e. VoIP, voice over internet protocol; VPN, virtual private network Broadband Telecommunications Technologies and Management Time Division Multiple Access In Time Division Multiple Access (TDMA) transmission capacity on one or more transpon- ders is allocated to a VSAT user for a certain period of time. Several VSAT users may consec- utively gain access to a satellite, each within a well-defined time slot. In general these VSAT subscribers' needs are intermittent and therefore constant access to a VSAT is not necessary. Frequency Reuse The same transponder carrier frequency may be reused in a number of different regions if these are sufficiently separated SO that their signals do not interfere. This technique can be used to increase the total transmission rates a satellite may support in the downlink. This is illustrated in Figure 11.10, where different shades indicate the carrier frequency used in a region. As can be seen, the same frequency can be used multiple times, thereby increasing the system's capacity several fold. Frequency reuse requires multiple spot beams and/or multiple polarisation beams. Mutual geographical isolation ensures that little interference is perceived for ground receivers. VSAT systems can provide data communication rates from a low of 9.6 kilobits per second (kbps) to upwards of 50 megabits per second (Mbps) [10]. They are used in a number of appli- cations: from conflict-zone reporting, to remote-field exploration data connectivity, to internet service provision to rural areas. Rural and underdeveloped regional internet connectivity are sometimes funded through philanthropic institutions such as the Belinda and Bill Gates Foundation. Inmarsat has announced plans to provide services branded as the Broadband Global Area Network (BGAN) using spectrum in the K band. The spectrum in this band is available to Figure 11.10 Frequency reuse in satellite communications [10] Satellite Communications both civilian and military applications, and as a result Inmarsat toggles services using the band