Subject: RE: Multiple Levels of LMM agents (was: RE: [mobile-ip] Revised L ocalized Mobility Management Requirement s)

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Thu, 10 May 2001 00:13:00 +0200

Just a couple of minor comments / questoins below.

> > The highest FA could be fully utilized for multiple reasons:
> > 1. running out of processing power to handle the rate of binding updates
> > 2. running out of memory to store the state for the bindings
> > 3. running out of bandwidth on its network interfaces for all
> >    the traffic to (and from?) the MNs
> > 
> > If you add a hierarchy of LMMs below this box and have the box continue to
> > serve the same number of MNs you can improve #1 but it doesn't change
> > #2 or #3.
> > If you instead of a hierarchy add N equal LMM agents at the top level
> > (e.g., with each MN in the domain randomly selecting which LMM agent to use)
> > then you can address scaling along all of the above axis.
> > 
> > So it all depends along what axis you think the agent will max out first.
> 
> I think the main reasons for intermediate levels are:
> 
> - Shorter signaling paths -- fewer chances for congestion and delays,
>   fewer nodes to process the control messages, and (O.K. maybe not huge)
>   better average performance -- but probably more consistent performance
> 
	=> The argument thus far has been whether there is any significant 
	improvement (in delays) that could outweigh the introduced
	complexity within the network. So far I haven't seen an argument
	to prove that there is such _significant_benefit.

> - Natural fit to hierarchical network architectures
> 
	=> There is hierarchy of a routers within the Internet today, 
	but do they all need to be mobile aware ? That is not 
	a trivial conclusion. The routing within a hierarchy of 
	routers is handled by standard routing protocols. 
	I don't think MIP is needed for this task.

>   ---- Backbone/Core Network/IP RAN at least, 
> 
	=> I don't know if there are any RAN standards
	that require this. However, if in future open RANs
	are standardised then the argument is the same 
	whether a network is a RAN or not.

>   But why should we have to botch the
> obvious network architecture in order to support something only marginally
> easier (if at all!) to implement
> 
	=> To avoid multiple single point of failiures and keeping unnecessary 
	state within the network. The solution is not so trivial IMO. 
	There are several downfalls to consider. Robustness is only one, 
	Security is another, network availability is another one. All that 
	amounts to cost. 

	Regards,
	Hesham

---

From: Jim Bound <[email-masked]>
Date: Wed, 9 May 2001 21:54:58 -0400 (EDT)

Hi Hesham,

> 	Security is another, network availability is another one. All that 

Your argument above is that the implementation is too complex not that
the idea of hierarchy is not valid.  I have heard this from Erik too.
From one implementor to the other I don't agree at all.  I cannot see why
your or Erick do not want to permit the ability tomorrow to distributed
the problems at hand to LMMs in a hierarchy.  I "think" what your saying
is that this working group should support forcing forever that the network
principles of hierarchy cannot be used for Mobile IP.

Will it cost more is a good and important question.  Yes it will.  And one
of our jobs as engineers is keep cost in mind with any solution (a
practice that is not followed widely in our community of late) and if the
only solution a hierarchial approach could implement was multiple levels
of hiearchy then I would agree.  But 1 level can be implemented which is
no hiearchy and that is the least cost.  But if a vendor and user want to
spend more money and use the principles of LMM with hierarchy then they
would not be able to with your view.  

To understand your view better are you and Erik (Erik can speak for
himself of course) saying that you want to prohibit LMM hierarchy forever
for Mobile IP LMMs.  Just to get exactly where people are coming from in
the most direct manner.

thanks
/jim

---

From: Charlie Perkins <[email-masked]>
Date: Wed, 09 May 2001 19:32:05 -0700

Hello Hesham,

Here are my comments.  After reading my last note, perhaps some
of the wording was too vigorous -- I got carried away.

>         to prove that there is such _significant_benefit.

There is obviously some benefit.  Any time you can put fewer
processing nodes in the middle of the signaling path, you will
get improved performance, surely at least by having less jitter.
I am worried that mistakes at this basic level will have ramifications
for future handling of video/multimedia streams, and various other
QoS (especially delay-oriented) reservations.

Plus it seems to stand out as the right thing to do.  Whether the
performance gain is significant probably depends on the particular
network architecture.  As has been noted, restricting the number
of levels introduces a new requirement to figure out how high or
low to place the LMM agents.  Having multiple levels of hierarchy
eliminates that particular design requirement, because of the next
main point -- that enabling multiple levels allows us to adapt
better to the natural design of networks.

>         I don't think MIP is needed for this task.

Nobody is saying that all the routers have to be mobile aware.
Only the LMM agents have to be aware, and not all routers are
expected to be LMM agents.

>         whether a network is a RAN or not.

It is very likely that we'll eventually have open RAN.
To me, it's clear that a RAN should be a collection of
IP routable networks.  Do you say otherwise?

If your argument is that we don't have IP RAN, so we
don't need leveled LMMs, then I believe that is a very
short-sighted argument.

>         Security is another, network availability is another one. All that

First, we should get the LMM agent architecture right.  Security will
not add any particular penalty here.  Network availability and robustness
are the same in this context.  That requirement can be met by some
protocol that resolves node failures (a routing protocol).  Whether
it's a modification to OSPF, or a manet, or something in-between,
is a problem we can solve in due time.  Getting the LMM architecture
wrong, though, is not so easily corrected.

Regards,
Charlie P.

---

From: Erik Nordmark <[email-masked]>
Date: Thu, 10 May 2001 21:29:50 +0200 (CEST)

> for Mobile IP LMMs.  Just to get exactly where people are coming from in

My message just before this one on the same topic can be summarized as:
I believe we either need a rich LMM solution (which has the same properties
as IP routing today - IP routing doesn't assume a hierarchical topology)
or we don't need any LMM solution at all.

  Erik

---

From: Jim Bound <[email-masked]>
Date: Fri, 11 May 2001 08:48:05 -0400 (EDT)

I agree Erik.  I need to go look at all the mail again.  My impression too
in my input is that while at the lower LMMs there would never be reason to
use LMMs at higher level but only adjacent LMMs.  That the CoA at each
hierarchy would not have to reported to the above levels.  Even the home
agent would not have to be notified of temporary CoAs as they only appl to
the LMM level in the hiearchy one is operating in as Mobile Terminal. The
Mobile Terminal would have a CoA that would in fact work anywhere in the
hierarchy at any level.  The temp CoAs are for that LMM level only.

Hence, I pretty much ignored the routing issues you stated to Charlie.

But if a CN sent a packet to the global CoA (for lack of better wording
now) all your routing issues become relevant to the Mobile Terminal being
found at say 3 levels deep in the LMM hierarchy for routing updates.

I believe supporting LMM hierarchy should demonstrate routing updates will
work.

But this is not something I for one can figure out in 1 or 2 days. I will
go look at it as others.  But this will take some thought.

Good come back and catch.......................

/jim