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VPLS Circut Slow Speed - TCP Window Size

Posted on 2013-06-12
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Last Modified: 2013-07-22
Hey Guys,

We just got a VPLS circuit installed between two office locations and I’m running some initial tests on the connection. We are committed to 10mbps at each of the endpoints, however when running ipref tests looks as though we are getting 500-700kbs. I spoke to the provider who seems to be blaming it on our Windows OS Operating System TCP Window size. After changing the windows size in the ipref test this increases the bandwidth speed up to about 5-7mbps.

So because of these tests the slow speed looks like its isolated to the TCP window size. The question is why is the bandwidth transfer from our other providers absolutely fine, however with this one they are telling me to change my TCP window size across the whole network ???
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Question by:supportemea
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by:giltjr
giltjr earned 250 total points
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It not clear from your post, but are the " .... bandwidth transfer from our other providers ...." going over the same physical link?

If not, what is the latency on the other link?

To fully utilize the available bandwidth of a link you have to send enough data to keep the pipe full while you wait for an ACK to send more data.  In TCP this is the "window size".  The window size is determined by the speed of the link and the latency.

If you are comparing two different links, you have to know the latency on both and the bandwidth is on both.  If you have two links with equal bandwidth, but one has twice the latency than the other one, the one with the higher latency will get lower through-put.
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harbor235 earned 250 total points
ID: 39254167
5-7 Mbps using TCP as transport is not out of line for a 10Mbps connection, remember there is overhead when using TCP.

Try using udp for the test, it should provide better numbers.


iperf -su  (server side)
iperf -c <server_ip> -u -i 1 -b 10m  (client side)

for a longer test specify  (-t 300) in the command line for a 5 minute test

iperf -c <server_ip> -u -i 1 -t 300 -b 10m  (client side)

harbor235 ;}
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