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38-466: The precise tone plan is a signaling specification for the public switched telephone network (PSTN) in North America . It defines the call-progress tones used for indicating the status and progress of telephone calls to subscribers and operators. All signals in the specification use combination (by addition) of audible tones of four frequencies: 350 Hz , 440 Hz, 480 Hz, and 620 Hz. Equipment

76-406: 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, the multiplexing function

114-653: 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

152-438: A finger into the corresponding hole and rotated the dial to the finger stop. When released from this position, the dial pulsing contacts were opened and closed repeatedly, thus interrupting the loop current in a pattern on the return to the home position. The exchange switch decoded the pattern for each digit thus transmitted by stepping relays or by accumulation in digit registers. In the first electromechanical switching systems,

190-569: 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

228-471: A telephone call directly dialed by the subscriber. An automatic switch-hook was designed by Hilborne Roosevelt . The first commercial automatic telephone exchange, designed by Almon Brown Strowger , opened in La Porte , Indiana on 3 November 1892, and used two telegraph-type keys on the telephone, which had to be operated the correct number of times to control the vertical and horizontal relay magnets in

266-488: 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

304-520: Is required to maintain tolerances within ± 0.5% in frequency and ±1.5 dB in amplitude stability. Harmonic distortion is to be at least 30 dB below the applied tone level. The tones are as follows: Prior to the precise tone plan, parts of the Bell System and various switching systems used various similar signal frequencies and levels, without standardization, often referred to as nonprecise call progress tones. The standardization process began with

342-399: 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 a telephone exchange. A DS0 is also known as

380-622: 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 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

418-472: The General Post Office , which operated the telephone system, and several cases were prosecuted. In popular culture, tapping was shown in the film Red Dragon when prisoner Hannibal Lecter dialed out on a telephone without dialing mechanism. The technique was also used by the character Phantom Phreak in the film Hackers . It was recognized as early as the 1910s that push button dialing

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456-421: 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 is then transmitted from one end to another via telephone exchanges. The call

494-485: 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 the same pattern as voice services and conceived end-to-end circuit-switched services, known as

532-567: 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 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

570-480: 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 the network operators . The first company to be incorporated to provide PSTN services was the Bell Telephone Company in

608-645: 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 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

646-409: The allowable pulse rate up to twenty pulses per second, and the inter-digital pause could be reduced as the switch selection did not have to be completed during the pause. These included access lines to the panel switch in the 1920s, crossbar systems, the later version (7A2) of the rotary system , and the earlier 1970s stored program control exchanges. In some telephones, the pulses may be heard in

684-482: The current pulses generated by the rotary dial on the local loop directly operated electrical stepping switches at the central office. The mechanical nature of these relays generally limited the speed of operation, the pulsing rate, to ten pulses per second. The specifications of the Bell System in the US required service personnel to adjust dials in customer stations to a precision of 9.5 to 10.5 pulses per second (PPS), but

722-413: The development of local telephone networks, primarily in 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

760-553: The digit 0; this makes the code unary , excepting the digit 0. Exceptions to this are Sweden, with one pulse for 0, two pulses for 1, and so on, and New Zealand, with ten pulses for 0, nine pulses for 1, etc. Oslo, the capital city of Norway, used the New Zealand system, but the rest of the country did not. Systems that used this encoding of the ten digits in a sequence of up to ten pulses are known as decadic dialing systems. Some switching systems used digit registers that doubled

798-399: 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 the number of personnel required to deliver a specific level of service. In

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836-412: The exchange principle already employed in telegraph networks. Each telephone was wired to a telephone exchange established for 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

874-521: 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 the Signalling System 7 (SS7) network that controlled calls between most exchanges by

912-445: The exchange. But the use of separate keys with separate conductors to the exchange was not practical. The most common signaling system became a system of using direct-current pulse trains generated in the telephone sets of subscribers by interrupting the single-pair wire loop of the telephone circuit. Strowger also filed the first patent for a rotary dial in 1891. The first dials worked by direct, forward action. The pulses were sent as

950-902: The installation of the first electronic switching system , a Western Electric 1ESS at Succasunna, NJ in 1965. All subsequent switching systems, such the 2/2B ESS, 4ESS , 5ESS , DMS-10, DMS-100 , TOPS, EWSD , and NEAX-61E followed this practice. Public switched telephone network 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

988-562: 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. Pulse dial The pulse repetition rate was historically determined based on the response time needed for electromechanical switching systems to operate reliably. Most telephone systems used

1026-505: 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 the expense and complexity of running two separate technology infrastructures for PSTN and Internet access. Several large private telephone networks are not linked to

1064-423: The nominal rate of ten pulses per second, but operator dialing within and between central offices often used pulse rates up to twenty per second. Automatic telephone exchange systems were developed in the late 19th and early 20th century. For identification, telephone subscribers were assigned a telephone number unique to each circuit. Various methods evolved to signal the desired destination telephone number for

1102-415: 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 the exchanges are also digital, called circuits or channels. However analog two-wire circuits are still used to connect

1140-506: 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

1178-437: 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

Precise tone plan - Misplaced Pages Continue

1216-467: The public dual-tone multi-frequency (DTMF) technology under the name Touch-Tone, which was a trademark in the U.S. until 1984. The Touch-Tone system used push-button telephones . In the decades after 1963, rotary dials were gradually phased out on new telephone models in favor of keypads and the primary dialing method to the central office became touchtone dialing. Most central office systems still support rotary telephones today. Some keypad telephones have

1254-413: The receiver as clicking sounds. However, in general, such effects were undesirable and telephone designers suppressed them by mechanical means with off-normal switches on the dial, or greatly attenuated them by electrical means with a varistor connected across the receiver. As pulse dialing is achieved by interruption of the local loop , it was possible to dial digits by rapidly tapping, i.e. depressing,

1292-428: The switch hook the corresponding number of times at approximately ten taps per second. However, many telephone makers implemented a slow switch hook release to prevent rapid switching. In the United Kingdom, it was once possible to make calls from coin-box phones by tapping the switch hook without depositing coins. Unlawfully obtaining a free telephone call was deemed a criminal offence, abstracting electricity from

1330-502: 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 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

1368-402: The tolerance of the switching equipment was generally between 8 and 11 PPS. The British (GPO, later Post Office Telecommunications ) standard for Strowger switch exchanges has been ten impulses per second (allowable range 7 to 12) and a 66% break ratio (allowable range 63% to 72%). In most switching systems one pulse is used for the digit 1, two pulses for 2, and so on, with ten pulses for

1406-400: The user rotated the dial to the finger stop starting at a different position for each digit transmitted. Operating the dial error-free required smooth rotary motion of the finger wheel by the user, but was found as too unreliable. This mechanism was soon refined to include a recoil spring and a centrifugal governor to control the recoil speed. The user selected a digit to be dialed by inserting

1444-471: Was faster than with rotary dials, when the first panel switches used keys for dialing at the operator stations. In the 1940s, Bell Laboratories conducted field trials of pushbutton telephones for customer dialing to determine accuracy and efficiency. However, the technology of using mechanical reed relays was too unreliable until transistors transformed the industry. In 1963, the Bell System introduced to

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