1.
Telecommunication
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Telecommunication is the transmission of signs, signals, messages, writings, images and sounds or intelligence of any nature by wire, radio, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology and 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. The term is used in its plural form, telecommunications. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, and loud whistles. Zworykin, John Logie Baird and Philo Farnsworth, the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, and the Latin communicare, meaning to share. Its modern use is adapted from the French, because its use was recorded in 1904 by the French engineer. Communication was first used as an English word in the late 14th century, in the Middle Ages, chains of beacons were commonly used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could pass a single bit of information. One notable instance of their use was during the Spanish Armada, 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. Homing pigeons have occasionally used throughout history by different cultures. Pigeon post is thought to have Persians roots and was used by the Romans to aid their military, frontinus said that Julius Caesar used pigeons as messengers in his conquest of Gaul. The Greeks also 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 Java and Sumatra. And in 1849, Paul Julius Reuter started a 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. Sir Charles Wheatstone and Sir William Fothergill Cooke invented the telegraph in 1837. Also, the first commercial electrical telegraph is purported to have constructed by Wheatstone and Cooke. 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
2.
Telephone
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A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. In 1876, Scottish emigrant Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice and this instrument was further developed by many others. The telephone was the first device in history that people to talk directly with each other across large distances. Telephones rapidly became indispensable to businesses, government, and households, the essential elements of a telephone are a microphone to speak into and an earphone which reproduces the voice in a distant location. Until approximately the 1970s most telephones used a dial, which was superseded by the modern DTMF push-button dial. The receiver and transmitter are usually built into a handset which is held up to the ear, the dial may be located either on the handset, or on a base unit to which the handset is connected. The transmitter converts the sound waves to electrical signals which are sent through the network to the receiving phone. The receiving telephone converts the signals into audible sound in the receiver, telephones permit duplex communication, meaning they allow the people on both ends to talk simultaneously. The first telephones were connected to each other from one customers office or residence to another customers location. Being impractical beyond just a few customers, these systems were replaced by manually operated centrally located switchboards. For greater mobility, various systems were developed for transmission between mobile stations on ships and automobiles in the middle 20th century. Hand-held mobile phone]s was introduced for personal service starting in 1973, by the late 1970s several mobile telephone networks operated around the world. In 1983, the Advanced Mobile Phone System was launched, offering a standardized technology providing portability for users far beyond the residence or office. These analog cellular system evolved into digital networks with better security, greater capacity, better regional coverage, the public switched telephone network, with its hierarchical system of many switching centers, interconnects telephones around the world for communication with each other. With the standardized international numbering system, E.164, each line has an identifying telephone number. Although originally designed for voice communications, convergence has enabled most modern cell phones to have many additional capabilities. Since 1999, the trend for mobile phones is smartphones that integrate all mobile communication, a traditional landline telephone system, also known as plain old telephone service, commonly carries both control and audio signals on the same twisted pair of insulated wires, the telephone line. The control and signaling equipment consists of three components, the ringer, the hookswitch, and a dial, the ringer, or beeper, light or other device, alerts the user to incoming calls
3.
Telephone exchange
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A telephone exchange is a telecommunications system used in the public switched telephone network or in large enterprises. In historical perspective, telecommunication terms have been used with different semantics over time, the term telephone exchange is often used synonymously with central office, a Bell System term. Often, an office is defined as a building used to house the inside plant equipment of potentially several telephone exchanges. Such an area has also referred to as the exchange. Central office locations may also be identified in North America as wire centers, All central offices within a larger region, typically aggregated by state, were assigned a common numbering plan area code. For corporate or enterprise use, a telephone exchange is often referred to as a private branch exchange. Smaller installations might deploy a PBX or key telephone system in the office of a receptionist and this made it possible for subscribers to call each other at homes, businesses, or public spaces. These made telephony an available and comfortable communication tool for everyday use, one of the first to propose a telephone exchange was Hungarian Tivadar Puskás in 1877 while he was working for Thomas Edison. The first experimental telephone exchange was based on the ideas of Puskás, the worlds first commercial telephone exchange opened on November 12,1877 in Friedrichsberg close to Berlin. George W. Coy designed and built the first commercial US telephone exchange opened in New Haven. The switchboard was built from carriage bolts, handles from teapot lids and bustle wire, Charles Glidden is also credited with establishing an exchange in Lowell, MA. with 50 subscribers in 1878. In Europe other early telephone exchanges were based in London and Manchester, Belgium had its first International Bell exchange a year later. In 1887 Puskás introduced the multiplex switchboard, later exchanges consisted of one to several hundred plug boards staffed by switchboard operators. Each operator sat in front of a panel containing banks of ¼-inch tip-ring-sleeve jacks. In front of the jack panel lay a horizontal panel containing two rows of patch cords, each connected to a cord circuit. When a calling party lifted the receiver, the loop current lit a signal lamp near the jack. The operator responded by inserting the rear cord into the jack and switched her headset into the circuit to ask, Number. For a local call, the operator inserted the front cord of the pair into the partys local jack
4.
Trunking
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In telecommunications, trunking is a method for a system to provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually. This is analogous to the structure of a tree with one trunk, examples of this include telephone systems and the two-way radios commonly used by police agencies. More recently port trunking has been applied in computer networking as well, a trunk is a single transmission channel between two points, each point being either the switching center or the node. In two-way radio communications, trunking refers to the ability of transmissions to be served by free channels whose availability is determined by algorithmic protocols, the cashier represents each radio channel, and each customer represents a radio user transmitting on their radio. Trunked radio systems pool all of the cashiers into one group, in a TRS, individual transmissions in any conversation may take place on several different channels. In the shopping analogy, this is as if a family of shoppers checks out all at once and are assigned different cashiers by the traffic manager, similarly, if a single shopper checks out more than once, they may be assigned a different cashier each time. Trunked radio systems provide greater efficiency at the cost of greater management overhead, the store managers orders must be conveyed to all the shoppers. This is done by assigning one or more channels as the control channel. TRSs have grown massively in their complexity since their introduction, and this is similar to the idea of a chain of grocery stores. The shopper generally goes to the nearest grocery store, but if there are complications or congestion, TRSs have greater risks to overcome than conventional radio systems in that a loss of the store manager would cause the systems traffic to no longer be managed. In this case, most of the time the TRS will automatically switch to a control channel, or in more rare circumstances. In spite of these risks, TRSs usually maintain reasonable uptime, trunk lines are used for connecting a private branch exchange to a telephone service provider. When needed they can be used by any telephone connected to the PBX, Trunking saves cost, because there are usually fewer trunk lines than extension lines, since it is unusual in most offices to have all extension lines in use for external calls at once. Trunk lines transmit voice and data in such as analog, T1, E1. The dial tone lines for outgoing calls are called DDCO trunks, in the UK and the Commonwealth countries, a trunk call was the term for long distance calling, involving more than one telephone exchange, in contrast to making a local call. Trunking also refers to the connection of switches and circuits within a telephone exchange, Trunking is closely related to the concept of grading. Trunking allows a group of switches at the same time. Thus the service provider can provide a number of circuits than might otherwise be required, allowing many users to share a smaller number of connections
5.
