1.
Hayes Microcomputer Products
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Hayes Microcomputer Products was a U. S. -based manufacturer of modems. This smart modem approach dramatically simplified and automated operation, today almost all modems use a variant of the Hayes command set. Hayes was a brand in the modem market from the introduction of the original 300 bit/s Smartmodem in 1981. They remained a major throughout the 1980s, periodically introducing models with higher throughput. In the early 1990s a number of greatly cost-reduced high-performance modems were released by competitors, notably the SupraFAXModem 14400, Hayes was never able to respond effectively. The widespread introduction of ADSL and cable modems in the mid-1990s repeatedly drove the company in Chapter 11 protection before being liquidated in 1999, dennis C. Hayes job was to set up modem connections for NDCs customers. The connection and disconnection was entirely manual, with the picking up the phones handset, dialing manually. Disconnecting at the end of the session was also manual, with the user lifting the handset out of the coupler and hanging it up on the phone body. There were optional systems to dial the phone or pick it up, such devices were typically expensive, and generally used by larger organizations like banks, who might use one to send an end-of-day file to branch offices. Hayes was a computer hobbyist, and felt that modems would be compelling to users of the new 8-bit computers that would soon be known as home computers. However, existing modems were simply too expensive and difficult to use or be practical for most users. What was needed was a single modem that could do it all, connect directly to the phone, answer incoming calls, dial numbers to initiate outgoing calls, the main problem with producing such a modem was forwarding commands from the computer. This could be addressed in internal modems that plugged directly into the computers motherboard and this was a straightforward and thus a popular solution, the Novation APPLE-CAT II for the Apple II computer was an early programmable modem of this type. Hayes started producing similar products at a level in his kitchen in April 1977 with his friend and co-worker. Their first product was the 80-103A, a 300 bit/s Bell 103-compatible design for S-100 bus machines, business picked up quickly, and in January 1978 they quit their jobs at National Data to form their own company, D. C. Hayes Associates. In 1980 the company changed its name to Hayes Microcomputer Products, although powerful, the internal modem was commercially impractical. Not only did it require special software, but a different hardware design was needed for every computer bus, including Apple II, S-100, TRS-80. Some popular computers, like the Atari 400, did not even integrate internal slots, an obvious solution was to use the RS-232 serial port, modems were serial devices and generally driven off RS-232 anyway, and most computer designs included an RS-232 port, or some variant
2.
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
3.
USRobotics
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U. S. Robotics Corporation, often called USR, is a company that produces USRobotics computer modems and related products. Its initial marketing was aimed at bulletin board systems, where its high-speed HST protocol made FidoNet transfers much faster, during the 1990s it became a major consumer brand with its Sportster line. The company had a reputation for quality and support for the latest communications standards as they emerged, notably in its V. Everything line. With the reduced usage of analog or voiceband modems in North America in the early 21st century, the company purchased Palm, Inc. for its PalmPilot PDA, but was itself purchased by 3Com soon after. 3Com spun off USR again in 2000, keeping Palm and returning USR to the now much smaller modem market, after 2004 the company is formally known as USR. It is one of the few left in the modem market today. The company name is a reference to the fiction of Isaac Asimov, asimovs robot stories featured a fictional company named U. S. Cowell stated at a popular BBS convention they named the company as an homage to Asimov, robots eventually became the biggest company in the universe. USR was one of many companies to offer dial-up modems for personal computers, prior to the development of standards such as the V.32 family of protocols, USR introduced its own HST protocol in 1986, which operated at 9600 bit/s. In 1989 HST was expanded to 14.4 kbit/s,16.8 kbit/s in 1992, however, USR became the most successful of the three, due to a marketing scheme that offered large discounts to BBS sysops. The proprietary nature of HST allowed USR to maintain its market even when off-brand V. 32-based modems began selling for less than equivalent HST modems. As the price decreased, however, V. 32-based modems eventually became a cost-effective alternative to HST. The Sportster used the same motherboard as the Couriers, and on certain 14.4 kbit/s models a sequence of AT commands could be issued to enable the faster 16.8 kbit/s HST mode. The Courier modems remained a favorite in the BBS and emerging Internet service provider world, a similar situation emerged a few years later when the 56kbit/s V.90 standard was first being proposed. USR developed its own 56k standard known as X2, while a consortium of companies introduced its own K56flex. In contrast to the success of HST, neither X2 nor K56flex saw any real market uptake, after the introduction of V.90, USR abandoned support for X2. In a further effort to reduce the price of its modems. Some models of Courier modems were known for their long-term upgradeability, because they used an upgradeable DSP design
4.
