1.
Telephone exchange
–
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.
Modem
–
A modem is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is attempting to produce a signal that can be transmitted easily, modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second. Modems can also be classified by their rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the ITU V.21 standard used audio frequency shift keying with two frequencies, corresponding to two distinct symbols, to carry 300 bits per second using 300 baud. By contrast, the original ITU V.22 standard, which could transmit and receive four distinct symbols, news wire services in the 1920s used multiplex devices that satisfied the definition of a modem. However, the function was incidental to the multiplexing function, so they are not commonly included in the history of modems. S. SAGE modems were described by AT&Ts Bell Labs as conforming to their newly published Bell 101 dataset standard, while they ran on dedicated telephone lines, the devices at each end were no different from commercial acoustically coupled Bell 101,110 baud modems. The 201A and 201B Data-Phones were synchronous modems using two-bit-per-baud phase-shift keying, the famous Bell 103A dataset standard was also introduced by AT&T in 1962. It provided full-duplex service at 300 bit/s over normal phone lines, frequency-shift keying was used, with the call originator transmitting at 1,070 or 1,270 Hz and the answering modem transmitting at 2,025 or 2,225 Hz. The readily available 103A2 gave an important boost to the use of remote low-speed terminals such as the Teletype Model 33 ASR and KSR, AT&T reduced modem costs by introducing the originate-only 113D and the answer-only 113B/C modems. For many years, the Bell System maintained a monopoly on the use of its phone lines, however, the seminal Hush-a-Phone v. FCC case of 1956 concluded it was within the FCCs jurisdiction to regulate the operation of the Bell System. The FCC found that as long as a device was not electronically attached to the system and this led to a number of devices that mechanically connected to the phone through a standard handset. Since most handsets were supplied by Western Electric and thus of a standard design and this type of connection was used for many devices, such as answering machines. Acoustically coupled Bell 103A-compatible 300 bit/s modems were common during the 1970s, well-known models included the Novation CAT and the Anderson-Jacobson, the latter spun off from an in-house project at Stanford Research Institute. An even lower-cost option was the Pennywhistle modem, designed to be built using parts from electronics scrap, in December 1972, Vadic introduced the VA3400, notable for full-duplex operation at 1,200 bit/s over the phone network. Like the 103A, it used different frequency bands for transmit, in November 1976, AT&T introduced the 212A modem to compete with Vadic
3.
Telecommunication
–
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
4.
Coaxial cable
–
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
5.
D-subminiature
–
The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield, when they were introduced, D-subs were among the smallest connectors used on computer systems. The part containing pin contacts is called the male connector or plug, the sockets shield fits tightly inside the plugs shield. Panel mounted connectors usually have threaded nuts that accept screws on the cable end connector cover that are used for locking the connectors together, occasionally the nuts may be found on a cable end connector if it is expected to connect to another cable end. When screened cables are used, the shields are connected to the screens of the cables. This creates a continuous screen covering the whole cable and connector system. The D-sub series of connectors was introduced by Cannon in 1952, each shell size usually corresponds to a certain number of pins or sockets, A with 15, B with 25, C with 37, D with 50, and E with 9. For example, DB-25 denotes a D-sub with a 25-position shell size and this spacing is called normal density. The suffixes M and F are sometimes used instead of the original P and S for plug, later D-sub connectors added extra pins to the original shell sizes, and their names follow the same pattern. For example, the DE-15, usually found in VGA cables, has 15 pins in three rows, all surrounded by an E size shell, the pins are spaced at 0.090 inches horizontally and 0.078 inches vertically, in what is called high density. The other connectors with the pin spacing are the DA-26, DB-44, DC-62, DD-78. They all have three rows of pins, except the DD-78 which has four, and the DF-104 which has five rows in a new, the double density series of D-sub connectors features even denser arrangements and consists of the DE-19, DA-31, DB-52, DC-79, and DD-100. These each have three rows of pins, except the DD-100, which has four, however, this naming pattern is not always followed. It is now common to see DE-9 connectors sold as DB-9 connectors, DB-9 nearly always refers to a 9-pin connector with an E size shell. Cannon also produced combo D-subs with larger contacts in place of some of the contacts, for use for high-current, high-voltage. The DB-13W3 variant was used for high-performance video connections, this variant provided 10 regular pins plus three coaxial contacts for the red, green, and blue video signals. Some variants have current ratings up to 40 A or operating voltages as high as 13,500 V, others are waterproof, a smaller type of connector derived from the D-sub is called the microminiature D, or micro-D, which is a trademark of ITT Cannon. It is about half the length of a D-sub, a further family of connectors of similar appearance to the D-sub family uses names such as HD-50 and HD-68, and has a D-shaped shell about half the width of a DB25
6.