Switchboard operator
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Each pair of plugs was part of a cord circuit with a switch associated that let the operator participate in the call. Each jack had a light above it that lit when the receiver was lifted. Lines from the office were usually arranged along the bottom row. Switchboard operators are required to have very strong communication skills. Before the advent of automatic exchanges, an operators assistance was required for anything other than calling telephones across a party line. Callers spoke to an operator at a Central Office who then connected a cord to the circuit in order to complete the call. Being in complete control of the call, the operator was in a position to listen to private conversations, automatic, or Dial systems were developed in the 1920s to reduce labor costs as usage increased, and to ensure privacy to the customer. As phone systems became more sophisticated, less direct intervention by the operator was necessary to complete calls. As well as the people that were employed by the networks, operators were required at private branch exchanges to answer incoming telephone calls. Today, most large organizations have direct-dial extensions, smaller workplaces may have an automated system which allows callers to enter the extension of the called party, or a receptionist who answers calls and performs operator duties. Operators employed in healthcare settings have other duties, such as entry, greeting patients and visitors, taking messages, triaging. Experienced, well trained operators generally command a higher salary, in January 1878 George Willard Croy became the worlds first telephone operator when he started working for the Boston Telephone Dispatch company. Emma was hired by Alexander Graham Bell, and reportedly, could remember every number in the directory of the New England Telephone Company. Emma Nutt became the first female telephone operator on 1 September 1878 when she started working for the Boston Telephone Dispatch company, more women began to replace men within this sector of the workforce for several reasons. The companies observed that women were generally more courteous to callers, however, a contributing factor to women entering this workforce was because womens labour was cheap in comparison to mens. Specifically, women were paid from one half to one quarter of a mans salary, attendant console Operator assistance Private branch exchange Telephone operator Telephone switchboard Media related to Telephone operators at Wikimedia Commons
6.
Telephone plug
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A telephone plug is a type of connector used to connect a telephone set to the telephone wiring inside a building, establishing a connection to a telephone network. It is inserted into its counterpart, a jack, commonly affixed to a wall or baseboard. The standard for telephone plugs varies from country to country, though the RJ11 modular connector has become by far the most common. A connection standard, such as RJ11, specifies not only the aspects of an electrical connector. Historically telephones were owned by the telephone company and were usually permanently wired to the telephone line. However, for many installations it was necessary or convenient to provide portable telephone sets that could be moved to a different location within the customers premises, for this purpose telephone companies developed jacks and plugs with a varying number of contacts. 1930, concentric connectors with three contacts were sufficient, but the upgrade of telephone sets to anti-sidetone circuitry required four conductors between the set and the subscriber set. For this purpose, Bell System engineers developed a cube-shaped four-prong plug with uneven prong spacings to avoid improper insertion into the jack and this jack and plug combination later became the standard line connection for portable telephone sets. This type was redesigned as a version in the mid 1960s. The four-prong connector type was superseded by the connector in the 1970s. The installation of a wired telephone set has four connection points, each of which may be hardwired. This connection is the most standardized, and often regulated as the boundary between a telephone and the telephone network. Telephone cord to telephone set base, This connection is not regulated. It is often a 6P4C connector, which is often RJ11, Telephone set base to handset cord, By de facto standard, this is usually a 4P4C connector. Handset cord to handset, The handset end of the straight-through handset cord also uses a 4P4C connector, some of these may be absent, Wired telephones may not have a separate base and handset. The defining characteristic of wireless telephones is that they do not have a cord. A standard specifies both a connector and how it is wired. Sometimes the same connector is used by different countries but wired in different ways, thus cables are not in general compatible between different phones, as the phone base may have a socket with pins 2 and 5, or have an RJ11 socket
7.
Access network
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An access network is a type of telecommunications network which connects subscribers to their immediate service provider. It is contrasted with the network, which connects local providers to each other. The access network may be divided between feeder plant or distribution network, and drop plant or edge network. An access network or outside plant refers to the series of wires, cables, the local exchange contains banks of automated switching equipment to direct a call or connection to the consumer. The access network is one of the oldest assets a telecoms operator owns, and is constantly evolving, growing as new customers are connected. This makes the network one of the most complex networks in the world to maintain. In 2007–2008 many telecommunication operators experienced increasing problems maintaining the quality of the records which describe the network, in 2006, according to an independent Yankee Group report, globally operators experience profit leakage in excess of €15 Billion each year. The access network is perhaps the most valuable asset an operator owns. Access networks consist largely of pairs of wires, each traveling in a direct path between the exchange and the customer. In some instances, these wires may even be aluminum, the use of which was common in the 1960s and 1970s following an increase in the cost of copper. As it happened, the increase was temporary, but the effect of this decision is still felt today because the aluminum wires oxidize. Operators offered additional services such as xDSL based broadband and IPTV to guarantee profit, the access network is again the main barrier to achieving these profits since operators worldwide have accurate records of only 40% to 60% of the network. Access networks around the world evolved to more and more optical fiber technology. The process of communicating with a network begins with an access attempt, an access attempt itself begins with an issuance of an access request by an access originator. Access failure can be the result of access outage, user blocking, incorrect access, Access denial can include, Access failure caused by the issuing of a system blocking signal by a communications system that does not have a call-originator camp-on feature. Access failure caused by exceeding the maximum time and nominal system access time fraction during an access attempt. Although some access charges are billed directly to interexchange carriers, a significant percentage of all charges are paid by the local end users. Faster PON standards generally support a split ratio of users per PON
8.
Telephone call
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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 10,1876 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 and this event has been called Bells 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, the call may use land line, 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 callers wireline phone is connected directly to the party, when the caller takes their telephone off-hook. This is called a hot line or ringdown, otherwise, the calling party is usually given a tone to indicate they should begin dialing the desired number. In some cases, if the party cannot dial calls directly. Calls may be placed through a public network provided by a telephone company or a private network called a PBX. In most cases a private network is connected to the network in order to allow PBX users to dial the outside world. 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 QSIG, DPNSS or variants. Some types of calls are not charged, such as local calls dialed directly by a subscriber in Canada. In most other areas, all calls are charged a fee for the connection. Fees depend on the provider of the service, the type of service being used, in most circumstances, the calling party pays this fee. However, in circumstances such as a reverse charge or collect call. In some circumstances, the caller pays a flat charge for the telephone connection. The caller then rotary dials or presses buttons for the number needed to complete the call. The second phone makes a noise to alert its owner
9.
Telephone number
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A telephone number serves as an address for switching telephone calls using a system of destination code routing. Telephone numbers are entered or dialed by a party on the originating telephone set. The exchange completes the call either to another locally connected subscriber or via the PSTN to the called party, telephone numbers were first used in 1879 in Lowell, Massachusetts when they replaced the request for subscriber names by callers connecting to the switchboard operator. Telephone numbers are dialed in conjunction with other signaling code sequences, such as vertical service codes. When telephone numbers were first used they were short, from one to three digits, and were communicated orally to a switchboard operator when initiating a call. As telephone systems have grown and interconnected to encompass worldwide communication, in addition to telephones, they have been used to access other devices, such as computer modems, pagers, and fax machines. The number contains the necessary to identify uniquely the intended endpoint for the telephone call. Each such endpoint must have a number within the public switched telephone network. Most countries use fixed length numbers and therefore the number of endpoints determines the length of the telephone number. It is also possible for each subscriber to have a set of numbers for the endpoints most often used. These shorthand or speed calling numbers are translated to unique telephone numbers before the call can be connected. Some special services have their own short numbers The dialing plan in some areas permits dialing numbers in the local calling area without using area code or city code prefixes. For example, a number in North America consists of a three-digit area code, a three-digit central office code. If the area has no area code overlays, seven-digit dialing may be permissible for calls within the area, for each large metro area, all of these lines will share the same prefix, the last digits typically corresponding to the stations frequency, callsign, or moniker. In the international network, the format of telephone numbers is standardized by ITU-T recommendation E.164. This code specifies that the number should be 15 digits or shorter. For most countries, this is followed by a code or city code and the subscriber number. ITU-T recommendation E.123 describes how to represent an international telephone number in writing or print, starting with a plus sign and the country code
10.
