1.
Communication channel
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A channel is used to convey an information signal, for example a digital bit stream, from one or several senders to one or several receivers. A channel has a capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second. Communicating data from one location to another requires some form of pathway or medium and these pathways, called communication channels, use two types of media, cable and broadcast. Cable or wire line media use physical wires of cables to transmit data, twisted-pair wire and coaxial cables are made of copper, and fiber-optic cable is made of glass. In information theory, a channel refers to a theoretical channel model with certain error characteristics, in this more general view, a storage device is also a kind of channel, which can be sent to and received from. Examples of communications include, A connection between initiating and terminating nodes of a circuit. A single path provided by a transmission medium via either physical separation, such as by multipair cable or electrical separation, a path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths. A storage which can communicate a message over time as well as space The portion of a medium, such as a track or band. A buffer from which messages can be put and got, see Actor model and process calculi for discussion on the use of channels. In a communications system, the physical or logical link that connects a data source to a data sink, a specific radio frequency, pair or band of frequencies, usually named with a letter, number, or codeword, and often allocated by international agreement. Examples, Marine VHF radio uses some 88 channels in the VHF band for two-way FM voice communication, Channel 16, for example, is 156.800 MHz. In the US, seven additional channels, WX1 - WX7, are allocated for weather broadcasts, television channels such as North American TV Channel 2 =55.25 MHz, Channel 13 =211.25 MHz. Each channel is 6 MHz wide, besides these physical channels, television also has virtual channels. Wi-Fi consists of unlicensed channels 1-13 from 2412 MHz to 2484 MHz in 5 MHz steps, the radio channel between an amateur radio repeater and a ham uses two frequencies often 600 kHz apart. For example, a repeater that transmits on 146.94 MHz typically listens for a ham transmitting on 146.34 MHz, all of these communications channels share the property that they transfer information. The information is carried through the channel by a signal, a channel can be modelled physically by trying to calculate the physical processes which modify the transmitted signal. For example, in wireless communications the channel can be modelled by calculating the reflection off every object in the environment, a sequence of random numbers might also be added in to simulate external interference and/or electronic noise in the receiver. Statistical and physical modelling can be combined, for example, in wireless communications the channel is often modelled by a random attenuation of the transmitted signal, followed by additive noise
2.
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
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.
Patch cable
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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
5.
Modem
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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
6.
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
7.
Transceiver
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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
8.
X.21
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X.21 is an interface specification for differential communications introduced in the mid-1970s by the ITU-T. X.21 was first introduced as a means to provide a digital signaling interface for telecommunications between carriers and customers equipment, when X.21 is used with V.11, it provides synchronous data transmission at rates from 600 bit/s to 10 Mbit/s. There is also a variant of X.21 that is used in select legacy applications. X.21 normally is found on a 15-pin D-Sub connector and is capable of running full-duplex data transmissions, the Signal Element Timing, or clock, is provided by the carrier, and is responsible for correct clocking of the data. X.21 is primarily used in Europe and Japan, for example in the Scandinavian DATEX, article based on X.21 at FOLDOC, and X.21 Pinouts, used with permission. An X.21 brief Tutorial and overview X.21 pinout and some explanations
9.
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
10.
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
11.
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
12.
RS-232
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In telecommunications, RS-232 is a standard for serial communication transmission of data. It formally defines the signals connecting between a DTE such as a terminal, and a DCE, such as a modem. The RS-232 standard is used in computer serial ports. The standard defines the characteristics and timing of signals, the meaning of signals. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997. An RS-232 serial port was once a feature of a personal computer, used for connections to modems, printers, mice, data storage, uninterruptible power supplies. However, RS-232 is hampered by low speed, large voltage swing. In modern personal computers, USB has displaced RS-232 from most of its peripheral interface roles, nevertheless, RS-232 devices are still used, especially in industrial machines, networking equipment, and scientific instruments. Interface mechanical characteristics, pluggable connectors and pin identification, functions of each circuit in the interface connector. Standard subsets of interface circuits for selected telecom applications, the standard does not define such elements as the character encoding, the framing of characters, transmission order of bits, or error detection protocols. The character format and transmission bit rate are set by the serial port hardware which may also contain circuits to convert the internal logic levels to RS-232 compatible signal levels. The standard does not define bit rates for transmission, except that it says it is intended for bit rates lower than 20,000 bits per second, RS-232 was first introduced in 1960 by the Electronic Industries Association as a Recommended Standard. The original DTEs were electromechanical teletypewriters, and the original DCEs were modems, when electronic terminals began to be used, they were often designed to be interchangeable with teletypewriters, and so supported RS-232. The C revision of the standard was issued in 1969 in part to accommodate the electrical characteristics of these devices, the resulting common problems were non-standard pin assignment of circuits on connectors, and incorrect or missing control signals. The lack of adherence to the standards produced a thriving industry of breakout boxes, patch boxes, test equipment, books, a common deviation from the standard was to drive the signals at a reduced voltage. Some manufacturers therefore built transmitters that supplied +5 V and −5 V, later personal computers started to make use of the standard so that they could connect to existing equipment. For many years, an RS-232-compatible port was a feature for serial communications, such as modem connections. It remained in use into the late 1990s
13.
