Subject: [MOBILE-IP] handoffs

From: Gwendal LE GRAND <[email-masked]>
Date: Tue, 25 Jan 2000 18:23:35 +0100

Hello,

I would like to know how much time is necessary to complete a handoff. Is
there a minimum value since a certain number of Router Advertisement have to
be missed ?

Thanks

Gwendal

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From: "[email-masked]" <[email-masked]>
Date: Tue, 25 Jan 2000 10:14:58 -0800

There is a considerable amount of work in progress that will ensure that the
delay in the hand-off will be minimized. The new I-D that I announced
recently, which allows the FA to send a hand-off request to a MN will reduce
the delay.

Right now the said draft isn't a WG item, but I hope to make it by Adelaide.

PatC

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From: Francis Dupont <[email-masked]>
Date: Tue, 25 Jan 2000 20:08:47 +0100

In your previous mail you wrote:

=> I think this is very dependent of the kind of movements (according
to experiments with IPv6 mobility where there are Router Advertisements
but where they are not used as you have suggested, ie. detection is
mostly based on prefixes).

Regards

[email-masked]

PS: this is not a new question then there are some papers about this
(just wait for more answers?)

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From: Tom Weckström <[email-masked]>
Date: Tue, 25 Jan 2000 23:24:51 +0200

Hello,

Yes, there has been lots of work going on in minimizing the handoff
time.

There are several 'variables' affecting the handoff time:
        - Robustness of the FA equipment
        - Network speed
        - Network latency between the Foreign network and MN's Home Network
        - Link layer quality (probability of packet loss)
        - etc...

One of the most important variables is the network latency between the
FA and HA. E.g. This latency can easily be N * 100ms. For example:

--- www.cisco.com ping statistics ---
41 packets transmitted, 41 packets received, 0% packet loss
round-trip min/avg/max = 173.1/175.1/182.7 ms

And this was done with a 100Mbps connection to a switched core. :)

Some customized proposals, like:
 R.Caceres and V.Padmanabhan,
 `Fast and scalable handoffs for wireless internetworks,'
 in Proceedings of the 2nd IEEE Annual International
 Conference on Mobile Computing and Networking (MOBICOM),
 Rye, NY, USA, November 1996.
have achieved really short handoff times, but they mainly use link layer
optimizations and/or then make specific assumptions on the underlying
link layer - which the basic Mobile IP does not do.

In optimizing the handoff time, localized handoffs have an important
role.
Handoffs can be localized entirely on the network layer with a
hierarchical Mobile IP solution, where the signalling required in
handoffs only travel a minimal distance to a point in the FA hierarchy,
where the previous location (and thus the session information) of the MN
is known.

Dynamics team at Helsinki University of Technology has been implementing
and testing Dynamics - HUT Mobile IP, a hierarchical Mobile IP on Linux.

We have achieved handoff times of 20ms, when the full advantage of the
hierarchy is achieved. Passing one more layer in the hierarhcy has
brought some 19ms more to the handoff time, but this is mainly dependant
on the core network speed and the robustness of the FA machines, and can
be further decreased.

These results are from our tests, where the FAs in the hierarchy have
been relatively slow i486/120MHz based computers with WaveLAN adapters
(downlink) and 10Mbps Ethernet connections (uplink).

These results show that hierarchical Mobile IP, like Dynamics, can
provide secure and fast handoffs to support e.g. glitchless audio
streaming to mobile devece while roaming in campus area wireless LAN.

A research paper about our hierarchical solution was presented in
MoMuC'99 conference. The paper is available from Dynamics web site
http://www.cs.hut.fi/Research/Dynamics/

Best regards,
                Tom

--
        Tom Weckström           Dynamics group
                                Helsinki University of Technology
                                [email-masked]
                                http://www.cs.hut.fi/Research/Dynamics/

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From: Foo Siang Fook <[email-masked]>
Date: Wed, 26 Jan 2000 09:29:59 +0800

Gwendal,
        Yuh, there is a minimum value if u strictly follows RFC2002
protocol which uses ICMP messages (minimum value one second for each
messages) for the router advertisement. Since it requires three
advertisements to be missed (assuming without using any link layer
protocol), the minimum value is >2 seconds to complete a handoff (this
excludes the distant registration time period,CPU processing etc.). The
average value is 2.5 seconds (also excludes the distant registration time
period, CPU processing etc.)

        However, there are a lot of proposals to shorten the advertisement
periods or to use link protocol for handoff. Note that we also need to
consider the distant registration period during handoff. There are a few
drafts to solve the distant registration period such as HFA, RAFA etc.

regards,
Foo Siang Fook

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From: "Andrew T. Campbell" <[email-masked]>
Date: Tue, 25 Jan 2000 21:10:36 -0800

Best I've seen Cellular IP do between bases lab is 3 ms ;-)
We demoed this at IEEE MOMUC99.