What is the difference between a gateway, router, and switch in terms of BACnet?

  Gateway Router Switch
Purpose Makes it possible for two dissimilar network protocols (BACnet/Modbus) to communicate and regulates the traffic between them. It is a translator. Regulates traffic between two similar network protocols that may use different communication protocols. Allows for more devices to be connected to the same network.
Summary
Analogy A translator in a business meeting translating English to Japanese A mediator in a debate relaying information A postman bringing a letter from one town to the next