200G QSFP56 optical module and 200G QSFP-DD optical module are two mainstream solutions for 200G optical interconnection. QSFP56 uses mainstream digital signal processors (DSP) to help cloud data centers cope with severe challenges and achieve more efficient optical interconnection with flexible expansion scale and low cost. This article will mainly introduce the packaging technology of 200G QSFP56 optical module and the difference between QSFP56 packaging and QSFP28 and QSFP+ packaging.
Optical module packaging type
200G QSFP56 optical module packaging technology overview
Before understanding the QSFP56 packaging, let's take a look at the appearance design of the QSFP packaging. QSFP stands for Quad Small Form-Factor Pluggable, which refers to a four-channel small hot-pluggable SFP interface. Its original design purpose was to replace the single-channel SFP optical module with a high-density optical module. Compared with the SFP optical module, the QSFP optical module has a higher bandwidth.
Developed on the basis of QSFP packaging, 40G QSFP+ optical modules and 100G QSFP28 optical modules are gradually being used in high-density data center network deployments. As data center traffic continues to grow, bandwidth requirements are also increasing, and QSFP packaging types have also appeared in more form factors, such as 200G QSFP56 and 400G QSFP56-DD.
QSFP+ optical module packaging type
200G QSFP56 optical module is an upgraded version of 40G QSFP+ and 100G QSFP28 optical modules, and is specially designed for 200G Ethernet interconnection. QSFP56 means that the transmission rate of 4x 50Gb/s to 56Gb/s can be transmitted in a QSFP package size. QSFP56 optical module is also called 200G QSFP optical module. According to different transmission distances, 200G QSFP56 optical module is divided into QSFP56 CR, SR, DR, FR, LR types, which can achieve different distance transmission on single-mode and multi-mode optical fiber.
Generally, inserting two 200G QSFP56 optical modules into the corresponding switch ports and connecting them with a single-mode or multi-mode optical fiber can achieve a 200G transmission rate. In addition, inserting the QSFP56 DAC/AOC high-speed cable into the corresponding port can also achieve 200G transmission. If you want to achieve 2x100G or 4x50G transmission, you can use 200G QSFP56 to 2x100G QSFP28 branch cables and 200G QSFP56 to 4x50G SFP56 branch cables to achieve it.
The difference between QSFP56 vs QSFP28 vs QSFP+
From the name, QSFP56, QSFP28 and QSFP+ optical modules have the same packaging type, but their transmission rates, modulation technologies, interfaces, etc. are different. The following table lists the basic parameters of these packaging types of optical modules:
| Package type | Year | Full name | Number of electrical channels | Number of optical port channels | Single channel rate | Modulation technology | Transmission rate |
| QSFP+ | 2013 | 10G Quad Channel Small Form Factor Hot-swappable Optical Module | 4 | 4 | 10Gbps | NRZ | 40G |
| QSFP28 | 2016 | 28G Quad Channel Small Form Factor Hot-swappable Optical Module | 4 | 4 | 25Gbps | NRZ | 100G |
| QSFP56 | 2017 | 50G Quad Channel Small Form Factor Hot-swappable Optical Module | 4 | 4 | 50Gbps | PAM4 | 200G |
As can be seen from the table, the QSFP56 package type optical module can support 4x50G transmission to achieve a transmission rate of 200G. The QSFP+ optical module is an upgraded version of the QSFP optical module, which can support 4x10G transmission to achieve the transmission of 10G Ethernet, 10G Fibre Channel and QDR InfiniBand. It can multiplex four channels to increase bandwidth and achieve a transmission rate of 40Gbps (10GBaud NRZ per channel). The QSFP28 optical module, like the QSFP+ optical module, contains 4 optical transmitters and 4 optical receivers, supports 4x25G transmission, and thus achieves a transmission rate of 100G.
The biggest difference between QSFP56 packaging and QSFP+ and QSFP28 packaging is that QSFP56 no longer uses 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 existing optical fibers and is more suitable for use in ultra-large-scale data center networks.
The transition from 200G QSFP56 to 400G QSFP-DD
With the rapid development of data centers, the demand for data transmission has increased, prompting the network to develop towards higher bandwidth and higher density. At present, a new generation of 400G optical module packaging type has appeared on the market - 400G QSFP-DD. The "DD" here refers to double density, which means that the number of channels of 400G QSFP-DD has increased from 4 to 8, which can achieve a transmission rate of 400G.
The size of 400G QSFP-DD optical module is very similar to that of 200G QSFP56 optical module, but 400G QSFP-DD optical module is backward compatible with 40G QSFP+, 100G QSFP28, 200G QSFP56 and other QSFP packaged optical modules. In other words, as long as the switch supports it, 200G QSFP56 optical module can work on 400G QSFP-DD port. When using 200G QSFP56 optical module on 400G QSFP-DD port, the switch port will be configured with 200G transmission rate instead of 400G.
Although QSFP-DD is the most popular package type in the current 400G Ethernet market, this does not mean that the QSFP56 package type will be eliminated. For some data centers that do not have high speed requirements like 400G, using 200G QSFP56 packaged optical modules to deploy 200G Ethernet is still an ideal solution.
