Channel Service Unit/Digital Service Unit (CSU/DSU)

Definition - What does Channel Service Unit/Digital Service Unit (CSU/DSU) mean?

Channel service unit/digital service unit (CSU/DSU) refers to two digital hardware devices that provide an interface between digital circuits and data terminal equipment (DTE). A CSU/DSU unit operates at the physical layer of the Open Systems Interconnection (OSI) model. A CSU/DSU unit is required for both ends of a T1 or T3 connection.

A CSU/DSU is also known as a channel service unit/data service unit (CSU/DSU).

Techopedia explains Channel Service Unit/Digital Service Unit (CSU/DSU)

AT&T originally developed the CSU/DSU as an interface for non-switched digital data systems. A CSU/DSU unit is required for digital lines.

A CSU is a device that serves as a buffer between a local area network (LAN) and a public carrier’s wide area network (WAN). It ensures that signals are placed on public lines in a timely manner. A CSU is categorized by supported service classes and class capabilities. When a customer premises equipment (CPE) signal is lost, a CSU, such as DS-1, supports interface loopback and produces alarm signals to the provider’s network interface device (NID). Advanced data units include internal and bidirectional performance carrier monitors and have test pattern generation and monitor capabilities.

A DSU is a hardware device that serves as an interface between the CSU and computer. It transmits digital data over hardware channels and converts signals from bridges, multiplexers and routers into bipolar digital signals that are used on digital phone lines while ensuring correct voltage levels. A DSU also manages signal regeneration and timing errors.

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