SupraFAXModem 14400
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The SupraFAXModem 14400 was a v. 32bis modem. Launched in January 1992 at a price point, the 14,400 bit/s model was less expensive than most 9600 bit/s models, supported many additional features. Whereas a 9600 bit/s model was perhaps only a month before its introduction. Supra, Inc. had been a player in the computer market through the mid-to-late 1980s, known originally for their external hard drives for the Atari ST. During 1991, Rockwell Internationals chip-making arm developed a new modem driver chipset that included all of the latest standards that were then under development. Supra, never having been known as a player in the world, designed a modem based on the new chipset. Not content with simply being the first consumer v. 32bis modem on the market, one was the use of a much smaller case, about half the size of most models. The Supras smaller design made it easier to fit on a desk. Later models such as the LC used individual lamps that were a feature of external modems. In addition to the modem, Supra also introduced software to make better use of all the features of the modem. In particular, Supra re-packaged FAXstf as FAXCilitate, a Macintosh fax application that any application that supported printing to send the output as a fax instead. They later introduced Supra VoiceMail, another Mac application written by STF Technologies that turned the computer into a digital answering machine with caller id routing, the SupraFAXModem was by no means a perfect product. Both of these make them unsuitable for host side use on a bulletin board system or internet service provider. Supra also released a v.32 version at the same time, mentions of it disappear by late 1992. The 144LC was a Low-Cost version that lacked the alphanumeric display and they followed up the 14400s with the SupraFAXModem 288, the first consumer v.34 modem, and then a series of various versions with different features. The SupraExpress was a low-cost series that scaled to lower price points, housed in an all-plastic case, news/Networking, InfoWorld,10 February 1992, pg.53. SupraFAXModem, news release in the Atari SIG of the Cleveland Freenet
5.
Bulletin board system
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A bulletin board system, or BBS, is a computer server running software that allows users to connect to the system using a terminal program. Many BBSes also offer on-line games, in users can compete with each other. Bulletin board systems were in many ways a precursor to the form of the World Wide Web, social networks. Low-cost, high-performance modems drove the use of services and BBSes through the early 1990s. Infoworld estimated there were 60,000 BBSes serving 17 million users in the United States alone in 1994, over the next year, many of the leading BBS software providers went bankrupt and tens of thousands of BBSes disappeared. Today, BBSing survives largely as a hobby in most parts of the world. Most BBSes are now accessible over Telnet and typically offer free email accounts, FTP services, IRC, some offer access through packet switched networks, or packet radio connections. A precursor to the bulletin board system was Community Memory, started in August 1973 in Berkeley. Useful microcomputers did not exist at that time, and modems were both expensive and slow, Community Memory therefore ran on a mainframe computer and was accessed through terminals located in several San Francisco Bay Area neighborhoods. The poor quality of the original modem connecting the terminals to the mainframe prompted a user to invent the Pennywhistle modem, Community Memory allowed the user to type messages into a computer terminal after inserting a coin, and offered a pure bulletin board experience with public messages only. It did offer the ability to tag messages with keywords, which the user could use in searches, the system acted primarily in the form of a buy and sell system with the tags taking the place of the more traditional classifications. But users found ways to express themselves outside these bounds, unfortunately, the system was expensive to operate, and when their host machine became unavailable and a new one could not be found, the system closed in January 1975. Similar functionality was available to most mainframe users, which might be considered a sort of ultra-local BBS when used in this fashion. Commercial systems, expressly intended to offer features to the public, became available in the late 1970s. Early modems were very simple devices using acoustic couplers to handle telephone operation. The user would first pick up the phone, dial a number, disconnecting at the end of a call required the user to pick up the handset and return it to the phone. With the introduction of microcomputers with expansion slots, like the S-100 bus machines and Apple II, it possible for the modem to communicate instructions. A number of modems of this sort were available by the late 1970s
6.
Telephone line
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A telephone line or telephone circuit is a single-user circuit on a telephone communication system. Telephone lines are used to deliver landline telephone service and Digital subscriber line phone service to the premises. Telephone overhead lines are connected to the switched telephone network. Modern lines may run underground, and may carry analog or digital signals to the exchange, often the customer end of that wire pair is connected to a data access arrangement, the telephone company end of that wire pair is connected to a telephone hybrid. In most cases, two wires for each telephone line run from a home or other small building to a local telephone exchange. The wires between the box and the exchange are known as the local loop, and the network of wires going to an exchange. The vast majority of houses in the U. S. are wired with 6-position modular jacks with four conductors wired to the junction box with copper wires. Those wires may be connected back to two telephone lines at the local telephone exchange, thus making those jacks RJ14 jacks. More often, only two of the wires are connected to the exchange as one line, and the others are unconnected. In that case, the jacks in the house are RJ11, inside the walls of the house—between the houses outside junction box and the interior wall jacks—the most common telephone cable in new houses is Category 5 cable—4 pairs of 24 AWG solid copper. Inside large buildings, and in the cables that run to the telephone company POP
7.
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
8.
