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Emerging wireless communication for smart grid applications Chapter 5 195

5.4.1 Network architectures of IEEE 802.11 standards
Network architectures of the IEEE 802.11 standards can be classified into two
categories that are referred as infrastructure network architecture and ad hoc
network architecture. In an IEEE 802.11 network, a device having the commu-
nication ability is called a station while a device establishing an infrastructure
network is referred as an access point (AP). A connection between a station and
an AP should be realized to enable communication in an infrastructure network.
Hence, communication among the stations is generally relayed through the AP.
Whole stations containing APs in the network establish a Basic Service Set
(BSS). A Basic Service Set Identifier (BSSID) that identifies a MAC address
of the AP in the network defines this service group. Each 802.11 network
has a Service Set Identifier (SSID) that can be identified by using case-sensitive
text strings as long as 32 characters. In addition, WLAN networks can be com-
bined to extend range of network, which is referred as Extended Service Set
(ESS). In ad hoc network architectures, Independent Basic Service Set (IBSS)
authorizes the stations to enable P2P communication where the use of the APs
does not require.
The RTS and CTS may optionally be employed to prevent frame collisions
in IEEE 802.11 networks. The main aim of the use of RTS and CTS is to over-
come hidden terminal problem (HTP) that is illustrated in Fig. 5.10. The HTP
appears if there exists one AP (or station, Station 2) in the middle of two or more
stations (Stations 1 and 3). In the event of the Stations 1 and 3 are remotely
located, the stations are not able to connect with each other. However, they
can contact with the Station 1. If the Stations 1 and 3 simultaneously send mes-
sage to Station 2, a collision called HTP appears. This collision, the HTP, can be

FIG. 5.10 Illustration of hidden terminal problem.