Subject: [Mip6] Delay Analysis for Handoffs with Mobile IPv6 Route Optimization

From: Christian Vogt <[email-masked]>
Date: Fri, 13 Jan 2006 13:50:29 +0100

I would like to call your attention on work that we have done on IPv6 
handoff procedures:

   "A Comprehensive Delay Analysis
    for Reactive and Proactive Handoffs
    with Mobile IPv6 Route Optimization"

http://doc.tm.uka.de/2006/vogt-2006-delay-analysis-for-reactive-and-proactive-handoffs.pdf

   Abstract:  Optimizations to reduce handoff delays
   inherent in Mobile IPv6 Route Optimization as well
   as IPv6 router discovery, address configuration,
   and movement detection have so far been mostly
   considered on an individual basis.  This document
   evaluates three integrated solutions for improved
   handoff experience in surroundings with different
   preconditions:  reactive handoffs with unmodified
   routers, reactive handoffs with router support, and
   movement anticipation and proactive handoff manage-
   ment.

Your feedback will be welcome!

Regards,
- Christian

-- 
Christian Vogt, Institute of Telematics, Universitaet Karlsruhe (TH)
www.tm.uka.de/~chvogt/pubkey/

_______________________________________________
Mip6 mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/mip6

---

From: Thomas C Schmidt <[email-masked]>
Date: Sun, 15 Jan 2006 16:00:23 +0100

Hi Christian,

the mailinglist seems to be gone for the weekend ... so this is very 
private ...

Christian Vogt wrote:

> While your results [1] on FMIPv6 and HMIPv6 shed light on the
> performance of proactivity in combination with local mobility
> optimizations and are as such undoubtedly very important, I do not
> necessarily consent with your statement that those results can be
> conveyed to the end-to-end mobility management that we have been
> analyzing [2].
> 

I perfectly agree with your characterisation. I did'nt mean to say that 
both approaches are the same. What I tried to suggest is that there 
might be some lessons to be learned from [1] for your work.

 From an abstract point of view the approaches of FMIPv6 (predictive 
part) and proactive end-to-end mobility management agree in hiding 
update delays by advancing handover negotiations on the basis of 
predictions.

Beside problems with the reliability of predictions they both rely on 
timing issues: negotiations have to be successfully completed for the 
schemes to work. You are addressing this issue in section 7.1 of [2], 
but what we would like to contribute as the essence of [1] reads:

There are three different timescales, one defined by the HO scheme + 
Internet topology, another by the L2 technologie and the third by the 
actual movement of the mobile user. They are fairly independent of each 
other.

It may as well happen that the degree of coincidence required by your 
scheme corresponds to a quite narrow regime in phase space, which is 
hardly ever met. Thus it is *possible* that the fascinating perspective 
of zero update delay is just a conceptual result, which basically does 
not hold in reality. Details of course are subject to a thorough 
analysis, which you will probably do.

Best regards,

thomas

> [1] http://www.informatik.haw-hamburg.de/~schmidt/papers/telesys05.pdf
> [2]

---

From: Christian Vogt <[email-masked]>
Date: Sun, 15 Jan 2006 14:40:23 +0100

> We analysed these properties for the case of FMIPv6 (which should be
> transferable in major parts, e.g., fmip needs fback, you need BU to
> arrive ...) and found no significant improvement by predicitions (see
> bib-reference attached).

Thomas,

thanks for bringing this up.

During an end-to-end Mobile IPv6 handoff, communications are delayed for
at least a global RTT between the MN and the CN (assuming that
end-to-end optimizations such as EBU and CBA are deployed).  This
minimum delay can basically be eliminated in two ways:

- Proactivity, i.e., send a BU from the old location and move to the new
location only when packets can expected to have arrived there.

- Local mobility optimizations such as FMIPv6 and HMIPv6, which either
eliminate global signaling (HMIPv6), or move it off the critical
blackout period (FMIPv6).

Your work [1] deals with the second option, our's [2] deals with the first.

To be more explicit, let's assume we use FMIPv6.  All global signaling
is then deferred until the MN has already resumed communications, from
the new link, through the AR-to-AR tunnel.  This is true for both
proactive and reactive FMIPv6 modes.  What *FMIPv6 proactivity* saves
you is just an FBU's propagation time from the new AR to the old AR.
Compare this to the global RTT that *end-to-end proacitvity* potentially
saves you.

Referring to the problems with predictive handoff procedures that you
mention:  You are correct, and section 7.1 in our analysis duely
discusses this.  As far as unreliability in predictions goes:
Unfortunately, you are right, but that's a different construction site. ;)

Regards,
- Christian

-- 
Christian Vogt, Institute of Telematics, University of Karlsruhe
www.tm.uka.de/~chvogt/pubkey/