Computer terminal
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A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system. The function of a terminal is confined to display and input of data, a terminal that depends on the host computer for its processing power is called a dumb terminal or thin client. A personal computer can run terminal emulator software that replicates the function of a terminal, sometimes allowing concurrent use of local programs and access to a distant terminal host system. The terminal of the first working programmable, fully automatic digital Turing-complete computer, the Z3, had a keyboard, early user terminals connected to computers were electromechanical teleprinters/teletypewriters, such as the Teletype Model 33 ASR, originally used for telegraphy or the Friden Flexowriter. Later printing terminals such as the DECwriter LA30 were developed, however printing terminals were limited by the speed at which paper could be printed, and for interactive use the paper record was unnecessary. The problem was that the amount of memory needed to store the information on a page of text was comparable to the memory in low end minicomputers then in use. Displaying the information at video speeds was also a challenge and the control logic took up a rack worth of pre-integrated circuit electronics. Another approach involved the use of the tube, a specialized CRT developed by Tektronix that retained information written on it without the need to refresh. The Datapoint 3300 from Computer Terminal Corporation was announced in 1967 and shipped in 1969 and it solved the memory space issue mentioned above by using a digital shift-register design, and using only 72 columns rather than the later more common choice of 80. Some type of blinking cursor that can be positioned, the term intelligent in this context dates from 1969. Notable examples include the IBM2250 and IBM2260, predecessors to the IBM3270, providing even more processing possibilities, workstations like the Televideo TS-800 could run CP/M-86, blurring the distinction between terminal and Personal Computer. Most terminals were connected to minicomputers or mainframe computers and often had a green or amber screen, typically terminals communicate with the computer via a serial port via a null modem cable, often using an EIA RS-232 or RS-422 or RS-423 or a current loop serial interface. In fact, the design for the Intel 8008 was originally conceived at Computer Terminal Corporation as the processor for the Datapoint 2200. While early IBM PCs had single color green screens, these screens were not terminals. The screen of a PC did not contain any character generation hardware, all signals and video formatting were generated by the video display card in the PC, or by the CPU. An IBM PC monitor, whether it was the monochrome display or the 16-color display, was technically much more similar to an analog TV set than to a terminal. With suitable software a PC could, however, emulate a terminal, the Data General One could be booted into terminal emulator mode from its ROM. Since the advent and subsequent popularization of the computer, few genuine hardware terminals are used to interface with computers today
9.
Mainframe computer
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The term originally referred to the large cabinets called main frames that housed the central processing unit and main memory of early computers. Later, the term was used to distinguish high-end commercial machines from less powerful units, most large-scale computer system architectures were established in the 1960s, but continue to evolve. Their high stability and reliability enable these machines to run uninterrupted for decades, Mainframes are defined by high availability, one of the main reasons for their longevity, since they are typically used in applications where downtime would be costly or catastrophic. The term reliability, availability and serviceability is a characteristic of mainframe computers. Proper planning and implementation is required to exploit these features, and if improperly implemented, in the late 1950s, most mainframes had no explicitly interactive interface, but only accepted sets of punched cards, paper tape, or magnetic tape to transfer data and programs. In cases where interactive terminals were supported, these were used almost exclusively for applications rather than program development, typewriter and Teletype devices were also common control consoles for system operators through the 1970s, although ultimately supplanted by keyboard/display devices. By the early 1970s, many mainframes acquired interactive user interfaces and operated as timesharing computers, users gained access through specialized terminals or, later, from personal computers equipped with terminal emulation software. By the 1980s, many mainframes supported graphical terminals, and terminal emulation and this format of end-user computing reached mainstream obsolescence in the 1990s due to the advent of personal computers provided with GUIs. After 2000, most modern mainframes have partially or entirely phased out classic green screen terminal access for end-users in favour of Web-style user interfaces, the infrastructure requirements were drastically reduced during the mid-1990s, when CMOS mainframe designs replaced the older bipolar technology. IBM claimed that its newer mainframes could reduce data center energy costs for power and cooling, modern mainframes can run multiple different instances of operating systems at the same time. This technique of virtual machines allows applications to run as if they were on physically distinct computers, in this role, a single mainframe can replace higher-functioning hardware services available to conventional servers. While mainframes pioneered this capability, virtualization is now available on most families of computer systems, Mainframes can add or hot swap system capacity without disrupting system function, with specificity and granularity to a level of sophistication not usually available with most server solutions. Modern mainframes, notably the IBM zSeries, System z9 and System z10 servers, such a two-mainframe installation can support continuous business service, avoiding both planned and unplanned outages. In practice many customers use multiple mainframes linked either by Parallel Sysplex and shared DASD, or with shared, Mainframes are designed to handle very high volume input and output and emphasize throughput computing. Since the late-1950s, mainframe designs have included subsidiary hardware which manage the I/O devices and it is common in mainframe shops to deal with massive databases and files. Gigabyte to terabyte-size record files are not unusual, compared to a typical PC, mainframes commonly have hundreds to thousands of times as much data storage online, and can access it reasonably quickly. Other server families also offload I/O processing and emphasize throughput computing, Mainframes also have execution integrity characteristics for fault tolerant computing. This hardware-level feature, also found in HPs NonStop systems, is known as lock-stepping, not all applications absolutely need the assured integrity that these systems provide, but many do, such as financial transaction processing
10.
