It is variable-bandwith spread spectrum modulation, so talking about discrete channels does not make that much sense. But each of frequency bands it operates in is notionally divided into 9-11 uplink and downlink channels.
The modulation scheme is essentially FM with a twist: high bitrate mode is essentially straight FSK and lower rate modes are FM modulated with sawtooth, which is or is not inverted in each period depending on the transmitted bit. The idea is essentially same as various QRP modes involving painting images on waterfall diagram. (Full gateway nodes receive full band and can track ~50 transmitting nodes at once)