Channel Service Unit (CSU)

Channel Service Unit is a digital communication device that is used to connect a digital line to a digital device.

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What is Channel Service Unit

A digital communication device that is used to connect a digital line to a digital device. Channel Service Units (CSUs) can be used to link local area networks (LANs) into a wide area network (WAN) using telecommunications carrier services such as:

  • Digital data service (DDS)
  • T-carrier services such as a T1 line
  • Frame relay links

How it works

The CSU is used to terminate the end of the digital telecommunications line located at the customer premises. It terminates on the customer premises end with a data terminal equipment (DTE) device such as a router, switch, multiplexer (MUX), or dedicated server. The connection to a DTE is typically an RS-232 or a V.35 serial transmission interface. The service provider interface of the CSU must connect to a Data Service Unit (DSU), which is a data communications equipment (DCE) device responsible for converting signals into a format suitable for transmission over the digital communications line, and for creating and maintaining the connection.

Channel Service Unit (CSU)

Typically, the telecommunications service provider will lease the CSU to the customer, having preconfigured it for the type of communications to be supported. CSUs typically include remote diagnostic capabilities, such as remote loop testing and even Simple Network Management Protocol (SNMP) features that allow the unit to be monitored by the service provider.


Currently, CSUs are usually combined with DSUs to create a single device called a CSU/DSU (Channel Service Unit/Data Service Unit). Dedicated stand-alone CSUs are typically used only for interfacing with installed customer premises telecommunications equipment that contains integrated DSUs. This installed equipment could be a channel bank, Private Branch Exchange (PBX), T1 multiplexer, or some other device.