QSFP28 (Quad Small Form-Factor Pluggable 28) and QSFP56 (Quad Small Form-Factor Pluggable 56) refer to different generations of QSFP transceiver modules with different data rates and electrical specifications. While they share the same form factor, they are not directly compatible due to differences in their electrical interfaces and capabilities.

Here are the key differences between QSFP28 and QSFP56:

1. Data Rate:

• QSFP28: Supports data rates up to 100 gigabits per second (Gbps) per port. It is commonly used for 100 Gigabit Ethernet (100GbE) applications.

• QSFP56: Supports data rates up to 200 Gbps per port. It is used for applications such as 200 Gigabit Ethernet (200GbE) and 400 Gigabit Ethernet (400GbE).

2. Electrical Interface:

• QSFP28: Utilizes 25 Gbps electrical lanes.

• QSFP56: Utilizes 50 Gbps electrical lanes.

3. Lane Configuration:

• QSFP28: Typically, QSFP28 modules have four electrical lanes, each operating at 25 Gbps, resulting in an aggregate data rate of 100 Gbps.

• QSFP56: Typically, QSFP56 modules have eight electrical lanes, each operating at 50 Gbps, resulting in an aggregate data rate of 200 Gbps.

4. Applications:

• QSFP28: Commonly used in data center environments for high-speed networking applications, including 100GbE connections.

• QSFP56: Designed for higher-speed networking applications, including 200GbE and 400GbE connections.

While both QSFP28 and QSFP56 modules share a similar physical form factor, the electrical and data rate differences mean they are not interoperable. When selecting transceiver modules, it is crucial to ensure compatibility with the specific networking equipment and standards in use. Always refer to the manufacturer's specifications and compatibility guidelines to ensure proper functionality in your network environment.