Class B and Class C SFP (Small Form-Factor Pluggable) refer to different types of transceiver modules used in networking equipment. The main differences between the two are as follows:

1. Transmission Distance: Class B SFP modules typically support shorter transmission distances, usually up to 10 kilometers, while Class C SFP modules support longer transmission distances, up to 100 kilometers.

2. Power Consumption: Class B SFP modules generally consume more power compared to Class C SFP modules due to the higher transmission distance capability.

3. Cost: Class C SFP modules are usually more expensive than Class B SFP modules due to their longer transmission distances and higher performance capabilities.

4. Application: Class B SFP modules are commonly used for shorter distance connections within data centers or local area networks, while Class C SFP modules are used for longer distance connections between data centers or in metropolitan area networks.

Ultimately, the choice between Class B and Class C SFP modules depends on the specific requirements of the networking application, including the distance of the connections and the available budget.