Another expansion on the original SFP concept, QSFP uses double fiber pairs. The Q stands for “quad,” and the additional pair allows for substantially more powerful data transmission. QSFP connectors are still small and hot-pluggable, and they still support Ethernet and fiber optics. Added to the supported list is InfiniBand.

QSFP data rates get up to 1 Gbps per channel, allowing for 4X1 G cables and stackable networking designs that achieve better throughput.

40G QSFP+ LR4/ZR4/ER4

4 Gbit/s

The original QSFP document specified four channels carrying Gigabit Ethernet, 4GFC (FiberChannel), or DDR InfiniBand.

40 Gbit/s (QSFP+)

QSFP+ is an evolution of QSFP to support four 10 Gbit/s channels carrying 10 Gigabit Ethernet, 10GFC FiberChannel, or QDR InfiniBand.The 4 channels can also be combined into a single 40 Gigabit Ethernet link.

50 Gbit/s (QSFP14)

The QSFP14 standard is designed to carry FDR InfiniBand, SAS-3 or 16G Fibre Channel.

100 Gbit/s (QSFP28)

The QSFP28 standard[6] is designed to carry 100 Gigabit Ethernet, EDR InfiniBand, or 32G Fibre Channel. Sometimes this transceiver type is also referred to as QSFP100 or 100G QSFP for sake of simplicity.

200 Gbit/s (QSFP56)

QSFP56 is designed to carry 200 Gigabit Ethernet, HDR InfiniBand, or 64G Fibre Channel. The biggest enhancement is that QSFP56 uses four-level pulse-amplitude modulation (PAM-4) instead of non-return-to-zero (NRZ). It uses the same physical specifications as QSFP28 (SFF-8665), with electrical specifications from SFF-8024 and revision 2.10a of SFF-8636. Sometimes this transceiver type is referred to as 200G QSFP for sake of simplicity.

Switch and router manufacturers implementing QSFP+ ports in their products frequently allow for the use of a single QSFP+ port as four independent 10 Gigabit Ethernet connections, greatly increasing port density. For example, a typical 24-port QSFP+ 1U switch would be able to service 96x10GbE connections.[55][56][57] There also exist fanout cables to adapt a single QSFP28 port to four independent 25 Gigabit Ethernet SFP28 ports (QSFP28-to-4×SFP28)[58] as well as cables to adapt a single QSFP56 port to four independent 50 Gigabit Ethernet SFP56 ports (QSFP56-to-4×SFP56).

You might be interested in 40G QSFP+ BIDI

What is a QSFP Port?

QSFP, or quad small form factor pluggable, is another type of compact, hot-swappable transceiver. It supports Ethernet, Fibre Channel, InfiniBand and SONET/SDH standards with different data rate options. QSFP modules are commonly available in several different types: 4x1Gbps QSFP, 4x10Gbps QSFP+, 4x28Gbps QSFP28.

QSFP+ and QSFP28 are the most recent versions, which support numerous 40Gbps and 100Gbps applications. Both QSFP+ and QSFP28 modules integrate 4 transmit and 4 receiver channels. While QSFP+ supports 4x10Gbps or 1x40Gbps, QSFP28 can do 4x25Gbps, 2x50Gbps or 1x100Gbps, depending on the transceiver used. The specifications for QSFP are based on SFF-8436.

How to Choose SFP Transceivers?

In addition to SFP vs SFP+ vs QSFP, you’ll also need to consider the application. SFP transceivers are available in different types depending on what they will be used for, for example single-mode vs multimode SFP. Single-mode SFP transceivers work with single-mode fibre, whereas multimode SFPs are compatible with multimode fibre. Additionally, there are long-reach WDM SFP transceivers for multiplexing, simplex SFPs for single fibre applications, video SFP transceivers for transmission of high-definition video, and PON SFP transceivers for fibre-based access networks. SFPs are available in commercial and extended operating temperature ranges, with or without extended diagnostics capabilities.

How Do You Choose Between SFP, SFP+, QSFP and QSFP+?

Selecting the right connector is essential to building a network that functions correctly at an efficient price point. While it won’t always be easy to make the decision, there are a few considerations that can completely dictate what you use.

How Much Traffic Does Your Network Handle?

As you just read, the capacity of each form factor is pretty different. If you’re running a high-end data center, you’ll probably need QSFP+ and possibly even QSFP28. For lower demands, the other forms might suffice.

It’s also important to anticipate traffic growth. It might feel good to save money and go with lower capacity now, but if you’re going to have to make major replacements in two years, then there is no real saving taking place. Weighing the value of future-proof networking equipment is always one of the hardest parts of design.

How Long Is Your Network?

SFP and all of its variants work with both single and multi-mode fiber. So, the physical length of your network might determine which of the modes you’ll be utilizing. Then again, if all of the form factors support both modes, why does it matter?

It comes down to cost. If you have to invest in the higher cost of single-mode fiber, it might be prudent to downscale the connector. Conversely, a shorter, multi-mode network might leave room in the budget for future proofing and bigger data capacity.

How Hot Is Your Network?

It’s pretty simple math. Adding channels and data throughput increases the heat of the system. It’s inevitable. Planning around cooling costs and heat management can help you determine when and where to invest in higher data rates or make cuts.

The variable forms of SFP are easy enough to separate. Each has its own set of benefits and drawbacks, and all of them are still widely in use today.