1.
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
2.
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
3.
Coaxial cable
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Coaxial cable, or coax, is a type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an outer sheath or jacket. The term coaxial comes from the conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers with their antennas, computer network connections, digital audio and this allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference, the cable is protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor, the advantage of coaxial design is that electric and magnetic fields are restricted to the dielectric with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable, larger diameter cables and cables with multiple shields have less leakage. Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, the characteristic impedance of the cable is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. A controlled cable characteristic impedance is important because the source and load impedance should be matched to ensure maximum power transfer, other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality. Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, the inner conductor might be solid or stranded, stranded is more flexible. To get better performance, the inner conductor may be silver-plated. Copper-plated steel wire is used as an inner conductor for cable used in the cable TV industry. The insulator surrounding the conductor may be solid plastic, a foam plastic. The properties of control some electrical properties of the cable. A common choice is a solid polyethylene insulator, used in lower-loss cables, solid Teflon is also used as an insulator. Some coaxial lines use air and have spacers to keep the conductor from touching the shield. Many conventional coaxial cables use braided copper wire forming the shield and this allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because the braid cannot be flat
4.
Microwave transmission
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Microwave transmission is the transmission of information or energy by electromagnetic waves whose wavelengths are measured in small numbers of centimetre, these are called microwaves. This part of the spectrum ranges across frequencies of roughly 1.0 gigahertz to 300 GHz. These correspond to wavelengths from 30 centimeters down to 0.1 cm, communication satellites which transferred data between ground stations by microwaves took over much long distance traffic in the 1960s. This allows nearby microwave equipment to use the same frequencies without interfering with each other, a disadvantage is that microwaves are limited to line of sight propagation, they cannot pass around hills or mountains as lower frequency radio waves can. Microwave radio transmission is used in point-to-point communication systems on the surface of the Earth, in satellite communications. Other parts of the radio band are used for radars, radio navigation systems, sensor systems. Radio waves in this band are usually strongly attenuated by the Earthly atmosphere and particles contained in it, also, in wide band of frequencies around 60 GHz, the radio waves are strongly attenuated by molecular oxygen in the atmosphere. Wireless transmission of power Proposed systems e. g, in microwave radio relay, microwaves are transmitted between the two locations with directional antennas, forming a fixed radio connection between the two points. The requirement of a line of sight limits the distance between stations to 30 or 40 miles. Beginning in the 1950s, networks of microwave links, such as the AT&T Long Lines system in the U. S. carried long distance telephone calls. The first system, dubbed TD-2 and built by AT&T, connected New York and these included long daisy-chained series of such links that traversed mountain ranges and spanned continents. Much of the traffic is now carried by cheaper optical fibers and communication satellites. Antennas must be highly directional, these antennas are installed in elevated locations such as radio towers in order to be able to transmit across long distances. Typical types of antenna used in radio relay link installations are parabolic antennas, dielectric lens, and horn-reflector antennas, highly directive antennas permit an economical use of the available frequency spectrum, despite long transmission distances. Because of the frequencies used, a line-of-sight path between the stations is required. Additionally, in order to avoid attenuation of the beam an area around the beam called the first Fresnel zone must be free from obstacles, obstacles in the signal field cause unwanted attenuation. In the planning process, it is essential that path profiles are produced, multipath fades are usually deep only in a small spot and a narrow frequency band, so space and/or frequency diversity schemes can be applied to mitigate these effects. Rare events of temperature, humidity and pressure profile versus height, may produce large deviations and distortion of the propagation and affect transmission quality
5.
