QSFP56-DD (Quad Small Form Factor Pluggable Double Density) is a high-speed optical transceiver form factor designed for data communication applications, particularly in data centers and networking. The "56" in QSFP56-DD refers to the data rate per channel, and "DD" signifies double density. QSFP56-DD is an evolution of QSFP, designed to support higher data rates. 

The speed of QSFP56-DD is typically associated with the aggregate data rate, considering that it has two sets of four channels each (hence, double density). Here are the common data rates associated with QSFP56-DD:

1. Aggregate Data Rate:

• QSFP56-DD can support an aggregate data rate of 200 Gbps or 400 Gbps.

2. Per-Channel Data Rate:

• Each channel within QSFP56-DD typically operates at a data rate of 50 Gbps.

It's important to note that the specific data rates and standards associated with QSFP56-DD may evolve as technologies advance. The above figures are based on the information available up to my last knowledge update in January 2022. Always check the latest specifications and standards for the most accurate and up-to-date information, as the technology landscape can change over time.