The simplest form of telecommunications takes place between two stations, but it is common for multiple transmitting and receiving stations to exchange data among themselves. Such an arrangement is called a telecommunications network. The internet is the largest example of a telecommunications network. On a smaller scale, examples include:
Data is transmitted in a telecommunications circuit by means of an electrical signal called the carrier or the carrier wave. In order for a carrier to convey information, some form of modulation is required. The mode of modulation can be broadly categorized as either analog or digital.
Corporate and academic wide-area networks (WANs)
Police and fire communications systems
Taxi dispatch networks
Groups of amateur (ham) radio operators
Consider for a moment all the different communications that take place in an organization. Some communications are face to face, but others use some type of technology. Think of email, phone calls, text messaging, viewing pages on the Internet, downloading files. All of these communications make use of a telecommunications system. A telecommunications system is a collection of nodes and links to enable telecommunication. Telecommunication is communication at a distance using electrical signals or electromagnetic waves.
Examples of telecommunications systems are the telephone network, the radio broadcasting system, computer networks and the Internet. The nodes in the system are the devices we use to communicate with, such as a telephone or a computer.