Subject: Re: TCP/IP tuning
To: None <>
From: Thomas Miller <>
List: current-users
Date: 02/28/2004 10:21:48
Matt Thomas <> 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 the average times reported for large 
and small packets by 

ping -c 5 and 
ping -c 5 -s 1400 

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.