What is the function of a communication protocol?

The communication protocol is the technique, methods, wording of communcating with people.
This proctocol includes rules, procedures, and policies which should be followed.
All this will help to conduct effective, efficient and professional communication.

Hardware and software standards that govern data transmission between computers.
The term "protocol" is very generic and is used for hundreds of different communications methods.
A protocol may define the packet structure of the data transmitted or the control commands that manage the session, or both.
A protocol suite such as TCP/IP is made up of several levels of functionality.
Learning the7-layer protocol hierarchy, known as the "OSI model," is essential for understanding protocols This link will help http://www.erg.abdn.ac.uk/~gorry/course/intro-pages/protocols.html