Misplaced Pages

#447552

56-601: The public switched telephone network ( PSTN ) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony . The PSTN consists of telephone lines , fiber-optic cables , microwave transmission links, cellular networks , communications satellites , and undersea telephone cables interconnected by switching centers , such as central offices , network tandems , and international gateways, which allow telephone users to communicate with each other. Originally

112-652: A benchmark for the development of the Telecommunications Industry Association 's TIA-TSB-116 standard on voice-quality recommendations for IP telephony, to determine acceptable levels of audio latency and echo. In most countries, the government has a regulatory agency dedicated to provisioning of PSTN services. The agency regulate technical standards, legal requirements, and set service tasks may be for example to ensure that end customers are not over-charged for services where monopolies may exist. These regulatory agencies may also regulate

168-625: A network of fixed-line analog telephone systems, the PSTN is almost entirely digital in its core network and includes mobile and wireless networks, all of which are currently transitioning to use the Internet Protocol to carry their PSTN traffic. The technical operation of the PSTN adheres to the standards internationally promulgated by the ITU-T . These standards have their origins in the development of local telephone networks, primarily in

224-473: A sense of community. 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

280-419: 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,

336-544: 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. 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). The first telephones were connected directly in pairs. Each user had

392-425: A telephone exchange. A DS0 is also known as a timeslot because DS0s are aggregated in time-division multiplexing (TDM) equipment to form higher capacity communication links. A Digital Signal 1 (DS1) circuit carries 24 DS0s on a North American or Japanese T-carrier (T1) line, or 32 DS0s (30 for calls plus two for framing and signaling) on an E-carrier (E1) line used in most other countries. In modern networks,

448-649: A town or area. For communication outside this exchange area, trunks were installed between exchanges. Networks were designed in a hierarchical manner until they spanned cities, states, and international distances. Automation introduced pulse dialing between the telephone and the exchange so that each subscriber could directly dial another subscriber connected to the same exchange, but long-distance calling across multiple exchanges required manual switching by operators. Later, more sophisticated address signaling, including multi-frequency signaling methods, enabled direct-dialed long-distance calls by subscribers, culminating in

504-508: 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

560-439: 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). Digital telephony

616-456: Is also used on private networks which may or may not have a connection to the global telephone network. 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

SECTION 10

#1732783600448

672-566: 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. A specialization of digital telephony, Internet Protocol (IP) telephony involves the application of digital networking technology that was the foundation to

728-455: 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

784-432: Is then transmitted from one end to another via telephone exchanges. The call is switched using a call set up protocol (usually ISUP ) between the telephone exchanges under an overall routing strategy . The call is carried over the PSTN using a 64 kbit/s channel, originally designed by Bell Labs . The name given to this channel is Digital Signal 0 (DS0). The DS0 circuit is the basic granularity of circuit switching in

840-507: Is well known, Wiesenfeld, Raghuram, and Garud point out that there is a value and efficiency to the type of communication for different tasks. 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

896-643: The Bell System in the United States and in the networks of European ITU members. The E.164 standard provides a single global address space in the form of telephone numbers . The combination of the interconnected networks and a global telephone numbering plan allows telephones around the world to connect with each other. Commercialization of the telephone began shortly after its invention, with instruments operated in pairs for private use between two locations. Users who wanted to communicate with persons at multiple locations had as many telephones as necessary for

952-1175: 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". As of 2006, many VoIP companies offer service to consumers and businesses . 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

1008-476: The Signalling System 7 (SS7) network that controlled calls between most exchanges by the end of the 20th century. The growth of the PSTN was enabled by teletraffic engineering techniques to deliver quality of service (QoS) in the network. The work of A. K. Erlang established the mathematical foundations of methods required to determine the capacity requirements and configuration of equipment and

1064-495: The last mile to the end-user. However, digital technologies such as DSL , ISDN , FTTx , and cable modems were progressively deployed in this portion of the network, primarily to provide high-speed Internet access. As of 2023, operators worldwide are in the process of retiring support for both last-mile analog telephony and ISDN, and transitioning voice service to Voice over IP via Internet access delivered either via DSL , cable modems or fiber-to-the-premises , eliminating