Telephone line
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A telephone line or telephone circuit is a single-user circuit on a telephone communication system. Telephone lines are used to deliver landline telephone service and Digital subscriber line phone service to the premises. Telephone overhead lines are connected to the switched telephone network. Modern lines may run underground, and may carry analog or digital signals to the exchange, often the customer end of that wire pair is connected to a data access arrangement, the telephone company end of that wire pair is connected to a telephone hybrid. In most cases, two wires for each telephone line run from a home or other small building to a local telephone exchange. The wires between the box and the exchange are known as the local loop, and the network of wires going to an exchange. The vast majority of houses in the U. S. are wired with 6-position modular jacks with four conductors wired to the junction box with copper wires. Those wires may be connected back to two telephone lines at the local telephone exchange, thus making those jacks RJ14 jacks. More often, only two of the wires are connected to the exchange as one line, and the others are unconnected. In that case, the jacks in the house are RJ11, inside the walls of the house—between the houses outside junction box and the interior wall jacks—the most common telephone cable in new houses is Category 5 cable—4 pairs of 24 AWG solid copper. Inside large buildings, and in the cables that run to the telephone company POP
11.
Integrated Services Digital Network
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It was first defined in 1988 in the CCITT red book. Prior to ISDN, the system was viewed as a way to transport voice. The key feature of ISDN is that it integrates speech and data on the same lines, the ISDN standards define several kinds of access interfaces, such as Basic Rate Interface, Primary Rate Interface, Narrowband ISDN, and Broadband ISDN. It offers circuit-switched connections, and packet-switched connections, in increments of 64 kilobit/s, in some countries, ISDN found major market application for Internet access, in which ISDN typically provides a maximum of 128 kbit/s bandwidth in both upstream and downstream directions. Channel bonding can achieve a data rate, typically the ISDN B-channels of three or four BRIs are bonded. ISDN is employed as the network, data-link and physical layers in the context of the OSI model, or could be considered a suite of digital services existing on layers 1,2, and 3 of the OSI model. In a videoconference, ISDN provides simultaneous voice, video, Integrated services refers to ISDNs ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed and that means an ISDN line can take care of most peoples complete communications needs at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. It also refers to integrated switching and transmission in that telephone switching, the entry level interface to ISDN is the Basic Rate Interface, a 128 kbit/s service delivered over a pair of standard telephone copper wires. The 144 kbit/s payload rate is broken down into two 64 kbit/s bearer channels and one 16 kbit/s signaling channel and this is sometimes referred to as 2B+D. The T interface is an interface between a computing device and a terminal adapter, which is the digital equivalent of a modem. The S interface is a bus that ISDN consumer devices plug into. The R interface defines the point between a device and a terminal adapter which provides translation to and from such a device. BRI-ISDN is very popular in Europe but is less common in North America. It is also common in Japan — where it is known as INS64, the other ISDN access available is the Primary Rate Interface, which is carried over an E1 in most parts of the world. An E1 is 30 B channels of 64 kbit/s, one D channel of 64 kbit/s and this is often referred to as 30B+2D. In North America PRI service is delivered on one or more T1 carriers of 1544 kbit/s, a PRI has 23 B channels and 1 D channel for signalling. Inter-changeably but incorrectly, a PRI is referred to as T1 because it uses the T1 carrier format, a true T1 uses 24 channels of 64 kbit/s of in-band signaling
12.
Digital subscriber line
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Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line, DSL service can be delivered simultaneously with wired telephone service on the same telephone line. This is possible because DSL uses higher frequency bands for data, on the customer premises, a DSL filter on each non-DSL outlet blocks any high-frequency interference to enable simultaneous use of the voice and DSL services. Bit rates of 1 Gbit/s have been reached in trials, in ADSL, the data throughput in the upstream direction is lower, hence the designation of asymmetric service. In symmetric digital subscriber line services, the downstream and upstream data rates are equal, researchers at Bell Labs have reached speeds of 10 Gbit/s, while delivering 1 Gbit/s symmetrical broadband access services using traditional copper telephone lines. These higher speeds are lab results, however, a 2012 survey found that DSL continues to be the dominant technology for broadband access with 364.1 million subscribers worldwide. For a long time it was thought that it was not possible to operate a conventional phone-line beyond low-speed limits, in the 1950s, ordinary twisted-pair telephone-cable often carried four megahertz television signals between studios, suggesting that such lines would allow transmitting many megabits per second. One such circuit in the UK ran some ten miles between the BBC studios in Newcastle-upon-Tyne and the Pontop Pike transmitting station and it was able to give the studios a low quality cue feed but not one suitable for transmission. However, these cables had other impairments besides Gaussian noise, preventing such rates from becoming practical in the field, the 1980s saw the development of techniques for broadband communications that allowed the limit to be greatly extended. A patent was filed in 1979 for the use of existing telephone wires for both telephones and data terminals that were connected to a computer via a digital data carrier system. Joseph W. Lechleiders contribution to DSL was his insight that an asymmetric arrangement offered more than double the capacity of symmetric DSL. ADSL supports two modes of transport—fast channel and interleaved channel, fast channel is preferred for streaming multimedia, where an occasional dropped bit is acceptable, but lags are less so. Interleaved channel works better for file transfers, where the data must be error-free. Older ADSL standards delivered 8 Mbit/s to the customer over about 2 km of unshielded twisted-pair copper wire, distances greater than 2 km significantly reduce the bandwidth usable on the wires, thus reducing the data rate. But ADSL loop extenders increase these distances by repeating the signal, until the late 1990s, the cost of digital signal processors for DSL was prohibitive. All types of DSL employ highly complex digital signal processing algorithms to overcome the inherent limitations of the twisted pair wires. Due to the advancements of very-large-scale integration technology, the cost of the equipment associated with a DSL deployment lowered significantly, the two main pieces of equipment are a digital subscriber line access multiplexer at one end and a DSL modem at the other end. A DSL connection can be deployed over existing cable, such deployment, even including equipment, is much cheaper than installing a new, high-bandwidth fiber-optic cable over the same route and distance
13.
Telephony
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The history of telephony is intimately linked to the invention and development of the telephone. The term is used frequently to refer to computer hardware, software, and computer network systems. In this context the technology is referred to as Internet telephony. The first telephones were connected directly in pairs, each user had a separate telephone wired to the locations he might wish to reach. This quickly became inconvenient and unmanageable when people wanted to communicate with more than a few people, the inventions 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 via one wire pair, 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 the switchboards were manually operated by an attendant, a switchboard operator, when a customer cranked a handle on the telephone, it turned on an indicator on the board in front of the operator who would plug the operator headset into that jack and offer service. The caller had to ask for the party by name, later by number. If the called station answered the operator disconnected their headset and completed the station-to-station circuit, trunk calls were made with the assistance of other operators at other exchangers in the network. In modern times, most telephones are plugged into telephone jacks, the jacks are connected by inside wiring to a drop wire which connects the building to a cable. Cables usually bring a number of drop wires from all over a district access network to one wire center or telephone exchange. Most of the exchanges in the world are interconnected through a system of larger switching systems, today, telephony uses digital technology in the provisioning of telephone services and systems. This advancement has reduced costs in communication, and improved the quality of voice services, the first implementation of this, ISDN, permitted all data transport from end-to-end speedily over telephone lines. This service was made much less important due to the ability to provide digital services based on the IP protocol. The integration of software and computer systems is a major development in the evolution of the automated office. The term is used in describing the services of call centers. Its also sometimes used to describe the ability to use your personal computer to initiate, CTI is not a new concept and has been used in the past in large telephone networks, but only dedicated call centers could justify the costs of the required equipment installation. Dialed Number Identification Service on a scale is wide enough for its implementation to bring value to business or residential telephone usage
14.