Microcomputer revolution
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Prior to 1977, the only contact most of the population had with computers was through utility bills, bank and payroll services, or computer-generated junk mail. Within a decade, computers became common consumer goods, the advent of affordable personal computers has had lasting impact on education, business, music, social interaction, and entertainment. The minicomputer ancestors of the personal computer used early integrated circuit technology, which reduced size and cost. This meant that they were large and difficult to manufacture just like their mainframe predecessors. After the computer-on-a-chip was commercialized, the cost to manufacture a computer system dropped dramatically, the arithmetic, logic, and control functions that previously occupied several costly circuit boards were now available in one integrated circuit, making it possible to produce them in high volume. Concurrently, advances in the development of solid state memory eliminated the bulky, costly, after the 1971 introduction of the Intel 4004, microprocessor costs declined rapidly. In 1974 the American electronics magazine Radio-Electronics described the Mark-8 computer kit, in January of the following year, Popular Electronics magazine published an article describing a kit based on the Intel 8080, a somewhat more powerful and easier to use processor. The Altair 8800 sold remarkably well even though initial memory size was limited to a few hundred bytes, expansion memory boards and peripherals were soon listed by the original manufacturer, and later by plug compatible manufacturers. The very first Microsoft product was a 4 kilobyte paper tape BASIC interpreter, the alternative was to hand-assemble machine code that could be directly loaded into the microcomputers memory using a front panel of toggle switches, pushbuttons and LED displays. Children would use disk-based encyclopedias for school work and would be avid video gamers, home automation would bring about the intelligent home of the 1980s. Using Videotex, NAPLPS or some sort of as-yet unrealized computer technology, the personalized newspaper was a commonly predicted application. Morning coffee would be brewed automatically under computer control, the same computer would control the house lighting and temperature. Robots would take the garbage out, and be programmable to perform new tasks by the home computer, all this was predicted to be commonplace sometime before the end of the decade, but virtually every aspect of the predicted revolution would be delayed or prove entirely impractical. The computers available to consumers of the period just werent powerful enough to perform any single task required to realize this vision. The home computers of the early 1980s could not multitask, before long, a backlash set in—computer users were geeks, nerds or worse, hackers. The North American video game crash of 1983 soured many on home computer technology, predicted aspects of the revolution were left by the wayside or modified in the face of an emerging reality. The cost of electronics dropped precipitously and today many families have a computer for each family member, encyclopedias, recipe catalogs and medical databases are kept online and accessed over the world wide web not stored locally on floppy disks or CD-ROM. Our coffee may be brewed automatically every morning, but the computer is a simple one embedded in the coffee maker, as of 2008, robots are just beginning to make an impact in the home, with Roomba and Aibo leading the charge
11.
Internationalization and localization
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In computing, internationalization and localization are means of adapting computer software to different languages, regional differences and technical requirements of a target market. Internationalization is the process of designing a software application so that it can potentially be adapted to various languages, localization is the process of adapting internationalized software for a specific region or language by adding locale-specific components and translating text. Localization uses the infrastructure or flexibility provided by internationalization, the terms are frequently abbreviated to the numeronyms i18n and L10n for localization, due to the length of the words. Some companies, like IBM and Sun Microsystems, use the term globalization, g11n, Microsoft defines Internationalization as a combination of World-Readiness and localization. World-Readiness is a task, which enables a product to be used with multiple scripts and cultures. Hewlett-Packard and HP-UX created the system called NLS to produce localizable software, translation is typically the most time-consuming component of language localization. These differences may need to be taken account by the internationalization process in preparation for translation. Many of these differences are so regular that a conversion between languages can be easily automated, the Common Locale Data Repository by Unicode provides a collection of such differences. Its data is used by operating systems, including Microsoft Windows, OS X and Debian, and by major internet companies or projects such as Google. Examples of such include, Different scripts in different writing systems use different characters - a different set of letters, syllograms, logograms. Modern system use the Unicode standard to represent many different languages with a character encoding. Writing direction is left to right in most European languages, right-to-left in Hebrew and Arabic, complex text layout, for languages where characters change shape depending on context. Capitalization exists in some scripts and not in others, other grammar rules might also vary, e. g. genitive. Keyboard shortcuts can only use of buttons actually on the keyboard layout which is being localized for. If a shortcut corresponds to a word in a particular language, other areas often follow one of these. Specific third-party services, such as maps, weather reports, or payment service providers, might not be available worldwide from the same carriers. Time zones vary across the world, and this must be taken into account if a product originally only interacted with people in a time zone. For internationalization, UTC is often used internally and then converted into a time zone for display purposes
12.
