Subject: Re: [Mip6] Mobile IPv6 handoff latency... (timeout)

From: "Jon-Olov Vatn" <[email-masked]>
Date: Mon, 28 Mar 2005 00:51:24 +0200 (CEST)

On Sun, March 27, 2005 8:31 pm, Alexandru Petrescu said:
> Thanks for the reference, after scanning the slides I must say I'm
surprised by the number of environmental factors...
>
> I'm also surprised that no presentation/paper I've seen until now talks
about the MN's actual processing power being an important factor in
handover latency.
>
> The MN's processing power is an essential factor in handover latency.
For example, for a inter-subnet handover set of DHCP message exchanges
the latency constantly stays around 1s (measured with Ethereal), but
measuring the time of the successful dhclient command with the Unix time
command gives ranges from 2s to 6s.  The difference can only be due to
the processing of different kernel and userspace data structures,
syncing, etc, on the MN.

No, DHCP has some timeouts for detecting duplicate address assignments,
see e.g. http://www.tele.dtu.dk/nts14/post-program/papers/paper25.pdf
These timeouts are implementation dependent, but has nothing to do with
the processing power on the DHCP clients and servers.

BW J-O

>
> Potentially, for optimizing handover latency there are bigger
> opportunities at software level and at topology-design level.  Looking
at measurement figures, I can say that optimizing protocol design can
have less of an impact than the two previously mentioned factors, just
an oppinion.
>
> Alex
>
> Jari Arkko wrote:
>> Handoff latency depends on a number of environmental factors. Not just
related to Mobile IPv6! A good overview of overall stack latency
>>  issuesin a 802.11 case can be found from
>>
>> http://www.drizzle.com/~aboba/IEEE/11-04-0377-01-frfh-analysis-roaming-techniques.ppt
>>
>>
>>
>>
>>
>>
>> Note that this considers full functionality, not just pure
>> non-secured 802.11. Typically, in commercial deployments you'd want the
L2 security turned on. And since you are mobile, pre-configured WEP
keys are unlikely to work for you.
>>
>> If you look at this, you'll realize that there's a lot of latency
around the whole stack. Fortunately, there are optimization attemps
trying to reduce delays for, I believe, each individual part of the
protocols that you need in a movement. For instance, in IETF we have
discussed optimistic DAD, better DNA procedures, and some schemes for
reducing Mobile IPv6 related delays.
>>
>> --Jari
>
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From: "Jon-Olov Vatn" <[email-masked]>
Date: Mon, 28 Mar 2005 00:59:05 +0200 (CEST)

...
> the processing power on the DHCP clients and servers.

Sorry, I did not realize that the link was outdated. Instead use
http://www.it.kth.se/~vatn/research/nts14-coloc.pdf
Some data on this paper:
Jon-Olov Vatn and Gerald Q. Maguire Jr., "The effect of using co-located
care-of addresses on macro handover latency", Fourteenth Nordic
Tele-traffic Seminar (NTS 14), August 18 - 20, 1998, Lyngby, Denmark.

You may also be interested in the following paper:
Jon-Olov Vatn, "Long Random Wait Times for Getting a Care-of Address are a
Danger to Mobile Multimedia", 1999 IEEE International Workshop on Mobile
Multimedia Communications (MoMuC'99), 15-17 November 1999, San Diego, CA
USA. Available at http://www.it.kth.se/~vatn/research/momuc-copyright.pdf

BW J-O