An OTDR is the tool that shows where a fiber is broken or degrading, but it tests one fiber at a time. A network with dozens of fibers per site cannot justify an OTDR on each one. Placing an optical switch in front of a single OTDR lets it test every fiber in turn, on a schedule, without anyone on site.
How it works
- The OTDR connects to the common port of a 1×N switch, or to an input of an N×M cross-connect.
- Monitoring software steps the switch through the fibers, takes a trace on each and compares it with a reference trace.
- A new reflection or a rise in loss raises an alarm with the distance to the event, before customers notice the fault.
What to look for in the switch
- Channel count: the 7202 documents 1×N configurations with up to 128 channels; the 7221 rack OXC documents 16×16 to 48×48 and OTDR test support.
- Low insertion loss and high return loss, because both reduce the dynamic range left for the fiber. The 7221 documents 45 dB return loss.
- Durability for continuous polling: the 7221 documents 10⁹ switching cycles.
- Remote control over RS232 or RJ45 so the monitoring system can drive it.
Dark fiber or live fiber
Spare (dark) fibers can be tested at any wavelength. Fibers that carry traffic need an OTDR wavelength outside the traffic band and filters that keep the test signal away from the receivers, so plan the wavelength and the filters together with the switch.
Monitoring with protection
Monitoring finds the fault; protection keeps the traffic running while it is repaired. On protected routes, OLP switches traffic to the standby fiber and the OTDR locates the cut on the failed one. For DWDM networks, the DCI5800 OTDR card works at 1625 nm ±10 nm, outside the traffic band, with a 30–40 dB dynamic range and polling in eight directions.
What to send us
The number of fibers per site, typical fiber lengths, your OTDR model and how you want to receive alarms. We reply within 24 hours with a configuration.