Bandwidth issues in the Sprint network

Lincoln Dale ltd at
Fri Apr 18 03:15:40 UTC 2008

even with tuned TCP window sizes, make sure you don't have TCP syncookies
enabled on either endpoint.

many syncookie implementations have implications on supporting RFC1323 options.



> -----Original Message-----
> From: owner-nanog at [mailto:owner-nanog at] On Behalf Of Brian
> Raaen
> Sent: Friday, 18 April 2008 7:00 AM
> To: nanog at
> Subject: Re: Bandwidth issues in the Sprint network
> 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.

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