Community Wireless Networking

Community Wireless Networking (CWN) is a ground roots movement that takes advantage of the availability of IEEE 802.11 wireless technologies to create wireless computer networks which are 100% controlled by individuals or groups of people in the community. This means creating a wide area computer network that is independent of any telco or internet service provider.

The CWN movement has taken off because the frequencies that are used by 802.11 are regulated under the "Radiocommunications (Low Interference Potential Devices) Class Licence" which essentially means that the average person does not need a special licencee to operate a device that falls within the radiated power limit (known as Effective Isotropic Radiated Power) specified in the LIPD Class Licence. In Australia these radiation limits are very generous compared to some parts of the world, we are regulated to 36 dBm (4 Watt) EIRP in the 2.4 GHz ISM band (used by 802.11 b/g). This is plenty of power for long range links. The EIRP includes antenna gain, see our calculator to work out if your planned link is legal.

To start a CWN the minimum you need, in theory, is a mate and two of our BungUp Kits. Place one on your roof, one on your mates roof and point them at each other, if all goes well (ie there is good Line of Sight) you will soon have network connectivity. The biggest problem with this scenario is that this wireless technology requires good "line of sight" to operate, which means there can not be any solid objects (such as trees, hills, buildings) in between the antenna on your roof and the antenna on your mates roof. It is not often that you and a mate have good line of sight, this is where CWN groups come into the equation. There may be a third party, whose premesis both you and your mate have line of sight to, willing to connect wirelessly to both of you. There would now be three people in the CWN and you have achieved the goal of making a network with your mate. How do you find this third person? The answer is a CWN group or club where people can meet and exchange ideas. Many CWNs begin like this, and some have taken off. Some consist of a small group of friends and others are fully incorporated entities. One of the largest in Australia, that we are proud to sponsor, is South Australian based Air-Stream Wireless Inc. The Air-Stream network spans over 50km North-to-South and 20km East-to-West of metropolitan and regional Adelaide. If you live in Adelaide you should definitely consider aligning your CWN project with Air-Stream. We stock all the products you need to connect to an existing CWN or begin one yourself. Don't hesitate to send us an email for advice on the best products for your CWN situation.

If you are starting a CWN, you should decide what type of network it is going to be. Although technically the types can be combined, it is useful to begin with a clear network type defined, so that everyone can agree on the same protocols once your network expands beyond 2 or 3 people. We will introduce the concept of a wireless 'node' which means 1 or more 802.11 wireless devices coupled with antennas at a single location. The mode of operation of the devices at a node, as well as the antenna configuration, depends on the type of network one is building.

1. Bridged Network

The simplest kind of network, there are no routers on the network, only switches. Everyone is on the same 'subnet.' Good for networks of 2 to 3 people, or parts of a network that all share the same "air space." The wireless devices can be bridged wirelessly by using WDS bridging, or connected as normal and bridged manually. This type of network is very easy to set up.

2. Dynamic Adhoc Mesh

This network has no centralised access points. Every wireless device tries to connect to every other wireless device it can find. Link state information has to be known by all of the devices. This type of network is dynamic, when a new wireless node joins the network the link information is automatically passed to the rest of the wireless nodes. This information passing is a complex problem and is an area of active research. The most popular method at the moment is the OLSR (Optimized Link State Routing) protocol for mobile ad-hoc networks (RFC3626.) It is currently implemented in the OLSR Daemon. This type of network is easy to set up.

3. Static Routed Network

This type of network uses routers to sort packets and send them along the correct path, compared to a bridged network that doesn't have any idea about the network structure. A routed network becomes useful when wireless nodes start to operate 2 or more wireless devices on different channels. A bridged network would just transmit a packet on both devices, a waste of precious air space on the device that is not connected to the destination, where as a routed network would select the correct device to send the packet for it to end up at its final destination. A static routed network means that everyone manually updates their "routing table" (ie the table of information about the network structure) every time a new wireless router is added to the network. This type of network is good for small networks that do not expand very quickly and do not have multiple paths in their structure. This type of network is moderately difficult to set up.

4. Dynamic Routed Network

A dynamic routed network operates much like the Internet model of various independent organisations connecting together at defined points and sharing routing information. When a new organisation joins the Internet, they don't have to notify every other organisation to update their routers, there are protocols that automatically propogate the information to all routers connected to the Internet. Furthermore, the protocol also selects the 'best' path to take in the case there are multiple paths to send a packet. There are endless ways to define what the 'best' path is, but for wireless networks one way to define it would be whether the wireless link is connected or not. This type of network is good for moderate to large networks that may expand quickly, may have multiple paths in their structure, and want distributed administration. Common routing protocols to achieve this are RIP2, OSPF and BGP. These are all implemented in, amongst others, Quagga routing software. This type of network is moderately difficult to set up.