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 10:35:40 +0200

Hi Jim, 

> > 	=> 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. 
> > 
> 
> 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.  
> 
	=> First of all it's not just me an Erik. Others can speak for
	themelves of course, but several people have expressed 
	similar opinions. The discussion is not limited to the 
	"today" time frame in any way. In fact the discussion has 
	been quite abstract, conceptual and constructive. 

	Just some background here, we have another draft that 
	just went through a WG last call (RegRegv4) and it does
	the exact same thing. This requirement never came up.
	So since it just came up suddenly I think it is important
	to understand whether:

	- There is anything specific to be considered for v6
	- If the need is justified.

> 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.
> 
	=> We can't control "forever", we can only design a protocol
	as we think it will be deployed. And to reiterate, the current
	protocol is extremely simple that I find it very hard to 
	see how it can't be extended in future should the need arise. 
	Of course the same can be done now, multi-level hierarchy
	can be optimised (it is already supported), but again 
	every requirement must be justified.

> 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.  
> 
	=> I don't think anyone can be so sure about "forever", I'm certainly 
	not. But we can't just put everything we can think of "just in case". 
	This can also make the design unusable and unrealistic. 

	Regards,
	Hesham

---

From: Jim Bound <[email-masked]>
Date: Thu, 10 May 2001 09:19:08 -0400 (EDT)

Hi Hesham,

> 	been quite abstract, conceptual and constructive. 

I agree sorry about just saying you and Erik but I know you guys best.
This is definitely constructive I think.
 
> 	- There is anything specific to be considered for v6

Not specific.  But generally all protocol work in the IETF need to be
aware of the scoping of IPv6 addresses in the sense will they affect
protocol operation. Also a new IPv4 protocol that can think transition
to IPv6 for deployment would be wise and not do anything to hinder that
eventuality but at the same time not negatively impact the performance of
the IPv4 stack would be wonderful or a router code base for fast path.

> 	-  If the need is justified.

Always an axiom IMO.

> 	every requirement must be justified.

That is a fair response.  If a first iteration of a spec does not prevent
evolution to other models thats a good spec.  The issue is then if people
want it now.
 
> 	This can also make the design unusable and unrealistic. 

I understand and not advocating the kitchen sink approach as that is
really bad design.  But as you I have real MIPv4 deployment going on with
real customers (3GGP2 and IMT-2000) and just the other day I saw a
customer scenario where multiple LMM levels of hiearchy could apply and
would reduce the signal delay at a local level.  They don't know about LMM
abstraction but they do want to reduce the scalability problems locally at
a cell remote from the Packet Data Switching Node (PDSN) and not duplicate
the entire PDSN when roaming under the same domain of RAN administration.

regards,
/jim