Thomas C Schmidt wrote:
> Dear Christian,
> 
> thanks for bringing your technical report to our attention!
> 
> For a comment: it is our experience that the optimistic concept of zero
> handover delay due to predictive procedures does not survive reality.
> 
> This is mainly due to
> 
>   - the independence of anticipation, signaling and handoff in
>     occurrence and timescale.
> 
>   - predictions turning out as rather unreliable.
> 
> We analysed these properties for the case of FMIPv6 (which should be
> transferable in major parts, e.g., fmip needs fback, you need BU to
> arrive ...) and found no significant improvement by predicitions (see
> bib-reference attached).
> 
> Song et al. ([11] in our references) made empirical studies on
> predicitions including the campus geometry, statistical correlation
> analysis of user date ... and arrived at dissapointing 72 %.
> 
> It's a nice vision - but sometimes real-world isn't as nice ;)
> 
> Best regards,
> 
> thomas
> 
> Christian Vogt wrote:
> 
> ------------------------------------------------------------------------
> 
> @article{sw-pvrah-05,
>   author = {Thomas C. Schmidt and Matthias W{\"a}hlisch},
>   title = {{P}redictive versus {R}eactive -- {A}nalysis of {H}andover {P}erformance and {I}ts {I}mplications on {IP}v6 and {M}ulticast {M}obility},
>   journal = {Telecommunication Systems},
>   volume = {30},
>   number = {1--3},
>   pages = {123--142},
>   month = {November},
>   year = {2005},
>   publisher = {Springer},
>   address = {Berlin Heidelberg},
>   url = {http://dx.doi.org/10.1007/s11235-005-4321-4},
>   abstract = {Handovers in mobile packet networks commonly produce packet loss, delay and jitter, thereby significantly degrading network performance. Mobile IPv6 handover performance is strongly topology dependent and results in inferior service quality in wide area scenarios. To approach seamless mobility in IPv6 networks predictive, reactive and proxy schemes have been proposed for improvement. In this article we analyse and compare handover performance and frequencies for the corresponding protocols, as they are an immediate measure on service quality. Using analytical methods as well as stochastic simulations, we calculate the performance decreases originating from different handover schemes, the expected number of handovers as functions of mobility and proxy ratios, as well as the mean correctness of predictions. In detail we treat the more delicate case of these rates in mobile multicast communication.
>  It is obtained that performance benefits, expected from simple analysis of predictive schemes, do not hold in practice. Reactive and predictive handovers rather admit comparable performance. Hierarchical proxy environments -- foremost in regions of high mobility -- can significantly reduce the processing of inter--network changes. Reliability of handover predictions is found on average at about 50 \%.},
>   theme = {mipv6|mmcast},
>   file = {http://www.informatik.haw-hamburg.de/~schmidt/papers/telesys05.pdf}
> }

---

From: Thomas C Schmidt <[email-masked]>
Date: Sat, 14 Jan 2006 16:44:05 +0100

Dear Christian,

This is mainly due to

Best regards,

thomas

@article{sw-pvrah-05,

---

From: Christian Vogt <[email-masked]>
Date: Mon, 16 Jan 2006 08:39:51 +0100

Hi Thomas.

> I perfectly agree with your characterisation. I did'nt mean to say
> that both approaches are the same. What I tried to suggest is that
> there might be some lessons to be learned from [1] for your work.

Yes, in particular with respect to the reliability of movement 
predictions, which you are considering in [1].  This is definitely an 
interesting issue, albeit it is the link-layer folks that must 
eventually solve it.

I would also assume that the reliability of predictions strongly depends 
on the access technology.  E.g., in GSM, you have bidirectional 
measurements that you can take into account.  This is not necessarily 
true for other link layers, such as IEEE 802.11.

 >  hardly ever met.

Zero handoff delay, at the IP layer, is indeed possible only when 
certain assumptions hold.  And as discussed in section 7.1 of [2], this 
is not always the case.  However, end-to-end proactivity can perform 
better than reactive approaches even when conditions are sub-optimal.

To exemplify this, let's consider the packet-propagation latencies on 
the old path versus the new path during a proactively managed handoff: 
If the new path is longer, the mobile node may have to wait for packets 
after it has switched links (subsequent to receiving a Binding 
Acknowledgment on the old link).  If the new path is shorter, some 
packets may already be lost on the new link before the mobile node 
arrives there.  But in both cases, the blackout time is usually shorter 
than in a pure reactive approach.

Anyway, all this is discussed in more detail in [2].

- Christian

[1]
http://www.informatik.haw-hamburg.de/~schmidt/papers/telesys05.pdf
[2]
http://doc.tm.uka.de/2006/vogt-2006-delay-analysis-for-reactive-and-proactive-handoffs.pdf

Thomas C Schmidt wrote:
> I perfectly agree with your characterisation. I did'nt mean to say
> that both approaches are the same. What I tried to suggest is that
> there might be some lessons to be learned from [1] for your work.
> 
>  timing issues: negotiations have to be successfully completed for
> the schemes to work. You are addressing this issue in section 7.1 of
> [2], but what we would like to contribute as the essence of [1]
> reads:
> 
>  Internet topology, another by the L2 technologie and the third by
> the actual movement of the mobile user. They are fairly independent
> of each other.
> 
>  hardly ever met. Thus it is *possible* that the fascinating
> perspective of zero update delay is just a conceptual result, which
> basically does not hold in reality. Details of course are subject to
> a thorough analysis, which you will probably do.
> 
> Best regards,
> 
> thomas
> 
>> [1]
>> http://www.informatik.haw-hamburg.de/~schmidt/papers/telesys05.pdf 
>> [2]