A telephone call is a connection over a telephone network between the called party and the calling party. The first telephone call was made on March 1876 by Alexander Graham Bell. Bell demonstrated his ability to "talk with electricity" by transmitting a call to his assistant, Thomas Watson; the first words transmitted were "Mr Watson, come here. I want to see you."This event has been called Bell's "greatest success", as it demonstrated the first successful use of the telephone. Although it was his greatest success, he refused to have one in his own home because it was something he invented by mistake and saw it as a distraction from his main studies. A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile transmission when they are using fax machines; the call may use mobile phone, satellite phone or any combination thereof. When a telephone call has more than one called party it is referred to as a conference call.
When two or more users of the network are sharing the same physical line, it is called a party line or Rural phone line. If the caller's wireline phone is connected directly to the calling party, when the caller takes their telephone off-hook, the calling party's phone will ring; this is called a hot ringdown. Otherwise, the calling party is given a tone to indicate they should begin dialing the desired number. In some cases, if the calling party cannot dial calls directly, they will be connected to an operator who places the call for them. Calls may be placed through a public network provided by a commercial telephone company or a private network called a PBX. In most cases a private network is connected to the public network in order to allow PBX users to dial the outside world. Incoming calls to a private network arrive at the PBX in two ways: either directly to a users phone using a DDI number or indirectly via a receptionist who will answer the call first and manually put the caller through to the desired user on the PBX.
Most telephone calls through the PSTN are set up using ISUP signalling messages or one of its variants between telephone exchanges to establish the end to end connection. Calls through PBX networks are set up using DPNSS or variants; some types of calls are not charged, such as local calls dialed directly by a telephone subscriber in Canada, the United States, Hong Kong, United Kingdom, Ireland or New Zealand. In most other areas, all telephone calls are charged a fee for the connection. Fees depend on the provider of the service, the type of service being used and the distance between the calling and the called parties. In most circumstances, the calling party pays this fee. However, in some circumstances such as a reverse charge or collect call, the called party pays the cost of the call. In some circumstances, the caller pays a flat rate charge for the telephone connection and does not pay any additional charge for all calls made. Telecommunication liberalization has been established in several countries to allows customers to keep their local phone provider and use an alternate provider for a certain call in order to save money.
A typical phone call using a traditional phone is placed by picking the phone handset up off the base and holding the handset so that the hearing end is next to the user's ear and the speaking end is within range of the mouth. The caller rotary dials or presses buttons for the phone number needed to complete the call, the call is routed to the phone which has that number; the second phone makes a ringing noise to alert its owner, while the user of the first phone hears a ringing noise in its earpiece. If the second phone is picked up the operators of the two units are able to talk to one another through them. If the phone is not picked up, the operator of the first phone continues to hear a ringing noise until they hang up their own phone. One of the main struggles for Alexander Graham Bell and his team was to prove to non-English speakers that this new phenomenon "worked in their language." It was a concept, hard for people to understand at first. In addition to the traditional method of placing a telephone call, new technologies allow different methods for initiating a telephone call, such as voice dialing.
Voice over IP technology allows calls to be made through a PC. Other services, such as toll-free dial-around enable callers to initiate a telephone call through a third party without exchanging phone numbers. No phone calls could be made without first talking to the Switchboard operator. Using 21st century mobile phones does not require the use of an operator to complete a phone call; the use of headsets is becoming more common for receiving a call. Headsets can either be wireless. A special number can be dialed for operator assistance, which may be different for local vs. long-distance or international calls. Preceding and after a traditional telephone call is placed, certain tones signify the progress and status of the telephone call: a dial tone signifying that the system is ready to accept a telephone number and connect the call either: a ringing tone signifying that the called party has yet to answer the telephone a busy signal signifying that the called party's telephone is being used in a telephone call to another person a fast busy signal (also called reorder tone or overflow bu
Traffic on roads consists of road users including pedestrians, ridden or herded animals, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel. Traffic laws are the laws which govern traffic and regulate vehicles, while rules of the road are both the laws and the informal rules that may have developed over time to facilitate the orderly and timely flow of traffic. Organized traffic has well-established priorities, right-of-way, traffic control at intersections. Traffic is formally organized in many jurisdictions, with marked lanes, intersections, traffic signals, or signs. Traffic is classified by type: heavy motor vehicle, other vehicle, pedestrian. Different classes may be segregated; some jurisdictions may have detailed and complex rules of the road while others rely more on drivers' common sense and willingness to cooperate. Organization produces a better combination of travel safety and efficiency. Events which disrupt the flow and may cause traffic to degenerate into a disorganized mess include road construction and debris in the roadway.