Last mile
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More specifically, the last mile refers to the portion of the telecommunications network chain that physically reaches the end-users premises. The word mile is used metaphorically, the length of the last mile link may be more or less than a mile. Because the last mile of a network to the user is conversely the first mile from the premises to the outside world when the user is sending data. The last mile is typically the speed bottleneck in communication networks and this is because retail telecommunication networks have the topology of trees, with relatively few high capacity trunk communication channels branching out to feed many final mile leaves. To resolve, or at least mitigate, the problems involved with attempting to provide enhanced services over the last mile, one example is fixed wireless access, where a wireless network is used instead of wires to connect a stationary terminal to the wireline network. Various solutions are being developed which are seen as an alternative to the last mile of standard incumbent local exchange carriers and these include WiMAX and broadband over power lines. This ISDN30 can carry 30 simultaneous telephone calls and many direct dial telephone numbers, when leaving the telephone exchange, the ISDN30 cable can be buried in the ground, usually in ducting, at very little depth. Loss, therefore, of the last mile link, means the non-delivery of calls, any business with ISDN30 type connectivity must anticipate such failure in its business continuity planning. There are many options, as documented in customer proprietary network information, if the cable is damaged from one telephone exchange to the customer premises most of the calls can be delivered from the surviving route to the customer. Diverse routing is where the carrier can provide more than one route to supply ISDN30 connectivity from the exchange, or exchanges, carrier diversions are usually limited to all of the ISDN30 direct dial telephone numbers being delivered to one single number. Carrier diversions are usually limited to all of the ISDN30 direct dial telephone numbers being delivered to one single number, in the UK Teamphone offers this service in association with British Telecom. By not being in the exchanges, the Teamphone version offers an all or nothing diversion service if required and these are generally carrier-independent and there are a number of companies offering such solutions in the UK and AirNorth Communications in the United States. Hosted numbers is where the carriers or specialist companies can host the customers numbers within their own or the carriers networks, when a diversion service is required, the calls can be routed to alternative numbers. Both carriers and specialist companies offer this type of service in the UK, as demand has escalated, particularly fueled by the widespread adoption of the Internet, the need for economical high-speed access by end-users located at millions of locations has ballooned as well. As requirements have changed, the systems and networks that were initially pressed into service for this purpose have proven to be inadequate. To date, although a number of approaches have been tried, since the integral of the rate of information transfer with respect to time is information quantity, this requirement leads to a corresponding minimum energy per bit. The problem of sending any given amount of information across a channel can therefore be viewed in terms of sending sufficient Information-Carrying Energy, for this reason the concept of an ICE pipe or conduit is relevant and useful for examining existing systems. The distribution of information to a number of widely separated end-users can be compared to the distribution of many other resources
15.
Internet Protocol
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The Internet Protocol is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet, IP has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered and it also defines addressing methods that are used to label the datagram with source and destination information. The Internet protocol suite is often referred to as TCP/IP. The first major version of IP, Internet Protocol Version 4, is the dominant protocol of the Internet and its successor is Internet Protocol Version 6. The Internet Protocol is responsible for addressing hosts and for routing datagrams from a source host to a destination host across one or more IP networks. For this purpose, the Internet Protocol defines the format of packets, each datagram has two components, a header and a payload. The IP header is tagged with the source IP address, the destination IP address, the payload is the data that is transported. This method of nesting the data payload in a packet with a header is called encapsulation, IP addressing entails the assignment of IP addresses and associated parameters to host interfaces. The address space is divided into networks and subnetworks, involving the designation of network or routing prefixes, IP routing is performed by all hosts, as well as routers, whose main function is to transport packets across network boundaries. Routers communicate with one another via specially designed routing protocols, either interior gateway protocols or exterior gateway protocols, IP routing is also common in local networks. For example, many Ethernet switches support IP multicast operations and these switches use IP addresses and Internet Group Management Protocol to control multicast routing but use MAC addresses for the actual routing. The versions currently relevant are IPv4 and IPv6, in May 1974, the Institute of Electrical and Electronic Engineers published a paper entitled A Protocol for Packet Network Intercommunication. The papers authors, Vint Cerf and Bob Kahn, described a protocol for sharing resources using packet switching among network nodes. A central control component of this model was the Transmission Control Program that incorporated both connection-oriented links and datagram services between hosts, the model became known as the Department of Defense Internet Model and Internet protocol suite, and informally as TCP/IP. IP versions 0 to 3 were experimental versions, used between 1977 and 1979, IEN26, dated February 1978 describes a version of the IP header that uses a 1-bit version field. IEN28, dated February 1978 describes IPv2, IEN41, dated June 1978 describes the first protocol to be called IPv4. The IP header is different from the modern IPv4 header, IEN44, dated June 1978 describes another version of IPv4, also with a header different from the modern IPv4 header
16.
Telephone directory
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Its purpose is to allow the telephone number of a subscriber identified by name and address to be found. The advent of the Internet and smart phones in the 21st century greatly reduced the need for a phone book. Some communities, such as Seattle and San Francisco, sought to ban their unsolicited distribution as wasteful, unwanted, subscriber names are generally listed in alphabetical order, together with their postal or street address and telephone number. It may also have civil defense or emergency management information, there may be transit maps, postal code/zip code guides, international dialing codes or stadium seating charts, as well as advertising. In the US, under current rules and practices, mobile phone, efforts to create cellular directories have met stiff opposition from several fronts, including those who seek to avoid telemarketers. A telephone directory and its content may be known by the color of the paper it is printed on, white pages generally indicates personal or alphabetic listings. Grey pages, sometimes called a telephone directory, allowing subscriber details to be found for a given number. Other colors may have meanings, for example, information on government agencies is often printed on blue pages or green pages. Telephone directories can be published in hard copy or in electronic form, in the latter case, the directory can be provided as an online service through proprietary terminals or over the Internet, or on physical media such as CD-ROM. In many countries directories are published in book form and also available over the Internet. Printed directories were usually supplied free of charge, Telephone directories are a type of city directory. Books listing the inhabitants of a city were widely published starting in the 18th century. The first British telephone directory was published on 15 January 1880 by The Telephone Company and it contained 248 names and addresses of individuals and businesses in London, telephone numbers were not used at the time as subscribers were asked for by name at the exchange. The directory is preserved as part of the British phone book collection by BT Archives, in 1981 France was the first country to have an electronic directory on a system called Minitel. The directory is called 11 after its telephone access number,1996 is the year the first telephone directories go online in the USA. Yellowpages. com and Whitepages. com both see their start in April, in 1999, the first online telephone directories and people finding sites such as LookupUK. com go online in the UK. In 2003, more advanced UK searching including Electoral Roll become available on LocateFirst. com, in the 21st century, printed telephone directories are increasingly criticized as waste. In 2012, after some North American cities passed laws banning the distribution of telephone books, manufacture and distribution of telephone directories produces over 1,400,000 metric tons of greenhouse gases and consumes over 600,000 tons of paper annually
17.