Network interface controller
–
A network interface controller is a computer hardware component that connects a computer to a computer network. Early network interface controllers were commonly implemented on expansion cards that plugged into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard. The network controller implements the electronic circuitry required to communicate using a physical layer and data link layer standard such as Ethernet, Fibre Channel. The NIC allows computers to communicate over a network, either by using cables or wirelessly. Although other network technologies exist, IEEE802 networks including the Ethernet variants have achieved near-ubiquity since the mid-1990s, newer server motherboards may even have dual network interfaces built-in. The Ethernet capabilities are integrated into the motherboard chipset or implemented via a low-cost dedicated Ethernet chip. A separate network card is not required unless additional interfaces are needed or some type of network is used. The NIC may use one or more of the techniques to indicate the availability of packets to transfer. Interrupt-driven I/O is where the peripheral alerts the CPU that it is ready to transfer data, also, NICs may use one or more of the following techniques to transfer packet data, Programmed input/output is where the CPU moves the data to or from the NIC to memory. Direct memory access is where some other device other than the CPU assumes control of the bus to move data to or from the NIC to memory. This removes load from the CPU but requires more logic on the card, in addition, a packet buffer on the NIC may not be required and latency can be reduced. There are two types of DMA, third-party DMA in which a DMA controller other than the NIC performs transfers, an Ethernet network controller typically has an 8P8C socket where the network cable is connected. Older NICs also supplied BNC, or AUI connections, a few LEDs inform the user of whether the network is active, and whether or not data transmission occurs. Ethernet network controllers typically support 10 Mbit/s Ethernet,100 Mbit/s Ethernet, such controllers are designated as 10/100/1000, meaning that they can support a notional maximum transfer rate of 10,100 or 1000 Mbit/s. 10 Gigabit Ethernet NICs are also available, and, as of November 2014, are beginning to be available on computer motherboards, multiqueue NICs provide multiple transmit and receive queues, allowing packets received by the NIC to be assigned to one of its receive queues. The hardware-based distribution of the interrupts, described above, is referred to as receive-side scaling, purely software implementations also exist, such as the receive packet steering and receive flow steering. Examples of such implementations are the RFS and Intel Flow Director, with multiqueue NICs, additional performance improvements can be achieved by distributing outgoing traffic among different transmit queues. By assigning different transmit queues to different CPUs/cores, various operating systems internal contentions can be avoided and those NICs support, Accessing local and remote memory without involving the remote CPU
7.
Optical fiber
–
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
8.
Transceiver
–
A transceiver is a device comprising both a transmitter and a receiver that are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver, the term originated in the early 1920s. Similar devices include transponders, transverters, and repeaters, in radio terminology, a transceiver means a unit which contains both a receiver and a transmitter. From the beginning days of radio the receiver and transmitter were separate units, amateur radio or ham radio operators can build their own equipment and it is now easier to design and build a simple unit containing both of the functions, transmitting and receiving. Almost all modern radio equipment is now a transceiver but there is an active market for pure radio receivers. An example of a transceiver would be a walkie-talkie or a CB radio, on a wired telephone, the handset contains the transmitter and receiver for the audio and in the 20th century was usually wired to the base unit by tinsel wire. The whole unit is referred to as a receiver. On a mobile telephone or other radiotelephone, the unit is a transceiver. A cordless telephone uses an audio and radio transceiver for the handset, if a speakerphone is included in a wired telephone base or in a cordless base station, the base also becomes an audio transceiver in addition to the handset. A modem is similar to a transceiver, in that it sends and receives a signal and it modulates a signal being transmitted and demodulates a signal being received. Transceivers are called Medium Attachment Units in IEEE802.3 documents and were used in 10BASE2. Fiber-optic gigabit,10 Gigabit Ethernet,40 Gigabit Ethernet, and 100 Gigabit Ethernet utilize transceivers known as GBIC, SFP, SFP+, QSFP, XFP, XAUI, CXP, and CFP. 4P4C, de facto standard connector for telephone handsets Duplex, two-Way communications capability Transponder#Optical communications U. S, patent 0,716,136, John Stone Stone, Apparatus for simultaneously transmitting and receiving space telegraph signals 7 MHz SSB transceiver Homebrew HF transceivers
9.
