The document discusses three models of communication:
1) The Continuous Loop Model is the earliest and simplest model, showing the basic parts of the communication process including sender, message, channels, receiver, and feedback. However, it assumes continuous communication.
2) The Shannon and Weaver Model was developed in 1949 based on a study of telephone conversations. It includes a sender, transmitter, receiver, noise, and how noise can alter the message.
3) Berlo's model was intended to be all-inclusive but was never tested. It is therefore considered a theory rather than a true model, showing elements like content, code, and characteristics of both the sender and receiver.