Misplaced Pages

#7992

28-402: The field was created by the work of A. K. Erlang for circuit-switched networks but is applicable to packet-switched networks , as they both exhibit Markovian properties, and can hence be modeled by e.g. a Poisson arrival process. The crucial observation in traffic engineering is that in large systems the law of large numbers can be used to make the aggregate properties of a system over

56-522: A basic tariff system but, as telecommunication advances, tariff structures become increasingly more complex. Usually there is the option of calling collect (in the UK known as reversing charges ), where responsibility for charges normally paid by the caller is accepted by the recipient. Tariffs also depend on the bandwidth provided. For example, dial-up modem connections are charged at normal telephone costs, but connections such as DSL are usually charged using

84-496: A completely different accounting system due to their always on nature. Increasingly, in some countries, the call charges are fixed at a monthly rate and included as a supplement to the standing charges, known as inclusive calls . Emergency calls can invariably be made without charge. Most countries have a number sequence that enable the caller to make calls without charge, sometimes known as free calls or freephone , these are usually used by companies for their sales line (in

112-435: A long period of time much more predictable than the behaviour of individual parts of the system. The measurement of traffic in a public switched telephone network (PSTN) allows network operators to determine and maintain the quality of service (QoS) and in particular the grade of service (GoS) that they promise their subscribers. The performance of a network depends on whether all origin-destination pairs are receiving

140-409: A loss of traffic and therefore revenue; if they charge too little, they will have insufficient capital to maintain the network's quality of service . Over time this will result in customer attrition . Tariffing systems vary from country to country and company to company, but in general they are based on several simple principles. Tariffs are generally made up of two components: These components form

168-523: A satisfactory service. Networks are handled as: Congestion is defined as the situation when exchanges or circuit groups are inundated with calls and are unable to serve all the subscribers. Special attention must be given to ensure that such high loss situations do not arise. To help determine the probability of congestion occurring, operators should use the Erlang formulas or the Engset calculation . Exchanges in

196-578: A scholarship to the university and majored in mathematics , and also studied astronomy , physics and chemistry . He graduated in 1901 with an MA and over the next 7 years taught at several schools. He maintained his interest in mathematics, and received an award for a paper that he submitted to the University of Copenhagen. He was a member of the Danish Mathematicians' Association (DMF) and through this met amateur mathematician Johan Jensen ,

224-470: A supporting network, it carries all the signalling messages necessary to set up, break down or provide extra services. The signalling enables the PSTN to control the manner in which traffic is routed from one location to another. Transmission and switching of calls is performed using the principle of time-division multiplexing (TDM). TDM allows multiple calls to be transmitted along the same physical path, reducing

252-595: A very brief style and can be difficult to understand without a background in the field. One Bell Telephone Laboratories researcher 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 also been named in his honour. Erlang also made an important contribution to physiologic modeling with

280-471: Is noticeable, for both business and residential customers on international or local calls. This means that it is often the case that more revenue is achievable at lower prices, that is, E < -1. Internet traffic research show that the traffic intensity is directly affected by the tariffs charged in connecting customers to their Internet Service Provider (ISP). For example, a circuit-switched network provider charges different tariffs at different times of

308-454: Is the possibility that extremely infrequent occurrences are more likely than anticipated. This situation is known as long-tail traffic . In some designs, the network might be required to withstand the unanticipated traffic. As mentioned in the introduction, the purpose of teletraffic theory is to reduce cost in telecommunications networks. An important tool in achieving this goal is forecasting . Forecasting allows network operators to calculate

SECTION 10

#1732851001008

336-537: The Krogh-Erlang capillary cylinder model describing oxygen supply to living tissue. Tariffing A telecommunications tariff is an open contract between a telecommunications service provider and the public, filed with a regulating body such as state and municipal Public Utilities Commissions and federal entities such as the Federal Communications Commission (FCC). Such tariffs outline

364-830: The Chief Engineer of the Copenhagen Telephone Company ( KTAS in Danish), an offshoot of the International Bell Telephone Company . Erlang worked for the Copenhagen Telephone Company from 1908 for almost 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

