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New Member

8Mbps Point to Point under utilize

I have a 8Mbps serial WAN point to point connection for 2

sites. The round-trip latency is 20 msec, packet loss very low 0%.

The challange is to ensure can FTP 1 GByte file in 30 minutes.

Current results, it needs more than 1 hour to complete the transfer, and during the transfer the bandwidth used was not more than 3.3Mbps (even hough I have 8Mbps, 41% only).

Is there anyway we can achieve the requirement? boost up the transfer rate? Do I need to apply a certain QoS? Or maybe due to application FTP server capability?

I've also increased the routers 'ip tcp window-size 20000'- based on formula window-size = (bandwidth * latency) but no improvement.



Thanks in advance.


Re: 8Mbps Point to Point under utilize

I see you set the TCP windowing on the router however did you set the TCP windowing on the server and client? Another thing you may want to try is Jumbo frames. Make sure the server, router interfaces, switch ports and endpoints all support Jumbo frmaes. This will increase the troughput. Good Luck..Please rate...

New Member

Re: 8Mbps Point to Point under utilize

There is no such thing as setting TCP windowing on a router

New Member

Re: 8Mbps Point to Point under utilize


Aboutthe jumbo frame settings, I need to apply both LAN and WAN interface right? How about the server/client settings?

thanks in advance.


New Member

Re: 8Mbps Point to Point under utilize

This is a very common question that people have; if no other application is using the bandwidth why don't I get it all. I think you are on the right track in increasing the window size, but this is still an individual flow and there is still a lot of latency inherent to the communication. You are subject to things like path MTU (big), TCP acknowledgments, Round-Trip-Time, application level acknowledgments, tcp buffer spaced (limited to 64K, I think), application buffers,etc.

There is something called the Bandwidth Delay Product (BDP) that calculates how much data can be on the wire on a network at any given time. This is ultimately limited by the TCP buffer space. There is a great document on this on the Pittsburg Supercomputing Center's website:

I hope this helps!

New Member

Re: 8Mbps Point to Point under utilize

Thanks for the url.

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