The Difference Between SFP, SFP+, SFP28, QSFP+

Optical module types such as SFP, SFP+, SFP28, QSFP+ and QSFP28 are not unfamiliar to professionals. These hot-swappable modules can be used to connect network switches and other network devices (such as servers or transceivers) for data transmission. But do you understand the specific differences between these modules? Are QSFP28 and QSFP+ compatible? Can SFP28 modules be used in SFP+ slots? If you have these questions, please read on, this article will take you to find the answer.

Understanding the Types of Optical Modules

Before figuring out the differences between these modules, you need to know what the SFP, SFP+, SFP28, QSFP and QSFP28 modules are. The following will introduce these modules respectively.

SFP

SFP can be understood as an upgraded version of GBIC, its volume is only 1/2 of GBIC module, which greatly increases the port density of network equipment. In addition, the data transfer rate of SFP varies from 100Mbps to 4Gbps.

SFP+

SFP+ is an enhanced version of SFP, supporting 8Gbit/s fiber channel, 10G Ethernet and optical transmission network standard OTU2. In addition, SFP+ direct-attach cables (that is, SFP+ DAC high-speed cables and AOC active optical cables) can connect two SFP+ ports without adding additional optical modules and cables (network cables or optical fiber jumpers). It is a good choice for direct connection of adjacent short-distance network switches.

SFP28

SFP28 is an enhanced version of SFP+, which has the same size as SFP+, but it can support a single-channel 25Gb/s rate. SFP28 provides an efficient solution for 10G-25G-100G network upgrades, which can meet the growing demands of next-generation data center networks.

QSFP+

QSFP+ is an upgraded version of QSFP. QSFP can support 4-channel transmission at the same time, and the data rate of each channel is 1Gbit/s, but QSFP+ is different from QSFP, it supports 4×10Gbit/s channel transmission, and can achieve 40Gbps transmission rate through 4 channels. Compared with SFP+, the transmission rate of QSFP+ optical module can reach four times that of SFP+ optical module. When deploying 40G network, QSFP+ optical module can be used directly, so as to effectively save costs and increase port density.

QSFP28

QSFP28 was born to meet the requirements of 100G applications. It has 4 high-speed differential signal channels, and the transmission rate of each channel varies from 25Gbps to 40Gbps, which can meet the application requirements of 100G Ethernet (4×25Gbps) and EDR InfiniBand. There are many types of QSFP28 products, and there are different ways to realize 100G transmission, such as 100G direct connection, 100G to 4 25G branch links or 100G to 2 50G branch links.

Differences and Similarities Between SFP, SFP+, SFP28, QSFP+, and QSFP28

After understanding what SFP, SFP+, SFP28, QSFP+, and QSFP28 are, the specific similarities and differences between the two will be introduced next.

SFP and SFP+: Same Size, Different Speed and Compatibility

SFP and SFP+ modules are identical in size and appearance, so equipment manufacturers can use the SFP physical design on switches with SFP+ ports. Due to the same size, many customers use the SFP module on the SFP+ port of the switch. This operation is feasible, but the rate will be reduced to 1Gbit/s. Also note that SFP+ modules cannot be used in SFP slots, otherwise the port or module may be damaged. In addition to differences in compatibility, the transmission rates and standards of SFP and SFP+ are also different. SFP can transmit up to 4Gbit/s, and SFP+ can transmit up to 10Gbit/s; SFP is based on the SFF-8472 protocol, while SFP+ is based on the SFF-8431 and SFF-8432 protocols.

SFP28 and SFP+: SFP28 Ooptical Modules Can be Used in SFP+ Ports

As mentioned above, SFP28 is an upgraded version of SFP+. The two have the same size, but the transmission rate is different. The transmission rate of SFP+ is 10Gbit/s, and the transmission rate of SFP28 is 25Gbit/s. If the SFP+ optical module is inserted into the SFP28 port, the link transmission rate is 10Gbit/s, and vice versa. In addition, the SFP28 direct-attach copper cable has higher bandwidth and lower loss than the SFP+ direct-attach copper cable.

SFP28 and QSFP28: Different Protocol Standards

Although both SFP28 and QSFP28 carry the number “28”, both have different dimensions and protocol standards. SFP28 supports 25Gbit/s single channel, and QSFP28 supports four 25Gbit/s channels. Both can be used in 100G networks, but the usage methods are different. QSFP28 can achieve 100G transmission through the three methods mentioned above, but SFP28 needs to rely on QSFP28 to SFP28 branch high-speed cables. The figure below shows the direct connection of 100G QSFP28 to 4×SFP28 DAC.

QSFP and QSFP28: different rates, different applications

QSFP+ and QSFP28 optical modules have the same size, and both have 4 integrated transmit and receive channels. In addition, although QSFP+ and QSFP28 series products also have optical modules and DAC/AOC high-speed cables, their speeds are different. QSFP+ module supports 40Gbit/s single-channel rate, and QSFP+ DAC/AOC supports 4×10Gbit/s transmission rate. The QSFP28 module transmits data at a rate of 100Gbit/s, and the QSFP28 DAC/AOC supports 4×25Gbit/s or 2×50Gbit/s. It should be noted that QSFP28 modules cannot be used for 10G branch links, but if the switch with QSFP28 ports supports QSFP+ modules, QSFP+ modules can be inserted into the QSFP28 ports to implement 4×10G branch links. For the specific implementation method, please refer to the article on how to use the QSFP28 port to transmit 10G/25G/40G.

Conclusion

The differences between SFP and SFP+, SFP28 and SFP+, QSFP+ and QSFP28 optical modules have been explained in detail above. Although some of them are similar in size and shape, they all work at different speeds. It is not difficult to see from the comparison that the main driving force for the development of optical modules is to achieve higher bandwidth while pursuing small size. This is proved by the fact that QSFP28 has the same size as QSFP+ but has higher bandwidth.