The telephony is a system of Télécommunication the purpose of which is the transmission of sound and in particular the transmission of the word.

Uses

Telephony, it is the Téléphone, the apparatus which is used to telephone, i.e. to hold a conversation with a person who is far, more exactly, too far being able to hear us of sharp voice. Current telephony is bidirectional: the two people in conversation can speak each other and get along at the same time, as in a conversation opposite with face. Thus, telephony is used for private title, to keep the contact with its close relations where that they are and on a purely professional basis, to exchange oral information without having to meet physically.

Telephony also allows more advanced services such as the voice mail, the conference call or the service vocal.

Principles of operation

Principal equipment

Telephony rests on a network of Télécommunications adapted to telephony.

A phone network consists of three types of principal equipment:

• terminals;
• central systems;
• connections between this various equipment.

The terminals are the apparatuses of which the users are useful themselves to telephone, and thus in particular the Téléphone. The Fax or telecopier, the Minitel, the software telephone ( software-phon ), the Responder, the Modem, the interactive vocal Serveur are other types of terminals.

The central systems (telephone center or telephone Commutateur) are the systems which have the intelligence to establish the communications, to invoice them and provide all the functions necessary to the telephony and which the terminals do not provide. The diffusion of a message announcing to the appealing one that the made up number is not allotted any more is an example of the services rendered by a central system.

The connections are the means, such as the cables of telephone (copper or Fiberoptic) or the antennas of mobile telephony, which allow the transport of the communication of a terminal the other.

The customer connects his equipment to the network, in the case of telegraphic telephony by plugging in connectors in catches in particular Prise in T, RJ-11, RJ-45.

Networks

There exist two distinct types of telephony:

• the telegraphic telephony
• the Radiotelefony

Telegraphic telephony uses several principal technologies:

• the Phone network commutated, or analogical telephony based the Modulation low frequency of a running electric carrier. The transmitter and the receiver are fixed or almost (case of the use of cordless phones bases + mobile connected according to technologies CT0 or DECT)
• the Integrated services digital network or ISDN, where the voice is digitized as of the telephone terminal.
• since, the Voice on IP (VoIP), using technologies of the network Internet.

The radiotelefony uses radioelectricity, i.e. the Hertzian waves. It is about the use of radio operator transmitters fixed, mobile or transportables to dialog, while possibly passing by relay stations. This telephony type took an important rise these last years in particular with the establishment of networks of Mobile telephony, initially to the standard GSM. The radiotelefony migrates gradually towards UMTS. One can also quote the networks of telephony per satellite.

Principal telephone functions

The basic communication

The basic communication makes it possible to establish a connection between a user calling and a user called. A call seen of the appealing user is named outgoing Appel , on the side of called one speaks about Incoming call .

The sequence making it possible to establish the communication is traditionally the following one:

• Unhooking of compound of the appealing terminal. The user hears a tonality then indicating that the network is ready to establish the communication.
• Classification: to give to the network the final destination of the call, the user seizes a sequence of figures, for example on a keyboard.
• the incoming call is announced to the user called for example by a ringing.
• the user called can establish the voice communication by taking down its compound.
• the end of communication is started by the accosting of compound of one or other of the interlocutors.

The increase in the functionalities of the terminals has as a consequence which this sequence is sometimes realizable other ways. For example:

• Use without taking down the compound (conversation in Hand-free)
• Assistance with classification (memories, repertories or Voice recognition)
• etc…

Complementary services

The service rendered by the basic communication seemed rather quickly being insufficient, in particular in professional environment. Many complementary services were developed to improve the use of the telephone.

Some examples:

• the transfer allows a person called to pass her call to another terminal in the course of communication.

• the reference allows a person called to return her calls towards another terminal before being in communication. This service can be returned in various cases (failure to reply, occupation, immediate). In France, this service is sometimes called also transfer because of commercial name of the service Transfert of call of France Telecom.
• the three-party call makes it possible three people to converse together on the same line.
• the ISDN makes it possible an operator to rebook a communication which he does not manage to establish towards another terminal.
• the Interception makes it possible a user to answer a call which is not intended initially for its terminal.
• the Identification of appealing the (To fix Line Identification Presentation or CLIP) allows the user called to be informed (by posting for example) number or name of appealing before answering the call
• the Indication of call in Authority (Cal Waiting Indication) makes it possible to indicate in the course of communication, by an aural signal or posting, that another correspondent calls. This service is called Signal of Call in France by France Telecom.

Impacts in the company

Telephony had since its beginnings an impact growing on the company.

Political impacts

Very early, the states were aware of the strategic issue of the telephony, which was the first modern telecommunication network.

Concept of Public service, and other considerations (Secret of the correspondence,…) very often led to the creation of dedicated administrations of state. One spoke then about postal and telecommunications authorities.

For a few years, within the framework of the movement of Deregulation which also touched other sectors of the economy, the model generally adopted in the Western economies has been that of a whole of companies with private capital (Telecommunications operator) offering their services under the control of regulatory agencies (for example the Regulatory agency of the electronic communications and the stations in France).

Economic impacts

Sticks to it an economic network (Opérateur S, invoicing, manufacturers of equipment, etc…)

Social impacts

The Telephone ladies

Cultural impacts

The Scandinavian countries adopted before everyone mobile telephony; the North-American countries adopted before everyone telegraphic telephony.

See too

• Téléphone
• Approche concretes telecommunications
• concrete Approche of the fixed telephone

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