QSFP vs QSFP28 - What is the Difference?

The ever increasing demand for higher bandwidth is the main driving factor behind the technological advancement we see these days. There is an enormous amount of internet traffic which is being generated by a huge number of devices. The IT industry is also moving towards cloud computing which in simple terms is a datacenter at a remote location being accessed through the network connection. This cloud datacenter could be hosting simple applications like file server, email server etc. or very complex applications like ERP, real-time monitoring systems, or online databases.

The traditional fast ethernet or gigabit ethernet connections cannot meet the above mentioned massive bandwidth requirements. Hence, some other technique was needed to be developed to make sure the data is transferred from one place to other at a much more rapid pace. Engineers started working on various methods and technologies to achieve this task, below are some of the transceivers that they developed which support higher bandwidths than the traditional copper wire networks:

• SFP+ (10Gbps)
• QSFP (4Gbps, 40Gbps, 100Gbps)
• CFP (100Gbps)

This article will dig deeper in to the QSFP class of transceivers. QSFP transceivers are a variant of the SFP transceivers. They are a little larger in size than the SFPs but overall form-factor is quite similar. Figure 1 shows different types of QSFP transceivers available.

The Quad Small Form-Factor Pluggable (QSFP) was developed after SFP to provide an increase in bandwidth capacity of a single link by using multiple channels over the same fiber. QSFP can carry four channels simultaneously hence the name Quad SFP.

The development of QSFP as a standard was started by the SFF Committee in 2006. Initially QSFP was designed to support four channels of Gigabit Ethernet, 4G Fiber Channel or DDR Infiniband, the bandwidths for the aforementioned standards are 4Gbps, 4.5Gbps and 5Gbps respectively. The research and development work on QSFP transceivers continued and in 2013, SFF published QSFP+ as a standard. QSFP+ is able to support four channels of 10Gigabit Ethernet, 8G Fiber Channel or QDR Infiniband. The four channels of 10GbE can be used both as 10Gbps ports separately or as a single 40Gbps link. The ability to convert the single 40GbE port to 4 x 10GbE ports greatly increases the port density in higher end network equipment without a significant rise in cost.

Other variants of QSFP include:

• QSFP14
• QSFP28

QSFP 14 was the next member in the family of QSFP transceivers. It was developed to support FDR Infiniband.

QSFP28 is the latest addition to the QSFP family, QSFP28 can carry four channels of 28Gbps each. It can support 100Gbps Ethernet connection as well as FDR Infiniband. Similar to the QSFP+ transceiver, QSFP28 can also be used to split the single link to four 25Gbps links or vice versa. Figure 2 shows a break-out cable used for this purpose.

The QSFP28 transceiver can also support SAS and SONET/SDH specifications. QSFP28 transceiver is used to connect back-bone networks due to its ability to support very high bandwidths.

Based on the above mentioned details, let us draw a comparison of different types of QSFP transceivers based on their specifications and uses. Table 1 depicts the comparison between QSFP and QSFP28.

Table 1: Comparison of QSFP Transceiver

In light of the above comparison, we can come to the conclusion that the main driving force behind the evolution of QSFP transceivers is the need to achieve higher bandwidth rates with smaller form-factor. QSFP28 provides 25x more bandwidth than the QSFP in the same form-factor. This evolution seems to be a never-ending process and we might be seeing even higher bandwidth support in similar or smaller form-factor transceivers.