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I have a log pipe between two facilities (gigiabit circuit with RTT latency of 17ms). When doing system-to-system file transfer (file sharing, rsync, ftp, sftp) I'm hitting maximum speed of approx 30 megabits, which is less than I expect.

OS: Windows XP and Windows Server 2003

Here is what I did:

  1. Modified registry setting as follows:


  2. iperf shows near ideal 900 megabit transfers, so pipe can handle it.

I understand, that using some kind of UDP layer can help me, but here this isn't an option.


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Is this a WAN circuit of some kind or a direct link you own and manage? – Dave M Jun 23 '11 at 1:02
direct link managed by me. – sashk Sep 26 '11 at 18:47

I would try messing with your MTU as well. For systems that use a PPPoE connection, an MTU of 1492 (1500 being default) works better than anything else. If all the networking gear supports jumbo frames, you can try pushing it all the way up to 9000. It should be located at:


Also, a Link about tweaking for network speed

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Increasing MTU isn't an option for those systems. As to tweaking - I've tried most of them - don't see ANY change in transfer rate. iperf testing shows some minor changes when apply one or another option.. – sashk Jun 27 '11 at 2:14

Independent of the OS being used, TCP settings tremendously affect the perceived maximum throughput. E.g. the chosen congestion avoidance algorithm greatly affects it (especially when using fat pipes). Others can be seen here:

Note that TCP settings only affect upstream traffic.

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