Welcome to the CSIR Meraka Institute's "COIN" Blog

Tuesday, June 28, 2005

Linksys WRT54G hardware differences

This has been bothering me - there are 5 different hardware versions of the WRT54G wireless router (1.0, 1.1, 2.0, 2.2, 3.0) and many of the open firmware platforms like openwrt or sveasoft (The betrayer of the word open) only run on particular hardware versions. The main changes are the processor, amount of RAM/FLASH, the wireless hardware and the ethernet hardware

Check out all the differences here

We have ordered three batches of Linksys hardware - I must check which hardware platforms we have

My Linksys on my roof gave the following results

Result of the command
$>cat /proc/cpuinfo

system type : Broadcom BCM947XX
processor : 0
cpu model : BCM3302 V0.7
BogoMIPS : 199.47
wait instruction : no
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : no
hardware watchpoint : no
VCED exceptions : not available
VCEI exceptions : not available
dcache hits : 3472555964
dcache misses : 1631950511
icache hits : 264142837
icache misses : 2075639807
instructions : 0

Some of the possible clue NVRAM settings when running the command
$>NVRAM show


Thursday, June 23, 2005

Setting up OLSR mesh on a Linksys

Setting up OLSR mesh on a Linksys ( Assumes a stock standard Linksys out of the box)

1. Download freifunk firmware from (http://www.freifunk.net/wiki/FreifunkFirmwareEnglish) - openwrt-g-freifunk-1.0.2-en.bin

2. Set boot wait on linksys

Web method:

Navigate to web page were you can send pings and type each of these lines one line at a time


NVRAM method:

telnet into box and type the following

nvram set boot_wait=on
nvram commit

3. Upload firmware

Give yourself a fixed IP in the 192.168.1.x range e.g.

Use tftp to upload firmware

tftp> binary
tftp> rexmt 1
tftp> trace
Packet tracing on.
tftp> put openwrt-g-freifunk-1.0.2-en.bin

Wait for the power light to stop flashing
Power cycle the box

4. Check that the web interface is working. Visit the site on your web browser - you should see the main freifunk web interface appear

5. Set up the wireless interface

WLAN protocol: Static
Ip Address:
WLAN Mode: Ad Hoc (Peer to Peer)
ESSID: mesh
Channel: 6
TX Power: 100

6. Set up the LAN interface

LAN protocol: Static
LAN Netmask:
Disable NAT: yes
Disable Firewall: yes

7. Set up the WAN interface

WAN Protocol: DHCP
Host name: Lawrence

8. Set up OLSR


9. Restart the Linksys

You should now be given an IP address in the 192.168.3.x range
You should be able to connect to another mesh access point and even get a default gateway to an internet point, if one exists

Monday, June 20, 2005

How the ETX metric in OLSR is calculated

The ETX of a link is the predicted number of data transmissions required to send a packet over that link, including retransmissions. The ETX of a route is the sum of the ETX for each link in the route. For example, the ETX of a three-hop route with perfect links is three; the ETX of a one-hop route with a 50% delivery ratio is two.

The ETX of a link is calculated using the forward and reverse delivery ratios of the link. The forward delivery ratio, df , is the measured probability that a data packet successfully arrives at the recipient; the reverse delivery ratio, dr , is the probability that the ACK packet is successfully received. The expected probability that a transmission is successfully received and acknowledged is df x dr .

A sender will retransmit a packet that is not successfully acknowledged. Because each attempt to transmit a packet can be considered a Bernoulli trial, the expected number of transmissions is:

ETX = 1/ (df x dr)

For a full description of how df and dr is actually calculated see MIT's publication site

Mesh scalability by modifying the MAC layer in Altheros

This is a great article that discusses the whole issue of loss of performance in a single radio mesh network with many hops. Modifying the MAC layer on our 50 Altheros cards we are getting for the massive mesh could prove a very novel way of dealing with the inherent problems in the WiFi spec when trying to build large mesh networks

Getting Kismet working with IPW2200 driver

Thanks to ubuntu forums for this linkLink

Tuesday, June 14, 2005

Drawing(almost realtime) pretty network topology pictures with

Tried it, works well'ish.

Yusuf Kaka


Mobile Platforms Engineer

CSIR - Meraka Institute (African Advanced Institute for ICT)
Web Address: www.csir.co.za or www.meraka.co.za