Re: [linuxperf] TCP/PPP latency

Paul Jakma (paul@clubi.ie)
Sat, 8 May 1999 18:33:40 +0100 (IST)


On Sat, 8 May 1999, Rik van Riel wrote:

Hi,

I'm experiencing _bad_ trouble with TCP/PPP latency lately.

About half of my calls to demon.nl gives normal PPP latency
and performance (100 to 200 ms latency), but sometimes I get
a network latency of 20 to 30(!) seconds on the PPP link.

I'm using kernel 2.2.7 with the following PPP command line:

/usr/sbin/pppd lock modem /dev/modem 115200 idle 90 demand \
defaultroute mru 296 mtu 296 bsdcomp 15,15 $LOCAL_IP:$REMOTE_IP\
novj netmask $NETMASK connect $DIALER_SCRIPT

Before switching off Von Jacobson compression the network
latency was usually worse, but now it's all right about
50% of the time...

Running 'mtr' for some time (or ping) usually brings back
the latency to about half of what it was before, but it
still sucks eggs :(

Anybody got an idea what to do?

thanks,

I use dial-up aswell, and havn't noticed any problems.

Your mtu/mru settings are extremely low (tcp/ip overhead is a minum
of 40bytes iirc), maybe there's some new hardware at demon that
chokes on it.

try it at 1024 and see, and set a window size aswell, eg about 2,3
times your mtu.

-Paul.

-- 
Paul Jakma
paul@clubi.ie	http://hibernia.clubi.ie
PGP5 key: http://www.clubi.ie/jakma/publickey.txt
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