In terms of structure,there are some differences between qsfp-dd and qsfp+/qsfp28/qsfp56 in the depth of the mechanical interface of the main board,the number of channels of the electrical interface and the number of integrated circuits.The details are as follows:

　　Depth of mechanical interface on the main board-when designing qsfp-dd,MSA team members designed the mechanical interface on the main board to make qsfp-dd have the same port density as qsfp+/qsfp28/qsfp56 and can accommodate an additional row of contacts.The mechanical interface on the main board is slightly deeper than that of qsfp+/qsfp28/qsfp56.

　　Number of channels of electrical interface-it can be seen from the above that qsfp-dd package is equipped with 8-channel electrical interface.Compared with qsfp+/qsfp28/qsfp56 package with 4-channel electrical interface,the number of channels of electrical interface is doubled,which is also attributed to a row of additional contacts in qsfp-dd package.

　　Number of integrated circuits-although the size of qsfp-dd is the same as that of qsfp+/qsfp28/qsfp56,since qsfp-dd has 8-channel electrical interfaces,the number of integrated circuits(i.e.,ASICs)and density of qsfp+/qsfp28/qsfp56 with 4-channel electrical interfaces have been doubled.

　　Bandwidth&Applications

　　It can be seen from the above that the maximum bandwidth of qsfp-dd can reach 400gbps,while the maximum bandwidth of qsfp+/qsfp28/qsfp56 can only reach 40Gbps/100gbps/200gbps respectively.Qsfp-dd is much higher than qsfp+/qsfp28/qsfp56.For this reason,qsfp-dd is generally used as the package of 400g optical modules and 400g high-speed cables(i.e.DAC and AOC)for the interconnection of 400g data centers to solve the problem of high-speed migration of massive data between data centers;While qsfp+/qsfp28/qsfp56 are respectively used for the packaging of 40g/100g/200g optical modules and high-speed cables,and for the interconnection of 40g/100g/200g networks.

　　compatibility

　　Qsfp-dd has backward compatibility and supports modules or connectors encapsulated by existing qsfp+/qsfp28/qsfp56 to be inserted into the ports of qsfp-dd;However,qsfp+/qsfp28/qsfp56 ports cannot support modules or connectors packaged with qsfp-dd.

transceiver definition

800G QSFP-DD

QDD800-2LR4-C1