Adjusted TCP Window Size on IPERF/JPERF but unable to verify w/ Wireshark

[yuchenglai]

Hello All,

I recently downloaded JPERF to better understand how throughput is affected by changing Buffer length and TCP window size values.

I installed JPERF on two machines with one running as a server and the other as a client. On both the client and the server, the buffer length and TCP window size have been set to 1 Kilobit. Needless to say, the throughput was pretty bad given that the NICs of these two hosts were capable of 100Mbps.

Give the settings above, JPERF was able to report a low throughput of 30 to 40 Kbits/sec from the client to the server.

At the same time I ran this test, I also turned on Wireshark to sniff the traffic. Even though I configured JPERF w/ a TCP window size of 1 KBits on both the client and the server, I was not able see a reflection of this value in my packet captures...particularly in the TCP header, Window Size field.

Am I looking at the wrong field?

[yuchenglai]

Attached is also a screenshot of JPERF showing the TCP Window Size and Buffer Length settings and the resulting througput. Screenshot was pasted to OpenOffice's equivalent of MS powerpoint.