1120-401: 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

1176-478: The modified discrete cosine transform (MDCT), has been widely adopted for speech coding in voice-over-IP (VoIP) applications since the late 1990s. 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

SECTION 20

#1732783600448

1232-554: The network operators . The first company to be incorporated to provide PSTN services was the Bell Telephone Company in the United States. In some countries, however, the job of providing telephone networks fell to government as the investment required was very large and the provision of telephone service was increasingly becoming an essential public utility . For example, the General Post Office in

1288-410: The rapid scaling and miniaturization of MOS technology. Uncompressed PCM digital audio with 8-bit depth and 8   kHz sample rate requires a bit rate of 64   kbit/s , 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

1344-446: 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

1400-418: The 1980s, the telecommunications industry expected that digital services would follow much the same pattern as voice services did on the public switched telephone network , and conceived an end-to-end circuit switched service, known as Broadband Integrated Services Digital Network ( B-ISDN ). Before B-ISDN, the original ISDN attempted to substitute the analog telephone system with a digital system which

1456-626: 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. 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. MOS analog-to-digital converter (ADC) and DAC chips were commercialized by 1974. MOS SC circuits led to

1512-676: The United Kingdom brought together a number of private companies to form a single nationalized company . In more recent decades, these state monopolies were broken up or sold off through privatization . The architecture of the PSTN evolved over time to support an increasing number of subscribers, call volume, destinations, features, and technologies. The principles developed in North America and in Europe were adopted by other nations, with adaptations for local markets. A key concept

1568-416: 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

1624-459: 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

1680-399: 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

1736-422: 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

Public switched telephone network - Misplaced Pages Continue

1792-420: 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. 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

1848-1115: The development of PCM codec-filter chips in the late 1970s. The silicon-gate CMOS (complementary MOS) PCM codec-filter chip, developed by Hodges and W.C. Black in 1980, has since been the industry standard for digital telephony. 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 . The bandwidth of digital telecommunication networks has been rapidly increasing at an exponential rate, as observed by Edholm's law , largely driven by

1904-465: The exchanges are also digital, called circuits or channels. However analog two-wire circuits are still used to connect the last mile from the exchange to the telephone in the home (also called the local loop ). To carry a typical phone call from a calling party to a called party , the analog audio signal is digitized at an 8 kHz sample rate with 8-bit resolution using a special type of nonlinear pulse-code modulation known as G.711 . The call

1960-452: The expense and complexity of running two separate technology infrastructures for PSTN and Internet access. Several large private telephone networks are not linked to the PSTN, usually for military purposes. There are also private networks run by large companies that are linked to the PSTN only through limited gateways , such as a large private branch exchange (PBX). The task of building the networks and selling services to customers fell to

2016-455: The first transistors in which drain and source were adjacent at the surface. Subsequently, a team demonstrated a working MOSFET at Bell Labs 1960. 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 . MOS technology eventually became practical for telephone applications with

2072-620: 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. Telephones, depending on the person, help attain certain goals like accessing information, keeping in contact with others, sending quick communication, entertainment, etc. Broadband Integrated Services Digital Network In

2128-490: The interface to end-users remaining the same. Several other European countries, including Estonia, Germany, Iceland, the Netherlands, Spain and Portugal, have also retired, or are planning to retire, their PSTN networks. Countries in other continents are also performing similar transitions. Telephony Telephony is commonly referred to as the construction or operation of telephones and telephonic systems and as

2184-400: The low performance and high costs of early PCM codec-filters. Practical digital telecommunication was enabled by the invention of the metal–oxide–semiconductor field-effect transistor (MOSFET), which led to the rapid development and wide adoption of PCM digital telephony. In 1957, Frosch and Derick were able to manufacture the first silicon dioxide field effect transistors at Bell Labs,

2240-514: The multiplexing function is moved as close to the end user as possible, usually into cabinets at the roadside in residential areas, or into large business premises. These aggregated circuits are conveyed from the initial multiplexer to the exchange over a set of equipment collectively known as the access network . The access network and inter-exchange transport use synchronous optical transmission, for example, SONET and Synchronous Digital Hierarchy (SDH) technologies, although some parts still use

