MPLS DS3 throughput question

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Jun 5th, 2008
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Hi all,

Some new DS3s have been installed between two sites. Site A is in Chicago. Site B is in Los Angeles.

We've been testing file downloads and latency in preparation for utilizing an application of this new MPLS WAN. 9mb sub-rate DS3 ports have been allocated for each site.

During file-copies between sites, I've noticed that the TCP session for the file-copies do not utilize entire bandwidth. In fact, the file-copies only utilize a small portion of the bandwidth.

The LANs on each side of the MPLS DS3 (9mb) connections are Ethernet.

When are ran a packet capture on one end of this connection, the packetscoming from the WAN (into the LAN)were mostly only 64 bytes in size.

Would this explain the lack of bandwidth utilization? Why would this happen? DS3 MTU is approx. 4420 and Ethernet is MTU approx. 1500 bytes.

Does this have to do with TCP window sizes? The servers that we using for testing are Windows Server 2003.

Thanks for the help.


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msrohman Fri, 06/06/2008 - 20:48
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I think this problem is related to file-copying over long fat pipes.

Round trip time is 68ms.

THe larger the file (1gB), the more bandwidth the tcp session eventually builds up to.



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