Editing Telephony (section)

==Overview==
The first telephones were connected directly in pairs: each user had a separate telephone wired to each location to be reached. This quickly became inconvenient and unmanageable when users wanted to communicate with more than a few people. The invention of the [[telephone exchange]] provided the solution for establishing telephone connections with any other telephone in service in the local area. Each telephone was connected to the exchange at first with one wire, later one wire pair, the [[local loop]]. Nearby exchanges in other service areas were connected with [[Trunking|trunk lines]], and long-distance service could be established by relaying the calls through multiple exchanges.

Initially, exchange [[Telephone switchboard|switchboards]] were manually operated by an attendant, commonly referred to as the "[[switchboard operator]]".  When a customer cranked a handle on the telephone, it activated an indicator on the board in front of the operator, who would in response plug the operator headset into that jack and offer service. The caller had to ask for the called party by name, later by number, and the operator connected one end of a circuit into the called party jack to alert them.  If the called station answered, the operator disconnected their headset and completed the station-to-station circuit. Trunk calls were made with the assistance of other operators at other exchangers in the network.

Until the 1970s, most telephones were permanently wired to the telephone line installed at customer premises. Later, conversion to installation of jacks that terminated the [[on-premises wiring|inside wiring]] permitted simple exchange of telephone sets with [[telephone plugs]] and allowed portability of the set to multiple locations in the premises where jacks were installed. The inside wiring to all jacks was connected in one place to the [[drop (telecommunication)|wire drop]] which connects the building to a cable. Cables usually bring a large number of drop wires from all over a district [[access network]] to one wire center or telephone exchange. When a telephone user wants to make a [[telephone call]], equipment at the exchange examines the dialed [[telephone number]] and connects that [[telephone line]] to another in the same wire center, or to a trunk to a distant exchange. Most of the exchanges in the world are interconnected through a system of larger switching systems, forming the [[public switched telephone network]] (PSTN).

In the second half of the 20th century, fax and data became important secondary applications of the network created to carry voices, and late in the century, parts of the network were upgraded with [[ISDN]] and [[DSL]] to improve handling of such traffic.

Today, telephony uses digital technology ([[digital telephony]]) in the provisioning of telephone services and systems. Telephone calls can be provided digitally, but may be restricted to cases in which the [[Last mile (telecommunications)|last mile]] is digital, or where the conversion between [[digital signal (signal processing)|digital]] and [[analog signal]]s takes place inside the telephone. This advancement has reduced costs in communication, and improved the quality of voice services. The first implementation of this, [[Integrated Services Digital Network|ISDN]], permitted all data transport from end-to-end speedily over telephone lines.<ref>{{Cite web |title=The Communications Museum Trust - eMuseum - History of Digital Switching -ISDN |url=https://www.communicationsmuseum.org.uk/emuseum/electronicswitching/digital/isdn/ |access-date=2022-08-25 |website=www.communicationsmuseum.org.uk}}</ref> This service was later made much less important due to the ability to provide digital services based on the [[Internet protocol suite]].<ref>{{Cite web |date=2022-03-07 |title=Why ISDN telephones are in decline - Sussex, Surrey, Brighton {{!}} Ingenio |url=https://ingeniotech.co.uk/isdn-telephones-decline/ |access-date=2022-08-25 |website=ingeniotech.co.uk |language=en-US}}</ref>

Since the advent of personal computer technology in the 1980s, [[computer telephony integration]] (CTI) has progressively provided more sophisticated telephony services, initiated and controlled by the computer, such as making and receiving voice, fax, and data calls with [[telephone directory]] services and [[caller identification]]. The integration of telephony software and computer systems is a major development in the evolution of office automation.  The term is used in describing the computerized services of call centers, such as those that direct your phone call to the right department at a business you're calling.  It is also sometimes used for the ability to use your personal computer to initiate and manage phone calls (in which case you can think of your computer as your personal call center).<ref>[http://searchnetworking.techtarget.com/definition/CTI What is CTI?] TechTarget</ref>