What is the difference between SFP, SFP+, SFP28, QSFP+ and QSFP28?

Optical modules such as SFP, SFP+, SFP28, QSFP+ and QSFP28 can all be used to connect network switches and other network devices (such as servers or transceivers) for data transmission. So what are the specific differences between these modules? Are QSFP28 and QSFP+ compatible? Can SFP28 modules be used in SFP+ slots? These are the questions that this article is about to address.

SFP

SFP can be understood as an upgraded version of GBIC. Its volume is only 1/2 of the GBIC module, which greatly increases the port density of network equipment. Additionally, SFP data transfer rates vary from 100Mbps to 4Gbps.

SFP+

SFP+ is an enhanced version of SFP that supports 8Gbit/s Fibre Channel, 10G Ethernet and the optical transmission network standard OTU2. In addition, SFP+ direct attach cables (i.e. 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 fiber patch cables), which is good for two It is a good choice for the direct connection of adjacent short-distance network switches.

SFP28

SFP28 is an enhanced version of SFP+ and 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 to meet the continued growth 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 directly used, which can effectively save cost and improve port density.

QSFP28

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

What is the difference between SFP, SFP+, SFP28, QSFP+, QSFP28?

SFP and SFP+: same size, different speed and compatibility

SFP and SFP+ modules are identical in size and appearance, so equipment manufacturers can adopt SFP physical designs on switches with SFP+ ports. Due to the same size, many customers use SFP modules on the SFP+ ports of switches. 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 it may cause damage to the port or module. In addition to the differences in compatibility, the transmission rates and standards of SFP and SFP+ are also different. SFP transmits 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 optical module can be used in SFP+ port

As mentioned above, SFP28 is an upgraded version of SFP+. The two have the same size but different transmission rates. 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, SFP28 direct attach copper cable has higher bandwidth and lower loss than SFP+ direct attach copper cable.

SFP28 and QSFP28: different protocol standards

Although both SFP28 and QSFP28 carry the number "28", both are different in size and protocol standard. SFP28 supports 25Gbit/s single channel, QSFP28 supports 4 25Gbit/s channels. Both can be used in 100G networks, but the usage is 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 a 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, the rates are different. QSFP+ module supports 40Gbit/s single channel rate, 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 achieve 4×10G branch links.

Conclusion

The differences between SFP and SFP+, SFP28 and SFP+, and QSFP+ and QSFP28 optical modules have been explained in detail above. Although some of them are similar in size and form factor, they all operate at different rates. 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 and QSFP+ have the same size but have higher bandwidth. For more information, please visit: www.fiberopticom.com.