Problem to transfer the data using CIPE

Hi.

I'm experimenting in the measurement of the data trasfer time using CIPE,
but a strange phenomemon occured occurred in the environment.
First of all, I would like to show the environment.

---------------------------------------------------------------

                                           CIPE
                                          server
                                            |
  client --------- Access Point ----------- + ---------- server
          wireless               ethernet      ethernet
        (802.11b 11Mbps)         (100Mbps)     (100Mbps)

client --- WindowsXP, CPU Pentium M 1300MHz, memory 768MB
            CIPE version CIPE-Win32-2.0-pre15

CIPE server --- Redhat Linux9, CPU Pentium 4 2.40GHz, memory 512MB
                 CIPE version 1.5.4, linux kernel 2.4.20-8

server --- FreeBSD5.1R, CPU Pentium 4 2.40GHz, memory 512MB

---------------------------------------------------------------

When a client connected a server directly (without CIPE),
1 byte of data was sent and received 100 times using an echo port (TCP).
It took about 0.2s to transfer the data (total 100 bytes).

                        (echo)
  client -------------- server
            ethernet
            (100Mbps)

---------------------------------------------------------------

Then, the client communicated with the server using CIPE
(a CIPE tunnel was made between the client and the CIPE server),
and the result was about 0.5s or 1s. (not between 0.5s and 1s)
I thought that it was strange at two points
  that the overhead was too large and one of two discrete values was taken.

                                           CIPE
                                          server
  (CIPE)                                    |            (echo)
  client --------- Access Point ----------- + ---------- server
          wireless               ethernet      ethernet
        (802.11b 11Mbps)         (100Mbps)     (100Mbps)

---------------------------------------------------------------

However, when the CIPE server communicated with another server
  (e.g. : 1 byte of data was sent and received 100000 times)
simultaneously along with the communication between the client and the
server,
and the result was about 0.22 to 0.26s in the above-mentioned experiment.

                                           CIPE
                                          server
  (CIPE)                                    |            (echo)
  client --------- Access Point ----------- + ---------- server
          wireless               ethernet   |  ethernet
        (802.11b 11Mbps)         (100Mbps)  |  (100Mbps)
                                            |
                                            +-------- another server
                                          ethernet
                                          (100Mbps)

---------------------------------------------------------------

That is, when the ethernet device of the CIPE server is busy,
transmission overhead reduces.
This is clearly strange.

Is this the problem of the kernel module?
Or is it the problem of the CIPE itself?

Anyone can give me some advice to solve this problems.
Thanks in advance.

Yuji Kanadechi.




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