Telephony

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Telephony ( /təˈlɛfəni/ tə-LEF-ə-nee) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is intimately linked to the invention and development of the telephone.

Contents

Telephony is commonly referred to as the construction or operation of telephones and telephonic systems and as a system of telecommunications in which telephonic equipment is employed in the transmission of speech or other sound between points, with or without the use of wires. [1] The term is also used frequently to refer to computer hardware, software, and computer network systems, that perform functions traditionally performed by telephone equipment. In this context the technology is specifically referred to as Internet telephony, or voice over Internet Protocol (VoIP).

Overview

The first telephones were connected directly in pairs. Each user had a separate telephone wired to each locations 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 trunk lines and long distance service could be established by relaying the calls through multiple exchanges.

Initially, exchange 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 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 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 is digital, or where the conversion between digital and analog signals takes place inside the telephone. This advancement has reduced costs in communication, and improved the quality of voice services. The first implementation of this, ISDN, permitted all data transport from end-to-end speedily over telephone lines. This service was later made much less important due to the ability to provide digital services based on the IP protocol.

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's 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). [2] CTI is not a new concept and has been used in the past in large telephone networks, but only dedicated call centers could justify the costs of the required equipment installation. Primary telephone service providers are offering information services such as automatic number identification, which is a telephone service architecture that separates CTI services from call switching and will make it easier to add new services. Dialed Number Identification Service (DNIS) on a scale is wide enough for its implementation to bring real value to business or residential telephone usage. A new generation of applications (middleware) is being developed as a result of standardization and availability of low cost computer telephony links.

Digital telephony

Digital telephony is the use of digital electronics in the operation and provisioning of telephony systems and services. Since the late 20th century, a digital core network has replaced the traditional analog transmission and signaling systems, and much of the access network has also been digitized.

Starting with the development of transistor technology, originating from Bell Telephone Laboratories in 1947, to amplification and switching circuits in the 1950s, the public switched telephone network (PSTN) has gradually moved towards solid-state electronics and automation. Following the development of computer-based electronic switching systems incorporating metal–oxide–semiconductor (MOS) and pulse-code modulation (PCM) technologies, the PSTN gradually evolved towards the digitization of signaling and audio transmissions. Digital telephony has since dramatically improved the capacity, quality and cost of the network. Digitization allows wideband voice on the same channel, with improved quality of a wider analog voice channel.

History

The earliest end-to-end analog telephone networks to be modified and upgraded to transmission networks with Digital Signal 1 (DS1/T1) carrier systems date back to the early 1960s. They were designed to support the basic 3 kHz voice channel by sampling the bandwidth-limited analog voice signal and encoding using pulse-code modulation (PCM). Early PCM codec-filters were implemented as passive resistor capacitor inductor filter circuits, with analog-to-digital conversion (for digitizing voices) and digital-to-analog conversion (for reconstructing voices) handled by discrete devices. Early digital telephony was impractical due to the low performance and high costs of early PCM codec-filters. [3] [4]

Practical digital telecommunication was enabled by the invention of the metal–oxide–semiconductor field-effect transistor (MOSFET), [5] which led to the rapid development and wide adoption of PCM digital telephony. [4] The MOSFET was invented by Mohamed M. Atalla and Dawon Kahng at Bell Telephone Laboratories in 1959, and the metal–oxide–semiconductor (MOS) integrated circuit (IC) chip was proposed soon after, but MOS technology was initially overlooked by Bell because they did not find it practical for analog telephone applications, before it was commercialized by Fairchild and RCA for digital electronics such as computers. [6] [4] MOS technology eventually became practical for telephone applications with the MOS mixed-signal integrated circuit, which combines analog and digital signal processing on a single chip, developed by former Bell engineer David A. Hodges with Paul R. Gray at UC Berkeley in the early 1970s. [4] In 1974, Hodges and Gray worked with R.E. Suarez to develop MOS switched capacitor (SC) circuit technology, which they used to develop a digital-to-analog converter (DAC) chip, using MOS capacitors and MOSFET switches for data conversion. [4] MOS analog-to-digital converter (ADC) and DAC chips were commercialized by 1974. [7]

MOS SC circuits led to the development of PCM codec-filter chips in the late 1970s. [4] [3] The silicon-gate CMOS (complementary MOS) PCM codec-filter chip, developed by Hodges and W.C. Black in 1980, [4] has since been the industry standard for digital telephony. [4] [3] By the 1990s, telecommunication networks such as the public switched telephone network (PSTN) had been largely digitized with very-large-scale integration (VLSI) CMOS PCM codec-filters, widely used in electronic switching systems for telephone exchanges, private branch exchanges (PBX) and key telephone systems (KTS); user-end modems; data transmission applications such as digital loop carriers, pair gain multiplexers, telephone loop extenders, integrated services digital network (ISDN) terminals, digital cordless telephones and digital cell phones; and applications such as speech recognition equipment, voice data storage, voice mail and digital tapeless answering machines. [3] The bandwidth of digital telecommunication networks has been rapidly increasing at an exponential rate, as observed by Edholm's law, [8] largely driven by the rapid scaling and miniaturization of MOS technology. [9] [4]

