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). == Common varieties == CSUs can be categorized by the class of service they support (DS1, DS3, DDS, etc.) and by the capabilities within that class.