D-subminiature
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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
14.
Internet protocol suite
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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
15.
Network interface controller
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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
16.
Unix-like
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A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like application is one that behaves like the corresponding Unix command or shell, there is no standard for defining the term, and some difference of opinion is possible as to the degree to which a given operating system or application is Unix-like. The Open Group owns the UNIX trademark and administers the Single UNIX Specification and they do not approve of the construction Unix-like, and consider it a misuse of their trademark. Other parties frequently treat Unix as a genericized trademark, in 2007, Wayne R. Gray sued to dispute the status of UNIX as a trademark, but lost his case, and lost again on appeal, with the court upholding the trademark and its ownership. Unix-like systems started to appear in the late 1970s and early 1980s, many proprietary versions, such as Idris, UNOS, Coherent, and UniFlex, aimed to provide businesses with the functionality available to academic users of UNIX. These largely displaced the proprietary clones, growing incompatibility among these systems led to the creation of interoperability standards, including POSIX and the Single UNIX Specification. Various free, low-cost, and unrestricted substitutes for UNIX emerged in the 1980s and 1990s, including 4. 4BSD, Linux, some of these have in turn been the basis for commercial Unix-like systems, such as BSD/OS and OS X. The various BSD variants are notable in that they are in fact descendants of UNIX, however, the BSD code base has evolved since then, replacing all of the AT&T code. Since the BSD variants are not certified as compliant with the Single UNIX Specification, dennis Ritchie, one of the original creators of Unix, expressed his opinion that Unix-like systems such as Linux are de facto Unix systems. Eric S. Raymond and Rob Landley have suggested there are three kinds of Unix-like systems, Genetic UNIX Those systems with a historical connection to the AT&T codebase. Most commercial UNIX systems fall into this category, so do the BSD systems, which are descendants of work done at the University of California, Berkeley in the late 1970s and early 1980s. Some of these systems have no original AT&T code but can trace their ancestry to AT&T designs. Trademark or branded UNIX These systems—largely commercial in nature—have been determined by the Open Group to meet the Single UNIX Specification and are allowed to carry the UNIX name, many ancient UNIX systems no longer meet this definition. Around 2001, Linux was given the opportunity to get a certification including free help from the POSIX chair Andrew Josey for the price of one dollar. Some non-Unix-like operating systems provide a Unix-like compatibility layer, with degrees of Unix-like functionality. IBM z/OSs UNIX System Services is sufficiently complete to be certified as trademark UNIX, cygwin and MSYS both provide a GNU environment on top of the Microsoft Windows user API, sufficient for most common open source software to be compiled and run. Subsystem for Unix-based Applications provides Unix-like functionality as a Windows NT subsystem, Windows Subsystem for Linux provides a Linux-compatible kernel interface developed by Microsoft and containing no Linux code, with Ubuntu user-mode binaries running on top of it
17.
