The first type of BSS is known as an ad hoc network, which consists of a group of stations within range of each other.
As its name implies, ad hoc networks are temporary in nature and are typically created and maintained as needed without prior administrative arrangement.
Ad hoc networks can be formed anywhere spontaneously and can be disbanded after a limited period of time. A typical ad hoc network is shown in the Figure below.
The second type of BSS is known as infrastructure BSS (IBSS), which is commonly used in practice. Here, several BSSs are interconnected by a distribution system to form an extended service set (ESS) as shown in Fig.
The BSSs are like cells in a cellular communications network.
Each BSS is provided with an Access point (AP) that has station functionality and provides access to the distribution system. APS operates on a fixed channel and remains stationary like base stations in a cellular communication system.
APS is located such that the BSSs they serve overlap slightly to provide continuous service to all the stations.