Caller identification
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Caller ID may be used by the recipient to avoid answering unwanted incoming calls by the concept of informed consent. However, it also poses problems for personal privacy, usually, the caller can disable or block the Caller ID facility, but some call capture technology can bypass a caller block. On the other hand, the possibility of caller ID spoofing may render received information unreliable, with appropriate hardware, networking and software, Caller ID can also be associated with a name of the calling telephone number. The information made available to the party may be displayed on a telephones display, on a separately attached device. However, many modems are designed and programmed to handle multiple signalling methods, the idea of CNID as a service for POTS subscribers originated from automatic number identification as a part of toll free number service in the United States. However, CNID and ANI are not the same thing, ANI was originally a term given to a system that identified the telephone number placing a call, in a non-electronic central office switch. Previous to this, the number could not be identified electronically. Caller ID is made up of two pieces of information, the calling number and the billing name where available. When a call is made from a name, this name can be passed on through a number of different methods. For example, the name may be datafilled in the originating switch. More commonly, a database is accessed by the receiving switch, if the name does not exist, then the city, State, Province, or other designation may be sent. Some of these databases may be shared among several companies, each paying every time a name is extracted and it is for this reason that mobile phone callers appear as WIRELESS CALLER, or the location where the phone number is registered. Additionally, nothing ensures that the number sent by a switch is the actual number where the call originated, as such, the telephone switch, and therefore the operating entity, must also be trusted to provide secure authentication. The displayed caller ID also depends on the equipment originating the call, if the call originates on a POTS line, then caller ID is provided by the service providers local switch. Since the network does not connect the caller to the callee until the phone is answered, most service providers however, allow the caller to block caller ID presentation through the vertical service code *67. A call placed behind a branch exchange has more options. In the typical telephony environment, a PBX connects to the service provider through Primary Rate Interface trunks. Generally, although not absolutely, the service provider simply passes whatever calling line ID appears on those PRI access trunks transparently across the Public Switched Telephone Network and this opens up the opportunity for the PBX administrator to program whatever number they choose in their external phone number fields
18.
Call centre
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A call centre or call center is a centralised office used for receiving or transmitting a large volume of requests by telephone. An inbound call centre is operated by a company to administer incoming product support or information enquiries from consumers, outbound call centres are operated for telemarketing, solicitation of charitable or political donations, debt collection and market research. A contact centre is a location for centralised handling of individual communications, including letters, faxes, live support software, social media, instant message, and e-mail. It can be operated or networked with additional centres, often linked to a corporate computer network, including mainframes, microcomputers. Increasingly, the voice and data pathways into the centre are linked through a set of new technologies called computer telephony integration, the contact centre is a central point from which all customer contacts are managed. Through contact centres, valuable information about company are routed to people, contacts to be tracked. It is generally a part of customer relationship management. The majority of companies use contact centres as a means of managing their customer interaction. These centres can be operated by either an in house department responsible or outsourcing customer interaction to a third party agency, during the late 1970s, call centre technology expanded to include telephone sales, airline reservations and banking systems. The term call centre was first published and recognized by the Oxford English Dictionary in 1983, the 1980s experienced the development of toll-free telephone numbers to increase the efficiency of agents and overall call volume. Call centres increased with the deregulation of long distance calling and growth in information dependent industries, as call centres expanded, unionisation occurred in North America to gain members including the Communications Workers of America and the United Steelworkers. In Australia, the National Union of Workers represents unionised workers, in Europe, Uni Global Union of Switzerland is involved in assisting unionisation in this realm and in Germany Vereinte Dienstleistungsgewerkschaft represents call centre workers. During the 1990s, call centres expanded internationally and developed two additional subsets of communication, contact centres and outsourced bureau centres. In contrast to in-house management, outsourced bureau contact centres are a model of contact centre that provide services on a pay per use model. The overheads of the centre are shared by many clients, thereby supporting a very cost effective model. Automatic lead selection or lead steering is also intended to improve efficiencies and this allows inbound calls to be directly routed to the appropriate agent for the task, whilst minimising wait times and long lists of irrelevant options for people calling in. The universal queue standardises the processing of communications across multiple technologies such as fax, phone, the virtual queue provides callers with an alternative to waiting on hold when no agents are available to handle inbound call demand. Historically, call centres have been built on Private branch exchange equipment that is owned, hosted, the PBX can provide functions such as automatic call distribution, interactive voice response, and skills-based routing
19.
Middleware
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Middleware is computer software that provides services to software applications beyond those available from the operating system. It can be described as software glue, middleware makes it easier for software developers to implement communication and input/output, so they can focus on the specific purpose of their application. The term is most commonly used for software that enables communication, an IETF workshop in 2000 defined middleware as those services found above the transport layer set of services but below the application environment. In this more specific sense middleware can be described as the dash in client-server, middleware includes web servers, application servers, content management systems, and similar tools that support application development and delivery. ObjectWeb defines middleware as, The software layer that lies between the system and applications on each side of a distributed computing system in a network. Services that can be regarded as middleware include enterprise application integration, data integration, message oriented middleware, object request brokers, database access services are often characterised as middleware. Some of them are language specific implementations and support heterogeneous features, examples of database-oriented middleware include ODBC, JDBC and transaction processing monitors. Distributed computing system middleware can loosely be divided into two categories—those that provide services and those that perform in machine-time. This latter middleware is somewhat standardized through the Service Availability Forum and is used in complex, embedded systems within telecom, defense. The term middleware is used in contexts as well. Middleware is sometimes used in a sense to a software driver. The mer software distribution is a middleware, it lacks the Linux kernel, mer is targeted at hardware vendors mobile-oriented operating systems. The Android operating system uses the Linux kernel at its core, in addition, Android provides a middleware layer including libraries that provide services such as data storage, screen display, multimedia, and web browsing. Because the middleware libraries are compiled to machine language, services execute quickly, middleware libraries also implement device-specific functions, so applications and the application framework need not concern themselves with variations between various Android devices. Androids middleware layer also contains the Dalvik virtual machine and its core Java application libraries, game engine software such as Gamebryo and Renderware are sometimes described as middleware, because they provide many services to simplify game development. In simulation technology, middleware is used in the context of the high level architecture that applies to many distributed simulations. It is a layer of software that lies between the code and the run-time infrastructure. Wireless networking developers can use middleware to meet the associated with a wireless sensor network
20.
Bell Labs
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Nokia Bell Labs is an American research and scientific development company, owned by Finnish company Nokia. Its headquarters are located in Murray Hill, New Jersey, in addition to laboratories around the rest of the United States. The historic laboratory originated in the late 19th century as the Volta Laboratory, Bell Labs was also at one time a division of the American Telephone & Telegraph Company, half-owned through its Western Electric manufacturing subsidiary. Eight Nobel Prizes have been awarded for work completed at Bell Laboratories, in 1880, the French government awarded Alexander Graham Bell the Volta Prize of 50,000 francs, approximately US$10,000 at that time for the invention of the telephone. Bell used the award to fund the Volta Laboratory in Washington, D. C. in collaboration with Sumner Tainter, the laboratory is also variously known as the Volta Bureau, the Bell Carriage House, the Bell Laboratory and the Volta Laboratory. The laboratory focused on the analysis, recording, and transmission of sound, Bell used his considerable profits from the laboratory for further research and education to permit the diffusion of knowledge relating to the deaf. This resulted in the founding of the Volta Bureau c,1887, located at Bells fathers house at 1527 35th Street in Washington, D. C. where its carriage house became their headquarters in 1889. In 1893, Bell constructed a new building, close by at 1537 35th St. specifically to house the lab, the building was declared a National Historic Landmark in 1972. In 1884, the American Bell Telephone Company created the Mechanical Department from the Electrical, the first president of research was Frank B. Jewett, who stayed there until 1940, ownership of Bell Laboratories was evenly split between AT&T and the Western Electric Company. Its principal work was to plan, design, and support the equipment that Western Electric built for Bell System operating companies and this included everything from telephones, telephone exchange switches, and transmission equipment. Bell Labs also carried out consulting work for the Bell Telephone Company, a few workers were assigned to basic research, and this attracted much attention, especially since they produced several Nobel Prize winners. Until the 1940s, the principal locations were in and around the Bell Labs Building in New York City. Of these, Murray Hill and Crawford Hill remain in existence, the largest grouping of people in the company was in Illinois, at Naperville-Lisle, in the Chicago area, which had the largest concentration of employees prior to 2001. Since 2001, many of the locations have been scaled down or closed. The Holmdel site, a 1.9 million square foot structure set on 473 acres, was closed in 2007, the mirrored-glass building was designed by Eero Saarinen. In August 2013, Somerset Development bought the building, intending to redevelop it into a commercial and residential project. The prospects of success are clouded by the difficulty of readapting Saarinens design and by the current glut of aging, eight Nobel Prizes have been awarded for work completed at Bell Laboratories
21.
