[e2e] YNT: A Question on the TCP handoff

Detlef Bosau detlef.bosau at web.de
Mon Dec 5 10:07:52 PST 2005

I will snip the reference network here. It can be found in the former
However, we should care for some readability here.

Alper, perhaps you please could check your linebreak settings.

Alper Kamil Demir wrote:

> >There is some pre-established connection between SA2 and MH


What are SA1 and SA2 doing?


In my former mails I asserted "routing".

> 1) There is a TCP connection ("actual connection") between MH and FH
> 2) Before MH moves into cell of SA2,  a new "warm-up connection" is established between SA2 and FH according to MH's User Mobility Pattern (UMP). (SA2 is  as much close to MH as possible)

Please define "close".

> 3) When MH enters cell of  SA2, "warm-up connection" becomes "actual connection" ( warm-up connection is handed over).
>     I am questioning if this is ever meaningful and/or possible?

I think, we should define the term "connection" here.

For me, a TCP connection has to endpoints.

So, if we talk about state variables: In that case it doesn´t make sense
to keep the old state variables around the cell change.
However, the term "connection" wouldn´t make sense here, because it´s
not clear what a "warm up connection" from BS to MH is.

If, however, a "warm up connection" means a TCP conection from BS to MH,
you would exchange components in Split connections.
Even in that case, the connection between FH and SA1 may be different
from that from FH and SA2.

To make a long story short: When a TCP path changes, its state variables
can change as well.

> >If there is no traffic vom SA2 to MH, there would be no channel storage
> >capacity being assigend to your flow. If you enter
> >this cell with some CWND, you would suddenly send packets to the new
> >path.
> If what we are proposing is meaningful, a new CWND and other congestion parameters 
> resulting from "wam-up connection" is handed over. Before and during handover, there will be some synchronization problems.

CWND estimates the available fair share for a connection. CWND is
estimated on an end to end basis.
I don´t quite understand, how you will get a CWND from a warm up

> >Perhaps, you do not even know whether the bottleneck between FH and MH
> >is situated in the Internet or whether the bottleneck
> >is the wireless network. Particularly, this may change as a result from
> >roaming.
> Assuming that SAs are somewhere close to MH.

Once again: Please define "close".

> >In some respekt, your approach reminds me of the M-TCP work by Brown and
> >Singh, 1997.
> >I still think that you try to keep state variables for a TCP connection
> >although its path changes fundamentally. And I´m not convinced that this
> >will work.
> That's correct. However, User Mobility Pattern (UMP) is proposed in our work. still not convinced?


Particularly, it would be _VERY_ hard to convince me of any kind of User
Mobility Patterns.

There are tons of UMP around. The ones are bad, the others are worse.
Nearly all of them are proven
by repeated assertion or by assistance of God or something like that.

First of all, UMP and paramter estimation appear to me as some
independent problems.
Second, when you want to convince me of a certain UMP, there is exactly
one way to do so:
You _must_ validate your model with _real_ observations, with
measurements from _real_ life.
I´m admittedly tired of all those endless "stochsastic automatons" or
"Markov Chains" etc, at least as
each and any textbook on Markov Chains starts in the introduction with
the remark, that 
reality is anything but markovian. And I´m tired to read, that some
researcher has
1. read this,
2. understood this,
3. ignored this.

Admittedly, I did not yet read your UMP. (My blood pressure ;-))

But once again: When we talk about a UMP, I only could be convinced,
when the pattern is 
validated with reality. A pure "system model" (hopefully, one of the
then thousands of them 
will mach reality or reality would change according to our system model)
is not sufficient.

Perhaps this sounds somewhat harsh.

It just reflects my own situation. For about several yeas now I think
about "interactions between L2 and L4
in mobile wireless networks."

And now, I´m desperately hoping for contradiction for the next sentence:

"There are none."

I know, that there are dozens of PhD theses wich solve these problems or
alleviate these interactions
or shield the Internet from the mobile network.

Interesting solutions.

Again waiting for contradition:

"These solutions are looking for problems."

Of course, I´m expecting tons of mails now :-) And I would be glad about

Our common problem is: Some problems cannot be identified by pure
thinking. (It´s to the best of my knowledge
the very change from the attidute of Plato to the research attidute of
Leonardo or Galieo Galilei and I´m ashamed
of all these people here in Stuttgart, who occasionaly ask for my
address and then are not able to spell
"Galilei" correctly when I tell them I would live in the
"Galileistrasse", it´s embarrassing that inhabitants
of a big city like Stuttgart do not even know the name of one of the
most important researchers and scientits
of all times, a man who formed some of the elementary basics of our
modern attitude to science.)

When we propose mobility patterns, when we assert the existence of
interactions, all these proposals and assertations
must be validated by _observations_  and _experiments_.

But this is off topic. It´s somewhat my own frustration and
disappointment that I frequently read about
things which do not match observations and that apparently do not exist
in reality.


> I appreciate your kind answers very much.
> A.
> Detlef
>  >However, IMHO there is some basic difficulty in any kind of TCP
> > >handover, which even holds in the existing and well known approaches.
> > Handover itsef is basicly difficult :)
> >
> > Alper K. Demir
> --
> Detlef Bosau
> Galileistrasse 30
> 70565 Stuttgart
> Mail: detlef.bosau at web.de
> Web: http://www.detlef-bosau.de <http://www.detlef-bosau.de>
> Mobile: +49 172 681 9937

Detlef Bosau
Galileistrasse 30
70565 Stuttgart
Mail: detlef.bosau at web.de
Web: http://www.detlef-bosau.de
Mobile: +49 172 681 9937

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