chniques have helped increase transmission rates to several hundred megabits per second. While Ethernet (wired local area networking) is still common, wireless office communications are largely replacing the wires in offices. Case Study Questions What were the business drivers behind the research and development of wireless systems for local area networking? What characterises the indoor office transmission medium? Is it conducive to high quality communications? The frequencies band used for wireless LAN systems are generally unlicensed? Why? Why is the frequency usage efficiency SO low in early wireless LAN systems? Why is CSMA used for resource sharing and media access? Generations of Mobile Communications Systems Mobile communications technologies have been broadly classified into a number of 'genera- tions'. Four generations are widely recognised in the industry and broadly defined as follows: First generation (1G) systems are analogue circuit-switched systems, and were used primarily for voice telecommunications, although minimal circuit-switched data com- munications capability also existed. Second generation (2G) systems are digital circuit-switched systems used primarily for voice telecommunications. Significant data communications capability, both on circuit- switched and minimal packet-switched systems was realised. Later generations of 2G systems standardised the capability of fully packet-switched communications (e.g. GPRS and EDGE). Third generation (3G) systems are digital circuit and packet-switched systems used for voice and data communications with variable transmission rate capabilities. Fourth generation (4G) systems are broadly, all-internet protocol (all-IP) end-to-end systems from a wireless mobile device all the way through the base station and core network to the internet. They are fully packet-switched systems with voice communi- cations also carried out using packet-switching protocols. The network architecture and nodes which support end-to-end connectivity are also based on IP systems.