Denial-of-service attack
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A DoS attack is analogous to a group of people crowding the entry door or gate to a shop or business, and not letting legitimate parties enter into the shop or business, disrupting normal operations. Criminal perpetrators of DoS attacks often target sites or services hosted on high-profile web servers such as banks or credit card payment gateways, revenge, blackmail and activism can motivate these attacks. Denial-of-service attacks are characterized by an attempt by attackers to prevent legitimate users of a service from using that service. In a distributed denial-of-service attack, the traffic flooding the victim originates from many different sources – potentially hundreds of thousands or more. There are two forms of DoS attacks, those that crash services and those that flood services. The most serious attacks are distributed, court testimony shows us the first demonstration of DoS attack was made by Khan C. A distributed denial-of-service is a cyber-attack where the perpetrator uses more than one unique IP address, the scale of DDoS attacks has continued to rise over recent years, by 2016 exceeding a terabit per second. APDoS attacks represent a clear and emerging threat needing specialised monitoring and incident response services and this type of attack involves massive network layer DDoS attacks through to focused application layer floods, followed by repeated SQLi and XSS attacks. These attacks can persist for several weeks- the longest continuous period noted so far lasted 38 days and this APDoS attack involved approximately 50+ petabits of malicious traffic. Some vendors provide so-called booter or stresser services, which have simple web-based front ends, additional symptoms may include, disconnection of a wireless or wired internet connection long-term denial of access to the web or any internet services. A wide array of programs are used to launch DoS-attacks, in cases such as MyDoom the tools are embedded in malware, and launch their attacks without the knowledge of the system owner. Stacheldraht is an example of a DDoS tool. Agents are compromised via the handlers by the attacker, using automated routines to exploit vulnerabilities in programs that accept remote connections running on the remote hosts. Each handler can control up to a thousand agents, in other cases a machine may become part of a DDoS attack with the owners consent, for example, in Operation Payback, organized by the group Anonymous. The LOIC has typically used in this way. Along with HOIC a wide variety of DDoS tools are available today, including paid and free versions, there is an underground market for these in hacker related forums and IRC channels. UKs GCHQ has tools built for DDoS, named PREDATORS FACE, various DoS-causing exploits such as buffer overflow can cause server-running software to get confused and fill the disk space or consume all available memory or CPU time. Other kinds of DoS rely primarily on brute force, flooding the target with a flux of packets
13.
Telecommunications Industry Association
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The Telecommunications Industry Assocs most widely adopted standards include, TIA-942 Telecommunications Infrastructure Standard for Data Centers TIA-568-C. TIA is a standards organization of the ITU-T Global Standards Collaboration initiative. The TIA2012 is Conference & Exhibition, scheduled for June 5–7 at the Gaylord Hotel in Dallas, Texas, focused on innovation and thought leadership, TIA2012 is the annual gathering of the community of technology suppliers that form the foundation of the global communications experience. TIA2012 is the annual community gathering of all who create, distribute and use network technologies, network engineers and designers, product managers. TIA Now is a media outlet of TIA that informs about ICT trends, event. They interview top level executives and thought leaders that shape the development of the information and communication industry ICT and it delivers a perspective on policy, industry news, new technologies and evolving business strategies designed to inform and educate an audience of ICT decision-makers
14.
Electronic Industries Alliance
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The Electronic Industries Alliance was a standards and trade organization composed as an alliance of trade associations for electronics manufacturers in the United States. They developed standards to ensure the equipment of different manufacturers was compatible and interchangeable, the EIA ceased operations on February 11,2011, but the former sectors continue to serve the constituencies of EIA. In 1924 United States-based radio manufacturers formed a group called the Associated Radio Manufacturers. Later that same year, the group renamed itself the Radio Manufacturers Association, the organizations headquarters were in Arlington, Virginia. The Alliance formally ceased to exist on February 11,2011, EIA designated ECA to continue to develop standards for interconnect, passive and electro-mechanical electronic components under the ANSI-designation of EIA standards. All other electronic components standards will be managed by their respective sectors, the ECA merged with the National Electronic Distributors Association in 2011 to form the Electronic Components Industry Association. However, the EIA standards brand will continue for IP&E standards within ECIA, with the changing names of the EIA, the naming convention of the standards was also adapted. For example, a standard defining serial communication between computers and modems e. g. was originally drafted as a Recommended Standard, thus the RS RS-232, later it was taken over by the EIA as EIA-232. Later this standard was managed by the TIA and the name was changed to the current TIA-232, because the EIA was accredited by ANSI to help develop standards in its areas, the standards are often described as e. g. ANSI TIA-232. As currently authorized, any ANSI standard designated at ANSI EIA-xxx is developed and/or managed by ECA, the JEDEC history page, including EIA history
15.
