Hi all,

I'm new here, actually I'm a HW engineer and not very experienced with
networking. To perform the other experiment I need to evaluate my ethernet
TPT to see if it gating my DUT's capability.

When I did the TPT test with iperf, there is something odd...
- If I use the default setting of UDP, the TPT is always around 29mbps. Even
I enlarge -b to 1000m. It always TX 25~29mbps from client. My commands is
iperf -c 192.168.1.150 -u -b1000m -w 2m -i1
------------------------------------------------------------
Client connecting to 192.168.1.150, UDP port 5001
Sending 1470 byte datagrams
UDP buffer size: 2.00 MByte
------------------------------------------------------------
[1912] local 192.168.1.99 port 1250 connected with 192.168.1.150 port 5001
[ ID] Interval       Transfer     Bandwidth
[1912]  0.0- 1.0 sec  2.92 MBytes  24.5 Mbits/sec
[1912]  1.0- 2.0 sec  3.33 MBytes  27.9 Mbits/sec
[1912]  2.0- 3.0 sec  3.18 MBytes  26.6 Mbits/sec
[1912]  3.0- 4.0 sec  3.25 MBytes  27.3 Mbits/sec
[1912]  4.0- 5.0 sec  3.20 MBytes  26.8 Mbits/sec

- If I use TCP, the TPT can reach 400m~500mbps. My commands is iperf -c
192.168.1.150 -w2m -i1
------------------------------------------------------------
Client connecting to 192.168.1.150, TCP port 5001
TCP window size: 2.00 MByte
------------------------------------------------------------
[1912] local 192.168.1.99 port 1252 connected with 192.168.1.150 port 5001
[ ID] Interval       Transfer     Bandwidth
[1912]  0.0- 1.0 sec  48.2 MBytes   404 Mbits/sec
[1912]  1.0- 2.0 sec  52.4 MBytes   439 Mbits/sec
[1912]  2.0- 3.0 sec  55.9 MBytes   469 Mbits/sec
[1912]  3.0- 4.0 sec  61.3 MBytes   514 Mbits/sec
[1912]  4.0- 5.0 sec  54.5 MBytes   457 Mbits/sec

- If I add in -l to 60000 then the UDP TPT can reach 500mbps, but limited on
500mbps. My commands is iperf -c 192.168.1.99 -u -b 1000m -w 2m -i 1 -l
60000.
------------------------------------------------------------
Client connecting to 192.168.1.150, UDP port 5001
Sending 60000 byte datagrams
UDP buffer size: 2.00 MByte
------------------------------------------------------------
[1912] local 192.168.1.99 port 1254 connected with 192.168.1.150 port 5001
[ ID] Interval       Transfer     Bandwidth
[1912]  0.0- 1.0 sec  57.2 MBytes   480 Mbits/sec
[1912]  1.0- 2.0 sec  59.6 MBytes   500 Mbits/sec
[1912]  2.0- 3.0 sec  61.4 MBytes   515 Mbits/sec
[1912]  3.0- 4.0 sec  61.4 MBytes   515 Mbits/sec
[1912]  4.0- 5.0 sec  59.7 MBytes   501 Mbits/sec

- I also try variable -l number from 10000~60000 the data transmitted from
client will change accordingly.
-l 10000 --> 160 Mbits/sec
-l 20000 --> 256 Mbits/sec
-l 30000 --> 339 Mbits/sec
-l 40000 --> 480 Mbits/sec
-l 50000 --> 504 Mbits/sec

Even the TPT >500m is enough to my experiment requirement, but I'm still
wondering is it safe to use the bigger number of -l? As the description said
it's default value is 1460.

Could anyone possibly to answer me:
Whats is the exactly meaning of the -l parameter (Iperf_length), I know it's
the buffer to write or read. But not very clear to me the buffer is for what
and why do we need buffer?
I also compare it with other windows machines, they needn't use this way to
get the TPT higher than 25~29mbps. Is there any modification my NB (or OS)
needing?

My environment:
OS: Windows XP SP3 version 2002
Ethernet: Realtek PCIe GBE Family Controller
Driver version: 5.774.1026.2010

Thanks in advance

Kircheis
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