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(DSU or "data service unit") A device used in digital transmission for connecting a CSU (Channel Service Unit) to Data Terminal Equipment (a terminal or computer), in the same way that a modem is used for connection to an analogue medium.
A DSU provides a standard interface to a user's terminal which is compatible with modems and handles such functions as signal translation, regeneration, reformatting, and timing. The transmitting portion of the DSU processeses the customers' signal into bipolar pulses suitable for transmission over the digital facility. The receiving portion of the DSU is used both to extract timing information and to regenerate mark and space information from the received bipolar signal.