Digital Diagnostics Monitoring Interface (DDMI) is an optional feature which is implemented for debugging optical transceivers. DDMI provides the critical system information about 1G, 10G and 40G Optical transceiver modules. 



Not all transceivers support DDMI. DDMI is supported for any optic that supports DDMI. For XFP, SFP, and SFP+, there is a bit in the eeprom that designates if support is included in the module. For QSFP, the transceiver must be fiberQSFP to support DDMI.
Digital diagnostics monitor:
  • Module temperature (in Celsius)
  • Receiver power
  • Transmitter bias current
  • Transmitter power
The output of the physical value of each parameter is an analog voltage or current from the transimpedance amplifier, the laser driver, or the postamplifier. The interface allows access to device-operating parameters, and includes alarm and warning flags which alert end users when particular operating parameters are outside of a normal range. The interface is compliant with SFF-8472, "Digital Diagnostic Monitoring Interface for Optical Transceivers."

In the detailed version of the CLI command, all the threshold values for warnings and alarms are displayed for the lower and higher side of the threshold. These thresholds are not user configurable. The status value is determined based on the current value complying with the high/low thresholds for each parameter. The media type, vendor name, part number, and serial number of the optical module are also displayed.

The interface is an extension of the serial ID interface defined in the GBIC specification as well as the SFP MSA. Both specifications define a 256-byte memory map in EEPROM, which is accessible over a two-wire serial interface at the 8 bit address 1010000X (A0h). The digital diagnostic monitoring interface makes use of the 8 bit address 1010001X (A2h), so the originally defined serial ID memory map remains unchanged. The interface is identical to and fully backward compatible with both the GBIC Specification and the SFP Multi Source Agreement. The operating and diagnostics information is monitored and reported by a Digital Diagnostics Transceiver Controller (DDTC), which is accessed via a 2-wire serial bus. For QSFPs, the eeprom uses the same address of A0, but different pages to access the data. The details of these pages can be found in the specification for QSFPs: SFF-8436: QSFP+ 10 Gbs 4X PLUGGABLE TRANSCEIVER.

As none of the DDMI information is notified through EMS or any other method of notification, all information needs to be drawn by executing CLI commands. For 40G transceivers (QSFPs), the port may be partitioned in either 1x40G mode or 4x10G mode. As a result, when in 4X10G mode, the 4 channels of the QSFP will be shown and reported as ports since they are utilized individually. When in 1X40G mode, all 4 channels are shown as the port is now the aggregate of the 4 channels and 1 channel could bring down the entire 40G port.