Internet Engineering Task Force
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The Internet Engineering Task Force develops and promotes voluntary Internet standards, in particular the standards that comprise the Internet protocol suite. It is a standards organization, with no formal membership or membership requirements. All participants and managers are volunteers, though their work is funded by their employers or sponsors. Each working group has a chairperson, along with a charter that describes its focus, and what. It is open to all who want to participate, and holds discussions on a mailing list or at IETF meetings. Rough consensus is the basis for decision making. There are no formal voting procedures, because the majority of the IETFs work is done via mailing lists, meeting attendance is not required for contributors. Each working group is intended to work on its topic. In some cases, the WG will instead have its charter updated to take on new tasks as appropriate, the working groups are organized into areas by subject matter. Current areas are Applications, General, Internet, Operations and Management, Real-time Applications and Infrastructure, Routing, Security, each area is overseen by an area director, with most areas having two co-ADs. The ADs are responsible for appointing working group chairs, the area directors, together with the IETF Chair, form the Internet Engineering Steering Group, which is responsible for the overall operation of the IETF. The IETF is overseen by the Internet Architecture Board, which oversees its external relationships, the IAB is also jointly responsible for the IETF Administrative Oversight Committee, which oversees the IETF Administrative Support Activity, which provides logistical, etc. support for the IETF. The IAB also manages the Internet Research Task Force, with which the IETF has a number of cross-group relations. A Nominating Committee of ten randomly chosen volunteers who participate regularly at meetings is vested with the power to appoint, reappoint, and remove members of the IESG, IAB, IASA, and the IAOC. To date, no one has been removed by a NomCom, although people have resigned their positions. Because the IETF itself does not have members, nor is it an organization per se, IETF activities are funded by meeting fees, meeting sponsors and by the Internet Society via its organizational membership and the proceeds of the Public Interest Registry. In December 2005 the IETF Trust was established to manage the copyrighted materials produced by the IETF, the first IETF meeting was attended by 21 U. S. -government-funded researchers on 16 January 1986. It was a continuation of the work of the earlier GADS Task Force, representatives from non-governmental entities were invited to attend starting with the fourth IETF meeting in October 1986
18.
Classless Inter-Domain Routing
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Classless Inter-Domain Routing is a method for allocating IP addresses and IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous addressing architecture of classful network design in the Internet and its goal was to slow the growth of routing tables on routers across the Internet, and to help slow the rapid exhaustion of IPv4 addresses. This division is used as the basis of routing between IP networks and for address allocation policies. Classful network design for IPv4 sized the network address as one or more 8-bit groups, resulting in the blocks of Class A, B, classless Inter-Domain Routing allocates address space to Internet service providers and end users on any address bit boundary, instead of on 8-bit segments. In IPv6, however, the interface identifier has a size of 64 bits by convention. It is based on the variable-length subnet masking technique with effective qualities of specifying arbitrary-length prefixes.168.2. 0/24 for IPv4, CIDR introduced an administrative process of allocating address blocks to organizations based on their actual and short-term projected needs. An IP address is interpreted as composed of two parts, a network-identifying prefix followed by a host identifier within that network, in the previous classful network architecture, IP address allocations were based on the bit boundaries of the four octets of an IP address. An address was considered to be the combination of an 8,16, or 24-bit network prefix along with a 24,16, as the initial TCP/IP network grew to become the Internet during the 1980s, the need for more flexible addressing schemes became increasingly apparent. This led to the development of subnetting and CIDR. The network class distinctions were removed, and the new system was described as being classless, with respect to the old system, an updated version of the specification was published as RFC4632 in 2006. Variable-length subnet masks are mentioned in RFC950, accordingly, techniques for grouping addresses for common operations were based on the concept of cluster addressing, first proposed by Carl-Herbert Rokitansky. CIDR notation is a representation of an IP address and its associated routing prefix. The notation is constructed from an IP address, a character. The number is the count of leading 1 bits in the routing mask, the IP address is expressed according to the standards of IPv4 or IPv6. The address may denote a single, distinct interface address or the address of an entire network. The maximum size of the network is given by the number of addresses that are possible with the remaining, the aggregation of these bits is often called the host identifier. For example,192.168.100. 14/24 represents the IPv4 address 192.168.100.14 and its associated routing prefix 192.168.100.0, or equivalently, its subnet mask 255.255.255.0, which has 24 leading 1-bits. The IPv4 block 192.168.100. 0/22 represents the 1024 IPv4 addresses from 192.168.100.0 to 192.168.103.255
19.
