The MON or Monitoring jack on Telect's DSX modules for the MON OUT port of single monitor ports, OUT or IN of dual monitor ports— accesses a –20 dB version of the signal present at the port and sends it to the MON port contacts. A jack inserted into the MON port also completes the tracer lamp circuit and lights the tracer LEDs.
 
Through monitoring, you can discover the type and frequency of hits or errors (voice or data deg- radiation from faults or connection anomalies):
• Error-free seconds (EFS)
• Loss of frame (LOF)
• Loss of signal (LOS)
• Unavailable seconds (UVS)
• Bit error rate (BER)
• Coding violation (CV)
• Framing error (FE)
• Degraded minutes (DM)