Subject: Re: [MOBILE-IP] Comparison of Fast Handoff and Proactive Handoff

From: "Karim El-Malki (ERA)" <[email-masked]>
Date: Thu, 13 Jul 2000 12:09:17 +0200

Hello James

>  I just had an opportunity to look through your draft,
>  draft-elmalki-mobile-ip-fast-handoffs-02.txt and compare it with the
>  work that Pat and I are doing.

Thanks for the comments, it's good we've started discussing this.
It would have been better though if you had looked at it before
issuing your draft since we could have started this exchange of
ideas earlier. Too bad :)

>  A major and important difference from our work is that in the
>  work we are doing agent advertisment beacons at L3 are not
>  necessary, nor
>  is there a need for the mobile node to register before receiving
>  packets from the new FA. The old FA directs the new FA to take
>  the handoff without the involvement of the mobile node, and the GFA
>  registers the mobile for some period of time.

Yes. That was what I was talking about in my past email.
You are performing registrations on behalf of the MN without
the MN having any control on this or being aware that it is happening.
I have reservations regarding this approach. First, this is different
from RFC2002 and Regional Registrations, since the MN is not involved
in the registration process. Also, say that the MN does not want to
register with certain FAs. Hiding the L3 handoff procedure from the
MN removes any possible L3 handoff control from the MN.

Network control of L3 handoff is possible in both our approaches, but
MN control of L3 handoff is not possible in your approach.

> The mobile, upon
>  receiving packets from the new FA, then performs a full registration.

I assume that one of these packets is an advertisement?

>  This has a number of consequences:
>
>  1) The lack of need for L3 beacons means that there is no need
>  to take up precious air time on a bearer channel for those
>  radio systems (like
>  3G systems) where spectrum is licensed, and often very expensive.

Well, it is not necessary to send advertisements all the time over the
air. This saves spectrum. Some systems specify that advertisements should
be sent over the air following L2 handoff. However I can't see how this
relates specifically to your draft. Please expand.

According to my understanding, in terms of spectrum there is no difference
between our approaches. We have the MN register before the handoff while
you have the MN register after the handoff. Therefore the same amount of
messages (advertisements and registrations) are sent over the air, just the
timing is different.

>
>  2) The new FA has an opportunity to perform checks of QoS
>  capacity and other
>  resource checks before admitting the mobile. A new FA can
>  additionally
>  reject a handoff if taking the mobile would exceed the QoS capacity.
>  In that case, the old FA can try to hand off the mobile to another
>  FA before the mobile's signal fades to the point where packet drop
>  becomes a problem.

This can all be done in our approach too. The new FA can reject the
MN's registration before the handoff, and multiple FAs may be advertised
to the MN in case of failure etc.. Our advantage is that the MN is aware
that it is registering and that it's registration is accepted/rejected.

>
>  3) As mentioned in my previous email, with our draft, it is possible
>  to perform handoff between two RANs that are not directly
>  connected at L2,
>  although it would require some L2 support and some exchange
>  of L2 information
>  between the two disconnected RANs through L3. This is important for
>  3G systems, but probably not something the mobile IP group wants to
>  dwell on, since it does involve L2 details.

I agree with you that we should not dwell on L2 details. However I don't
agree that what you are saying above is necessarily an important thing
for 3G systems. Radio networks don't always need to be directly connected,
but they exchange messages which we consider as radio-specific L2 messages.
That is our assumption which is applicable IMO and allows us to hide most
L2 details and concentrate on generic L3 handoffs.

Regards,
Karim

---

From: "[email-masked]" <[email-masked]>
Date: Thu, 13 Jul 2000 07:17:11 -0700

> ideas earlier. Too bad :)

I don't think it's too late. I believe that exchanging ideas in this fairly
complicated, and possibly controversial space, can only benefit the WG. We
need different mechanisms so that we can explore the alternatives, and agree
on the best solution. It could very well be that the best solution is a
combination of two or more.

> MN removes any possible L3 handoff control from the MN.

The draft makes it clear that the Mobile Node MAY ignore packets from a
Foreign Agent, and it certainly does not have to register with it either. Yes,
it is different from RFC 2002 and the Regional Registration draft, but keep in
mind that we are trying to solve a problem that I believe wasn't fully covered
in those specs. btw, the FA is NOT registering on behalf of the Mobile Node,
it is simply informing its GFA that a Mobile Node is entering its cell. The
Mobile Node STILL needs to register.

> MN control of L3 handoff is not possible in your approach.

Incorrect. The Mobile Node has full control over who it is willing to register
with. If two FAs share a common GFA, then the draft does allow new FAs to
receive traffic for the Mobile Node entering its cell before the registration
occurs. However, this assumes that the GFA and FAs are under the same
administrative control, so I see no harm since your traffic is already
traversing that net.

The advantage is that the Mobile Node sees virtually no packet drops as it
moves into a new cell.

> I assume that one of these packets is an advertisement?

Correct.

> relates specifically to your draft. Please expand.

We do not get into L2 advertisement issues in our draft, as the Mobile IP WG
tries to stay away from L2 issues. Certainly, an air interface is more than
welcome to add advertisements to their protocol.

I agree that advertisements must be issued sparingly, but when should the FA
issue them? That is the issue at hand. The longer the delay between a Mobile
Node entering a cell, and receiving the advertisement, the longer the
hand-off. We still require that the advertisements be sent by the FA to the
MN, but service is already provided before registration (again, this is
inter-domain).

> messages (advertisements and registrations) are sent over the air, just the

But how long does it take for the MN to detect that it needs to perform the
handoff? The timing is what fast hand-off is all about.

> that it is registering and that it's registration is accepted/rejected.

same here.

> L2 details and concentrate on generic L3 handoffs.

This is also NOT covered by the pro-active FA draft, and the draft works quite
well without the propagation of L2 data, so let's not worry about this in this
WG.

PatC