DDM basics

Digital Diagnostic Monitoring (DDM), also called DOM, lets a transceiver report its own operating condition in real time. CodingBox reads these values on the Check transceiver screen.

The four core parameters

• Temperature — the module's internal temperature, in °C.
• Supply voltage — the 3.3 V rail as measured inside the module.
• Laser bias current — the drive current of the transmit laser, in mA.
• TX / RX optical power — transmitted and received light power, in dBm.

Warning and alarm thresholds

Each parameter carries factory-set thresholds. Values are classified against them:

Reading RX power

Received optical power is the most useful field for diagnosing a link:

RX power = -3.2 dBm   → healthy
RX power = -18 dBm    → near receiver sensitivity, expect errors

A low RX power usually points to a dirty connector, a bent fibre or too much distance — not necessarily a faulty module.