Connections include the hardware (physical components) required to hook up a computer to the network. Two terms are important to network connections:
The network medium: The network hardware that physically connects one computer to another. This is the cable between the computers.
The network interface: The hardware that attaches a computer to the network medium and acts as an interpreter between the computer and the network. Attaching a computer to a network requires an add-in board known as a network interface card (NIC).
Communications establish the rules concerning how computers talk and understand each other. Because computers often run different software, in order to communicate with each other they must speak a "shared language." Without shared communications, computers cannot exchange information, and remain isolated.
A service defines those things a computer shares with the rest of the network. For example, a computer can share a printer or specific directories or files. Unless computers on the network are capable of sharing resources, they remain isolated, even though physically connected.
The basic elements of network connections
Next we look at how the basic elements of connections, communications, and services work together to make networks function properly:
The connections must operate so that any computer can send or receive electrical signals (data) across the physical media that link them.
Communications must function so that when one computer sends a message, the receiving computer can listen and understand the message.
Computers on a network must either provide a service to other computers or make use of a service provided by other computers.