Telebit
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Telebit was a US-based modem manufacturer, known for their TrailBlazer series of high-speed modems. They were particularly common in Unix installations in the 1980s and 1990s, Telebit was founded by Paul Baran, one of the inventors of the packet switching networking concept. Baran had recently started a company known as Packet Technologies on Bubb Road in Cupertino, California. While working there, he hit on the idea for a new way to implement high-speed modems, Packet Technologies was a major beta customer for Telebit in late 1985. Packet Technologies later failed, and several of their employees were folded into Telebit, while most of the others formed StrataCom, in contrast to then-existing ITU Telecommunication Standardization Sector V-series protocols, such as the common 2400 bit/s V. Under favorable conditions, the devices could reach data rates of 6 baud x 6 bits-per-baud x 512 carriers =18432 bits per second. If a particular carrier was distorted, attenuated or interfered with, it could be turned off, using a large number of carriers spread across the phone networks bandwidth meant that the chance that any one carrier would be subject to a problem was high. In order to correct for the errors this would cause. In contrast, something like a 2400 bit/s modem might suffer from a number of errors in a given time. And if those errors were being caused by a constant source of noise on those frequencies, PEP would simply turn those carriers off, while the 2400 bit/s modem could do nothing about this. Most modems of the era were set up with both channels with equal speed, or, in the case where data was sent in one direction. The TrailBlazer instead allowed any one of its 512 channels to be assigned to data in either direction. The modem was designed to use most of the bandwidth in a single direction, with a relatively low speed reverse channel. This also caused problems for file transfer protocols, e. g. UUCP g or Kermit, the TrailBlazer addressed this problem through a technique known as protocol spoofing. When the local computer sent a packet to the modem for transmission and this fooled the computer into thinking the packet had already reached the far end, prompting it to send another packet. The error correction normally being applied in the protocol was instead handled using a proprietary replacement protocol operating on top of the MNP protocols to talk to the remote modem. Support for these features did not come cheaply, the TrailBlazer Plus, for instance and this meant that the TrailBlazers were generally very expensive. Improvements of over 7 times faster than a 2400 bit/s modem were not uncommon, sites that required long-distance telephone calls to exchange UUCP mail could pay for the price of a TrailBlazer in long-distance savings fairly quickly
16.
Initialization vector
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In cryptography, an initialization vector or starting variable is a fixed-size input to a cryptographic primitive that is typically required to be random or pseudorandom. For block ciphers, the use of an IV is described by the modes of operation, randomization is also required for other primitives, such as universal hash functions and message authentication codes based thereon. Some cryptographic primitives require the IV only to be non-repeating, in this case, the IV is commonly called a nonce, and the primitives are described as stateful as opposed to randomized. This is because the IV need not be forwarded to a recipient. An example of stateful encryption schemes is the mode of operation. The size of the IV is dependent on the cryptographic primitive used, for block ciphers, ideally, for encryption schemes, the unpredictable part of the IV has the same size as the key to compensate time/memory/data tradeoff attacks. When the IV is chosen at random, the probability of collisions due to the problem must be taken into account. Traditional stream ciphers such as RC4 do not support an explicit IV as input, some designs realized in practice are known to be insecure, the WEP protocol is a notable example, and is prone to related-IV attacks. A block cipher is one of the most basic primitives in cryptography, however, by itself, it can only be used to encode a data block of a predefined size, called the block size. For example, an invocation of the AES algorithm transforms a 128-bit plaintext block into a ciphertext block of 128 bits in size. The key, which is given as one input to the cipher, if data of arbitrary length is to be encrypted, a simple strategy is to split the data into blocks each matching the ciphers block size, and encrypt each block separately using the same key. To hide patterns in encrypted data while avoiding the re-issuing of a new key after each block cipher invocation, the first mode implements the simple strategy described above, and was specified as the electronic codebook mode. In contrast, each of the other modes describe a process where ciphertext from one block encryption step gets intermixed with the data from the next encryption step. To initiate this process, an input value is required to be mixed with the first block. For example, the cipher-block chaining mode requires a value of the ciphers block size as additional input. In turn, the ciphertext produced in the first encryption step is added to the plaintext block. The ultimate goal for encryption schemes is to provide security, by this property. It can be shown that each of the three additional modes specified by the NIST are semantically secure under so-called chosen-plaintext attacks, properties of an IV depend on the cryptographic scheme used
17.
Data circuit-terminating equipment
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A data circuit-terminating equipment is a device that sits between the data terminal equipment and a data transmission circuit. It is also called data communication equipment and data carrier equipment, usually, the DTE device is the terminal, and the DCE is a modem. In a data station, the DCE performs functions such as conversion, coding. Interfacing equipment may be required to couple the data terminal equipment into a circuit or channel. Although the terms are most commonly used with RS-232, several data communication standards define different types of interfaces between a DCE and a DTE, the DCE is a device that communicates with a DTE device in these standards. D-sub connectors follow another rule for pin assignment, DTE devices usually transmit on pin connector number 2 and receive on pin connector number 3. DCE devices are just the opposite, pin connector number 2 receives, Data Terminating Equipment or Data Circuit-Terminating Equipment speeds, IBM
18.
