Channel service unit

In telecommunications, a channel service unit (CSU) is a line bridging device for use with T-carrier, which

• is used to perform loopback testing;
• may perform bit stuffing;
• may also provide a framing and formatting pattern compatible with the network;
• provides a barrier for electrical interference from either side of the unit; and
• is the last signal regeneration point, on the loop side, coming from the central office, before the regenerated signal reaches a multiplexer or data terminal equipment (DTE).