Yes, QSFP56 and QSFP-DD are compatible with each other. QSFP56 and QSFP-DD both use the same form factor and are designed to support higher data rates and increased port density in networking applications. This compatibility allows for flexibility in network design and the ability to use both QSFP56 and QSFP-DD modules and connectors within the same network infrastructure.

Here are the key differences:

1. Form Factor:

• QSFP56: Designed with a single row of electrical contacts.

• QSFP-DD: Designed with a double row of electrical contacts, allowing for higher data rate density.

2. Electrical Interface:

• QSFP56: Typically supports one channel of 50 gigabits per second (Gbps) for a total data rate of 50 Gbps.

• QSFP-DD: Supports double density, allowing for up to four channels of 50 Gbps each, resulting in a potential total data rate of 200 Gbps.

3. Compatibility:

• QSFP56 and QSFP-DD are not mechanically or electrically compatible, meaning you cannot directly plug a QSFP56 module into a QSFP-DD port or vice versa.

4. Applications:

• QSFP56: Used for high-speed connections, including 200 Gigabit Ethernet.

• QSFP-DD: Primarily designed for 400 Gigabit Ethernet applications.

While QSFP56 and QSFP-DD are not directly interchangeable, the industry has developed transceivers known as QSFP56-DD, which is a dual-density form factor. QSFP56-DD modules can be inserted into QSFP-DD ports, providing a transition path from 200 Gbps to 400 Gbps in networking equipment.

Always check the compatibility and specifications provided by the manufacturer for your specific networking equipment and transceivers to ensure proper operation and compatibility.