[MLB-WIRELESS] Speed degradation over multiple hops

[vak at alphalink.com.au]

Sounds like an MTU sizing issue.

Try pinging nodes 1 - 6 using different packet sizes. (assuming ICMP has
the same priority as other traffic).

By default, your gear is likely set to 1500 bytes, try forcing this to as
low as 1000 bytes.

Have you compared speeds from 1 to 6 progressively ? Ie, is it fine up to
node 3, but falls over at node 4 ?

Cheers,

Vaskos
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Original Message:
-----------------
From: Ben Short bshort at shortboy.net
Date: Sun, 28 Mar 2004 15:19:23 +1000
To: melbwireless at wireless.org.au, mesh at itee.uq.edu.au,
syd-wireless at lists.sydneywireless.com
Subject: [MLB-WIRELESS] Speed degradation over multiple hops


Hi All,

I am writing this in the hope that someone may provide a solution to a 
long standing problem that has
plagued me for a few months.

I am involved with StarNet, a community wifi mesh in Hobart. we have 
over 200kms of RF path, and
connections are achieved using a combination of Wireless cards in unix 
based routers, or Access points,
running in infrastructure or ad hoc mode depending on the location.

The best way to explain the problem is to use an example. Say we have 6 
wireless links, each link has its own
RF Channel, and SSID, using the same WEP. All these links are 
Point-to-Point, with no Multi-point (which rules out
halving the bandwidth available, by using the same interface for 
send/recieving between two nodes). Each of these links
runs at 11mbps, with a signal of > 82dB and SNR of over 20dB.

Now, each link from hop to hop you can send or recieve at about 400kb/s, 
which is to be expected. However if I download
direction from hop 6 to hop 1, I am usually lucky to get 10kb/s. There 
is no other traffic on the network at the time, and
hidden nodes are not an issue. I am assuming interference is not an 
issue, because each link can do 400kb/s.

tracerouting and pinging gibe favourable results, with no indication of 
why the above happens.

Can someone please tell me why this speed degradation occurs, and how I 
may be able to rectify it.

Thanks in advance
Ben


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