With the rapid development of data centers, the demand for data transmission grows, driving the network to higher bandwidth and higher density. Currently, a new generation of 400G optical module package type has appeared on the market - 400G QSFP-DD, where "DD" refers to double density, that is to say, the number of channels of 400G QSFP-DD has been changed from four to eight, which can reach 400G transmission rate. This means that the number of channels of 400G QSFP-DD has been changed from 4 to 8, and the transmission rate of 400G can be achieved.

I. Definition of 200G QSFP56 and 400G QSFP-DD

200G QSFP56 is a dual-channel optical module, each channel rate of 100Gbps, the use of 8 cores of fiber, support for SR4, DR4 and FR4 and other different interface types and distance requirements for high-speed, high-density data center networks. 200G QSFP-DD optical module can achieve low-cost optical interconnections in the data center.

The 400G QSFP-DD is a four-channel optical module, each channel rate of 100Gbps or 200Gbps, the use of 16 cores of optical fiber, support for SR8, DR4, FR4 and LR4 and other different interface types and distance requirements, applicable to the need for higher-speed and higher density data center network.

Differences between 200G QSFP56 and 400G QSFP-DD

Both 200G QSFP56 and 400G QSFP-DD are high-speed optical modules used for transmitting high-speed data in data centers and other occasions. The differences between them are mainly in the following aspects:

Transmission rate: 200G QSFP56 is an optical module that supports 200Gbps data transmission, while 400G QSFP-DD supports 400Gbps data transmission rate.

Form factor: 200G QSFP56 and 400G QSFP-DD are also different in terms of form factor. 200G QSFP56 measures 56mm x 18mm x 8.5mm, while 400G QSFP-DD measures 76mm x 36mm x 8.5mm, making the 400G QSFP-DD larger than 200G QSFP56.

Interface type: 200G QSFP56 and 400G QSFP-DD also have different interface types. 200G QSFP56 adopts QSFP56 interface while 400G QSFP-DD adopts QSFP-DD interface.

Number of Channels: The number of channels is also different between 200G QSFP56 and 400G QSFP-DD. 200G QSFP56 generally adopts a 4-channel optical module with a transmission rate of 50 Gbps per channel, while 400G QSFP-DD adopts an 8-channel optical module with a transmission rate of 50 Gbps or 100 Gbps per channel, so the bandwidth of 400G QSFP-DD is larger. DD has a larger bandwidth.

Usage Scenarios of 200G QSFP56 and 400G QSFP-DD

200G QSFP56 is a kind of optical module supporting 200Gbps transmission rate, which adopts QSFP56 interface and can be used for single-mode fiber and multi-mode fiber transmission. It is usually used in data centers, computer networks, cloud computing, and other occasions that require high-speed, long-distance data transmission, such as in high-speed network switches, routers, and other equipment.

400G QSFP-DD is an optical module that supports 400Gbps transmission rate, it adopts QSFP-DD interface and can also be used for single-mode fiber and multimode fiber transmission. It is usually used in higher-level data centers, supercomputers, and other occasions that require higher-speed transmission of data, such as high-speed servers, switches, and other equipment.

Fourth, 200G QSFP56 to 400G QSFP-DD transition

The size of 400G QSFP-DD optical module is very similar to that of 200G QSFP56 optical module, but 400G QSFP-DD optical module can be backward compatible with QSFP encapsulated optical modules such as 40G QSFP+, 100G QSFP28, 200G QSFP56, and so on. In other words, 200G QSFP56 optical modules can work on 400G QSFP-DD ports as long as the switch supports them. When using 200G QSFP56 optical modules on 400G QSFP-DD ports, the switch's ports will be configured for 200G transmission rates instead of 400G.

While the QSFP-DD package is currently the most popular package type in the 400G Ethernet market, this does not mean that the QSFP56 package type is obsolete, and for some data centers that do not have as high a rate requirement as 400G, deploying 200G Ethernet using 200G QSFP56 packaged optical modules is still the ideal solution.

Overall, the shift from 200G QSFP56 to 400G QSFP-DD is a reflection of the rapid development of data center networks, reflecting the need for higher rates, densities and flexibility. At the same time, with the continuous progress and innovation of technology, there will be more higher speed rate and higher density optical modules in the future.