According to E Computer Notes, the five major components of a data communications system are the message, sender, receiver, medium and protocol. All five are needed to work in tandem to send any data communications from the sender to the proper receiver.
The message part of the communications system is the actual data being exchanged between the sender and the receiver. It can contain anything from text to video. The sender is the device of origin for the message. The sender is any piece of hardware capable of sending a signal over a network, from a modern PC to a webcam.
The receiver is the end unit for the communications. Like the sender, the receiver is any device capable of receiving messages over a network, examples of which include computers and networked printers. The medium is the physical path that the message uses to go from sender to receiver. It includes the actual communications technology used to connect the two devices, such as fiber-optic cables and microwaves. The protocol includes the rules applied to the communication of the message. It provides a way to sync the sender and receiver so that they are both capable of handling the structure of the data sent between them.