CYGNUS 855 V21/V23 to Fiber Modem

CYGNUS 855 is ideal for use in Digital Axle Counter interconnection applications in Railway signaling. It allows Digital Axle Counters with ITU-T V.21 or V.23 compatible communication interface to connect to a Dark Fiber. Its built–in Copper Bypass facility with automatic changeover provides enhanced reliability for critical applications by automatically diverting V.21/V.23 traffic to a standby 6-Quad Copper Circuit in case the Fiber link fails or if the CYGNUS 855 units gets powered off for some reason.


  • CYGNUS 855 operates in pairs to transmit and receive ITU-T V.21/V.23 signals over a Dark/Dedicated optical fiber link.
  • User interface is compatible with ITU-T V.21/V.23 and allows transport of full-duplex voice band analog modem signals over a 2-wire interface. Compatible with all standard Digital Axle Counters used by Indian Railways.
  • Automatic Changeover to bypass copper circuit: This automatically switches data traffic between the Digital Axle Counters to a bypass copper circuit if the OFC link fails, or if the CYGNUS 855 unit is powered off for some reason.
  • Bypass link checking: The bypass 6-Quad Copper circuit is continuously checked even when the OFC link is being used
  • Facility is provided to record and display time stamped events related to Unit power On/Off, OFC link Up/Down, Bypass Link Up/Down.
  • Unit provides Potential free relay contacts to indicate events such as Unit power down, OFC link down, Bypass link down. These relay contacts may be connected to a Data Logger for centralised monitoring of these alarms.
  • SMS Alert: Facility to send SMS messages to specified phone numbers on specific alarms.
  • Operate from either 24 VDC or 48 VDC power supply.
  • Industrial temperature grade components.

Application Diagram