Uncompressed PCM digital audio with 8-bit depth and 8  kHz sample rate requires a bit rate of 64  kbps, which was impractical for early digital telecommunication networks with limited network bandwidth. A solution to this issue was linear predictive coding (LPC), a speech coding data compression algorithm that was first proposed by Fumitada Itakura of Nagoya University and Shuzo Saito of Nippon Telegraph and Telephone (NTT) in 1966. LPC was capable of audio data compression down to 2.4 kbps, leading to the first successful real-time conversations over digital networks in the 1970s. [10] LPC has since been the most widely used speech coding method. [11] Another audio data compression method, a discrete cosine transform (DCT) algorithm called the modified discrete cosine transform (MDCT), has been widely adopted for speech coding in voice-over-IP (VoIP) applications since the late 1990s. [12]

The development of transmission methods such as SONET and fiber optic transmission further advanced digital transmission. Although analog carrier systems existed that multiplexed multiple analog voice channels onto a single transmission medium, digital transmission allowed lower cost and more channels multiplexed on the transmission medium. Today the end instrument often remains analog but the analog signals are typically converted to digital signals at the serving area interface (SAI), central office (CO), or other aggregation point. Digital loop carriers (DLC) and fiber to the x place the digital network ever closer to the customer premises, relegating the analog local loop to legacy status.

Milestones in digital telephony

IP telephony

A commercial IP telephone, with keypad, control keys, and screen functions to perform configuration and user features. Cisco7960G.jpg
A commercial IP telephone, with keypad, control keys, and screen functions to perform configuration and user features.

The field of technology available for telephony has broadened with the advent of new communication technologies. Telephony now includes the technologies of Internet services and mobile communication, including video conferencing.

The new technologies based on Internet Protocol (IP) concepts are often referred to separately as voice over IP (VoIP) telephony, also commonly referred to as IP telephony or Internet telephony. Unlike traditional phone service, IP telephony service is relatively unregulated by government. In the United States, the Federal Communications Commission (FCC) regulates phone-to-phone connections, but says they do not plan to regulate connections between a phone user and an IP telephony service provider.[ citation needed ]

A specialization of digital telephony, Internet Protocol (IP) telephony involves the application of digital networking technology that was the foundation to the Internet to create, transmit, and receive telecommunications sessions over computer networks. Internet telephony is commonly known as voice over Internet Protocol (VoIP), reflecting the principle, but it has been referred with many other terms. VoIP has proven to be a disruptive technology that is rapidly replacing traditional telephone infrastructure technologies. As of January 2005, up to 10% of telephone subscribers in Japan and South Korea have switched to this digital telephone service. A January 2005 Newsweek article suggested that Internet telephony may be "the next big thing". [13] As of 2006, many VoIP companies offer service to consumers and businesses.[ needs update ]

IP telephony uses an Internet connection and hardware IP phones, analog telephone adapters, or softphone computer applications to transmit conversations encoded as data packets. In addition to replacing plain old telephone service (POTS), IP telephony services compete with mobile phone services by offering free or lower cost connections via WiFi hotspots. VoIP is also used on private networks which may or may not have a connection to the global telephone network.

Fixed telephone lines per 100 inhabitants 1997-2007 Fixed telephone lines per 100 inhabitants 1997-2007 ITU.png
Fixed telephone lines per 100 inhabitants 1997–2007

Social impact research

Direct person-to-person communication includes non-verbal cues expressed in facial and other bodily articulation, that cannot be transmitted in traditional voice telephony. Video telephony restores such interactions to varying degrees. Social Context Cues Theory is a model to measure the success of different types of communication in maintaining the non-verbal cues present in face-to-face interactions. The research examines many different cues, such as the physical context, different facial expressions, body movements, tone of voice, touch and smell.

Various communication cues are lost with the usage of the telephone. The communicating parties are not able to identify the body movements, and lack touch and smell. Although this diminished ability to identify social cues is well known, Wiesenfeld, Raghuram, and Garud point out that there is a value and efficiency to the type of communication for different tasks. [14] They examine work places in which different types of communication, such as the telephone, are more useful than face-to-face interaction.

The expansion of communication to mobile telephone service has created a different filter of the social cues than the land-line telephone. The use of instant messaging, such as texting, on mobile telephones has created a sense of community. [15] In The Social Construction of Mobile Telephony it is suggested that each phone call and text message is more than an attempt to converse. Instead, it is a gesture which maintains the social network between family and friends. Although there is a loss of certain social cues through telephones, mobile phones bring new forms of expression of different cues that are understood by different audiences. New language additives attempt to compensate for the inherent lack of non-physical interaction.

Another social theory supported through telephony is the Media Dependency Theory. This theory concludes that people use media or a resource to attain certain goals. This theory states that there is a link between the media, audience, and the large social system. [16] Telephones, depending on the person, help attain certain goals like accessing information, keeping in contact with others, sending quick communication, entertainment, etc.

See also

Related Research Articles

Telephone Telecommunications device

A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. A telephone converts sound, typically and most efficiently the human voice, into electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user.

