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Chapter 16 DDM Configuration
16.1 Introduction to DDM
16.1.1 Brief Introduction to DDM
DDM (Digital Diagnostic Monitor) makes the detailed digital diagnostic function standard in
SFF-8472 MSA. It set that the parameter signal is monitored and make it to digitize on the
circuit board of the inner module. After that, providing the demarcated result or the digitize
measure result and the demarcate parameter which are saved in the standard memory
framework, so as to expediently read by serial interface with double cables.
Normally, intelligent fiber modules support Digital Diagnostic function. Network management
units is able to monitor the parameters (temperature, voltage, bias current, tx power and rx
power) of the fiber module to obtain theirs thresholds and the real-time state of the current fiber
module by the inner MCU of the fiber module. That is able to help the network management
units to locate the fault in the fiber link, reduce the maintenance workload and enhance the
system reliability.
DDM applications are shown in the following:
1. Module lifetime forecast
Monitoring the bias current is able to forecast the laser lifetime. Administrator is able to find
some potential problems by monitoring voltage and temperature of the module.
（1）High Vcc voltage will result in the breakdown CMOS, low Vcc voltage will result in the
abnormity work.
（2）High rx power will damage the receiving module, low rx power will result that the
receiving module cannot work normally.
（3）High temperature will result in the fast aging of the hardware.
（4）Monitoring the received fiber power to monitor the capability of the link and the remote
switch.
2. Fault location
In fiber link, locating the fault is important to the fast overload of the service, fault isolation is
able to help administrator to fast locate the location of the link fault within the module (local
module or remote module) or on the link, it also reduce the time for restoring the fault of the
system.
Analyzing warning and alarm status of real-time parameters (temperature, voltage, bias
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Troubleshooting
