The Ultimate Guide to SFP Compatibility: SFP SFP+ vs SFP28 SFP+ vs QSFP28 QSFP+

An optical transceiver module is a small, hot-pluggable device used in high-speed data communication to convert electrical signals to optical signals between devices like network switches and routers. These transceivers come in various types, distinguished by their connector types and form factors, such as SFP, SFP+, SFP28, QSFP+, and QSFP28. A common question is whether these different transceivers are compatible with each other. For example, can an SFP module operate in an SFP+ port? Or is an SFP+ transceiver backward compatible with an SFP module?

This article serves as a guide to SFP compatibility, addressing the compatibility between key transceiver types—SFP and SFP+, SFP28 and SFP+, and QSFP28 and QSFP+.

What Is SFP Compatibility？

To better explore the compatibility issues of the transceiver modules mentioned above, we first need to understand what SFP compatibility is. Before that, it is essential to learn about the Multi-Source Agreement (MSA). The MSA is a collaboration among various transceiver manufacturers aimed at creating standardized products. Unlike official standards, the specifications for SFP modules are defined by the MSA, covering aspects such as size, connectors, and signaling to ensure compatibility with branded SFP devices. There are also MSA standards for other optical transceivers like SFP+, XFP, and QSFP. SFP transceivers that meet the compatibility requirements are generally interoperable across a range of telecommunications vendors’ hardware, allowing users to mix and match components from different manufacturers. In summary, if an SFP module can be correctly connected to cables and switches and facilitates successful device operation, its compatibility is validated.

Compatibility Between SFP and SFP+ Modules

The compatibility between SFP and SFP+ can vary based on different usage scenarios. In this section, we will clarify SFP SFP+ compatibility by examining three key aspects.

Case 1: Using an SFP Module in an SFP+ Port

SFP+, or SFP plus, is the enhanced version of SFP, increasing the data rate from 1Gbps to 10Gbps. While SFP and SFP+ modules look identical, plugging an SFP optic into an SFP+ port may not deliver full functionality. Generally, SFP modules can operate in SFP+ ports, but they will be limited to a maximum speed of 1Gbps. This is because SFP+ ports are backward compatible with SFP modules, but not the other way around. However, compatibility can vary based on the specific SFP models, networking equipment, and vendors involved. It’s advisable to consult your vendor for precise information regarding compatibility.

① Insert a 1000BASE-SX SFP transceiver into the SFP port of a gigabit switch.

② Install a 1000BASE-SX SFP transceiver into the SFP+ port of a 10G switch.

③ Use an OM3 multimode fiber optic cable to connect the two transceivers, enabling 1Gbps data transmission.

Steps:

• Connect a 1000BASE-SX SFP transceiver to the SFP port of a gigabit switch.

• Insert the same 1000BASE-SX SFP transceiver into the SFP+ ports of a 10G switch.

• Link the two modules using an OM3 multimode fiber optic cable to establish a 1Gbps data rate connection.

Recommended Products:

• GLC-SX-MM Compatible 1000BASE-SX SFP Transceiver Module (for steps 1 and 2)

• LC UPC Duplex OM3 Multimode Fiber Patch Cable (for step 3)

Case 2: Inserting an SFP+ Module into an SFP Port

What happens when you try to insert an SFP+ module into an SFP port? While it may seem unlikely that anyone would do this, it's important to note that a 10G SFP+ module will not operate at its full 10Gbps capacity when connected to an SFP port. So, what’s the advantage of using a 10G module in an SFP port? Generally, it’s more practical and cost-effective to use a 1G module directly in such scenarios, as it avoids unnecessary complications.

Case 3: Connectivity Between SFP+ and SFP Modules

Now, let’s look at the interconnectivity between SFP+ and SFP modules. Can a 10G SFP+ module connect to an SFP module in a gigabit switch? The answer depends on the types of modules and the transmission link involved.

Most 10G SFP+ fiber optics operate at a fixed speed of 10Gbps and cannot auto-negotiate down to 1Gbps or lower to support an SFP module. However, there are two scenarios where this connection is possible.

First, if the transmission medium between the two switches is Ethernet over copper cabling, the situation changes. The 10GBASE-T SFP+ copper transceiver supports auto-negotiation for speeds of 10/100/1000Mbps, allowing both ends of the link to maintain compatible speeds. For example, you can easily connect a 10GBASE-T SFP+ module in a 10-gigabit switch to a copper SFP module in a gigabit switch using a Cat5e Ethernet cable.