On busy freeways, a minor disruption may persist in a phenomenon known as traffic waves. A complete breakdown of organization may result in traffic gridlock. Simulations of organized traffic involve queuing theory, stochastic processes and equations of mathematical physics applied to traffic flow; the word traffic meant "trade" and comes from the Old Italian verb trafficare and noun traffico. The origin of the Italian words is unclear. Suggestions include Catalan trafegar "decant", an assumed Vulgar Latin verb transfricare'rub across', an assumed Vulgar Latin combination of trans- and facere'make or do', Arabic tafriq'distribution', Arabic taraffaqa, which can mean'seek profit'. Broadly, the term covers many kinds of traffic including network traffic, air traffic, marine traffic and rail traffic, but it is used narrowly to mean only road traffic. Rules of the road and driving etiquette are the general practices and procedures that road users are required to follow; these rules apply to all road users, though they are of special importance to motorists and cyclists.
These rules govern interactions with pedestrians. The basic traffic rules are defined by an international treaty under the authority of the United Nations, the 1968 Vienna Convention on Road Traffic. Not all countries are signatory to the convention and among signatories, local variations in practice may be found. There are unwritten local rules of the road, which are understood by local drivers; as a general rule, drivers are expected to avoid a collision with another vehicle and pedestrians, regardless of whether or not the applicable rules of the road allow them to be where they happen to be. In addition to the rules applicable by default, traffic signs and traffic lights must be obeyed, instructions may be given by a police officer, either or as road traffic control around a construction zone, accident, or other road disruption; these rules should be distinguished from the mechanical procedures required to operate one's vehicle. See driving. Traffic going in opposite directions should be separated in such a way that they do not block each other's way.
The most basic rule is. In many countries, the rules of the road are codified, setting out the legal requirements and punishments for breaking them. In the United Kingdom, the rules are set out in the Highway Code, which includes not only obligations but advice on how to drive sensibly and safely. In the United States, traffic laws are regulated by the states and municipalities through their respective traffic codes. Most of these are based at least in part on the Uniform Vehicle Code, but there are variations from state to state. In states such as Florida, traffic law and criminal law are separate, unless someone flees a scene of an accident, commits vehicular homicide or manslaughter, they are only guilty of a minor traffic offense. However, states such as South Carolina have criminalized their traffic law, so, for example, one is guilty of a misdemeanor for travelling 5 miles over the speed limit. Vehicles come into conflict with other vehicles and pedestrians because their intended courses of travel intersect, thus interfere with each other's routes.
The general principle that establishes who has the right to go first is called "right of way", or "priority". It establishes who has the right to use the conflicting part of the road and who has to wait until the other does so. Signs, signals and other features are used to make priority explicit; some signs, such as the stop sign, are nearly universal. When there are no signs or markings, different rules are observed depending on the location; these default priority rules differ between countries, may vary within countries. Trends toward uniformity are exemplified at an international level by the Vienna Convention on Road Signs and Signals, which prescribes standardized traffic control devices for establishing the right of way where necessary. Crosswalks are common in populated areas, may indicate that pedestrians have priority over vehicular traffic. In most modern cities, the traffic signal is used to establish the right of way on the busy roads, its primary purpose is to give each road a duration of time in which its traffic may use the intersection in an organized way.
General Services Administration
The General Services Administration, an independent agency of the United States government, was established in 1949 to help manage and support the basic functioning of federal agencies. GSA supplies products and communications for U. S. government offices, provides transportation and office space to federal employees, develops government-wide cost-minimizing policies and other management tasks. GSA employs about 12,000 federal workers and has an annual operating budget of $20.9 billion. GSA oversees $66 billion of procurement annually, it contributes to the management of about $500 billion in U. S. federal property, divided chiefly among 8,700 owned and leased buildings and a 215,000 vehicle motor pool. Among the real estate assets managed by GSA are the Ronald Reagan Building and International Trade Center in Washington, D. C. – the largest U. S. federal building after the Pentagon – and the Hart-Dole-Inouye Federal Center. GSA's business lines include the Federal Acquisition Service and the Public Buildings Service, as well as several Staff Offices including the Office of Government-wide Policy, the Office of Small Business Utilization, the Office of Mission Assurance.
