The ComNet FDX55 series consists of fully-digital transceiver units designed for implementing simplex or full-duplex RS232 Drop-and-Repeat poll-and-respond traffic signalization/communications data networks utilizing one or two optical fibers. These environmentally-hardened units are ideal for use in unconditioned out-of-plant or roadside installations and the master-configured transceiver unit may be located anywhere within the network, making this equipment ideal for applications involving on-street master controllers with upstream and downstream communication requirements. These units are compatible with FDX50, FDX51 and FDX52 Series of optical modems. Manually resettable anti-streaming is included for unparalleled network protection. Optional battery backup capability provides the highest level of network reliability in the event of a loss of local prime operating power, and maintains continuous communications channel operation.