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I want to know how about when I put a huge TCP window in iperf,eg 64MB, not give me errors, but gives me wrong measurement for example 54Mbits/sec in bandwindth and my connection upload is only 1 Mbps. Is it bug of iperf?

i put in command this: iperf -w 64MB -c IPaddress -p and_the_port

and i received this:

Interval Transfer Bandwidth

0.0-10.1sec 65.0MBytes 54.2 Mbits/sec

which is wrong because my connection is: Bandwidth(Up/Down)[kbps/kbps]: 1.023/15.000

gma
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  • How do you know your connection bandwidth? Is this set on a bandwidth limiting switch? – Dima Chubarov Jan 20 '16 at 11:44
  • From my router settings, i went to 192.168.1.1 and after to broadband connection, to DSL connection and Bandwidth(Up/Down)[kbps/kbps]: 1.023/15.000. – gma Jan 20 '16 at 19:15

1 Answers1

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Your TCP window size looks to be way too large for your bandwidth. The TCP window size should be just large enough to accommodate the so-called "Bandwidth Delay Product," which is the highest bandwidth of your channel multiplied by the round trip delay time. You should be able to get the round trip time from the BW test you performed.

Ex. 10 Mbps * 98 mS = 0.98 Mbits

Penny L.
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  • *Lowest* bandwidth of your *path,* multiplied by the *one-way* delay time, actually. – user207421 Jan 22 '16 at 01:00
  • Yes, i know that is too large. But my question is why didn't give me error, if i put too large TCP window? Is it bug of iperf? – gma Jan 22 '16 at 02:26
  • i found that is something happened with the buffer. thank you all!! – gma Feb 01 '16 at 18:12