As part of FAS, GSA's Technology Transformation Services helps federal agencies improve delivery of information and services to the public. Key initiatives include FedRAMP, Cloud.gov, the USAGov platform, Data.gov, Performance.gov, Challenge.gov. GSA is a member of the Procurement G6, an informal group leading the use of framework agreements and e-procurement instruments in public procurement. In 1947 President Harry Truman asked former President Herbert Hoover to lead what became known as the Hoover Commission to make recommendations to reorganize the operations of the federal government. One of the recommendations of the commission was the establishment of an "Office of the General Services." This proposed office would combine the responsibilities of the following organizations: U. S. Treasury Department's Bureau of Federal Supply U. S. Treasury Department's Office of Contract Settlement National Archives Establishment All functions of the Federal Works Agency, including the Public Buildings Administration and the Public Roads Administration War Assets AdministrationGSA became an independent agency on July 1, 1949, after the passage of the Federal Property and Administrative Services Act.
General Jess Larson, Administrator of the War Assets Administration, was named GSA's first Administrator. The first job awaiting Administrator Larson and the newly formed GSA was a complete renovation of the White House; the structure had fallen into such a state of disrepair by 1949 that one inspector of the time said the historic structure was standing "purely from habit." Larson explained the nature of the total renovation in depth by saying, "In order to make the White House structurally sound, it was necessary to dismantle, I mean dismantle, everything from the White House except the four walls, which were constructed of stone. Everything, except the four walls without a roof, was stripped down, that's where the work started." GSA worked with President Truman and First Lady Bess Truman to ensure that the new agency's first major project would be a success. GSA completed the renovation in 1952. In 1986 GSA headquarters, U. S. General Services Administration Building, located at Eighteenth and F Streets, NW, was listed on the National Register of Historic Places, at the time serving as Interior Department offices.
In 1960 GSA created the Federal Telecommunications System, a government-wide intercity telephone system. In 1962 the Ad Hoc Committee on Federal Office Space created a new building program to address obsolete office buildings in Washington, D. C. resulting in the construction of many of the offices that now line Independence Avenue. In 1970 the Nixon administration created the Consumer Product Information Coordinating Center, now part of USAGov. In 1974 the Federal Buildings Fund was initiated, allowing GSA to issue rent bills to federal agencies. In 1972 GSA established the Automated Data and Telecommunications Service, which became the Office of Information Resources Management. In 1973 GSA created the Office of Federal Management Policy. GSA's Office of Acquisition Policy centralized procurement policy in 1978. GSA was responsible for emergency preparedness and stockpiling strategic materials to be used in wartime until these functions were transferred to the newly-created Federal Emergency Management Agency in 1979.
In 1984 GSA introduced the federal government to the use of charge cards, known as the GMA SmartPay system. The National Archives and Records Administration was spun off into an independent agency in 1985; the same year, GSA began to provide governmentwide policy oversight and guidance for federal real property management as a result of an Executive Order signed by President Ronald Reagan. In 2003 the Federal Protective Service was moved to the Department of Homeland Security. In 2005 GSA reorganized to merge the Federal Supply Service and Federal Technology Service business lines into the Federal Acquisition Service. On April 3, 2009, President Barack Obama nominated Martha N. Johnson to serve as GSA Administrator. After a nine-month delay, the United States Senate confirmed her nomination on February 4, 2010. On April 2, 2012, Johnson resigned in the wake of a management-deficiency report that detailed improper payments for a 2010 "Western Regions" training conference put on by the Public Buildings Service in Las Vegas.
In July 1991 GSA contractors began the excavation of what is now the Ted Weiss Federal Building in New York City. The planning for that buildin
Telecommunication is the transmission of signs, messages, writings and sounds or information of any nature by wire, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology, it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term telecommunications is used in its plural form because it involves many different technologies. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, loud whistles. 20th- and 21st-century technologies for long-distance communication involve electrical and electromagnetic technologies, such as telegraph and teleprinter, radio, microwave transmission, fiber optics, communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909, other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included Charles Wheatstone and Samuel Morse, Alexander Graham Bell, Edwin Armstrong and Lee de Forest, as well as Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth; the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, the Latin communicare, meaning to share. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié. Communication was first used as an English word in the late 14th century, it comes from Old French comunicacion, from Latin communicationem, noun of action from past participle stem of communicare "to share, divide out.