Roaming
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To roam is to wander around, to go from place to place without a certain direction or purpose. In the context of mobile networks the word is used when a mobile phone is used outside of the range of its home network. Roaming ensures that a wireless device is kept connected to a network without breaking the connection. For example, should a subscriber travel beyond their cell phone companys transmitter range, their cell phone would automatically hop onto another phone companys service, Using another phone companys service can be done by using the subscriber identity in the visited network. Roaming is technically supported by mobility management, authentication, authorization, device equipment and functionality, such as SIM card capability, antenna and network interfaces, and power management, determine the access possibilities. Username/password based roaming, GSM subscriber roams onto a Public WLAN operated by, although these user/network scenarios focus on roaming from GSM Network Operators network, clearly roaming can be bi-directional, i. e. from Public WLAN Operators to GSM Networks. Traditional roaming in networks of the standard, e. g. In the case of session continuity, seamless access to these services across different access types is provided, the differentiation between home network and visited network is technically given by the type of subscriber entry in a specific network. The visiting subscriber acquires an entry in a database of the visited network. Thus, the term roaming is not linked to a specific network standard, if a subscriber can use their personal service profile, which they use in the home network, in the visited network as well, this is also referred to as Global Service Roaming Capability. The legal roaming business aspects negotiated between the partners for billing of the services obtained are usually stipulated in so called roaming agreements. The GSM Association broadly outlines the content of such roaming agreements in standardized form for its members, if there is no roaming agreement between the two networks, maintenance of service is impossible, and service is denied by the visited network. The visited network contacts the home network and requests information about the roaming device using the IMSI number. If successful, the visited network begins to maintain a temporary subscriber record for the device, likewise, the home network updates its information to indicate that the cell phone is on the host network so that any information sent to that device can be correctly routed. It occurs for example when a call is made to a cell phone. Signaling process, The calling subscriber dials the mobile subscribers MSISDN of the cell phone. Based on the contained in the MSISDN, the call is routed to the mobile network gateway MSC. Its done with an ISUP IAM message, to locate the MS, the GMSC sends to the HLR a MAP SRI message
6.
Media gateway
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Media gateways enable multimedia communications across packet networks using transport protocols such as Asynchronous Transfer Mode and Internet Protocol. Because the media gateway connects different types of networks, one of its functions is to convert between different transmission and coding techniques. Media streaming functions such as echo cancellation, DTMF, and tone sender are also located in the media gateway, Media gateways are often controlled by a separate Media Gateway Controller which provides the call control and signaling functionality. Communication between media gateways and Call Agents is achieved by means of such as MGCP or Megaco or Session Initiation Protocol. Modern media gateways used with SIP are often stand-alone units with their own call and signaling control integrated, mobile access media gateways connect the radio access networks of a public land mobile network PLMN to a next-generation core network. 3GPP standards define the functionality of CS-MGW and IMS-MGW for UTRAN and GERAN based PLMNs
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.
Orange S.A.
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Orange S. A. formerly France Télécom S. A. is a French multinational telecommunications corporation. It has 256 million customers worldwide and employs 95,000 people in France, in 2015, the group had revenue of €40 billion. The companys head office is located in the 15th arrondissement of Paris, the current CEO is Stéphane Richard. The company is a component of the Euro Stoxx 50 stock market index, Orange has been the companys main brand for mobile, landline, internet and IPTV services since 2006. It originated in 1994 when Hutchison Whampoa acquired a stake in Microtel Communications during the early 1990s. It became a subsidiary of Mannesmann in 1999 and was acquired by France Télécom in 2000, the company was rebranded as Orange in July 2013. In 1792, under the French Revolution, the first communication network was developed to enable the rapid transmission of information in a warring and that was the optical telegraphy network of Claude Chappe. In 1878, after the invention of the telegraph and then the invention of the telephone. Telephone Services were added to the ministry when they were nationalised in 1889, however, it was not until 1923 that the second T appeared and the department of P&T became PTT. In 1941, a General Direction of Telecommunications was created within this ministry, then, in 1944, the National Centre of Telecommunications Studies was created to develop the telecommunications industry in France. In the 1970s, France tried extra hard to make up its delay on other countries with the programme delta LP and it was at the time when the majority of the local loop was built, that is all the cables linking the users to the operator. Moreover, with the help of French manufacturers, digital switching, the Minitel, until 1988, France Télécom was known as the Direction Générale des Télécommunications, a division of the Ministry of Posts and Telecommunications. This was in response to a European directive, aimed at making competition mandatory in public services from 1 January 1998, the 2 July 1990 Bill changed France Télécom into an operator of public law, with Marcel Roulet the first Chairman. Since then, the company has had a body corporate from the State. It was privatised by Lionel Jospins Plural Left government starting on 1 January 1998, the French government, both directly and through its holding company ERAP, continues to hold a stake of almost 27% in the company. In addition, the government Conseil of Ministers names the CEO, in 1982 Telecom introduced Minitel online ordering for its customers. In September 1995, Michel Bon was appointed to run France Télécom Group, in 1997, the capital of the new public company was successfully floated whereas the dot-com bubble phenomenon made the stock exchanges bullish. A second share offering occurred in 1998, Hutchison renamed Microtel to Orange Personal Communications Services Ltd, and on 28 April 1994 the Orange brand was launched in the UK mobile phone market
