What is the differences between QSFP56, QSFP28, QSFP+

In terms of names, the package types of QSFP56, QSFP28 and QSFP+ optical modules are the same, but their transmission rates, modulation technologies, and interfaces are different.

The optical module of QSFP56 package type can support 4x50G transmission to achieve 200G transmission rate.QSFP+ optical module is an upgraded version of QSFP optical module, which can support 4x10G transmission to realize the transmission of 10G Ethernet, 10G Fibre Channel and QDR InfiniBand.It can multiplex four channels to increase the bandwidth and achieve a transfer rate of 40Gbps (10GBaud NRZ per channel).Both QSFP28 optical modules and QSFP+ optical modules contain 4 optical transmitters and 4 optical receivers, supporting 4x25G transmission, thus achieving a transmission rate of 100G.

The biggest difference between QSFP56 package and QSFP+, QSFP28 package is that QSFP56 no longer adopts the previous NRZ modulation technology, but adopts PAM4 modulation technology.The transmission rate of each channel can reach 50G, which can transmit more data on the existing optical fiber, which is more suitable for application in the ultra-large-scale data center network.