Yes, QSFP28 (Quad Small Form-Factor Pluggable 28) is backward compatible with QSFP+ (Quad Small Form-Factor Pluggable Plus). This compatibility means that you can use a QSFP28 transceiver in a QSFP+ port, provided that the networking equipment supports the desired data rate. 

Here are the key points:

1. Physical Compatibility:

• QSFP28 and QSFP+ have the same physical form factor, which allows for mechanical compatibility. The connectors and cage are the same, making QSFP28 modules physically fit into QSFP+ ports.

2. Backward Compatibility:

• QSFP28 modules are designed to be backward compatible with QSFP+ ports. However, it's important to note that the data rate of the QSFP28 module must be supported by the QSFP+ port and the networking equipment.

3. Data Rates:

• QSFP28 supports higher data rates than QSFP+. QSFP28 is commonly used for 100 Gigabit Ethernet (100GbE) applications, while QSFP+ supports data rates up to 40 Gbps (Gigabits per second).

4. Optical and Electrical Compatibility:

• While QSFP28 supports higher data rates, it maintains compatibility with the optical and electrical specifications of QSFP+. This ensures that, when used in a QSFP+ port, the module will operate at the maximum supported data rate of the QSFP+ port.

It's important to check the specifications of your networking equipment and the QSFP28 module to ensure compatibility. Some devices may require firmware updates to fully support QSFP28 modules. Always refer to the documentation provided by the equipment manufacturer to verify compatibility and ensure proper operation.