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. cheers, lincoln.
-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Brian Raaen Sent: Friday, 18 April 2008 7:00 AM To: nanog@merit.edu 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@zcorum.com
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.