Homing pigeons have been used throughout history by different cultures. Pigeon post had Persian roots, was used by the Romans to aid their military. Frontinus said; the Greeks conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. In the early 19th century, the Dutch government used the system in Sumatra, and in 1849, Paul Julius Reuter started a pigeon service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. In the Middle Ages, chains of beacons were used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London. In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris.
However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres. As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. On 25 July 1837 the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke, English scientist Sir Charles Wheatstone. Both inventors viewed their device as "an improvement to the electromagnetic telegraph" not as a new device. Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837, his code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was completed on 27 July 1866, allowing transatlantic telecommunication for the first time; the conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849.
However Meucci's device was of little practical value because it relied upon the electrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said. The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Starting in 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean; this was the start of wireless telegraphy by radio. Voice and music had little early success. World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar. Development of stereo FM broadcasting of radio
Equalization or equalisation is the process of adjusting the balance between frequency components within an electronic signal. The most well known use of equalization is in sound recording and reproduction but there are many other applications in electronics and telecommunications; the circuit or equipment used to achieve equalization is called an equalizer. These devices strengthen or weaken the energy of specific frequency bands or "frequency ranges". In sound recording and reproduction, equalization is the process used to alter the frequency response of an audio system using linear filters. Most hi-fi equipment uses simple filters to make bass and treble adjustments. Graphic and parametric equalizers have much more flexibility in tailoring the frequency content of an audio signal. Since equalizers "adjust the amplitude of audio signals at particular frequencies," they are, "in other words, frequency-specific volume knobs."In the field of audio electronics, the term "equalization" has come to include the adjustment of frequency responses for practical or aesthetic reasons resulting in a net response, not "flat".
The term EQ refers to this variant of the term. Stereos and basic guitar amplifiers have adjustable equalizers which boost or cut bass or treble frequencies. Mid- to high-priced guitar and bass amplifiers have more bands of frequency control, such as bass, mid-range and treble or bass, low-mid, high-mid, treble; some amps have an additional knob for controlling high frequencies. Broadcast and recording studios use sophisticated equalizers capable of much more detailed adjustments, such as eliminating unwanted sounds or making certain instruments or voices more prominent. Equalizers are used in recording studios, radio studios and production control rooms, live sound reinforcement and in instrument amplifiers, such as guitar amplifiers, to correct or adjust the response of microphones, instrument pick-ups and hall acoustics. Equalization may be used to eliminate or reduce unwanted sounds, make certain instruments or voices more prominent, enhance particular aspects of an instrument's tone, or combat feedback in a public address system.
Equalizers are used in music production to adjust the timbre of individual instruments and voices by adjusting their frequency content and to fit individual instruments within the overall frequency spectrum of the mix. The most common equalizers in music production are parametric, semi-parametric, graphic and program equalizers. Graphic equalizers are included in consumer audio equipment and software which plays music on home computers. Parametric equalizers require more expertise than graphic equalizers, they can provide more specific compensation or alteration around a chosen frequency; this may be used in order to boost certain frequencies. For example, an acoustic guitarist who finds that her instrument sounds too "boomy" may ask the audio engineer to cut the low frequencies to correct this issue; the concept of equalization was first applied in correcting the frequency response of telephone lines using passive networks. Equalization was used to "compensate for" the uneven frequency response of an electric system by applying a filter having the opposite response, thus restoring the fidelity of the transmission.
A plot of the system's net frequency response would be a flat line, as its response at any frequency would be equal to its response at any other frequency. Hence the term "equalization." Much the concept was applied in audio engineering to adjust the frequency response in recording and live sound reinforcement systems. Sound engineers correct the frequency response of a sound system so that the frequency balance of the music as heard through speakers better matches the original performance picked up by a microphone. Audio amplifiers have long had controls to modify their frequency response; these are most in the form of variable bass and treble controls, switches to apply low-cut or high-cut filters for elimination of low frequency "rumble" and high frequency "hiss" respectively. Graphic equalizers and other equipment developed for improving fidelity have since been used by recording engineers to modify frequency responses for aesthetic reasons. Hence in the field of audio electronics the term "equalization" is now broadly used to describe the application of such filters regardless of intent.
