[e2e] YNT: A Question on the TCP handoff

Alper Kamil Demir demir at kou.edu.tr
Sun Dec 4 05:43:40 PST 2005

>> >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
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)
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? 

>Then MH enters the cell of SA2.
>What about the path of FH to SA1? Is it replaced by a path FH to SA2?
Yes. That's correct.

>In that case, you would even have to expect changes of the path capacity
>in the wired part of your connection.
"wam-up connection" does that.

>In addition: What does "pre established" mean? TCP state variables,
> particularly CWND, result from a dynamic settling process.
It means that there is a TCP connection between MH and FH.

>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
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.

>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
Assuming that SAs are somewhere close to MH. 

>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?
I appreciate your kind answers very much.

 >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

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