Digital electronics
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Digital electronics or digital circuits are electronics that handle digital signals rather than by continuous ranges as used in analog electronics. All levels within a band of values represent the information state. In most cases, the number of states is two, and they are represented by two voltage bands, one near a reference value, and the other a value near the supply voltage. These correspond to the false and true values of the Boolean domain respectively, Digital techniques are useful because it is easier to get an electronic device to switch into one of a number of known states than to accurately reproduce a continuous range of values. Digital electronic circuits are made from large assemblies of logic gates. The binary number system was refined by Gottfried Wilhelm Leibniz and he established that by using the binary system. Digital logic as we know it was the brain-child of George Boole, Boole died young, but his ideas lived on. In an 1886 letter, Charles Sanders Peirce described how logical operations could be carried out by electrical switching circuits, eventually, vacuum tubes replaced relays for logic operations. Lee De Forests modification, in 1907, of the Fleming valve can be used as an AND logic gate, ludwig Wittgenstein introduced a version of the 16-row truth table as proposition 5.101 of Tractatus Logico-Philosophicus. Walther Bothe, inventor of the circuit, got part of the 1954 Nobel Prize in physics. Mechanical analog computers started appearing in the first century and were used in the medieval era for astronomical calculations. In World War II, mechanical computers were used for specialized military applications such as calculating torpedo aiming. During this time the first electronic computers were developed. Originally they were the size of a room, consuming as much power as several hundred modern personal computers. The Z3 was a computer designed by Konrad Zuse, finished in 1941. It was the worlds first working programmable, fully automatic digital computer and its operation was facilitated by the invention of the vacuum tube in 1904 by John Ambrose Fleming. Purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, the bipolar junction transistor was invented in 1947. From 1955 onwards transistors replaced vacuum tubes in computer designs, giving rise to the generation of computers
22.
Backbone network
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A backbone is a part of computer network that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the building, in different buildings in a campus environment. Normally, the capacity is greater than the networks connected to it. The pieces of the connections that bring these departments together is often mentioned as network backbone. Network congestion is often taken into consideration while designing backbones, one example of a backbone network is the Internet backbone. This kind of topology allows for expansion and limited capital outlay for growth. Distributed backbones, in all practicality, are in use by all large-scale networks, applications in enterprise-wide scenarios confined to a single building are also practical, as certain connectivity devices can be assigned to certain floors or departments. Each floor or department possesses a LAN and a closet with that workgroups main hub or router connected to a bus-style network using backbone cabling. Another advantage of using a distributed backbone is the ability for network administrator to segregate workgroups for ease of management, there is the possibility of single points of failure, referring to connectivity devices high in the series hierarchy. The distributed backbone must be designed to separate network traffic circulating on each individual LAN from the network traffic by using access devices such as routers. A collapsed backbone is a type of network architecture. The traditional backbone network goes over the globe to provide interconnectivity to the remote hubs, in most cases, the backbones are the links while the switching or routing functions are done by the equipment at each hub. In the case of a collapsed or inverted backbone, each hub provides a back to a central location to be connected to a backbone-in-a-box. That box can be a switch or a router, the topology and architecture of a collapsed backbone is a star or a rooted tree. However, the drawback of the backbone is that if the box housing the backbone is down or there are reachability problem to the central location. These problems can be minimized by having redundant backbone boxes as well as having secondary/backup backbone locations, there are a few different types of backbones that are used for an enterprise-wide network. When organizations are looking for a strong and trustworthy backbone they should choose a parallel backbone. This backbone is a variation of a backbone in that it uses a central node
23.
Pulse-code modulation
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Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the form of digital audio in computers, compact discs, digital telephony. In a PCM stream, the amplitude of the signal is sampled regularly at uniform intervals. Linear pulse-code modulation is a type of PCM where the quantization levels are linearly uniform. This is in contrast to PCM encodings where quantization levels vary as a function of amplitude, though PCM is a more general term, it is often used to describe data encoded as LPCM. Early electrical communications started to sample signals in order to interlace samples from multiple telegraphy sources, the American inventor Moses G. Farmer conveyed telegraph time-division multiplexing as early as 1853. Electrical engineer W. M. Miner, in 1903, used an electro-mechanical commutator for time-division multiplexing multiple telegraph signals and he obtained intelligible speech from channels sampled at a rate above 3500–4300 Hz, lower rates proved unsatisfactory. This was TDM, but pulse-amplitude modulation rather than PCM, in 1920 the Bartlane cable picture transmission system, named after its inventors Harry G. Bartholomew and Maynard D. In 1926, Paul M. Rainey of Western Electric patented a machine which transmitted its signal using 5-bit PCM. The machine did not go into production, british engineer Alec Reeves, unaware of previous work, conceived the use of PCM for voice communication in 1937 while working for International Telephone and Telegraph in France. He described the theory and advantages, but no practical application resulted, Reeves filed for a French patent in 1938, and his US patent was granted in 1943. By this time Reeves had started working at the Telecommunications Research Establishment, the first transmission of speech by digital techniques, the SIGSALY encryption equipment, conveyed high-level Allied communications during World War II. In 1943 the Bell Labs researchers who designed the SIGSALY system became aware of the use of PCM binary coding as already proposed by Alec Reeves. In 1949 for the Canadian Navys DATAR system, Ferranti Canada built a working PCM radio system that was able to transmit digitized radar data over long distances, PCM in the late 1940s and early 1950s used a cathode-ray coding tube with a plate electrode having encoding perforations. The plate collected or passed the beam, producing current variations in binary code, rather than natural binary, the grid of Goodalls later tube was perforated to produce a glitch-free Gray code, and produced all bits simultaneously by using a fan beam instead of a scanning beam. Patent 2,801,281 filed in 1946 and 1952, another patent by the same title was filed by John R. Pierce in 1945, and issued in 1948, U. S. The three of them published The Philosophy of PCM in 1948, PCM is the method of encoding generally used for uncompressed audio, although there are other methods such as pulse-density modulation. The 4ESS switch introduced time-division switching into the US telephone system in 1976, LPCM is used for the lossless encoding of audio data in the Compact disc Red Book standard, introduced in 1982
24.
Synchronous optical networking
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At low transmission rates data can also be transferred via an electrical interface. SONET generic criteria are detailed in Telcordia Technologies Generic Requirements document GR-253-CORE, Generic criteria applicable to SONET and other transmission systems are found in Telcordia GR-499-CORE. The primary difficulty in doing this prior to SONET/SDH was that the sources of these various circuits were different. This meant that circuit was actually operating at a slightly different rate. SONET/SDH allowed for the transport of many different circuits of differing origin within a single framing protocol. SONET/SDH is not a protocol in itself, but a transport protocol. It quickly evolved mapping structures and concatenated payload containers to transport ATM connections, both SDH and SONET are widely used today, SONET in the United States and Canada, and SDH in the rest of the world. Although the SONET standards were developed before SDH, it is considered a variation of SDH because of SDHs greater worldwide market penetration, SONET is subdivided into four sublayer with some factor such as the path, line, section and physical layer. The SDH standard was defined by the European Telecommunications Standards Institute, and is formalized as International Telecommunication Union standards G.707, G.783, G.784. The SONET standard was defined by Telcordia and American National Standards Institute standard T1.105, which define the set of transmission formats and transmission rates in the range above 51.840 Mbit/s. SDH differs from Plesiochronous Digital Hierarchy in that the rates that are used to transport the data on SONET/SDH are tightly synchronized across the entire network. This synchronization system allows entire inter-country networks to operate synchronously, greatly reducing the amount of buffering required between elements in the network. Therefore, it is inaccurate to think of SDH or SONET as communications protocols in and of themselves, they are generic, the basic format of a SONET/SDH signal allows it to carry many different services in its virtual container, because it is bandwidth-flexible. SONET and SDH often use different terms to describe identical features or functions and this can cause confusion and exaggerate their differences. With a few exceptions, SDH can be thought of as a superset of SONET, SONET is a set of transport containers that allow for delivery of a variety of protocols, including traditional telephony, ATM, Ethernet, and TCP/IP traffic. SONET therefore is not in itself a native communications protocol and should not be confused as being necessarily connection-oriented in the way that term is usually used, the protocol is a heavily multiplexed structure, with the header interleaved between the data in a complex way. This permits the data to have its own frame rate and be able to float around relative to the SDH/SONET frame structure. This interleaving permits a low latency for the encapsulated data
25.