This broad definition therefore includes all linear filters at the disposal of a listener or engineer. A British EQ or British style equalizer is one with similar properties to those on consoles made in the UK by companies such as Amek and Soundcraft from the 1950s through to the 1970s. On, as other manufacturers started to market their products, these British companies began touting their equalizers as being a cut above the rest. Today, many non-British companies such as Behringer and Mackie advertise British EQ on their equipment. A British style EQ seeks to replicate the qualities of the expensive British mixing consoles. Filtering audio frequencies dates back at least to acoustic telegraphy and multiplexing in general. Audio electronic equipment evolved to incorporate filtering elements as consoles in radio stations began to be used for recording as much as broadcast. Early filters included basic bass and treble controls featuring fixed frequency centers, fixed levels of cut or boost; these filters
Probability is the measure of the likelihood that an event will occur. See glossary of probability and statistics. Probability quantifies as a number between 0 and 1, loosely speaking, 0 indicates impossibility and 1 indicates certainty; the higher the probability of an event, the more it is that the event will occur. A simple example is the tossing of a fair coin. Since the coin is fair, the two outcomes are both probable; these concepts have been given an axiomatic mathematical formalization in probability theory, used in such areas of study as mathematics, finance, science, artificial intelligence/machine learning, computer science, game theory, philosophy to, for example, draw inferences about the expected frequency of events. Probability theory is used to describe the underlying mechanics and regularities of complex systems; when dealing with experiments that are random and well-defined in a purely theoretical setting, probabilities can be numerically described by the number of desired outcomes divided by the total number of all outcomes.
For example, tossing a fair coin twice will yield "head-head", "head-tail", "tail-head", "tail-tail" outcomes. The probability of getting an outcome of "head-head" is 1 out of 4 outcomes, or, in numerical terms, 1/4, 0.25 or 25%. However, when it comes to practical application, there are two major competing categories of probability interpretations, whose adherents possess different views about the fundamental nature of probability: Objectivists assign numbers to describe some objective or physical state of affairs; the most popular version of objective probability is frequentist probability, which claims that the probability of a random event denotes the relative frequency of occurrence of an experiment's outcome, when repeating the experiment. This interpretation considers probability to be the relative frequency "in the long run" of outcomes. A modification of this is propensity probability, which interprets probability as the tendency of some experiment to yield a certain outcome if it is performed only once.
Subjectivists assign numbers per subjective probability. The degree of belief has been interpreted as, "the price at which you would buy or sell a bet that pays 1 unit of utility if E, 0 if not E." The most popular version of subjective probability is Bayesian probability, which includes expert knowledge as well as experimental data to produce probabilities. The expert knowledge is represented by some prior probability distribution; these data are incorporated in a likelihood function. The product of the prior and the likelihood, results in a posterior probability distribution that incorporates all the information known to date. By Aumann's agreement theorem, Bayesian agents whose prior beliefs are similar will end up with similar posterior beliefs. However, sufficiently different priors can lead to different conclusions regardless of how much information the agents share; the word probability derives from the Latin probabilitas, which can mean "probity", a measure of the authority of a witness in a legal case in Europe, correlated with the witness's nobility.
In a sense, this differs much from the modern meaning of probability, which, in contrast, is a measure of the weight of empirical evidence, is arrived at from inductive reasoning and statistical inference. The scientific study of probability is a modern development of mathematics. Gambling shows that there has been an interest in quantifying the ideas of probability for millennia, but exact mathematical descriptions arose much later. There are reasons for the slow development of the mathematics of probability. Whereas games of chance provided the impetus for the mathematical study of probability, fundamental issues are still obscured by the superstitions of gamblers. According to Richard Jeffrey, "Before the middle of the seventeenth century, the term'probable' meant approvable, was applied in that sense, unequivocally, to opinion and to action. A probable action or opinion was one such as sensible people would undertake or hold, in the circumstances." However, in legal contexts especially,'probable' could apply to propositions for which there was good evidence.
