Subject: [seamoby] To talk about L2 or not?

From: James Kempf <[email-masked]>
Date: Wed, 7 Mar 2001 11:06:41 -0800 (PST)

Hi Dave,

>However, I think it is perfectly reasonable to focus on protocol
>interoperability.  For example, I think it is perfectly acceptable for a
>micro-mobility protocol to have hooks built in for Layer 2 (aka access
>network) triggers in order to achieve greater efficiency.  Of course it
>would be great if existing layer 2 protocols could take advantage of these
>hooks from day one, but if not, that's a layer 2 problem.  I think of
>several examples of where this would help in the Mobile IP space, and my
>guess is that there maybe some that could help in the seamoby space as well
>(we'll find out as we start moving into the solution space).

This is an idea that I have been in favor of for some time, particularly
with respect to fast handoff in Mobile IP.

The problem is that it is very difficult to get good performance and
a clean design without making some assumptions about what L2 provides. My 
feeling is that one can come up with a set of abstractions which describe the L2
support required, then design the protocol around those. The abstractions
are not specific to any particular L2, and they can be structured such that a 
particular L2 can implement a certain set, and the L3 protocol can
be designed to reflect that. If the L2 implements none of these hooks,
then there needs to be a simple fallback L3 implementation which might not
perform the best, but nevertheless is possible.

A precedent is how maximum frame size is handled in the IPv6 specification.
In RFC 2460 on pg. 24, IPv6 requires that every link layer have an
MTU of 1280 octets or greater. This establishes an abstract L2 specification
for IPv6 with regard to MTU size, and specific L2 implementations must
match it by providing segmentation/reassembly if they don't support
that large an MTU.

It seems reasonable to me that the new functionality involved in mobility
(handoff, maybe paging) will naturally require similar L2 abstractions, 
because mobility has historically not been part of the base assumed
available for implementing IP. Naturally, one doesn't want to go
overboard, so the abstractions should be carefully chosen. 

There seems to be a certain amount of resistance to this position within
the mobile IP group, and I have not yet heard anyone articulate a clear
position why. Deering and Hinden could have left out the abstraction
of L2 included in the IPv6 spec, but they chose to include it, presumably
because it simplified the IPv6 design, or promised better performance,
or possibly both. I think the same will prove to be true of L2 
abstractions for mobility.

		jak

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From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Wed, 7 Mar 2001 21:23:14 +0100

> position why. 
	=> Actually I've talked to a few active members in the MIP group
	about that idea last year and they all seemed to be supportive. 
	I've had a half finished draft on this topic (with a couple of people 
	here ) for over a year and never got around to it. But I think it's 
	essential to do .... one day !

	Hesham

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From: "Martin, David P" <[email-masked]>
Date: Wed, 7 Mar 2001 16:51:24 -0500

James,
I agree as well, in fact it was probably you or someone else in one of these
groups that converted me :)

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From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Wed, 7 Mar 2001 23:29:10 +0100

Hi John,

> > 	here ) for over a year and never got around to it. But 
> >     I think it's essential to do .... one day !
> 
> I'm sure there are some folks on this list that will help you
> finish it.  Would you consider discussion of this work here?
> 
	=> Sure, it seems there is interest in this area. I've already
	received a couple of supporitve private mails expressing 
	interest. So hopefully we can have something out after 
	Minneapolis.

	Hesham

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From: [email-masked]
Date: Thu, 8 Mar 2001 00:03:06 +0200

Hi Hesham,

John