[MLB-WIRELESS] OpenWRT long distance utility

Ratbaggy wireless at smithsgully.net
Wed Mar 1 00:42:26 EST 2006

Hi Dan and All,

I am pleased to report that the utility works very well indeed.  I've
experimented on our 14 km link between Blackburn North and Kangaroo Ground
(ILW to HKG) and the throughput (doing a http download) has gone from around
60 KBytes/S to......

Now wait for it..........

Excuse me for getting a little excited........

1130 KILOBYTES PER SECOND!!!!!!!!!!!!!!

There are WRT54G Ver 2's running on each end with Freifunk version 1.1.4
firmware.  Antennas are 24 dB Hills grid and 19 dB Panel.

This link doesn't have a great path and the line of sight skims across the
roofs at the Blackburn end and the signal strength as reported on the crappy
WRT radios is -77 dBm with noise at -94.

My recommendation with setting the "distance" for dctrl is to start at
double the distance and reduce the number to the point where throughput
reaches a maximum.  Shortly beyond this point the throughput will drop
drastically.  In our case with the 14 k link the optimum speed was achieved
with the parameter set to about 21000 but we backed it off to 22000.  I
suspect the programmer may not have made allowance for the round trip delay.

Due to the poor signal to noise ratio on our link optimum performance was
achieved with the radios locked to 18 Megabits per second, any faster or
slower and the performance dropped off.  With another 10 dB of signal to
noise I suspect some further gains may be possible although at this point
the router may run out of steam before the radios.

The settings that were used:

WLAN Mode: Ad Hoc
Radio Mode: G Mode Performance (whatever that means)
Transmission Rate: 18 MBits/S
CTS Protection: Disabled
Frame Burst: Enabled
/usr/sbin/dctrl 22000

For other links with different S/N and distances Transmission Rate and dctrl
will need to be optimised.  Hopefully some others can do some more
experimenting on different links.


----- Original Message ----- 
From: "Dan Flett" <conhoolio at hotmail.com>
To: <melbwireless at wireless.org.au>
Sent: Monday, February 20, 2006 8:24 PM
Subject: [MLB-WIRELESS] OpenWRT long distance utility

> Hi all,
> I've found a few links regarding a utility for OpenWRT/broadloom-based
> routers.
> The utility is called dctrl and it works quite simply - you just put in
> distance of the link as a parameter and it tweaks the broadcom radio
> settings to be optimal for that distance.
> You can get it here:
> http://openwrt.inf.fh-brs.de/~nbd/dctrl.
> Further discussion of link tests here:
> http://forum.bsr-clan.de/viewtopic.php?p=10530.
> http://forum.openwrt.org/viewtopic.php?id=4447
> http://forum.openwrt.org/viewtopic.php?pid=21034
> I'd be keen to hear if people with WRT-based long-distance links have any
> success with this.
> Regards,
> Dan Flett
> Secretary
> Melbourne Wireless
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> Melbwireless mailing list
> Melbwireless at wireless.org.au
> http://wireless.org.au/mailman/listinfo/melbwireless
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