.
I don't see what benefits you could derive (and what the numbers would be
in terms of signalling traffic volume and signalling delay) by an
operator having e.g. both continent level LMMs as well as metro-area LMMs.
 
  Erik