4.3 Components of the IEEE 802.11 architecture
4.3.1 GeneralThe IEEE 802.11 architecture consists of several components that interact to provide a WLAN that supports
STA mobility transparently to upper layers.
The basic service set (BSS) is the basic building block of an IEEE 802.11 LAN. Figure 4-1 shows two BSSs,
each of which has two STAs that are members of the BSS.
It is useful to think of the ovals used to depict a BSS as the coverage area within which the member STAs of
the BSS may remain in communication. (The concept of area, while not precise, is often good enough.) This
area is called the Basic Service Area (BSA). If a STA moves out of its BSA, it can no longer directly
communicate with other STAs present in the BSA.
4.3.2 The independent BSS (IBSS) as an ad hoc network
The IBSS is the most basic type of IEEE 802.11 LAN. A minimum IEEE 802.11 LAN may consist of only
two STAs. Since the BSSs shown in Figure 4-1 are simple and lack other components (contrast this with
Figure 4-2), the two can be taken to be representative of two IBSSs.
This mode of operation is possible when IEEE 802.11 STAs are able to communicate directly. Because this
type of IEEE 802.11 LAN is often formed without preplanning, for only as long as the LAN is needed, this
type of operation is often referred to as an ad hoc network.
4.3.3 STA membership in a BSS is dynamic
A STA’s membership in a BSS is dynamic (STAs turn on, turn off, come within range, and go out of range).
To become a member of an infrastructure BSS or an IBSS, a STA joins the BSS using the synchronization
procedure described in 10.1.4.5. To start a new mesh BSS or to become a member of a mesh BSS, a STA
starts the transmission of Beacons and performs the synchronization maintenance procedure described in
13.13. To access all the services of an infrastructure BSS, a STA becomes “associated.” These associations
are dynamic and involve the use of the distribution system service (DSS), which is described in 4.4.3. A
mesh STA does not become associated as there is no central entity in a mesh BSS (MBSS). Instead, a mesh
STA peers with other mesh STAs.
