Abstract: A symmetric full duplex data communication device known as a communication interface unit (CUI) permitting transmission of signals on CATV infrastructure or on amplitude modulated (AM) analog fiber in a variety of configurations. The communication interface unit is capable of interfacing to a variety of signal types, including but not limited to: E1 (G.703), T1 NI and DSX-1), V.35 (N.times.64) or Ethernet. The CUI transmits in the upstream direction in the frequency range of 5 to 50 MHz and receives in the downstream direction in the range of 50 to 860 MHz. The communication interface unit is bandwidth efficient by the use of digital filters in the receive signal path. Management of the communication interface unit is performed via a GMSK internal modem under control of the same CPU. The GMSK internal modem is used to establish a control channel to a network management system (NMS). The control channel operates at a maximum rate of 38.4 Kbps and at a bandwidth of 50 KHz.