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QSFP-DD is a new module and cage/connector system similar to current QSFP, but with an additional row of contacts providing for an eight lane electrical interface. It is being developed by the QSFP-DD MSA as a key part of the industry’s effort to enable high -speed solutions. For QSFP-DD (Double Density) designers have made two key changes to the module, while maintaining the key features that enabled the rapid acceptance of QSFP+ and QSFP28.    The first is to increase the number of I/O lanes of the module from 4 to 8.    The second is to double the data rate of each lane to 50Gb/s effectively quadrupling the overall bandwidth of the module compared to QSFP28. The IEEE made the choice to standardize on PAM4 signaling (designated as CEI-56G-VSR-PAM4 ) as opposed to NRZ for the ASIC to Module interface and the QSFP-DD MSA has followed the recommendation.

  ODU maintenance signals  Three ODU maintenance signals are defined as per G.709: ODU-AIS, ODU-OCI and ODU-LCK ODU alarm indication signal (ODU-AIS)   ODUK-AIS-PM is a secondary condition that indicates a more serious condition such as the LOS (OCN/STMN) alarm occurring downstream. The ODUK-AIS-PM condition is reported in the path monitoring area of the optical data unit wrapper overhead. ODUK-AIS-PM is caused by the upstream ODUK-OCI-PM .   ODUk-AIS is specified as all "1"s in the entire ODU signal, excluding the frame alignment overhead (FA OH), OTU overhead (OTU OH)  The ODUk contains one instance of ODU AIS. The ODUCn contains n instances of ODU AIS, numbered 1 to n (ODU AIS #1 to #n). In addition, the ODU-AIS signal may be extend