1. The network architecture
The IEEE 802.11 architecture consists of several components that interact to provide a wireless LAN that supports station
mobility transparently to upper layers. The basic service set (BSS) is the basic building block of an IEEE 802.11 LAN.
The BSS is a set of stations controlled by a single coordination function that determines when a station is permitted to
transmit and may be able to receive the protocol data unit (PDU) via the wireless medium. Figure 7.1a shows an ad hoc network (independent BSS) which consists of two stations (STAs). STA is a device that contains an IEEE 802.11
conformant medium access control (MAC) and physical layer (PHY) interface to the wireless medium. Figure 7.1b shows an extended form
of network that is built with multiple BSSs. The architectural component used to interconnect BSSs is the distribution
system (DS). An access point (AP) is a STA that provides access to the DS.
Fig. 7.1. The IEEE 802.11 architecture: a) ad-hoc network, b) infrastructure network.