40G and 100G DDM Values

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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.

DDM values

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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