This lecture deals with several Media Access Control (MAC) protocols to be used for the satellite segment of future mobile communication networks. The scenario is given by Low Earth Orbit - Mobile Satellite Systems (LE-MSSs). Demand-assignment protocols are considered that are evolutions of the classical Packet Reservation Multiple Access (PRMA) scheme. Two types of traffic are considered: in other words, the voice traffic and a bursty data traffic related to the Internet surfing. Quality of service parameters are used in order to compare the performance of the different MAC schemes. The study presented in this lecture permits to highlight some interesting tradeoffs in the design of satellite MAC protocols.