Bandwidth issues in the Sprint network

Mike Gonnason gonnason at
Thu Apr 17 22:31:42 UTC 2008

On Thu, Apr 17, 2008 at 1:00 PM, Brian Raaen <braaen at> wrote:
> 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.
>  (((Ts/Tw)*Rtd)/1000)+((Ts*8)/(Lr*1000)))
>  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
>  am
>  > using a full OC3 circuit.  I am doing fine on downloading data, but
>  uploading
>  > 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
>  I
>  > 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
>  know
>  > if I was overlooking something else.
>  >
>  > --
>  > Brian Raaen
>  > Network Engineer
>  > braaen at
>  >

Thanks for reporting back to curious minds.

Mike Gonnason

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