Terminal emulator
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A terminal emulator, terminal application, term, or tty for short, is a program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the terminal covers all remote terminals. A terminal emulator inside a graphical interface is often called a terminal window. A terminal window allows the access to a text terminal and all its applications such as command-line interfaces. These may be running either on the machine or on a different one via telnet, ssh. On Unix-like operating systems, it is common to have one or more terminal windows connected to the local machine, terminals usually support a set of escape sequences for controlling color, cursor position, etc. Examples include the family of terminal control sequence standards known as ECMA-48, Terminal emulators may implement a local echo function, which may erroneously be named half-duplex, or still slightly incorrectly echoplex. Terminal emulators may implement local editing, also known as line-at-a-time mode and this is also mistakenly referred to as half-duplex. In this mode, the terminal emulator only sends complete lines of input to the host system, the user enters and edits a line, but it is held locally within the terminal emulator as it is being edited. It is not transmitted until the user signals its completion, usually with the ↵ Enter key on the keyboard or a button of some sort in the user interface. At that point the line is transmitted. Line-at-a-time mode implies local echo, since otherwise the user will not be able to see the line as it is being edited and constructed, however, line-at-a-time mode is independent of echo mode and does not require local echo. When entering a password, for example, line-at-a-time entry with local editing is possible, the complexities of line-at-a-time mode are exemplified by the line-at-a-time mode option in the telnet protocol. In asynchronous terminals data can flow in any direction at any time, in synchronous terminals a protocol controls who may send data when. IBM 3270-based terminals used with IBM mainframe computers are an example of synchronous terminals and they operate in an essentially screen-at-a-time mode. Users can make changes to a page, before submitting the updated screen to the remote machine as a single action. Other examples of synchronous terminals include the IBM5250, ICL7561, Honeywell Bull VIP7800, additionally, programs have been developed to emulate other terminal emulators such as xterm and assorted console terminals. Finally, some emulators simply refer to a standard, such as ANSI, such programs are available on many platforms ranging from DOS and Unix to Windows and macOS to embedded operating systems found in cellphones and industrial hardware
19.
NO CARRIER
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NO CARRIER is a text message transmitted from a modem to its attached device, indicating the modem is not connected to a remote system. NO CARRIER is a message that is defined in the Hayes command set. Due to the popularity of Hayes modems during the heyday of dial-up connectivity, for this reason, the NO CARRIER message was ubiquitously understood to mean that one was no longer connected to a remote system. A carrier tone is a carrier signal used by two modems to suppress echo cancellation and establish a baseline frequency for communication. When the answering modem detects a ringtone on the line, it picks up that line. If it does not receive data from the calling modem within a set amount of time, the calling modem waits for the tone after it dials the phone line before it initiates data transmission. If it does not receive a carrier tone within a set amount of time, it will disconnect the phone line, the actual data is transmitted from the answering modem to the calling modem via modulation of the carrier. A dial or answer command was aborted while in progress, the abort can be triggered by the computer receiving a keypress to abort or the computer dropping the Data Terminal Ready signal to hang up. A previously established data connection has ended, and the modem has now gone from the mode to the command mode. The NO CARRIER message can be used at the end of a sentence for humorous purposes in Internet messages and forum posts and this joke may mean that the typist was writing something excessively boring or illogical, or something the authorities would supposedly want to suppress. Alternatively, it may imply they were simply a victim of bad luck and this joke anachronistically continues to be seen on the Internet despite the waning use of modems in favor of broadband connectivity. In non-English speaking areas the joke may include the translation of carrier by using a word indicating aircraft carrier
20.
Least significant bit
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In computing, the least significant bit is the bit position in a binary integer giving the units value, that is, determining whether the number is even or odd. The LSB is sometimes referred to as the right-most bit, due to the convention in positional notation of writing less significant digits further to the right and it is analogous to the least significant digit of a decimal integer, which is the digit in the ones position. It is common to each bit a position number, ranging from zero to N-1. Normally, this is simply the exponent for the corresponding bit weight in base-2, although a few CPU manufacturers assign bit numbers the opposite way, the term least significant bit itself remains unambiguous as an alias for the unit bit. By extension, the least significant bits are the bits of the number closest to, and including, the least significant bits have the useful property of changing rapidly if the number changes even slightly. For example, if 1 is added to 3, the result will be 4, by contrast, the three most significant bits stay unchanged. Least significant bits are employed in pseudorandom number generators, hash functions. This table illustrates an example of value of 149 and the location of LSB. In this particular example, the position of unit value is located in bit position 0, MSB stands for Most Significant Bit, while LSB stands for Least Significant Bit. Position of LSB is independent of how the bit position is transmitted, LSB can also stand for least significant byte. The meaning is parallel to the above, it is the byte in that position of a number which has the least potential value. If the abbreviations meaning least significant byte isnt obvious from context, to avoid this ambiguity, the less abbreviated terms lsbit or lsbyte are often used. Binary numeral system Signed number representations Twos complement Bit numbering Endianness Binary logarithm Unit in the last place
21.
