Ad hoc wireless networks

Ad hoc wireless networks are PC-to-PC wireless networks. There are no dedicated wireless access points (WAPs) to send and receive data over the wireless medium-your PC or laptop acts as both a WAP and a client to send and receive wireless data from other ad hoc clients directly.

An ad hoc network can have a variety of icons, whereas an Infrastructure network will always show an antenna.

How do ad hoc networks work?

Ad hoc networks appear to work the same as other wireless networks, but you are really connecting to another person's computer. Your computer detects the ad hoc network, you double-click on the icon for that network and you will be prompted for a login if that network requires authentication.

In Windows the computer advertising the ad hoc network needs to have another active connection, such as a wired ethernet connection to the Internet, as well as Internet Connection Sharing (ICS) enabled for you to send and receive traffic over the ad hoc network. In most instances this is not the case and the ad hoc connection will not allow you to use the internet, even though it seems you have connected.

What is wrong with ad hoc networks?

1. You could be running an ad hoc network-without knowing it

Many people with a Windows computer don't know they are running an ad hoc network. If you have tried to join an ad hoc network, such as free WiFi in an airport, your computer will attempt to reconnect next time it is in range of that network-even if it didn't connect the first time. The problem is your computer will automatically advertise itself as an available ad hoc network in different locations whenever you are not connected to another wireless network, inviting random clients to try and connect to you.

2. Ad hoc networks spread to other

As was the case with your computer, when a random client tries to connect to your ad hoc network and then they roam elsewhere, their PC starts advertising an ad hoc network. This is how the ubiquitous 'Free Public WiFi' has spread around the world.

3. It could be a trap

When you connect to an unknown wireless network-both ad hoc and infrastructure-you offer a view of everything you do, which could include user-names and passwords. A person with malicious intent may intentionally set up a free wireless service with this specific intention. Even a mail client like Outlook Express may store and make visible your password to the device advertising the wireless network.

4. Ad hoc networks interfere with legitimate wireless networks

Wireless networking uses a very narrow band in the radio spectrum. Other devices use this range, or cause interference at the same frequencies, but the worst source of interference is other wireless networks-including ad hoc networks.

When there is interference, the WAP automatically scales down the speed of its connection to clients. Interference also cause errors in the data being exchanged, requiring that same data to be re-transmitted, causing more traffic and thus more congestion and interference.