DDM (Digital Diagnostic Monitoring) is a tool that Network engineers use to monitor optical transceiver performance in real time. Most transceivers in use today feature the DDM function.
Related Articles: What is DDMI?
How to use DDM information effectively
SFF-8636 is an MSA standard that defines a common management interface for 4-lane pluggable transceiver modules and cable assemblies. The following are the 5 important parameters that are monitored by DDM: Temperature, Voltage, Rx power, Bias current and Tx power.
Typical DDMI from 40G and 100G Transceivers
The values below were read from a 32 port 100G switch with an external VOA.
You can use the formulae below to calculate the exact values of the monitoring parameters.
- Mon_temp (Range = +/-128 oC max)
16-bit in increments of 1/256 oC
=HEX2DEC(CONCATENATE(MSB,LSM))/256. example: 1C,08 = 28.03 oC
- Mon_Vcc (Range = 6.55V max)
16-bit in increments of 0.1mV
=HEX2DEC(CONCATENATE(MSB,LSM))/(10^4). example: 7C,74 = 3.19V
- Mon_Txbias (Range = 131 mA max)
16-bit in increments of 2uA
=HEX2DEC(CONCATENATE(MSB,LSM))/(500). example: 96,E1 = 77.25mA
- Mon_Txpwr (Range = -40/+8.2dBm max)
16-bit in increments of 0.1uW
=10*LOG(HEX2DEC(CONCATENATE(MSB,LSM))/(10^4)). example: 2F,E4 = 0.88dBm
- Mon_Rxpwr (Range = -40/+8.2dBm max)
16-bit in increments of 0.1uW
=10*LOG(HEX2DEC(CONCATENATE(MSB,LSM))/(10^4)). example: 08,A0 = -6.56dBm
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