COMMUNICATION NETWORKS 13 TELECOMMUNICATIONS Answer these questions. a. When did you last telecommunicate ? b. Can you define a network? c. Try to write a definition for protocol. How can it apply to IT networks? megaphone: megafono transceiver: ricetrasmittente transducer: trasduttore The first television broadcast On 30th April 1939, the first ever regularly scheduled television broadcast began with scenes from the just-opened New York World s Fair. NBC transmitted Franklin D. Roosevelt s World s Fair inaugural address from the antenna of the Empire State Building, and it reached tens of households. Programs were sent initially for an hour at a time, twice a week, and covered news events, sporting events and interviews with celebrities. Communicating is the process of sending information from one place to another. When this process of transmission involves significant distances, it is called telecommunications. Telecommunications began with the invention of the electric telegraph in the 19th century, soon becoming one of the fastest growing fields of industry. Its objective is to convert the messages that have to be sent into signals that can be transmitted through wires, optical fibres and interplanetary space. Telecommunications consists of some basic blocks or components, which apply equally to telecommunication systems which are not electronic, but only electrical, as in the case of power-line communication (PLC). In telecommunications, a message is transferred along a channel, between a transmitter, i.e. the source, and a receiver, i.e. the destination. A transducer, e.g. a microphone, placed in the transmitter takes the message from the source, e.g. your voice, and translates it into a suitable form which can be transmitted along the communication channel. At the other end, in the receiver, another transducer, e.g. earphone, delivers a copy of the original message to the destination, e.g. your ear. The basic structure may be implemented by other components. An amplifier can be used to boost the strength of the signal either at the source or at destination; an encoder may be employed in the transmitter and a decoder in the receiver, to put the signal into a more suitable form of transmission. There are different types of telecommunication systems: simplex: a one-way system in which the message can travel only in one direction for a simple operation, e.g. using a megaphone. duplex: a two-way system in which the system works both as a transmitter and a receiver, or a transceiver. When the two directions are used one at a time, we have a half-duplex system as in the case of a walkie-talkie, while telecommunications over the phone is a full-duplex system, i.e. in both directions at the same time through a bi-dimensional transmission channel. Telecommunications over telephone lines is also called point-to-point because it is between one transmitter and one receiver. broadcast: a system with one powerful transmitter and many low-power, but sensitive receivers, as in radio and television broadcast. multiplex: a system in which multiple transmitters and multiple receivers cooperate and share the same physical channel, as in videoconferencing. However, before sending the information, the message has to be converted into electrical energy either in the analogue, i.e. continuous, or pulse, i.e. discrete or digital form, in order to be processed by electronic circuits. Roosevelt s World s Fair inaugural address 198 Module 5 FLOWCHARTING