nanog mailing list archives
Re: PC Bozo's World bites again (CNN, too)
From: Vadim Antonov <avg () pluris com>
Date: Thu, 28 May 1998 00:09:35 -0700
On Wed, 27 May 1998, Michael Dillon wrote:
Most people are changing the MTU to speed up web browsing which is data intensive, not interactive. I think Karl's explanation of broken Windows TCP/IP stacks is more likely the root cause of the problem. But has anyone ever done a proper test of this with sniffers at both the client end of the network and the webserver end of the network?
I don't know, but dropped or corrupted large packets is the reliable indicator of the flow control problems on async lines. I saw that million times, and that explanation is a lot more plausible than misterious bugs. The reason why broken flow control affects TCP performance is very simple: most dialup modems have buffers from 2 to 4 kilobytes. Now, given the large disparity in speed of dialup line and the serial port, that buffer limits window size to 2-3 large packets, with single packet lost due to modem buffer overflow every round-trip time. I.e. the steady-mode packet loss is 15-30%. Reducing MTU allows window to grow to 6-10 packets, thus reducing steady-mode packet loss to 3-5%. The real answer is: fix the !#@! CTS/RTS, so the buffering occurs in the host memory. (BTW, the recommendation to reduce MTU to increase interactive performance is only valid when connection is shared between interactive and non-interactive traffic. This is clearly not the case.) --vadim Who still remembers debugging 4800 bps backbone lines.
Current thread:
- PC Bozo's World bites again (CNN, too) Vadim Antonov (May 27)
- Re: PC Bozo's World bites again (CNN, too) Karl Denninger (May 27)
- Re: PC Bozo's World bites again (CNN, too) Dean Robb (May 28)
- Re: PC Bozo's World bites again (CNN, too) Matthew Marlowe (May 27)
- Re: PC Bozo's World bites again (CNN, too) Michael Dillon (May 27)
- Re: PC Bozo's World bites again (CNN, too) ken emery (May 27)
- Re: PC Bozo's World bites again (CNN, too) Vadim Antonov (May 28)
- Re: PC Bozo's World bites again (CNN, too) Darrell Fuhriman (May 28)
- Re: PC Bozo's World bites again (CNN, too) Richard Irving (May 28)
- Re: PC Bozo's World bites again (CNN, too) Forrest W. Christian (May 28)
- Re: PC Bozo's World bites again (CNN, too) Michael Dillon (May 27)
- Re: PC Bozo's World bites again (CNN, too) Karl Denninger (May 27)
- <Possible follow-ups>
- Re: PC Bozo's World bites again (CNN, too) Vern Paxson (May 29)
- RE: PC Bozo's World bites again (CNN, too) Doug Stanfield (May 29)
- RE: PC Bozo's World bites again (CNN, too) Jeff Victor - Sun Microsystems Systems Engineer (May 29)