With the popularization of VR / AR, data center, mobile devices, CDN and so on, hot-pluggable network interface modules have emerged, such as SFP, SFP+, SFP28, QSFP+ and QSFP28 optical transceiver. What is the difference between them? You may often hear the question: is QSFP28 compatible with QSFP+? Can I use the SFP28 transceiver on the SFP+ port? In this article, we will introduce these different types of modules and answer these questions.

1. SFP vs SFP+: 

SFP (small form-factor pluggable) is an upgraded version of GBIC (gigabit interface converter). Its size is only half of GBIC module, which greatly increases the port density of network equipment. And the data rate of SFP ranges from 100 Mbps to 4 Gbit/s.

Fiber Mall SFP&SFP+ Transceivers
Fiber Mall SFP&SFP+ Transceivers

SFP+ (small form-factor pluggable plus) is an enhanced version of SFP. It supports 8 Gbit/s Fibre Channel, 10 Gigabit Ethernet and OTU2.

Main features:

  • SFP and SFP+ have the same external dimensions.
  • The maximum rate of SFP up to 4G, while SFP+ is 10G.
  • SFP protocol specification: IEEE802.3, SFF-8472.
  • SFP+ supports digital diagnostics.

2. SFP28 vs SFP+: 

Fiber Mall 25G SFP28 LR Transceiver
Fiber Mall 25G SFP28 LR Transceiver

SFP+ is mainly linked to 10G, while SFP28 is commonly associated with 25G connections. They use the same form factor, and the pinouts of SFP28 and SFP+ connectors are mating compatible. So SFP28 will work with SFP+ optics but at a reduced speed of 10 Gbit/s. And SFP+ modules will work well with the SFP28 port on a network switch if the port can be set up for 10G transmission, otherwise, the SFP+ modules can not work. The current data center market is starting to transition from 10Gb/s to 25Gb/s solutions.

3. SFP28 vs QSFP28:

The SFP28 supports only one 25Gbit/s channel, while the QSFP28 supports four independent 25Gbit/s channels. They can both be used for 100G networks, but the SFP28 is applied as a breakout cable for the SFP28 in the form of the QSFP28.

The following diagram shows the direct connection from 100G QSFP28 to 4x SFP28 DACs:

The direct connection from 100G QSFP28 to 4x SFP28 DACs

4. QSFP+ vs QSFP28: 

The QSFP+ and QSFP28 transceivers integrate four transmit and four receive channels of the same size. In addition, both the QSFP+ and QSFP28 products include transceiver modules and DAC/AOC cables, but at different speeds. the QSFP+ modules support 1×40 gbit/s, and the QSFP+ DAC/AOC cables support 4×10 Gbit/s. While the QSFP28 modules can transmit 100 Gbit/s, and the QSFP28 DAC/AOC cables can run at 4x 25 Gbit/s or 2x 50 Gbit/s. Please note that normally QSFP28 modules cannot be broken into 10G links. However, inserting QSFP+ modules in QSFP28 ports is another case. If the switch supports it, QSFP28 can break into 4x10G just like QSFP+ transceiver modules.

Internal Structure of QSFP+ Module
Internal Structure of QSFP+ Module

5. Summary

Although some of the same designs are used by the SFP and SFP+, SFP28 and SFP+, and QSFP+ and QSFP28, they do not have the same data and rates. From the comparison, it is clear that the main driver for optical transceiver development is the need for higher bandwidth rates with smaller form-factors. For example, the QSFP28 can provide higher bandwidth than the QSFP+ in the same form-factor.

References:

  1. What is a Small form-factor pluggable transceiver(SFP+)?
  2. Small form-factor pluggable transceiver – Wikipedia
  3. SFP vs SFP+ vs SFP28 vs QSFP+ vs QSFP28, What Are the Differences?

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