QSFP+ (4x10Gbps Quad Small Form-Factor Pluggable) and QSFP28 (4x25Gbps Quad Small Form-Factor Pluggable28) are two QSFP form factors used to plug into compatible switches which use QSFP+ and QSFP-based switches. These two optical transceiver module types are used to connect different network equipment with fibre optic cables or patch cords. They are used predominantly in Data Centres, campus, and enterprise networks where high capacity is important. Different companies will offer different types of QSFP+ and QSFP28 transceivers. Some will come from the larger network equipment vendors and are known as original equipment manufacturer (or OEM), and other companies will offer compatible transceivers (or ‘compatibles’) which will operate the same as the original equipment versions and are usually more affordable and readily available. This article explores the differences between QSFP+ and QSFP28 transceivers and their optimal uses.


What is QSFP+?

QSFP+ optical transceiver modules are used in QSFP+ and QSFP-based switches, which are interconnected with optical fibre patchcords. They are also used in data centre networks, campus, and enterprise networks.

QSFP+ came from a group of companies who came together to form a multisource agreement (MSA) to agree on the optical, electrical, and physical interfaces and leveraging the support from the standards bodies (IEEE, ITU-T). The benefit of a QSFP+ optical module is having 4x10Gbps speed in little less the size of 2x SFP+ modules, as well as having the capacity at the optical end to be either 40Gbps, 4x10Gbps, or 2x20Gbps.

What is QSFP28?

QSFP28 essentially takes the elements of the QSFP+ form factor/module described above and increases the electrical data rate from 10Gbps to 25Gbps each. The total aggregate data rate is 100Gbps (or 4x25Gbps). There are many variants which determine the reach/distance, single mode or multimode fibre with all requiring to be interconnected with fibre optic cables/patchcords. There is a colour coding for the latch which releases a module from the switch socket and this will tell the network engineer what reach, architecture, and if it uses SMF or MMF.

For example, a 40G link may have a physical length of 500 metres. The most obvious choice here would be to select a QSFP28 transceiver that is capable of 500 metres distances and this would be a 100G DR1 QSDFP28 available from Westbury Photonics (here).

6 Differences (and Similarities) Between QFSP+ and QSFP28

1. Operating Temperature

One of the main similarities between the two devices is that QSFP28 and QSFP+ optical transceivers is the operating temperature. Consideration will need to be given to this in your application and the devices which work at 25C to 80C, 0C to 70C and -40 to +85C. The wider the operating temperature range the more expensive this is likely to be. Also, the higher the temperature the operating equipment will also contribute towards higher power consumption as there is usually an equal amount of energy required to cool the systems as it does to operate them.

2. Bandwidth (or speed)

QSFP28 will have an aggregate data rate of 100Gbps and this is usually 4x25Gbps at the electrical side which can translate to 100Gbps across a single wavelength on the optical side, or 2x50Gbps optical wavelengths, or 4x25Gbps wavelengths (or carriers as it is sometimes referred to). The optical interface will have different distances such as SR, LR, LR4, DR1, etc.

QSFP+ modules will have an aggregate data rate of 100Gbps at either end. The electrical interface is always 4x10Gbps (or 10Gbps Ethernet) and the optical side can be 40Gbps single wavelength, 2x20Gbps optical carriers, and also 4x10Gbps single carriers in either CWDM (coarse WDM) or WDM (wavelength division multiplexing – different wavelengths separated by 100GHz ITU-T grid).

3. Wavelengths

QSFP28 and QSFP+ are available in different wavelengths which range from 850nm to 1310nm, and 1550nm versions.

4. Fibre Type Difference

Both QSFP+ and QSFP28 will have differences in terms of multimode fibre (MMF) or single mode fibre (SMF). Consideration should also be given to the connector type used as different modules will have different versions which range from LC, MTP, and MPO. Also, ensure the fibre patchcord is clean before you plug this into your transceiver as it can contribute to loss or no optical power being transmitted or received.

In summary, QSFP28 appears to have lots of benefits over QSFP+. It has been known that QSFP28 is backwards compatible with QSFP+. However, it will be needed to consider the types of transceivers used and data rates when planning or upgrading a network to minimise any bottlenecks which might occur during peak periods.

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