SAT-C is a satellite based store-and-forward low speed message transmission system operating in the L-band to (forward direction) and from (return direction) the mobile earth stations (MES) and in the C-band to and from the land earth stations (LES) and network control stations (NCS).

Mobile stations may be maritime, land based or aeronautical. The channel rate in both directions is 1200 symbols/sec. Error protection is achieved by convolutional encoding with R = 1/2 and k = 7 giving a user bit rate of 600 bps.

A block or frame of data in the forward direction (TDM) comprises 10368 symbols (8.64 s). Data is highly interleaved to combat slow fades. It is also scrambled to ensure an even distribution of logical 1s and 0s for proper bit synchronization. Frame synch is achieved by using an unscrambled unique word at the beginning of the frame.

The coding will correct some errors otherwise ARQ is used.

The forward channels from the LES and NCS are continuous time division multiplex (TDM) channels and are used for message transmission and signaling.

In the return direction messages are transmitted by the MES on time division multiple access (TDMA) channels assigned by the NCS. The frame length varies between 2176 symbols and 10368 symbols in steps of 2048 symbols.