Optical fiber
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An optical fiber or optical fibre is a flexible, transparent fiber made by drawing glass or plastic to a diameter slightly thicker than that of a human hair. Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces, as in the case of a fiberscope. Specially designed fibers are used for a variety of other applications, some of them being fiber optic sensors. Optical fibers typically include a transparent core surrounded by a transparent cladding material with an index of refraction. Light is kept in the core by the phenomenon of internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, multi-mode fibers generally have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters, being able to join optical fibers with low loss is important in fiber optic communication. This is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the cores. For applications that demand a permanent connection a fusion splice is common, in this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors, the field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. The term was coined by Indian physicist Narinder Singh Kapany who is acknowledged as the father of fiber optics. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon, John Tyndall included a demonstration of it in his public lectures in London,12 years later. When the ray passes from water to air it is bent from the perpendicular. If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, unpigmented human hairs have also been shown to act as an optical fiber. Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century, image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for medical examinations by Heinrich Lamm in the following decade
26.
Multiplexing
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In telecommunications and computer networks, multiplexing is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share an expensive resource, for example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now applied in communications. In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910, the multiplexed signal is transmitted over a communication channel such as a cable. The multiplexing divides the capacity of the channel into several logical channels. A reverse process, known as demultiplexing, extracts the original channels on the receiver end, a device that performs the multiplexing is called a multiplexer, and a device that performs the reverse process is called a demultiplexer. Multiple variable bit rate digital bit streams may be transferred efficiently over a fixed bandwidth channel by means of statistical multiplexing. This is an asynchronous mode time-domain multiplexing which is a form of time-division multiplexing, digital bit streams can be transferred over an analog channel by means of code-division multiplexing techniques such as frequency-hopping spread spectrum and direct-sequence spread spectrum. In wired communication, space-division multiplexing, also known as Space-division multiple access is the use of separate point-to-point electrical conductors for each transmitted channel, in wireless communication, space-division multiplexing is achieved with multiple antenna elements forming a phased array antenna. Examples are multiple-input and multiple-output, single-input and multiple-output and multiple-input and single-output multiplexing, different antennas would give different multi-path propagation signatures, making it possible for digital signal processing techniques to separate different signals from each other. These techniques may also be utilized for space diversity or beamforming rather than multiplexing Frequency-division multiplexing is inherently an analog technology, FDM achieves the combining of several signals into one medium by sending signals in several distinct frequency ranges over a single medium. In FDM the signals are electrical signals, one of the most common applications for FDM is traditional radio and television broadcasting from terrestrial, mobile or satellite stations, or cable television. Only one cable reaches a customers residential area, but the provider can send multiple television channels or signals simultaneously over that cable to all subscribers without interference. Receivers must tune to the frequency to access the desired signal. A variant technology, called wavelength-division multiplexing is used in optical communications, time-division multiplexing is a digital technology which uses time, instead of space or frequency, to separate the different data streams. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, if done sufficiently quickly, the receiving devices will not detect that some of the circuit time was used to serve another logical communication path. Consider an application requiring four terminals at an airport to reach a central computer, each terminal communicated at 2400 baud, so rather than acquire four individual circuits to carry such a low-speed transmission, the airline has installed a pair of multiplexers. A pair of 9600 baud modems and one dedicated analog communications circuit from the ticket desk back to the airline data center are also installed
27.
Digital signal (signal processing)
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If that discrete set is finite, the discrete values can be represented with digital words of a finite width. Most commonly, these values are represented as fixed-point words or floating-point words. The process of analog-to-digital conversion produces a digital signal, common practical digital signals are represented as 8-bit, 16-bit, 24-bit and 32-bit. But the number of levels is not necessarily limited to powers of two
28.
Serving area interface
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The serving area interface or service area interface is an outdoor enclosure or metal box that allows access to telecommunications wiring. In the United Kingdom, the components from the PCP onwards to the customer are known as D-side, in the United States, the connection back to the MDF is known as the F2 and/or the F1 pairs. SAIs are used in suburban and low-density urban areas, serving some of the purposes that manholes do in high-density urban areas. Besides a cross connect point, they contain a DSLAM or more rarely a remote concentrator or both. Enclosure Fiber to the telecom enclosure Sub-loop unbundling Demarcation point
29.
Digital loop carrier
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A digital loop carrier is a system which uses digital transmission to extend the range of the local loop farther than would be possible using only twisted pair copper wires. A DLC digitizes and multiplexes the individual signals carried by the local loops onto a single datastream on the DLC segment, subscriber Loop Carrier systems address a number of problems, Electrical constraints on long loops. When the subscriber goes off-hook, a cable pair behaves like a single loop inductance coil with a -48 V dc potential, Electric current values vary with cable length and gauge. A minimum current of around 20 mA dc is required to convey terminal signalling information to the network, there is also a minimum power level required to provide adequate volume for the voice signal. A variety of schemes were implemented before DLC technology to offset the impedance long loops offered to signalling and they included the following, Use heavy-gauge conductors – Up to 19 gauge, which is costly and bulky. The heavy-gauge cables yielded far fewer pairs per cable and led to congestion in cable routes, especially in bridge crossings. Increase battery voltage – This violation of operating standards could pose a safety hazard, add amplifiers to power the voice signal on long loops. This however, requires volumes of auxiliary equipment, a number of cross wiring points. Add signal regeneration and signal extension equipment – The comments regarding amplifiers apply here as well, add loading coils to reduce the attenuation of voice signals over long loops. These have detrimental effect to new transmission technologies using the loop, like DSL. DLC eliminates the need for these remedies by extending out closer to the customer the line card which digitises the voice signal for use by the PSTN. Once the voice signal is digitised, it is manipulated and is no longer subject to the vagaries of the analog loop caused by distance, impedance, attenuation. The DLC solution was dubbed pair gain, a fibre optic cable or several copper pairs for the whole system from the CO to the DLC remote terminal replace the individual pair previously needed for each loop. DLC remote terminals are typically stored in Serving Area Interfaces–metal cabinets alongside or near roadways that overlie communications rights-of-ways, fibre in the loop systems are functionally equivalent to DLC. FITL accomplishes the same two primary functions DLC was intended for, pair gain and the elimination of electrical constraints due to long metallic loops. FITL architectures vary from simply deploying fibre feeder plants to fibre to the curb and, ultimately fibre to the home where an optical network unit is located at each home
30.
