appreciated that terrestrial networks also have framing structures e g e g for t1 or e1 framing etc fig2 illustrates the tdma frame structure with three bursts b 1 b 2 and b 3 it will be appreciated that tdma operates according to the following general rules 1 data is transmitted on the channels which are contained in bursts 2 each burst is defined at a fixed offset henceforth referred to as a burst offset relative to a start of frame sof instant 3 the network uses a pool of radio frequency rf carriers at different frequencies 5 bursts on the same carrier cannot overlap in time bursts on different carriers may however overlap in time 6 carriers are subdivided into slots no two bursts can begin in the same slot in one carrier burst offsets should fall in different slots 7 bursts are allocated among modems wherein the term u201c modem u201d or u201c terminal u201d is henceforth used to denote the earth station which transmits or receives a burst it should also be mentioned that in the network illustrated in fig1 it is assumed that the terminal that transmits e g mrt 400 a burst knows the offset of the burst relative to the start of frame the carrier frequency and the power level on the receive side the terminal e g tt 200 tunes to the corresponding carrier frequency and extracts the burst knowing the approximate position in time every terminal has a reliable control channel to and from the ncc 600 implemented using.