Advanced Linux Sound Architecture
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Advanced Linux Sound Architecture is a software framework and part of the Linux kernel that provides an application programming interface for sound card device drivers. Some of the goals of the ALSA project at its inception were automatic configuration of sound-card hardware, ALSA is released under the GNU General Public License and the GNU Lesser General Public License. Some frameworks such as JACK use ALSA to allow performing low-latency professional-grade audio editing and mixing, ALSA was designed with some features which were not, at the time of its conception, supported by the Open Sound System, Hardware-based MIDI synthesis. ALSA has a larger and more complex API than OSS, so it can be difficult to develop an application that uses ALSA as its sound technology. While ALSA may be configured to provide an OSS emulation layer and this goal is achieved in part by using software plug-ins, for example, many modern sound cards or built-in sound chips do not have a master volume control. This section provides an overview of basic concepts pertaining to ALSA, typically, ALSA supports up to eight cards, numbered 0 through 7, each card is a physical or logical kernel device capable of input, output. Furthermore, each card may also be addressed by its id, a device may have subdevices, numbered starting at 0, a subdevice represents some relevant sound endpoint for the device, such as a speaker pair. If the subdevice is not specified, or if subdevice number −1 is specified, a cards interface is a description of an ALSA protocol for accessing the card, possible interfaces include, hw, plughw, default, and plug, dmix. The hw interface provides direct access to the device. The project to develop ALSA was led by Jaroslav Kysela, and was based on the Linux device driver for the Gravis Ultrasound sound card and it started in 1998 and was developed separately from the Linux kernel until it was introduced in the 2.5 development series in 2002. In the 2.6 version, it replaced the system, Open Sound System. ALSA includes several pieces of application software, including alsactl, amixer, arecord/aplay command-line tools/utilities, as well as the alsamixer. Open Sound System DSSI udev JACK Audio Connection Kit KMid LADSPA PulseAudio Alsamixer Official website
20.
PulseAudio
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PulseAudio is a network-capable sound server program distributed via the freedesktop. org project. It runs on Linux, various BSD distributions such as FreeBSD and OpenBSD, macOS, microsoft Windows was previously supported via the MinGW toolchain. The Windows port has not been updated since 2011, however, PulseAudio is free and open-source software, and is licensed under the terms of the GNU Lesser General Public License. It is licensed under version 2.1 of the aforementioned license and it was created in 2004 under the name Polypaudio but was renamed in 2006 to PulseAudio. PulseAudio acts as a server, where a background process accepting sound input from one or more sources is created. The background process then redirects mentioned sound sources to one or more sinks, one of the goals of PulseAudio is to reroute all sound streams through it, including those from processes that attempt to directly access the hardware. PulseAudio achieves this by providing adapters to applications using other systems, like aRts. In a typical installation scenario under Linux, the user configures ALSA to use a device provided by PulseAudio. Thus, applications using ALSA will output sound to PulseAudio, which then uses ALSA itself to access the real sound card, in reality, their output is rerouted through PulseAudio. Libcanberra is an abstract API for desktop event sounds and a replacement for the PulseAudio sample cache API, Complies with the XDG Sound Theme. Defines a simple interface for playing event sounds. LibSydney is a replacement for the PulseAudio streaming API. The main PulseAudio features include, Per-application volume controls, an extensible plugin architecture with support for loadable modules. Compatibility with many audio applications. Support for multiple sources and sinks. Low latency operation and latency measurement, a zero-copy memory architecture for processor resource efficiency. Ability to discover other computers using PulseAudio on the local network, ability to change which output device applications use to play sound through while they are playing sound A command-line interface with scripting capabilities. A sound daemon with command line reconfiguration capabilities, built-in sample conversion and resampling capabilities
21.
Feedback
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Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself and this makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole. This action of feeding back of the signal output to input gave rise to the use of the term feedback as a distinct word by 1920. Over the years there has been dispute as to the best definition of feedback. According to Ashby, mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of circularity of action, for those with more practical aims, feedback should be a deliberate effect via some more tangible connection. Object to the definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum. Between its position and its momentum—a feedback that, from the point of view, is somewhat mystical. He emphasizes that the information by itself is not feedback unless translated into action, there are two types of feedback, positive feedback and negative feedback. As an example of feedback, the diagram might represent a cruise control system in a car, for example. The controlled system is the car, its input includes the combined torque from the engine, the cars speed is measured by a speedometer. The error signal is the departure of the speed as measured by the speedometer from the target speed and this measured error is interpreted by the controller to adjust the accelerator, commanding the fuel flow to the engine. The resulting change in torque, the feedback, combines with the torque exerted by the changing road grade to reduce the error in speed. The terms positive and negative were first applied to prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit, harold Stephen Blacks classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black, Positive feed-back increases the gain of the amplifier, according to Mindell confusion in the terms arose shortly after this. In contrast, Nyquist and Bode, when built on Black’s work. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition, the terms positive and negative feedback are defined in different ways within different disciplines. The altering of the gap between reference and actual values of a parameter, based on whether the gap is widening or narrowing
22.