Non-linear quantization
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In telecommunication and signal processing companding is a method of mitigating the detrimental effects of a channel with limited dynamic range. The name is a combination of the words compressing and expanding, the use of companding allows signals with a large dynamic range to be transmitted over facilities that have a smaller dynamic range capability. Companding is employed in telephony and other applications such as professional wireless microphones. The dynamic range of a signal is compressed before transmission and is expanded to the value at the receiver. The electronic circuit that does this is called a compander and works by compressing or expanding the range of an analog electronic signal such as sound recorded by a microphone. One variety is a triplet of amplifiers, an amplifier, followed by a variable-gain linear amplifier. Such a triplet has the property that its voltage is proportional to the input voltage raised to an adjustable power. This type of quantization is used in telephony systems. The two most popular compander functions used for telecommunications are the A-law and μ-law functions, companding is used in digital telephony systems, compressing before input to an analog-to-digital converter, and then expanding after a digital-to-analog converter. This is equivalent to using a non-linear ADC as in a T-carrier telephone system that implements A-law or μ-law companding and this method is also used in digital file formats for better signal-to-noise ratio at lower bit rates. This is effectively a form of audio data compression. Professional wireless microphones do this since the range of the microphone audio signal itself is larger than the dynamic range provided by radio transmission. Companding also reduces the noise and crosstalk levels at the receiver, companders are used in concert audio systems and in some noise reduction schemes such as dbx and Dolby NR. The use of companding in a picture transmission system was patented by A. B. In 1942, Clark and his team completed the SIGSALY secure voice system that included the first use of companding in a PCM system. In 1953, B. Smith showed that a nonlinear DAC could be complemented by the nonlinearity in a successive-approximation ADC configuration. In 1970, H. Kaneko developed the uniform description of segment companding laws that had by then adopted in digital telephony. In the 1980s, many of the equipment manufacturers used companding when compressing the library waveform data in their digital synthesizers
31.
Bit error rate
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The bit error rate is the number of bit errors per unit time. The bit error ratio is the number of bit errors divided by the number of transferred bits during a studied time interval. Bit error ratio is a performance measure, often expressed as a percentage. The bit error probability pe is the value of the bit error ratio. The bit error ratio can be considered as an estimate of the bit error probability. This estimate is accurate for a time interval and a high number of bit errors. The BER is 3 incorrect bits divided by 10 transferred bits, the packet error ratio is the number of incorrectly received data packets divided by the total number of received packets. A packet is declared incorrect if at least one bit is erroneous, for small bit error probabilities, this is approximately p p ≈ p e N. Similar measurements can be carried out for the transmission of frames, blocks, in a communication system, the receiver side BER may be affected by transmission channel noise, interference, distortion, bit synchronization problems, attenuation, wireless multipath fading, etc. The transmission BER is the number of detected bits that are incorrect before error correction, normally the transmission BER is larger than the information BER. The information BER is affected by the strength of the error correction code. The BER may be evaluated using stochastic computer simulations, if a simple transmission channel model and data source model is assumed, the BER may also be calculated analytically. An example of such a source model is the Bernoulli source. Examples of simple channel models used in theory are, Binary symmetric channel Additive white gaussian noise channel without fading. A worst-case scenario is a random channel, where noise totally dominates over the useful signal. This results in a transmission BER of 50%, in a noisy channel, the BER is often expressed as a function of the normalized carrier-to-noise ratio measure denoted Eb/N0, or Es/N0. For example, in the case of QPSK modulation and AWGN channel, people usually plot the BER curves to describe the performance of a digital communication system. In optical communication, BER vs. Received Power is usually used, while in wireless communication, measuring the bit error ratio helps people choose the appropriate forward error correction codes
32.
T-carrier
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The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls. The first version, the Transmission System 1, was introduced in 1962 in the Bell System, subsequent specifications carried multiples of the basic T1 data rates, such as T2 with 96 channels, T3 with 672 channels, and others. T-1 is a specification for telecommunications trunking. A trunk is a transmission channel between two points on the network, each point is either a switching center or a node. Initially, T-1 trunks were used only to connect major telephone exchanges, one transmit pair, one receive pair. If the exchanges were too far apart, a repeater boosted the signal, before the digital T-1 system, carrier wave systems such as 12-channel carrier systems worked by frequency division multiplexing, each call was an analog signal. A T-1 trunk could transmit 24 telephone calls at a time, dS-1 is a communications protocol for multiplexing the bitstreams of up to 24 telephone calls, along with two special bits, a framing bit and a maintenance-signaling bit. T-1s maximum data rate is 1.544 megabits per second. Throughout Europe and most of the rest of the world there is a transmission system called E-carrier. Existing frequency-division multiplexing carrier systems worked well for connections between distant cities, but required expensive modulators, demodulators and filters for every voice channel, for connections within metropolitan areas, Bell Labs in the late 1950s sought cheaper terminal equipment. Pulse-code modulation allowed sharing a coder and decoder among several voice trunks, the most common legacy of this system is the line rate speeds. T1 now means any data circuit that runs at the original 1.544 Mbit/s line rate, the T2 and T3 circuit channels carry multiple T1 channels multiplexed, resulting in transmission rates of 6.312 and 44.736 Mbit/s, respectively. A T3 line comprises 28 T1 lines, each operating at total signaling rate of 1.544 Mbit/s. It is possible to get a fractional T3 line, meaning a T3 line with some of the 28 lines turned off, resulting in a transfer rate. Supposedly, the 1.544 Mbit/s rate was chosen because tests done by AT&T Long Lines in Chicago were conducted underground, the optimum bit rate was chosen empirically—the capacity was increased until the failure rate was unacceptable, then reduced to leave a margin. Companding allowed acceptable audio performance with seven bits per PCM sample in this original T1/D1 system. The standard does not allow an all zero sample which would produce a string of binary zeros. However, when carrying data there could be long strings of zeros, a more detailed understanding of how the rate of 1.544 Mbit/s was divided into channels is as follows
33.
E-carrier
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The E-carrier is a member of the series of carrier systems developed for digital transmission of many simultaneous telephone calls by time-division multiplexing. It was widely adopted in almost all countries outside the US, Canada, E-carrier deployments have steadily been replaced by Ethernet as telecommunication networks transitions towards all IP. An E1 link operates two separate sets of wires, usually Unshielded twisted pair or using coaxial. A nominal 3 volt peak signal is encoded with pulses using a method avoiding long periods without polarity changes, the line data rate is 2.048 Mbit/s which is split into 32 timeslots, each being allocated 8 bits in turn. Thus each timeslot sends and receives an 8-bit PCM sample, usually encoded according to A-law algorithm,8,000 times per second and this is ideal for voice telephone calls where the voice is sampled at that data rate and reconstructed at the other end. The timeslots are numbered from 0 to 31, the E1 frame defines a cyclical set of 32 time slots of 8 bits. The time slot 0 is devoted to management and time slot 16 for signaling. The main characteristics of the 2-Mbit/s frame are described in the following, one timeslot is reserved for framing purposes, and alternately transmits a fixed pattern. This allows the receiver to lock onto the start of each frame, the standards allow for a full cyclic redundancy check to be performed across all bits transmitted in each frame, to detect if the circuit is losing bits, but this is not always used. An alarm signal may also be transmitted using timeslot TS0, finally, some bits are reserved for national use. One timeslot is reserved for signalling purposes, to control call setup. This includes channel-associated signaling where a set of bits is used to opening and closing the circuit. In an E1 channel, communication consists of sending consecutive frames from the transmitter to the receiver and this way, the bytes received in each slot are assigned to the correct channel. A synchronization process is established, and it is known as frame alignment. In order to implement the frame alignment system so that the receiver of the frame can tell where it begins, in the 2 Mbit/s frame system, the FAS is a combination of seven fixed bits transmitted in the first time slot in the frame. For the alignment mechanism to be maintained, the FAS does not need to be transmitted in every frame, instead, this signal can be sent in alternate frames. In this case, TS0 is used as the synchronization slot, the TS0 of the rest of the frames is therefore available for other functions, such as the transmission of the alarms. In the TS0 of frames with FAS, the first bit is dedicated to carrying the cyclic redundancy checksum and it tells us whether there are one or more bit errors in a specific group of data received in the previous block of eight frames known as submultiframe