Solution Product List:

① SFP-10G-T-S compatible 10GBASE-T SFP+ copper transceiver

② GLC-T compatible 1000BASE-T SFP copper transceiver

③ Cat5e/Cat6 Ethernet patch cable

Additionally, there are SFP+ optics available that function as dual-rate 1G/10G SFP+ fiber modules, allowing support for both 1G and 10G Ethernet links over single-mode fiber (SMF) or multimode fiber (MMF). Vendors like QSFPTEK offer various dual-rate modules, including 1000BASE-SX and 10GBASE-SR SFP+, 1000BASE-LX and 10GBASE-LR SFP+, as well as 10G/25GBASE-SR SFP28 modules. For a quote and tailored solutions, please contact us for the best pricing options.

Compatibility Between SFP28 and SFP+ Modules

A frequently asked question regarding SFP28 and SFP+ compatibility is whether SFP28 modules can be used with SFP+ ports. The short answer is yes—SFP optics can operate in SFP+ ports, but not vice versa.

SFP28 (Small Form-Factor Pluggable 28) is an enhanced version of SFP+, designed to support 25Gb/s data rate transmission while maintaining the same package type. SFP28 is backward compatible with SFP+. For instance, if an SFP+ module is inserted into an SFP28 port on a switch, the SFP+ module will function correctly, but its maximum transmission speed will automatically negotiate down to 10Gb/s.

Compatibility Between QSFP28 and QSFP+ Modules

As we enter the era of high-speed networking, a key question arises: "What is the QSFP28 and QSFP+ compatibility?"? To address this, let’s clarify the compatibility between these two optical modules. Similar to how SFP optics can be used in SFP+ ports, but not the other way around, QSFP+ optics can function in QSFP28 ports, whereas QSFP28 optics cannot be used in QSFP+ ports. This compatibility is due to the similarities in physical design between the QSFP28 and QSFP+ modules. Both share the same dimensions and feature four integrated transmit and receive channels.

However, their transmission rates differ. The QSFP+ module operates at 10 Gbit/s per channel, resulting in a total transmission rate of 40 Gbit/s, while the QSFP28 module supports 25 Gbit/s per channel, achieving a total rate of 100 Gbit/s. This allows the QSFP28 to support full-speed 100GbE as well as breakout modes like 4x 10GbE and 4x 25GbE. As a result, QSFP+ optics can be inserted into QSFP28 ports and operate at a 40Gbps rate.

When using a QSFP+ module in a QSFP28 port, it’s important to ensure that the QSFP28 port is configured to operate at 40Gbps. For example, if the connected device uses a 40G service speed, the QSFP28 port should be adjusted to match this speed. Here is an example configuration for an FS S5850-48S2Q4C LAN distribution switch to support a 40GbE QSFP+ module:

• S5850-48S2Q4C# configure terminal

• S5850-48S2Q4C(config)# interface eth-0-49

• S5850-48S2Q4C(config-if)# speed 40G

For hardware connections, when using QSFP+ optical modules in QSFP28 ports, there are several options to choose from, such as the following:

• QSFP+ 40G transceiver with MTP/MPO connector; MTP/MPO 12 Fiber Trunk Cable

• 40G QSFP+ to QSFP+ DAC Cable

• 40G QSFP+ to QSFP+ AOC Cable

In summary, the backward compatibility of QSFP28 ports with QSFP+ modules allows for flexible deployment as networks transition from 40G to 100G speeds. By adjusting the port configuration, QSFP+ optics can seamlessly operate in QSFP28 ports, providing a cost-effective solution for maintaining compatibility while upgrading network capacity.

Conclusion

Transceiver compatibility can often present challenges, particularly concerning the interoperability between optics and devices or between different optical modules. Key topics include the compatibility of SFP with SFP+, SFP28 with SFP+, and QSFP28 with QSFP+. Generally speaking, newer optical transceivers are designed to be backward compatible with their predecessors. This means that SFP+ ports can accommodate SFP modules, SFP+ modules can be plugged into SFP28 ports for 10G operation, and QSFP+ optics can function in QSFP28 ports, but not the other way around.

Understanding the underlying principles of SFP compatibility can make these issues much easier to navigate. To minimize the risk of errors arising from compatibility problems, it’s crucial to ensure that both ends of the link support the same data rates. Additionally, consulting with your supplier will help ensure compatibility without any exceptions.

For seamless integration and performance, consider exploring FS’s extensive range of optical transceivers. Our products are designed to meet compatibility standards and deliver optimal performance across various networking environments.