 airports and conference areas. The WLAN network consists of base stations, called access points and wireless clients. The clients can be 'anything', such as PDAs and portable or stationary PCs. Soon most new portable computers are expected to be equipped with WLAN chips. IP telephony and WLAN is a new combination. The access points are bridging wireless and wired communication. They can be con- nected as an extension to an existing wired network, but they can also be connected to other base stations by means of radio in totally wireless networks. Some possible accesses are illustrated in Figure 13.36. The WLAN development is shown in Figure 13.37. The first 802.11 standard came out in 1997. It specifies wireless communication with the speeds of 1 and 2 Mbit/s in the 2.4 GHz band. The next standard was called 802.11b. It specifies radio communication with speeds of 5.5 and 11 Mbit/s in the 2.4 GHz band. 802.11b is backward compatible with 802.11. 802.11g is an extension to 802.11b, the basis of the majority of WLANs in existence today. 802.11g broadens 802.11b's data rates to 54 Mbit/s within the 2.4 GHz band using OFDM (orthogonal frequency division multiplexing) technology. Because of backward compatibility, an 802.11b radio card will interface directly with an 802.11g access point (and vice versa) at 11 Mbit/s or lower depending on the range. Upgrading newer 802.11b access points to be 802.11g compliant is possible via relatively easy firmware upgrades. A complete upgrade in an area would create a need to move the access points closer together and include additional ones to accommodate higher data rates. Application scenarios GPRS/UMTS Bluetooth Internet On the move Office Ethernet Figure 13.36 WLAN Applications Understanding Changing Telecommunications - Building a Successful Telecom Business 2.4 GHz 802.11 802.11b 802.11e 802.11g Some QoS 802.11a 802.11e/h 5 GHz Coexistence Harmonised interworking HiperLAN2 60 GHz 1-2 Mbps 11 Mbps 20-54 Mbps >100 Mbps Figure 13.37 WLAN development A big issue with 802.11g, w