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Is QSFP28 backwards compatible?
Knowledge Base + 2024.01.05

Yes, QSFP28 is backward compatible with QSFP+ and QSFP modules, allowing for easy integration into existing networks.

QSFP and QSFP28 are both optical modules for high-speed data communications, but differ in some key aspects. In this paper, we will discuss the characteristics, performance, and application areas of these two types of optical modules in an exhaustive, detailed, and nuanced manner.

Introduction of QSFP and QSFP28

QSFP (Quad Small Form-factor Pluggable) is a high-density optical module that uses four transmission channels for data transmission. It is designed to enable support for multiple optical module specifications on a single interface.QSFP modules were primarily used in early applications for Gigabit Ethernet, Fibre Channel, and other low-rate applications.

The QSFP28 is a next-generation QSFP optical module that builds on the QSFP. 28 indicates that the module supports transmission rates of up to 28 Gbps per channel, which gives the module a significant advantage in adapting to current and future high-speed network requirements.

Physical Characteristics of QSFP and QSFP28

The QSFP and QSFP28 are very similar in terms of form factor, but differ in terms of electrical interfaces.The QSFP module has an MTP/MPO interface, while the QSFP28 utilizes the new SFP28 interface. This is because the QSFP28 requires higher electrical performance and transfer rate support. In addition, the QSFP28 has a more complex connector configuration with higher channel density.

Transmission rates for QSFP and QSFP28

QSFP modules can support up to 10 Gbps per channel, while QSFP28 modules support up to 28 Gbps per channel. Therefore, QSFP28 modules have more than double the advantage in terms of transmission rates.

Transmission Distance of QSFP and QSFP28

Both QSFP and QSFP28 are available in different variants (e.g., SR, LR, and ER), each of which offers optimal performance for a specific transmission distance. In general, QSFP modules have a maximum transmission distance of 2 kilometers, while QSFP28 modules can reach a maximum distance of 10 kilometers or more. If a longer transmission distance is required, you can choose the ER variant of the QSFP28.

Application areas of QSFP and QSFP28

As QSFP28 has higher transmission rate and longer transmission distance, it is widely used in data centers, supercomputing and high-performance computing to meet the demand for high-capacity and high-rate data transmission. QSFP modules, on the other hand, are mainly used in some low-rate applications such as Gigabit Ethernet and Fibre Channel.

QSFP and QSFP28 Compatibility

QSFP28 modules are not only compatible with QSFP modules, they can also be plugged in on QSFP ports. This is because the connector mechanism of the QSFP28 module is designed to accommodate QSFP ports for backward compatibility. This is useful for system upgrades and expansion.

To summarize, QSFP and QSFP28 are two different types of optical modules that differ in terms of transmission rate, transmission distance, application areas, and physical characteristics.QSFP modules are suitable for some low-rate applications, while QSFP28 modules are suitable for applications that require higher transmission rates and longer transmission distances. At the same time, QSFP28 modules also have backward compatibility with QSFP modules. These features make both QSFP and QSFP28 modules have their own advantages and applicability in different application scenarios.