With the popularization of VR / AR, data centers, 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 the 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.
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+:
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:
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.
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.
Some questions:
QSFP+ vs QSFP28: Different Speeds for Different Uses
QSFP+ module supports 1x 40 Gbit/s and QSFP+ DAC/AOC cable supports 4x 10 Gbit/s. QSFP28 module is capable of transmitting data at 100 Gbit/s, and the QSFP28 DAC/AOC cable can run at 4x 25 Gbit/s or 2x 50 Gbit/s.
The answer is definitely yes: SFP28 adopts the same form factor as SFP+, just running at 25 Gb/s instead of 10Gb/s, which offers better performance and higher speed. So SFP28 will work sufficiently on SFP+ ports, and SFP+ cables can be plugged into SFP28 ports although they are not designed for 25Gb/s data rates.
In brief, the new-gen optical transceiver is backward compatible with the previous version in most situations. In other words, SFP+ ports can take SFPs, it is possible to plug SFP+ into SFP28 ports to run 10G, and QSFP+ optics work fine in QSFP28 ports, but not vice versa.
SFP, a small form-factor pluggable for short, is a compact, hot-pluggable transceiver module used for both telecommunication and data communications applications. The Quad Small Form-factor Pluggable (QSFP) is a compact, hot-pluggable transceiver used for data communications applications.
SFP28 and QSFP28 transceivers actually adopt different sizes and working principles. SFP28 supports only one channel with 25 Gbit/s, while QSFP28 supports 4 separate lanes, and each is 25 Gbit/s. Both of them can be used in 100G networks, but the SFP28 is applied in the form of QSFP28 to the SFP28 breakout solution.
QSFP28 is a hot-pluggable transceiver module designed for a 100G data rate. QSFP28 integrates 4 transmit and 4 receiver channels. “28” means each lane carries up to 28G data rate. QSFP28 can do a 4x25G breakout connection, 2x50G breakout, or 1x100G depending on the transceiver used.
Can I use SFP28 Transceivers in SFP+ ports? The answer is yes because SFP28 is backward compatible with SFP+ ports and can be fully functional. SFP+ optical modules and SFP+ cables can be plugged into the SFP28 port, but do not support 25Gb / s data rate.
QSFP-DD is a new module and cage/connector system similar to the current QSFP, but with an additional row of contacts providing for an eight-lane electrical interface. It is being developed by the QSFP-DD MSA as a key part of the industry’s effort to enable high-speed solutions.
QSFP28 transceivers have the same form factor as the QSFP optical transceiver. The former has just 4 electrical lanes that can be used as a 4x 25GBE and also a 4x 10GbE, while the latter supports 40G ( 4x 10G).
As seen from their industry names, QSFP56, QSFP28, and QSFP+ are very similar in that they share the same QSFP form factor as their postfix shows, and they have the same size as each other.
References:
- What is a Small form-factor pluggable transceiver(SFP+)?
- 3 Tips on choosing a right optical transceiver
- Small form-factor pluggable transceiver – Wikipedia
- SFP vs SFP+ vs SFP28 vs QSFP+ vs QSFP28, What Are the Differences?
