The channel types for Aero are:
P-channel
A packet switched continuous channel in the forward direction ground-to-air from each GES carrying user data and signaling, e.g., system tables broadcast.
R-channel
A random access (slotted Aloha) channel in the return direction carrying user data and signaling if the signaling unit is 33 bytes or less.
T-channel
A TDMA channel in the return direction carrying user data and signaling. The GES allocates time slots according to requests from the AES.
C-channel
Circuit-switched SCPC voice channel in both directions.
A satellite region contains one or more Ground Earth Stations (GES). The GES manages the control channels, allocation of traffic channels, channel resources, interfacing to terrestrial networks (PSTN, data networks, Internet) and session control. The user terminals called an Aeronautical Earth Stations, AES, communicate with the GES. The GES communicate with other GES within and outside its region and broadcasts system information.
The only frequencies the AES initially knows are the frequencies of the GES in all regions - all other frequency information is dynamically extracted from the system broadcasts or in session oriented signaling messages. After being switched on, the AES must be told (or remembers) in which region it is currently located, and will automatically tune to the corresponding frequency of the GES and will identify the spot beam ID where it is located.