General Services Administration
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The General Services Administration is an independent agency of the United States government, established in 1949 to help manage and support the basic functioning of federal agencies. GSA employs about 12,000 federal workers and has an operating budget of roughly $26.3 billion. GSA oversees $66 billion of procurement annually and it contributes to the management of about $500 billion in U. S. federal property, divided chiefly among 8,300 owned and leased buildings and a 210,000 vehicle motor pool. GSAs business lines include the Federal Acquisition Service, the Public Buildings Service, the GSA is member of the Procurement G6, an informal group leading the use of framework agreements and e-procurement instruments in public procurement. In 1947 President Harry Truman asked former President Herbert Hoover to lead what became known as the Hoover Commission to make recommendations to reorganize the operations of the federal government, one of the recommendations of the commission was the establishment of an Office of the General Services. This proposed office would combine the responsibilities of the following organizations, General Jess Larson, Administrator of the War Assets Administration, was named GSAs first Administrator. The first job awaiting Administrator Larson and the newly formed GSA was a renovation of the White House. The structure had fallen into such a state of disrepair by 1949 that one inspector of the time said the structure was standing “purely from habit. Everything, except the four walls without a roof, was stripped down. GSA completed the renovation in 1952, GSA headquarters, located at Eighteenth and F Streets, NW, was U. S. General Services Administration Building listed on the National Register of Historic Places in 1986 as Interior Department Offices, in 1960, GSA created the Federal Telecommunications System, a government-wide intercity telephone system. In 1970, the Nixon administration created the Consumer Product Information Coordinating Center, the Federal Buildings Fund was initiated in 1974, which allowed the GSA to issue rent bills to federal agencies. In 1972, the GSA established the Automated Data and Telecommunications Service, in 1973, the GSA created the Office of Federal Management Policy. GSA’s Office of Acquisition Policy centralized procurement policy in 1978, in 1984, GSA introduced the federal government to the use of charge cards, known as the GMA SmartPay system. The National Archives and Records Administration was spun off into an independent agency in 1985, the same year, the GSA began to provide governmentwide policy oversight and guidance for federal real property management as a result of an Executive Order signed by President Ronald Reagan. In 2003, the Federal Protective Service was moved to the Department of Homeland Security, in 2005, GSA reorganized to merge the Federal Supply Service and Federal Technology Service business lines into the Federal Acquisition Service. On April 3,2009, President Barack Obama nominated Martha N. Johnson to serve as the GSA Administrator, after a 9-month delay, the United States Senate confirmed her nomination on February 4,2010. In July 1991, GSA contractors began the excavation of what is now the Ted Weiss Federal Building in New York City, when initial excavation disturbed burials, destroying skeletons and artifacts, GSA sent archaeologists to excavate—but hid their findings from the public
23.
MIL-STD-188
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MIL-STD-188 is a series of U. S. military standards relating to telecommunications. S. Department of Defense looked to develop a series of standards that would alleviate the problem, … systems developed for use by U. S. forces are considered to be for joint use. The MIL-STD-188 standards were created to address telecommunication design parameters based on proven technologies, to ensure interoperability, DISA made these standards mandatory for use in all new DoD systems and equipment, or major upgrades. The mandatory use of standards will aid significantly in achieving standardization and result in improvements in availability, maintainability, reliability. This, in turn, will enhance lifecycle configuration management and logistic support with subsequent reductions in life cycle costs, in line with a decision by the Joint Chiefs of Staff, these standards are published in the MIL-STD-188 series of documents. The MIL-STD-188 series standards are encompassed by the DoD’s Joint Technical Architecture, for any DoD Agency to get a waiver to receive an item that deviates from the standards they also must apply to the JSC. Currently the DoD is placing its emphasis on the development of standards for tactical. Note, The following list of documents are those that are presently active, documents with three digit numbers followed by a letter of the alphabet indicate that they are revisions of an older version of that document. According to the DoD the MIL-STD-188-100 series contains technical standards and design objectives which are common to both the long haul and tactical communications systems, database with most MILSTD and DEFSTAN publications
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).