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

From: James Kempf <[email-masked]>
Date: Thu, 7 Jun 2001 10:03:00 -0700 (PDT)

>> I don't think this text should be added.
>> 
>> It is entirely unclear at this point whether buffering will work without 
causing
>> user-perceivable artifacts in real time streams. In fact, I know of
>> at least one experiment with buffering (in IPv4) that showed it cannot be 
done.
>> This experiment was not definitive, of course, but I think it is
>> not wise to write buffering into the standard until more is known
>> about whether it will work or not.
>> 
>> There are other alternatives to handoff smoothing, for example bicasting,
>> that could handle some portion of the handoff smoothing task without
                     ^^^^^^^^^^^^  please note!

>> introducing artifacts. We need to leave the standard open on this
>> until there is more evidence.
>
>you didnt get it. consider this scenario. the MN has sent a F-BU
>to the oldAR. lost the link connection. the oldAR starts forwarding
>packets to the newAR. MN hasnt shown up yet at the newAR. it hasnt 
>sent a F-NA or a NA to the newAR yet. (there is some delay in
>the MN moving and establishing a link layer connection). if the 
>newAR does not buffer these packets it would have to drop it. 
>bicasting does not help here.
>

As I said, "some portion". I agree that there may be need for buffering
on newAR, but currently the draft does not mention any handoff smoothing
technique. I don't believe it should mention any, unless it clarifies
that bicasting can be used too.

		jak

---

From: "Charles E. Perkins" <[email-masked]>
Date: Thu, 07 Jun 2001 10:31:00 -0700

Hello again,

> that bicasting can be used too.

But I believe that bicasting is problematic in many ways that do not
apply to proper buffering techniques.  For instance, there is the
problem of how to handle multple levels of wireless IP routers.  We
should be very careful to avoid standardizing techniques for general
protocols that are only applicable to specific scenarios.  Then there
are the control issues (when to start? when to stop?), TCP issues,
and at least two or three others that I can't remember right now.

Buffering, on the other hand, can be made to be deterministic and
precise, as well as delay-bounded and time-limited.

I am not wholly against bicasting, because I think it can be made
into a useful addition to the set of smooth handover tools.  However,
it needs to have a lot of work I think before it can be considered
as part of network-layer standards.  The considerations seem to
be somewhat different at the physical layer.

Regards,
Charlie P.