A transmission-control character used for (a) switching on an answer-back unit in the station with which the connection has been established, (b) triggering the receiving unit to transmit an answer-back code to the terminal that transmitted the WRU signal, and (c) initiating a response that might include station identification, an indication of the type of equipment that is in service, and the status of the station. Note 1: The WRU signal corresponds to the 7-bit code assigned to the WRU. Note 2: The receiving unit may be a telegraph unit, data terminal equipment (DTE,) or other unit. Synonym WRU.