392-535: The PSTN make use of trunking concepts to help minimize the cost of the equipment to the operator. Modern switches generally have full availability and do not make use of grading concepts. Overflow systems make use of alternative routing circuit groups or paths to transfer excess traffic and thereby reduce the possibility of congestion. A very important component in PSTNs is the SS7 network used to route signalling traffic. As

420-531: 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, and Erlang prepared for and took the University of Copenhagen entrance examination in 1896, and passed with distinction. He won

448-534: The UK these are 0800 and 0808 numbers and in the US they are 800, 888, 877, 866, 855, 844 and 833). Tariffs substantially in excess of the normal rate, known as premium rate , are used for information services, competition entries and pornography calls. These telecommunications tariffs originated with the advent of public phone service. In these times, the services provided were less complex, and customers were able to simply read

476-437: 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 then 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 would conduct measurements and

504-577: The cost of infrastructure. A good example of the use of teletraffic theory in practice is in the design and management of a call center . Call centers use teletraffic theory to increase the efficiency of their services and overall profitability through calculating how many operators are really needed at each time of the day. Queueing systems used in call centers have been studied as a science. For example, completed calls are put on hold and queued until they can be served by an operator. If callers are made to wait too long, they may lose patience and default from

532-409: The need to file tariffs with federal regulatory agencies. However, to continue operating, many state and local governments still require telecommunications tariffs. Call minutes are highly elastic against price , this means that the demand for call minutes varies greatly according to price. A slight decrease in price leads to a great increase in call minutes. The higher the price, the more this effect

560-399: The potential cost of a new network / service for a given QoS during the planning and design stage, thereby ensuring that costs are kept to a minimum. An important method used in forecasting is simulation , which is described as the most common quantitative modelling technique in use today. An important reason for this is that computing power has become far more accessible, making simulation

588-595: The preferred analytical method for problems that are not easily solved mathematically. As in any business environment, network operators must charge tariffs for their services. These charges must be balanced with the supplied QoS. When operators supply services internationally, this is described as trade in services and is governed by the General Agreement on Trade in Services (GATS). Agner Krarup Erlang Agner Krarup Erlang (1 January 1878 – 3 February 1929)

SECTION 20

#1732851001008

616-444: The queue (hang up), resulting in no service being provided. Teletraffic engineering is a well-understood discipline in the traditional voice network, where traffic patterns are established, growth rates can be predicted, and vast amounts of detailed historical data are available for analysis. However, in modern broadband networks , the teletraffic engineering methodologies used for voice networks are inappropriate. Of great importance

644-493: The service. However, telecommunications service providers must be careful not to over-price each service, as prices have a direct influence on demand for that service (see supply and demand ). Such an operator must constantly balance the need to provide cheaper rates, especially if there is strong competition, with the cost of maintaining the service at an optimum quality that is acceptable to the customer. If an operator charges too much, it risks alienating its customers, resulting in

672-488: The tariffs to understand how much they would be charged for each type of call. Additionally, only a few telecommunication industries participated in the market, facilitating decision-making. As the market became increasingly competitive, the need for regulation decreased. In 2001, the U.S. Federal Communications Commission (FCC) declared the telecommunications market was fully competitive in the United States, and eliminated

700-531: The terms and conditions of providing telecommunications service to the public including rates, fees, and charges. At a minimum, tariffs imposed must cover the cost of providing the service to the consumer. The consumer may be the final user or an intermediary such as a service provider . If a telecommunications operator cannot recover its costs, it will make a loss and the company will go bankrupt. Tariffs must also be used to cover maintenance , additional research and other indirect costs associated with providing

728-495: The use of local, exchange 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 telecommunications network studies. Erlang was born at Lønborg, near Tarm , in Jutland . He was the son of a schoolmaster, and a descendant of Thomas Fincke on his mother's side. At age 14, he passed

756-452: Was a Danish mathematician , statistician and engineer , who invented the fields of traffic engineering and queueing theory . Erlang's 1909 paper, and subsequent papers over the decades, are regarded as containing some of most important concepts and techniques for queueing theory. By the time of his relatively early death at the age of 51, Erlang had created the field of telephone networks analysis. His early work in scrutinizing

784-469: Was prepared to climb into street manholes to do so. He was also an expert in the history and calculation of the numerical tables of mathematical functions, particularly 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: These and other notable papers were translated into English, French and German. His papers were prepared in

#7992