[103910] in North American Network Operators' Group
Re: Bandwidth issues in the Sprint network
daemon@ATHENA.MIT.EDU (Brian Raaen)
Thu Apr 17 17:28:00 2008
From: Brian Raaen <braaen@zcorum.com>
To: nanog@merit.edu
Date: Thu, 17 Apr 2008 17:00:12 -0400
In-Reply-To: <200804071506.34371.braaen@zcorum.com>
Errors-To: owner-nanog@merit.edu
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Some people wanted to know what I found the problem to be. I have discover=
ed.=20
the problem for a fact is the TCP window size on uploads. I have a Linux b=
ox=20
that I changed the Window sizes to match and I still get 32k on a upload=20
window and 64k on a download window. With a ping time of 50ms I have a max=
=20
theoretical throughput of 5.2Mbps Which is about what I was getting. The=20
formula to calculate this is the following.
(((Ts/Tw)*Rtd)/1000)+((Ts*8)/(Lr*1000)))
Where the following are
Ts =3D Transfer size in Bytes
Tw =3D Tcp Window size in Bytes
Rtd =3D Round trip Delay in milliseconds
Lr =3D Line rate in bps
At this point I am still trying to locate the offending device that is=20
changing the window size. After I determine for sure whether the problem i=
s=20
with my router, the sprint network, or another upstream system I will let=20
everybody know what I find.
=2D-=20
Brian Raaen
Network Engineer
braaen@zcorum.com
On Monday 07 April 2008, Brian Raaen wrote:
> I am currently having problems get upload bandwidth on a Sprint circuit. =
I=20
am=20
> using a full OC3 circuit. I am doing fine on downloading data, but=20
uploading=20
> data I can only get about 5Mbps with ftp or a speedtest. I have tested=20
> against multiple networks and this has stayed the same. Monitoring Cacti=
=20
> graphs and the router I do get about 30Mbps total traffic outbound, but=20
> individual (flows/ip?) test always seem limited. I would like to know if=
=20
> anyone else sees anything similar, or where I can get help. The assistan=
ce=20
I=20
> have gotten from Sprint up to this point is that they find no problems. =
Due=20
> to the consistency of 5Mbps I am suspecting rate limiting, but wanted to=
=20
know=20
> if I was overlooking something else.
>=20
> --=20
> Brian Raaen
> Network Engineer
> braaen@zcorum.com
>=20
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