Subject: Re: TCP/IP tuning
To: None <firstname.lastname@example.org>
From: Thomas Miller <email@example.com>
Date: 02/28/2004 10:21:48
Matt Thomas <firstname.lastname@example.org> wrote:
> 5Mb/s is not high-speed. :) There is no need to
> tune NetBSD for that speed.
Please explain to me where I am going wrong.
I am reading that the TCP/IP receive window should
exceed the size of the Bandwidth Delay Product for
a connection without packet loss. From me to
ftp.netbsd.org the average times reported for large
and small packets by
ping -c 5 ftp.netbsd.org and
ping -c 5 -s 1400 ftp.netbsd.org
were 92.855 and 95.475 ms, respectively. The average
of these averages is 94.165 ms or 0.094 sec. If the
connection speed really is 5,000,000 b/s, then the
BDP is 5,000,000 b/s x 0.094 sec = 470,000 bits.
Sysctl says, however,
# sysctl net.inet.tcp.recvspace
net.inet.tcp.recvspace = 32768
which, if that 32768 is bits, seems to be less than
1/10 of the BDP.
If the above is correct, doesn't my recvspace need to
be increased, and therefore, NetBSD needs to be "tuned"
for a 5 Mb/sec connection? I haven't done anything
consciously to change the receive space from the default.
P.S. I appreciate that 5,000,000 is not a power of 2,
so maybe the connection speed should be expressed as
5 x 1,048,576.