In the latest developments of satellite communication systems, functions such as routing and switching are performed on board, so that the satellite is now an intelligent switching node, while the previously developed satellites operated only as passive repeaters.
In designing a satellite communication system to be simultaneously used for different types of services, such as telephony, speech band data and/or other modulated data, videoconference, television etc., problems arise which basically concern the choices of frame lengths, access type, transmission band, and so on.