The sixteenth century Italian polymath Gerolamo Cardano demonstrated the efficacy of defining odds as the ratio of favourable to unfavourable outcomes. Aside from the elementary work by Cardano, the doctrine of probabilities dates to the correspondence of Pierre de Fermat and Blaise Pascal. Christiaan Huygens gave the earliest known scientific treatment of the subject. Jakob Bernoulli's Ars Conjectandi and Abraham de Moivre's Doctrine of Chances treated the subject as a branch of mathematics. See Ian Hacking's The Emergence of Probability and James Franklin's The Science of Conjecture for histories of the early development of the concept of mathematical probability; the theory of errors may be traced back to Roger Cotes's Opera Miscellanea, but a memoir prepared by Thomas Simpson in 1755 first applied the theory to the discussion of errors of observation. The reprint of this memoir lays down the axioms that positive and negative errors are probable, that certain assignable limits define the range of all errors.
Simpson discusses c
Agner Krarup Erlang
Agner Krarup Erlang was a Danish mathematician and engineer, who invented the fields of traffic engineering and queueing theory. By the time of his early death at the age of 51, Erlang had created the field of telephone networks analysis, his early work in scrutinizing the use of local and trunk telephone line usage in a small community to understand the theoretical requirements of an efficient network led to the creation of the Erlang formula, which became a foundational element of modern telecommunication network studies. Erlang was born near Tarm, in Jutland, he was the son of a schoolmaster, a descendant of Thomas Fincke on his mother's side. At age 14, he passed the Preliminary Examination of the University of Copenhagen with distinction, after receiving dispensation to take it because he was younger than the usual minimum age. For the next two years he taught alongside his father. A distant relative provided free board and lodging, Erlang prepared for and took the University of Copenhagen entrance examination in 1896, passed with distinction.
He won a scholarship to the University and majored in mathematics, studied astronomy and chemistry. He graduated in 1901 over the next 7 years taught at several schools, he maintained his interest in mathematics, received an award for a paper that he submitted to the University of Copenhagen. He was a member of the Danish Mathematicians' Association and through this met amateur mathematician Johan Jensen, the Chief Engineer of the Copenhagen Telephone Company, an offshoot of the International Bell Telephone Company. Erlang worked for the CTC from 1908 for 20 years, until his death in Copenhagen after an abdominal operation, he was an associate of the British Institution of Electrical Engineers. While working for the CTC, Erlang was presented with the classic problem of determining how many circuits were needed to provide an acceptable telephone service, his thinking went further by finding how many telephone operators were needed to handle a given volume of calls. Most telephone exchanges used human operators and cord boards to switch telephone calls by means of jack plugs.
Out of necessity, Erlang was a hands-on researcher. He was prepared to climb into street manholes to do so, he was an expert in the history and calculation of the numerical tables of mathematical functions logarithms. He devised new calculation methods for certain forms of tables, he developed his theory of telephone traffic over several years. His significant publications include: 1909 – "The Theory of Probabilities and Telephone Conversations", which proves that the Poisson distribution applies to random telephone traffic. 1917 – "Solution of some Problems in the Theory of Probabilities of Significance in Automatic Telephone Exchanges", which contains his classic formulae for call loss and waiting timeThese and other notable papers were translated into English and German. His papers were prepared in a brief style and can be difficult to understand without a background in the field. One researcher from Bell Telephone Laboratories is said to have learned Danish to study them; the British Post Office accepted his formula as the basis for calculating circuit facilities.
In 1946, the CCITT named the international unit of telephone traffic "the Erlang". A statistical distribution and programming language listed below have been named in his honour. Erlang – a unit of communication activity Erlang distribution – a statistical probability distribution Erlang programming language – developed by Ericsson for large industrial real-time systems Queueing theory Teletraffic engineering Angus, Ian. An Introduction to Erlang B and Erlang C Brockmeyer, E. Halstrøm, H. L. & Jensen, Arne. "The Life and Works of A. K. Erlang", O'Connor, John J.. Plus Magazine. Agner Krarup Erlang, Plus Magazine online, University of Cambridge, U. K. May 1997. Retrieved 22 November 2009 "Erlang Distribution". Example. Statistical Distributions. Xycoon. "Telefon-Ventetider. Et Stykke Sandsynlighedsregning". Matematisk Tidsskrift. Project Runeberg. 1920