RESTFUL Web Services uses the HTTP protocol. They use the HTTP protocol as a medium of communication between the client and the server.
RESTful web services primarily use the HTTP protocol for communication. HTTP (Hypertext Transfer Protocol) is a widely adopted protocol for transmitting data over the internet, and it serves as the foundation for RESTful APIs. REST (Representational State Transfer) is an architectural style that leverages the principles of HTTP for creating scalable and stateless web services. So, the correct answer to your question is HTTP.