In telecommunications, an electronic switching system (ESS) is a telephone switch that uses solid-state electronics, such as digital electronics) and computerized common control, to interconnect telephone circuits for the purpose of establishing telephone calls.

Data transmission is the transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibers, wireless communication channels, storage media and computer buses. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal.

Digital audio technology that records, stores, and reproduces sound

Digital audio is sound that has been recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is encoded as numerical samples in continuous sequence. For example, in CD audio, samples are taken 44100 times per second each with 16 bit sample depth. Digital audio is also the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s, it gradually replaced analog audio technology in many areas of audio engineering and telecommunications in the 1990s and 2000s.

Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet telephony, broadband telephony, and broadband phone service specifically refer to the provisioning of communications services over the public Internet, rather than via the public switched telephone network (PSTN), also known as plain old telephone service (POTS).

Plain old telephone service (POTS), or plain ordinary telephone service, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. POTS was the standard service offering from telephone companies from 1876 until 1988 in the United States when the Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) was introduced, followed by cellular telephone systems, and voice over IP (VoIP). POTS remains the basic form of residential and small business service connection to the telephone network in many parts of the world. The term reflects the technology that has been available since the introduction of the public telephone system in the late 19th century, in a form mostly unchanged despite the introduction of Touch-Tone dialing, electronic telephone exchanges and fiber-optic communication into the public switched telephone network (PSTN).

The public switched telephone network (PSTN) is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telephony operators, providing infrastructure and services for public telecommunication. The PSTN consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all interconnected by switching centers, thus allowing most telephones to communicate with each other. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital in its core network and includes mobile and other networks, as well as fixed telephones.

A softswitch is a call switching node in a telecommunications network, based not on the specialized switching hardware of the traditional telephone exchange, but implemented in software running on a general-purpose computing platform. Like its traditional counterparts it connects telephone calls between subscribers or other switching systems across a telecommunication network. Often a softswitch is implemented to switch calls using voice over IP (VoIP) technologies, but hybrid systems exist.

Telephone hybrid type of telephone circuit

A telephone hybrid is the component at the ends of a subscriber line of the public switched telephone network (PSTN) that converts between two-wire and four-wire forms of bidirectional audio paths. When used in broadcast facilities to enable the airing of telephone callers, the broadcast-quality telephone hybrid is known as a broadcast telephone hybrid or telephone balance unit.

Analog telephone adapter

An analog telephone adapter (ATA) is a device for connecting traditional analog telephones, fax machines, and similar customer-premises devices to a digital telephone system or a voice over IP telephony network.

A mixed-signal integrated circuit is any integrated circuit that has both analog circuits and digital circuits on a single semiconductor die. In real-life applications mixed-signal designs are everywhere, for example, smart mobile phones. Mixed-signal ICs also process both analog and digital signals together. For example, an analog-to-digital converter is a mixed-signal circuit. Mixed-signal circuits or systems are typically cost-effective solutions for building any modern consumer electronics applications.

History of mobile phones covers mobile communication devices which connect wirelessly to the public switched telephone network

The history of mobile phones covers mobile communication devices that connect wirelessly to the public switched telephone network.

Cable telephony is a form of digital telephony over cable TV networks. A telephone interface installed at the customer's premises converts analog signals from the customer's in-home wiring to a digital signal, which is then sent over the cable connection to the company's switching center. The signal is then sent on to the public switched telephone network (PSTN). Cable telephone provides another revenue stream for cable television system operators and gives the consumer the convenience of a single bill for combined television, internet and telephone services.

VoIP phone phone using one or more VoIP technologies

A VoIP phone or IP phone uses voice over IP technologies for placing and transmitting telephone calls over an IP network, such as the Internet, instead of the traditional public switched telephone network (PSTN).

History of telecommunication aspect of history relating to telecommunications

The history of telecommunication began with the use of smoke signals and drums in Africa, Asia, and the Americas. In the 1790s, the first fixed semaphore systems emerged in Europe. However, it was not until the 1830s that electrical telecommunication systems started to appear. This article details the history of telecommunication and the individuals who helped make telecommunication systems what they are today. The history of telecommunication is an important part of the larger history of communication.

History of the telephone aspect of history relating to telephones

This history of the telephone chronicles the development of the electrical telephone, and includes a brief review of its predecessors.

The following outline is provided as an overview of and topical guide to telecommunication:

Wideband audio, also known as wideband voice or HD voice, is high definition voice quality for telephony audio, contrasted with standard digital telephony "toll quality". It extends the frequency range of audio signals transmitted over telephone lines, resulting in higher quality speech. The range of the human voice extends from 80 Hz to 14 kHz but traditional, voiceband or narrowband telephone calls limit audio frequencies to the range of 300 Hz to 3.4 kHz. Wideband audio relaxes the bandwidth limitation and transmits in the audio frequency range of 50 Hz to 7 kHz or even up to 22 kHz. In addition, some wideband codecs may use a higher audio bit depth of 16-bits to encode samples, also resulting in much better voice quality.

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps.

David Albert Hodges is a noted American electrical engineer, currently Professor Emeritus at the University of California, Berkeley.

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