6.3 WLAN Configurations: From Ad Hoc to Wireless Bridging
All devices that use the same transmission channel to exchange data with each other form a basic service set (BSS). The definition of the BSS also includes the geographical area covered by the network. There are a number of different BSS operating modes.
6.3.1 Ad Hoc, BSS, ESS and Wireless Bridging
In ad hoc mode, also referred to as Independent Basic Service Set (IBSS), two or more wireless devices communicate with each other directly. Every station is equal in the system and data is exchanged directly between two devices. The ad hoc mode therefore works just like a standard wireline Ethernet, where all devices are equal and where data packets are exchanged directly between two devices. As all devices share the same transport medium (the airwaves), the packets are received by all stations that observe the channel. However, all stations except the intended recipient discard the incoming packets because the destination address is not equal to their hardware address. All participants of an ad hoc network have to configure a number of parameters before they can join the network. The most important parameter is the Service Set Identity (SSID), which serves as the network name. Furthermore, all users have to select the same frequency channel number (some implementations select a channel automatically) and ciphering key. While it is possible to use an ad hoc network without ciphering, it poses a great security risk and is therefore ...