A multiplexor that merges several low-speed voice or data lines into one high-speed digital line and vice versa. Channel banks use TDM (time division multiplexing) to combine the different signals into one by interleaving the bits.
Starting in the 1960s, channel banks converted 24 analog voice lines into digital and multiplexed them onto one T1 line. Towards the late 1980s, they became more sophisticated and accepted plug-in modules that took in a variety of digital signals and multiplexed them onto the T1. See TDM