Subject: Re: [mobile-ip] questions on fast handoffs for MIPv6

From: James Kempf <[email-masked]>
Date: Thu, 7 Jun 2001 10:30:41 -0700 (PDT)

Hi Charlie,

>There are already familiar cases where buffering occurs with
>IP, with good effects.  For instance, typically a packet
>will be buffered today if there isn't an ARP cache entry
>for a node on the same network as the sender.
>

Sure, I wasn't saying that it wouldn't work,  I was saying that
it is still not clear that it is the only solution. The draft
currently doesn't mention handoff smoothing techniques, I think
it should be left that way, unless bicasting is mentioned too.

>I find it very difficult to believe your statement that
>an experiment has shown that buffering cannot be done.
>Can you provide a citation for this work?  My guess is

The work was never published. It was communicated to me by
one of the engineers who were involved in the study (personal
communication).

>that some unnecessary assumption is being made to cause
>the particular buffering scheme not to work.  In fact,
>I can "prove" that buffering can be made to work, by a
>really simple-minded argument that is so silly that I
>don't want to repeat it here.  That would cause a lot of
>argument about the "proof", and deflect discussion away
>from the real point.  Which is, that whether buffering can
>work or not depends entirely on the restrictions being made.
>
>I support Vijay's suggestion to incorporate some very
>minimal buffering at the new access router during the
>time until which a positive indication of link establishment
>can be detected.  It seems almost intuitively obvious that
>it can work on the tiny timescale that is implied.
>

I would rather see the draft kept neutral with respect to handoff
smoothing, unless all possibilities are mentioned.

		jak

---

From: "Charles E. Perkins" <[email-masked]>
Date: Thu, 07 Jun 2001 10:40:42 -0700

Hello again Jim,

> it should be left that way, unless bicasting is mentioned too.

This was the intention all along; the fast handover draft was
specifically limited by choice of the design committee to
avoid issues of smoothing handovers.

> one of the engineers who were involved in the study (personal

I believe I am familiar with the work you mention, and I think
that the difficulty that was established was not intrinsic to
buffering but had more to do with tunnel establishment and a
particular race condtion with Mobile IPv4 at that very fine
timescale.

> smoothing, unless all possibilities are mentioned.

As noted above, I agree with this also.  My solution would
be to have a new draft, dealing with smooth handovers.

Regards,
Charlie P.

---

From: Behcet Sarikaya <[email-masked]>
Date: Thu, 07 Jun 2001 13:53:18 -0400

Hi Charlie,

"Charles E. Perkins" wrote:

>  My solution would

I second this. But at the same time there is the question of why in the
first place this was not included in the fast handover draft for
mipv6? The answer is (my guess) there was no agreement on which regional
registration protocol to use in the DT. Maybe now there
is an agreement. This leads me to suggest that DT could extend its life
a bit longer to come up with a single draft for fast and smooth
handover.
What do you think?

--
Behcet

---

From: "Charles E. Perkins" <[email-masked]>
Date: Thu, 07 Jun 2001 12:49:23 -0700

Hello Behcet,

You wrote:

>          ............        there is the question of why in the
> registration protocol to use in the DT.

No, this issue was not important in the decision.  The agreement
to concentrate on fast handover instead of smooth handover came
because we realized they were different problems.  There is a
relationship, because the faster the handover, the less time there
is to lose packets.  But the problems are different.

Furthermore, the choice of localized mobility management protocol
is not closely related (in my mind) to either problem.  This can be
seen by considering that handovers (can) depend on a "local" address,
and localized mobility management depends on a "remote" address.
Alternatively, one could say that fast handover deals with tunnel
extension, and localized mobility management deals with localized
signaling for tunnel re-establishment.  Nevertheless, the problems
are not completely independent.  They are different but loosely
related.

>                                                     Maybe now there

I think that there are still enough issues with the fast handover
draft, that we need to focus on that one thing and get it right.
Keeping smooth handovers in a separate draft document will help
to maintain focus.

Regards,
Charlie P.