T1 lines are digital facilities that provide a transmission rate of up to 1.544Mbps using Digital Signal Level 1 (DS1). The available bandwidth is divided into 24 channels that operate at 64Kbps each, plus an 8Kbps channel for basic supervision and control. Voice is sampled and digitized via Pulse-Code Modulation (PCM). T1 lines are used for more economical and efficient transport over the Wide-Area Network (WAN).

Economy is achieved by consolidating multiple lower-speed voice and data channels via a multiplexer or channel bank and sending the traffic over the higher-speed T1 line. This method is more cost-effective than dedicating a separate lower-speed line to each terminal device. The economics are such that only five to eight analog lines are needed to cost-justify the move to T1.

Efficiency is obtained by compressing voice and data to make room for even more channels over the available bandwidth. Individual channels also can be dropped or inserted at various destinations along the line s route. Network-management information can be embedded into each channel for enhanced levels of supervision and control.

Usually, a T1 multiplexer provides the means for companies to realize the full benefits of T1 lines, but channel banks offer a low-cost alternative. The difference between the two devices is that T1 multiplexers offer higher line capacity, support more types of interfaces, and provide more management features than channel banks.