An early device designed to interface analog PBX or central office (CO) voice circuits to a DS-1 circuit. Channel banks perform two functions, in sequence. First, they multiplex up to 24 analog signals on a common pulse amplitude modulation (PAM) electrical bus. Second, they encode the individual PAM channels into a digital format, using pulse code modulation (PCM), for transmission over a DS-1 circuit. Channel banks place each voice conversation on a separate channel. A given channel can support a digital data transmission, rather than a voice transmission. For example, a data transmission at 9.6 kbps or 19.2 kbps originally occupied a full DS-0 channel of 64 kbps, just as does a 56 kbps data transmission or a digitized voice conversation. Later, sub-rate multiplexing allowed as many as 5 channels of 9600 bps to share a DS-0 channel. See also bus, DS-0, DS-1, multiplexer, PAM, and PCM.
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 and T1.