Internet protocol suite
–
The Internet protocol suite is the conceptual model and set of communications protocols used on the Internet and similar computer networks. It is commonly known as TCP/IP because the protocols in the suite are the Transmission Control Protocol. It is occasionally known as the Department of Defense model, because the development of the model was funded by DARPA. The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, addressed, transmitted, routed and received and this functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved. Technical standards specifying the Internet protocol suite and many of its constituent protocols are maintained by the Internet Engineering Task Force, the Internet protocol suite model is a simpler model developed prior to the OSI model. The Internet protocol suite resulted from research and development conducted by the Defense Advanced Research Projects Agency in the late 1960s, after initiating the pioneering ARPANET in 1969, DARPA started work on a number of other data transmission technologies. In 1972, Robert E. Cerf credits Hubert Zimmermann and Louis Pouzin, designer of the CYCLADES network, the protocol was implemented as the Transmission Control Program, first published in 1974. Initially, the TCP managed both datagram transmissions and routing, but as the protocol grew, other researchers recommended a division of functionality into protocol layers, postel stated, “we are screwing up in our design of Internet protocols by violating the principle of layering”. Encapsulation of different mechanisms was intended to create an environment where the layers could access only what was needed from the lower layers. A monolithic design would be inflexible and lead to scalability issues, the Transmission Control Program was split into two distinct protocols, the Transmission Control Protocol and the Internet Protocol. The new suite replaced all protocols used previously and this design is known as the end-to-end principle. Using this design, it possible to connect almost any network to the ARPANET, irrespective of the local characteristics. One popular expression is that TCP/IP, the product of Cerf and Kahns work. A computer called a router is provided with an interface to each network and it forwards packets back and forth between them. Originally a router was called gateway, but the term was changed to avoid confusion with other types of gateways, from 1973 to 1974, Cerfs networking research group at Stanford worked out details of the idea, resulting in the first TCP specification. A significant technical influence was the early networking work at Xerox PARC, DARPA then contracted with BBN Technologies, Stanford University, and the University College London to develop operational versions of the protocol on different hardware platforms. Four versions were developed, TCP v1, TCP v2, TCP v3 and IP v3, the last protocol is still in use today. In 1975, a two-network TCP/IP communications test was performed between Stanford and University College London, in November,1977, a three-network TCP/IP test was conducted between sites in the US, the UK, and Norway
10.
Patch cable
–
A patch cable or patch cord or patch lead is an electrical or optical cable used to connect one electronic or optical device to another for signal routing. Devices of different types are connected with patch cords, patch cords are usually produced in many different colors so as to be easily distinguishable, and are relatively short, perhaps no longer than two metres. However, patch cords typically refer only to short cords used with patch panels, patch cord cable differs from standard structured cabling cable in that patch cable is stranded for flexibility, whereas standard cable is solid copper. Because the patch cord is stranded copper construction the attenuation is higher on patch cords than solid cable so short lengths should be adhered to. Patch cords can be as short as 3 inches, to connect stacked components or route signals through a patch bay, as length increases, the cables are usually thicker and/or made with more shielding, to prevent signal loss and the introduction of unwanted radio frequencies and hum. Patch cords are made of coaxial cables, with the signal carried through a shielded core. Each end of the cable is attached to a connector so that the cord may be plugged in, connector types may vary widely, particularly with adapting cables. A pigtail is similar to a cord and is the informal name given to a cable fitted with a connector at one end. In the context of copper cabling, these cables are sometimes referred to as blunt patch cords, optical fiber pigtails, in contrast to copper pigtails, can be more accurately described as a connector than a cable or cord. A fiber pigtail is a single, short, usually tight-buffered, optical fiber that has an optical connector pre-installed on one end, the end of the fiber pigtail is stripped and fusion spliced to a single fiber of a multi-fiber trunk. Splicing of pigtails to each fiber in the trunk breaks out the cable into its component fibers for connection to the end equipment. A variety of cables are used to carry electrical signals in sound recording studios, microphones are typically connected to mixing boards or PA systems with XLR microphone cables which use three-pin XLR connectors. DJs using record players connect their turntables to mixers or PA systems with stereo RCA connectors, to resolve this problem, DJs can either use adapters or special cables. Heavier-gauge cables are used for carrying amplified signals from amplifiers to speakers, ¼ TRS phone connector cables can carry stereo signals, so they are used for stereo headphones and for some patching purposes. The patch bay is a panel of audio connectors where XLR cables. The cables could get tangled or mixed up, and it would be hard to know, when faced with 20 connectors at the end of the cable run, which cable was associated with which microphone or instrument. The patch bay is numbered, so that the engineer can note which microphone or instrument is plugged into each numbered connection, Cable management Crossover cable White Papers - Cable Anatomy
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).