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

From: "Karim El-Malki (ERA)" <[email-masked]>
Date: Sun, 22 Apr 2001 16:23:12 +0200

Hello Raj and James

>>I do not think we should rule out multiple levels of LMM agents from
>>the requirements at this stage, but let's discuss the implications of
>>a multi-level hierarchy from a routing, deployment, failure-point etc.
>>perspective. Obviously there are quite a few people who feel quite
>>strongly about it and to rule it out would be unwise. 
>>
>
>Ulimately, the issue is one of deployment. The worst possible case
>is we cycle an LMM protocol without multiple levels of hierarchy
>to proposed and discover during deployment that we need it. 

We have been trying to identify what applications require multiple
levels of local agents (MAPs) linked to each other. This requirement
is still not clear to me, but I wouldn't rule out that we can
agree on reasons with more discussion.

What I would not like to see is a design which is made more
complex (and introduces multiple points of failure) solely to be
optimised for a special case of a hierarchy in which one BU is passed
on between mobility agents (MAPs). At least, this is what I'm
questioning. In fact the current WG draft (HMIPv6) does not rule out a
MAP hierarchy, but considers mostly a MN using one MAP. The v4 WG
draft (Regional Reg) also considers a 2-level hierarchy (one GFA
with one level of FAs below it) but allows multiple levels. Of
course, in v6 there can be multiple levels of ARs between MN and local
agent. As Raj wrote in a previous email, it is possible to have agents
(MAPs) located at different "levels" and the MN can use or be made to
use the appropriate one. These can be, but do not have to be necessarily
linked to each other. If packets need to be forwarded between local
agents, the MN can send appropriate BUs to the individual agents and
create a MAP hierarchy. This is allowed in the current draft and we can
work on further optimisations. It's need however is still being discussed.
I just wanted to clarify this point.

Regards
/Karim

---

From: Theo Pagtzis <[email-masked]>
Date: Mon, 23 Apr 2001 08:42:17 -0700

Hello Karim,

I personally think that by linking the LMMin a hierarchy will certainly
assist in the resiliency features that ensures survivability over single or
multiple points of failure.

I have further argued in previous emails that by providing a hierarchy of
LMMs the locality of signalling can be further optimized, to the closest LMM
point such that the velocity vector of the MN does not upset the transitive
permancency of the GMA/MAP/other point in an LMM scheme.

The above constitute serious reasons for me to include them in the
requirements set for LMM. Whether trivial domain depths want to default to a
single depth LMM is something that perhaps can initialise the LMM hierarchy
but SHOULD certainly be augmentable to more than one depths in the
LMM-aware (and subsequently underlying domain) routing element hierarchy.

You may see such need right now as redundant but I feel it is a requirement
waiting to arise when a more complex real-world LMM scenario _becomes_ the
norm..

Theo

UCL/ Mobile Systems