What are QSFP+ and QSFP28 transceivers?
As quad small form factor pluggable transceivers, QSFP+ and QSFP28 optics both have the capability to use 4 channels of data. With QSFP+ or QSFP28, there are a multitude of ways that you can use 10G and 25G channels as building blocks to achieve 40G and 100G data rates. Specifically, these 4 channels can either be used in parallel or combined, sent, and internally separated by each transceiver.
However, what are the differences between QSFP+ and QSFP28?
The Breakdown: QSFP+ vs. QSFP28
QSFP+ is essentially the same transceiver form factor as QSFP. QSFP+ transceivers support a variety of communication standards including Ethernet, Fibre Channel and InfiniBand. As previously mentioned, the 4 channels of a QSFP+ optic can be combined into a single 40G connection. So, you can increase bandwidth and port density while saving costs on inventory.
On the other hand, QSFP28 is an upgraded version of QSFP+.They even have almost identical form factors which allows QSFP28 ports in network equipment to accept both 100G QSFP28 and 40G QSFP+ transceivers. However, the big difference between the two is that QSFP28 transceivers are designed for 100G applications. QSFP28 supports 4 channels, and it can transmit 25G per channel to get a combined 100G of throughput.
However, the QSFP28 interface is very flexible as it can achieve 100G in other ways. Using a breakout connection, QSFP28 transceivers can use just 2 channels at 50G each or they can even achieve a single channel of 100G depending on the transceiver type being used. 100G QSFP28 transceivers are available in several different standards including SR4, LR4, PSM4 and CWDM4.
You can also consider dual rate options such as 40G/100G QSFP28 SR4, which is interoperable with legacy 40G SR4s in the network. With these available standards, you can achieve 100G in many different applications from short reach to extended reach.
Conclusion
In the end, both QSFP+ and QSFP28 transceivers are great options for network operators to seamlessly upgrade to 40G and 100G without ripping and replacing existing infrastructures. However, you will get even more flexibility with advanced QSFP28 options.