G <1 km GEO satellite Continental LEO satellite Regional Few km Optical fibre Few km Number of Simultaneous Connections User capacity or the maximum number of users that can simultaneously access the communi- cations medium is an important parameter for wireless and to a lesser degree fixed broadband telecommunications systems. Fixed systems generally are dedicated: for example, one pair of copper wires connect a DSL subscriber to a telephone exchange at the infrastructure layer. Retail layer networks are shared to serve a large number of subscribers and therefore broad- band traffic needs to be managed to ensure high QoS. In contrast, all wireless systems serve subscribers in a coverage area using a common frequency spectrum in the infrastructure layer, and therefore the resources must be shared at both infrastructure and retail layers. For example, the number of simultaneous phone calls that can be made on a mobile telecommunications system is a function of the technologies used and available frequency spectrum. In general, higher possible transmission rates may result in a larger number of users that may simulta- neously connect to the network. Another technology parameter is the total number of users that can remain connected to a network even when they are inactive. This is important for a data communications system where users become active only when they have data to send. Maintaining network connection allows these users to transmit their data quickly without needing to go through the necessary processes of registration with a server. All broadband telecommunications systems need to carry a significant amount of traffic and therefore user QoS management is an important issue. Again, figures for different broadband telecommunications systems are examined in Chapters 9-11. Power Consumption Power requirements differ for different technologies. Generally, the higher the desired trans- mission rate, the larger the required transmission power. Coverage area also features in deter- mining the transmission power