Yes, QSFP28 (Quad Small Form-factor Pluggable 28) transceivers are designed to be backward compatible with QSFP+ (Quad Small Form-factor Pluggable) ports. QSFP28 modules are an evolution of the QSFP+ modules and have the same form factor but support higher data rates. 

The key points to note:

1. Physical Compatibility:

• QSFP28 modules have the same physical form factor as QSFP+ modules, with the same connector and cage. This allows QSFP28 transceivers to fit into QSFP+ ports.

2. Electrical Compatibility:

• QSFP28 modules support higher data rates compared to QSFP+ modules. While QSFP+ supports data rates up to 10 Gbps per channel, QSFP28 supports data rates of 25 Gbps per channel and beyond. Despite the difference in supported data rates, the electrical interface is backward compatible, allowing a QSFP28 module to work in a QSFP+ port.

3. Data Rate Compatibility:

• When a QSFP28 module is inserted into a QSFP+ port, the data rate is limited to the capabilities of the QSFP+ port. For example, if you insert a QSFP28 module capable of 25 Gbps per channel into a QSFP+ port, the link will operate at the QSFP+ maximum data rate (e.g., 10 Gbps per channel).

It's important to check the specifications of your networking equipment and transceivers to ensure compatibility. If your infrastructure includes both QSFP28 and QSFP+ ports, you can use QSFP28 modules in QSFP+ ports, but keep in mind that the data rate will be limited to the capabilities of the QSFP+ port.