InetDaemon.Com

Frequency Division Multiplexing is a communications method that allows the use of multiple electromagnetic frequencies to transmit information, thereby overcoming the limitations of a single carrier frequency. To utilize Frequency Division Multiplexing, data must be transmitted separately on different channels. The first, simplest example of Frequency Division Multiplexing is FM Radio with different stations broadcasting at different frequencies called 'channels'.

AT&T's voice network used a hierarchy of Frequency Division configurations organizing individual voice Channels into Groups (12 channels), Groups into Supergroups (5 groups) and Supergroups into Mastergroups (10 supergroups).