Bandwidth issues in the Sprint network

Brian Raaen braaen at
Thu Apr 17 21:00:12 UTC 2008

Some people wanted to know what I found the problem to be.  I have discovered. 
the problem for a fact is the TCP window size on uploads.  I have a Linux box 
that I changed the Window sizes to match and I still get 32k on a upload 
window and 64k on a download window.  With a ping time of 50ms I have a max 
theoretical throughput of 5.2Mbps Which is about what I was getting.  The 
formula to calculate this is the following.


Where the following are

Ts = Transfer size in Bytes
Tw = Tcp Window size in Bytes
Rtd = Round trip Delay in milliseconds
Lr = Line rate in bps

At this point I am still trying to locate the offending device that is 
changing the window size.  After I determine for sure whether the problem is 
with my router, the sprint network, or another upstream system I will let 
everybody know what I find.

Brian Raaen
Network Engineer
braaen at

On Monday 07 April 2008, Brian Raaen wrote:
> I am currently having problems get upload bandwidth on a Sprint circuit. I 
> using a full OC3 circuit.  I am doing fine on downloading data, but 
> data I can only get about 5Mbps with ftp or a speedtest.  I have tested 
> against multiple networks and this has stayed the same.  Monitoring Cacti 
> graphs and the router I do get about 30Mbps total traffic outbound, but 
> individual (flows/ip?) test always seem limited.  I would like to know if 
> anyone else sees anything similar, or where I can get help.  The assistance 
> have gotten from Sprint up to this point is that they find no problems.  Due 
> to the consistency of 5Mbps I am suspecting rate limiting, but wanted to 
> if I was overlooking something else.
> -- 
> Brian Raaen
> Network Engineer
> braaen at
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