QSFP28 vs. QSFP+: Compatibility, Use Cases, and Backwards Compatibility

Is QSFP28 Compatible with QSFP+?

In the evolving world of data centers and high-speed networking, compatibility between different generations of transceivers is a critical consideration. QSFP28 and QSFP+ are two such transceiver types commonly used for 100G and 40G Ethernet networks, respectively. This article explores QSFP+ and QSFP28 compatibility and whether QSFP+ modules can be used in QSFP28 ports and vice versa.

Understanding QSFP28 and QSFP+

QSFP28:

• Designed for 100 Gigabit Ethernet (100GbE) networks.
• Provides four 25Gbps lanes, totaling 100Gbps.
• Used for high-density, high-speed network connections.

QSFP+:

• Designed for 40 Gigabit Ethernet (40GbE) networks.
• Provides four 10Gbps lanes, totaling 40Gbps.
• Widely used for moderate-speed data center and enterprise network applications.

Can QSFP+ Be Plugged into QSFP28 Ports and Vice Versa?

QSFP+ in QSFP28 Ports:

• Backward Compatibility: QSFP28 ports are generally backward compatible with QSFP+ modules. This means you can plug a QSFP+ module into a QSFP28 port, and it will function properly. The port will automatically downgrade to support 40Gbps transmission, utilizing the QSFP+ module’s capability.
• Use Case: This backward compatibility is useful for network upgrades, allowing for a phased approach where existing QSFP+ modules can still be utilized while new QSFP28 infrastructure is deployed.

QSFP28 in QSFP+ Ports:

• Forward Compatibility: QSFP+ ports are not forward compatible with QSFP28 modules. A QSFP28 module cannot be used in a QSFP+ port because the QSFP+ port lacks the necessary hardware and signaling capabilities to support the higher data rates and specifications of QSFP28.
• Use Case Limitation: Therefore, if you need to upgrade a QSFP+ network to 100Gbps, replacing both the transceivers and the switch or router ports to QSFP28 is necessary.

Conclusion

In summary, QSFP28 ports offer backward compatibility with QSFP+ modules, allowing for flexible and cost-effective network upgrades. However, QSFP28 modules cannot be used in QSFP+ ports. Understanding these compatibility dynamics helps in planning and executing network infrastructure upgrades, ensuring seamless transitions and optimal performance in high-speed networking environments.

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