Why Should We Choose 25G SFP28?

Nowadays, with the advancement in the network technology, the Ethernet migration path could shift from 10G-40G-100G to 10G-25G-100G, or 10G-25G-50G-100G. While among the 10G, 25G, 40G Ethernet, it seems that only 25G is more efficient for the use of hardware and can offer a more logical upgrade path to 100G, which may explain why 25G SFP28 is so popular in the communications to some degree. Well, why should we choose it on earth? Maybe we can get the specific answers in these aspects.

To have a better comprehension of the below contents about SFP28, we had better get its some basic knowledge first.

SFP28 stands for Small Form-Factor Pluggable 28,the third generation of the SFP interconnecting systems designed for 25G performance per the IEEE 802.3 by specification (25GBASE-CR). It has many types, such as SFP28 25G-LR optical transceiver, SFP28 25G-SR optical transceiver and SFP28 DAC & AOC. Though these SFP28 assemblies have been used in 25 Gigabit Ethernet connecting requiring high density and low power dissipation, and they are still different in optical communications.

After have a basic knowledge of SFP28, I trust it will be easier for us to understand these explanations about it. Now, let’s have officially get it together.

On the one hand, to meet the growth for bandwidth in data center, 25G SFP28 brings great benefits for system operators to achieve better network performance.

To some degree, it provides more logical upgrade paths for server connections. Before the 25GBASE-T standard arises, the Ethernet speed upgrade path was clearly defined as 10G – 40G -100G. However, the SFP28 provides a new way for server connections: 10G – 25G- 40G -100G.

Meanwhile, it also offers more cost effective cabling choices. 25G SFP28 takes existing module form factors, such as SFP28 and QSFP28, and allows for a breakout connection that is configurable as either 25G per lane or the full 100G without changing the port on the front of switches. For example, SFP28 twianx cable, also called SFP28 DAC, is a type of 25G SFP28 assembly. It has a similar structure with other DACs like SFP+ DAC or QSFP+ DAC whose connectors are not real optical transceiver. Due to this reason, SFP28 twinax cable is cheaper than SFP28 AOCs and SFP28 optical transceiver, which offers a cost-effective solution for high density, high speed I/O data center applications.

Furthermore, QSFP28 to SFP28 breakout cable provides various cabling choices for switches and servers. In the following figure, there are two different links between the switch and servers: 25G and 50G server links. Both of them use the 100G QSFP28 to SFP28 breakout cables.

On the other hand, SFP28 cables can be connected with SFP+ ports. As we all know, SFP+ form factor is for 10G Ethernet. And it was later adopted for 25G but the electrical interface had to be upgraded to handle 25Gbps per lane. The ports of SFP28 and SFP+ connectors are mating compatible. Therefore, to some degree, SFP28 is backwards compatible with SFP+ ports and will work sufficiently and SFP+ cables can be plugged into SFP28 ports but they are not designed for 25Gb/s data rates. Besiedes, compared with SFP+, SFP28 has increased bandwidth, superior impedance control and less cross talk in network connections. And SFP28 copper cable has significantly greater bandwidth and lower loss than SFP+ version.

In addition, different from 40G and 100G, 25G is a single-lane variant for 25Gbps operation, allowing a breakout of 100G, which fit the most popular form factors. Based on existing module form factors, such as SFP28 and QSFP28, 25G operations allow for a breakout connection that is configurable as either 25G per lane or the full 100G without changing the port on front of switches, and bring more flexibility in the rack and front-panel connections. Besides, with the 25G Ethernet, network operators are no longer forced to use a 40G QSFP port to go from one individual device to another to achieve 100G throughput. The final advantage of 25G is that it can use existing optical plants ,depending on what was installed, and can increase the bandwidth by 2.5x without changing the physical infrastructure.

Above all is contents about why we should choose 25G SFP28. By getting its benefits ,applications and comparing with SFP+ and 40G, I believe the answer is very clear.

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