[e2e] A Question on the TCP handoff

Detlef Bosau detlef.bosau at web.de
Thu Dec 1 12:50:35 PST 2005

Alper Kamil Demir wrote:
> >Admittedly, I don´t quite understand what you mean by "warm up
> >connection".
> In our work, there is an "actual connection" between a "fixed host" 
> and a mobile terminal. "warm-up connection" is a pre-established connection 
> between a "synchronization agent-SA" and a "fixed-host" on behalf of a mobile
> terminal. When a mobile terminal enters into a new cell, we assume that 
> "warm-up connection" replaces the "actual connection" (SA handovers 
> new congestion state to mobile terminal) and becomes a new "actual connection" 
> so that mobile terminal learns the congestion state of the new path. 
> I was questioning if this is ever possible and/or meaningful ? If so, is
> there any tool that can be useful for us?
> tcpcp was suggested. I think it can not be used to solve our problem.

That´s what I feared.

Let´s drah a network in order to see if I understand you correctly.

FH ------------Internet---------------SA1 !!!!wireless network!!!!MH

                                      SA2 !!!!wireless network!!!

There is some pre-established connection between SA2 and MH

Then MH enters the cell of SA2.

What about the path of FH to SA1? Is it replaced by a path FH to SA2?

In that case, you would even have to expect changes of the path capacity
in the wired part of your connection.
In addition: What does "pre established" mean? TCP state variables,
particularly CWND, result from a dynamic settling process.
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

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

Please correct me, when I got you totally wrong.

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.

 >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
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