The maximum distance that QSFP28 (Quad Small Form-Factor Pluggable 28) transceivers can reach depends on the specific type of module and the optical technology used. QSFP28 modules are commonly used in high-speed data center and telecommunications applications, supporting various data rates and reach requirements. Here are some common types of QSFP28 modules and their associated maximum reach:

1. QSFP28 SR4 (Short Range 4 lanes):

• Maximum Reach: Up to 100 meters (328 feet).

• Application: Typically used for short-distance connections within a data center.

2. QSFP28 LR4 (Long Range 4 lanes):

• Maximum Reach: Up to 10 kilometers (6.2 miles).

• Application: Suitable for longer-distance connections in metropolitan and enterprise networks.

3. QSFP28 ER4 (Extended Range 4 lanes):

• Maximum Reach: Up to 40 kilometers (24.8 miles).

• Application: Designed for extended-distance connections in metro and regional networks.

4. QSFP28 PSM4 (Parallel Single-Mode 4 lanes):

• Maximum Reach: Up to 500 meters (1640 feet).

• Application: Used for short- to medium-distance connections in data centers.

It's important to note that these reach values are general guidelines, and actual performance can vary based on factors such as the quality of the optical fibers, the presence of connectors and splices, and the specific implementation of the transceiver module.

When selecting QSFP28 modules for a particular application, it's crucial to consider the specific reach requirements and choose the module that best aligns with those needs. Always refer to the documentation provided by the module manufacturer for accurate and detailed specifications, including reach characteristics.