The maximum transmission speed of a QSFP (Quad Small Form-Factor Pluggable) module depends on its specific variant or generation. QSFP modules are designed to support various data rates, and newer generations have been introduced to meet the increasing demand for higher bandwidth in data center and high-performance computing environments. here are the maximum data rates associated with different QSFP variants: 

1. QSFP:

• Maximum Data Rate: Up to 40 Gigabits per second (Gbps).

• Applications: Commonly used for 40 Gigabit Ethernet (40GbE) connections.

2. QSFP+ (Quad Small Form-Factor Pluggable Plus):

• Maximum Data Rate: Up to 40 Gbps per channel.

• Applications: Used for 40GbE and 10 Gigabit Ethernet (10GbE) connections.

3. QSFP28 (Quad Small Form-Factor Pluggable 28):

• Maximum Data Rate: Up to 100 Gbps per channel.

• Applications: Widely used for 100GbE connections and other high-speed networking applications.

4. QSFP56 (Quad Small Form-Factor Pluggable 56):

• Maximum Data Rate: Supports data rates of 200 Gbps and 400 Gbps.

• Applications: Used for 200GbE and 400GbE connections.

5. QSFP-DD (Quad Small Form-Factor Pluggable Double Density):

• Maximum Data Rate: Supports higher data rates, including 200 Gbps and 400 Gbps per module.

• Applications: Designed for next-generation high-density and high-speed networking applications.

It's important to note that the term "QSFP" by itself may refer to the original QSFP or QSFP+ modules, and the specific data rate will depend on the generation of the module. Advancements in technology have led to higher-speed variants like QSFP28, QSFP56, and QSFP-DD to meet the growing need for faster data transmission.

Always refer to the documentation provided by the equipment manufacturer for accurate information on the supported data rates of QSFP modules in your network infrastructure.