2296-433: 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

Public switched telephone network - Misplaced Pages Continue

2352-467: The number of personnel required to deliver a specific level of service. In the 1970s, the telecommunications industry began implementing packet-switched network data services using the X.25 protocol transported over much of the end-to-end equipment as was already in use in the PSTN. These became known as public data networks , or public switched data networks. In the 1980s, the industry began planning for digital services assuming they would follow much

2408-506: The older PDH technology. The access network defines a number of reference points. Most of these are of interest mainly to ISDN but one, the V reference point , is of more general interest. This is the reference point between a primary multiplexer and an exchange. The protocols at this reference point were standardized in ETSI areas as the V5 interface . Voice quality in PSTN networks was used as

2464-437: The prices charged between the operators to carry each other's traffic . In the United Kingdom, the copper POTS and ISDN-based PSTN is being retired in favour of SIP telephony , with an original completion date of December 2025, although this has now been put back to January 2027. See United Kingdom PSTN switch-off . Voice telephony will continue to follow the E.163 and E.164 standards, as with current mobile telephony, with

2520-531: The primary rate" referring to the primary rate which ranged from about 1.5 to 2 Mbit/s. Services envisioned included video telephone and video conferencing . Technical papers were published in early 1988. Standards were issued by the Comité Consultatif International Téléphonique et Télégraphique (CCITT, now known as ITU-T), and called "Recommendations". They included G.707 to G.709, and I.121 which defined

2576-475: The principal aspects of B-ISDN, with many others following through the 1990s. The designated technology for B-ISDN was Asynchronous Transfer Mode (ATM), which was intended to carry both synchronous voice and asynchronous data services on the same transport. The B-ISDN vision has been overtaken by other disruptive technologies used in the Internet . The ATM technology survived as a low-level layer in most digital subscriber line (DSL) technologies, and as

2632-488: 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

2688-402: The purpose. Alerting another user of the desire to establish a telephone call was accomplished by whistling loudly into the transmitter until the other party heard the alert. Bells were soon added to stations for signaling . Later telephone systems took advantage of the exchange principle already employed in telegraph networks. Each telephone was wired to a telephone exchange established for

2744-503: The same pattern as voice services and conceived end-to-end circuit-switched services, known as the Broadband Integrated Services Digital Network (B-ISDN). The B-ISDN vision was overtaken by the disruptive technology of the Internet . At the turn of the 21st century, the oldest parts of the telephone network still used analog baseband technology to deliver audio-frequency connectivity over

2800-465: 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. The field of technology available for telephony has broadened with

2856-552: Was already obsolete. For home use the largest demand for new services was video and voice transfer, but the ISDN basic rate lacks the necessary channel capacity . This led to introduction of B-ISDN, by adding the word broadband . Although the term had a meaning in physics and engineering (similar to wideband ), the CCITT defined it as: "Qualifying a service or system requiring transmission channels capable of supporting rates greater than

SECTION 50

#1732783600448

2912-425: Was appropriate for both voice and non-voice traffic. Obtaining worldwide agreement on the basic rate interface standard was expected to lead to a large user demand for ISDN equipment, hence leading to mass production and inexpensive ISDN chips. However, the standardization process took years while computer network technology moved rapidly. Once the ISDN standard was finally agreed upon and products were available, it

2968-417: 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

3024-451: 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   kbit/s, leading to the first successful real-time conversations over digital networks in the 1970s. LPC has since been the most widely used speech coding method. Another audio data compression method, a discrete cosine transform (DCT) algorithm called

3080-514: Was later made much less important due to the ability to provide digital services based on the Internet protocol suite . 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

3136-476: Was that the telephone exchanges are arranged into hierarchies, so that if a call cannot be handled in a local cluster, it is passed to one higher up for onward routing. This reduced the number of connecting trunks required between operators over long distances, and also kept local traffic separate. Modern technologies have brought simplifications Most automated telephone exchanges use digital switching rather than mechanical or analog switching. The trunks connecting

#447552