The DDM module is particularly useful in solving transmission problems. It is the first tool we use to check what issues we are dealing with in the network. Depending on the manufacturer, after entering the appropriate command in the management console of the switch, we receive data such as the power of the transmitted and received signal. The displayed information will help us determine the cause of transmission errors.
The basic command displays the most important information about the module.
Switch#show transceiver
Interface Temp(°C) Voltage(V) Bias(mA) RX Power(dBm) TX Power(dBm)
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1/0/25 56 3.22 20.05 -7.60 -5.16
One of the significant features of DDM is the ability to generate alarms and flags that indicate incorrect module operation and exceedance of defined alarm thresholds, e.g. operating temperature, which enables early problem detection and prevents interruptions in network access.
Below we can see the results of detailed DDM diagnostics
Switch#show transceiver detail
Ethernet1/0/25 transceiver detail information:
Base information:
SFP found in this port, manufactured by LightOptics, on Oct 29, 2019.
Type is 1000BASE-LX. Serial number is LOF19112000497
Link length is 20000 m for Single Mode Fiber.
Link length is 550 m for 50um Multi-Mode OM2 Fiber.
Link length is 550 m for 62.5um Multi-Mode OM1 Fiber.
Nominal bit rate is 1300 Mb/s.
Laser wavelength is 1310 nm.
Brief alarm information:
None
Detail diagnostic and threshold information:
Diagnostic Threshold RealTime_Value High_Alarm Low_Alarm High_Warn Low_Warn
--------------------------------------------------------------------------------------------------
Temperature(C°) 58 110 -45 95 -42
Voltage(V) 3.22 3.60 3.00 3.50 3.05
Bias Current(mA) 20.10 80.00 2.00 70.00 3.00
RX Power(dBm) -7.28 -3.00 -22.01 -3.50 -21.49
TX Power(dBm) -5.13 -3.00 -8.00 -3.50 -7.50
Sometimes we come across the term DOM, which stands for Digital Optical Monitoring in the context of technology that allows monitoring of important parameters of optical modules. Both concepts, DDM and DOM, can be used interchangeably.
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