n 802.11. range but not with those in another BSS that is outside of The operational specifics of WLAN are described in this range. In order to interconnect terminals that are not IEEE 802.11 in terms of defined protocols between in direct range one with the other, the distributed system lower-level software layers. In general, networks may be shown in Figure 5.2-2 is needed. Here, terminals that are described by the communication of data and control in range of a station designated as an access point (AP) between adjacent layers of the Open System Inter- can communicate with other terminals not in direct range connection Reference Model (OSI/RM), shown in but who are associated with the same or another AP. Two Figure 5.2-4, or the peer-to-peer communication between or more such access points communicate between like layers of two or more terminals in the network. The themselves either by a wireless or wired medium, and bottom layer, physical, represents the hardware connec- therefore data exchange between all terminals in the tion with the transmission medium that connects the network is supported. The important thing here is that the terminals of the network-cable modem, radio trans- media connecting the STAs with the APs, and connecting ceiver and antenna, infrared transceiver, or power line the APs among themselves are totally independent. transceiver, for example. The software of the upper layers A network of arbitrary size and complexity can be is wholly independent of the transmission medium and in maintained through the architecture of the extended principle may be used unchanged no matter what the service set (ESS), shown in Figure 5.2-3. Here, STAs have nature of the medium and the physical connection to it. full mobility and may move from one BSS to another IEEE 802.1 is concerned only with the two lowest layers, while remaining in the network. Figure 5.2-3 shows an- physical and data link. other element type-a portal. The portal is a gateway IEEE 802.11 prescribes the protocols between the between the