Plug and play
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Plug and play devices can be due to boot-time assignment of device resources and to hotplug systems such as USB and IEEE1394. In the beginnings of data processing technology, the hardware was just a collection of modules, and this linking was usually done by connecting some wires between modules and disconnecting others. Some early microcomputing devices such as the Apple II sometimes required the end-user to physically cut some wires, the changes were intended to be largely permanent for the life of the hardware. As computers became more accessible to the public, the need developed for more frequent changes to be made by computer users unskilled with using soldering irons. Rather than cutting and soldering connections, configuration was accomplished by jumpers or DIP switches, however, the process of configuring devices manually using jumpers or DIP switches, could be quite difficult, and there was usually no forgiveness for technical inexperience. Incorrect settings could render either the system or just the expansion device completely or partially inoperable. The system might still have seemed to work properly with a setting, until the IRQ or DMA was actually needed. No jumpers or any manual configuration was required, and the independent address space for each slot allowed very cheap & commonplace chips to be used, alongside with cheap glue logic. On the software site, the drivers and extensions were supplied in the cards own ROM, the ROM extensions abstracted any hardware differences and offered standard APIs as specified by ASCII Corporation. In 1984, the NuBus architecture was developed by the Massachusetts Institute of Technology as a platform agnostic peripheral interface that fully automated device configuration, the specification was sufficiently intelligent that it could work with both big endian and little endian computer platforms that had previously been mutually incompatible. However, this agnostic approach increased interfacing complexity and required support chips on every device which in the 1980s was expensive to do, in 1984, Commodore developed the AutoConfig protocol and the Zorro expansion bus for its Amiga line of expandable computers. The first public appearance was in the CES computer show at Las Vegas in 1985, like NuBus, Zorro devices had absolutely no jumpers or DIP switches. The Zorro architecture did not spread to general computing use outside of the Amiga product line, in 1987, IBM released an update to the IBM PC known as the Personal System/2 line of computers using the Micro Channel Architecture. The PS/2 was capable of totally automatic self-configuration, every piece of expansion hardware was issued with a floppy disk containing a special file used to auto-configure the hardware to work with the computer. The user would install the device, turn on the computer, load the configuration information from the disk, and the hardware automatically assigned interrupts, DMA, and so forth. However, the disks posed a problem if they were damaged or lost, without the disks, any new hardware would be completely useless and the computer would not boot at all until the unconfigured device was removed. Microchannel did not gain support, because IBM wanted to exclude clone manufacturers from this next generation computing platform. Anyone developing for MCA had to sign agreements and pay royalties to IBM for each device sold
22.
Tilde
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The tilde is a grapheme with several uses. The name of the character came into English from Spanish, which in came from the Latin titulus. The reason for the name was that it was written over a letter as a scribal abbreviation, as a mark of suspension. Thus the commonly used words Anno Domini were frequently abbreviated to Ao Dñi, such a mark could denote the omission of one letter or several letters. This saved on the expense of the labour and the cost of vellum. Medieval European charters written in Latin are largely made up of such abbreviated words with suspension marks and other abbreviations, the tilde has since been applied to a number of other uses as a diacritic mark or a character in its own right. These are encoded in Unicode at U+0303 ◌̃ Combining Tilde and U+007E ~ Tilde, in lexicography, the latter kind of tilde and the swung dash are used in dictionaries to indicate the omission of the entry word. This symbol informally means approximately, about, or around, such as ~30 minutes before and it can mean similar to, including of the same order of magnitude as, such as, x ~ y meaning that x and y are of the same order of magnitude. The tilde is used to indicate equal to or approximately equal to by placing it over the = symbol, like so. The text of the Domesday Book of 1086, relating for example, the text with abbreviations expanded is as follows, Mollande tempore regis Edwardi geldabat pro iiii hidis et uno ferling. In dominio sunt iii carucae et x servi et xxx villani et xx bordarii cum xvi carucis, ibi xii acrae prati et xv acrae silvae. Pastura iii leugae in longitudine et latitudine, elwardus tenebat tempore regis Edwardi pro manerio et geldabat pro dimidia hida. Ibi sunt v villani cum i servo, valet xx solidos ad pensam et arsuram. Eidem manerio est injuste adjuncta Nimete et valet xv solidos, ipsi manerio pertinet tercius denarius de Hundredis Nortmoltone et Badentone et Brantone et tercium animal pasturae morarum. The incorporation of the tilde into ASCII is a result of its appearance as a distinct character on mechanical typewriters in the late nineteenth century. Any good typewriter store had a catalog of alternative keyboards that could be specified for machines ordered from the factory, at that time, the tilde was used only in Spanish and Portuguese typewriters. In Modern Spanish, the tilde is used only with n and N, both were conveniently assigned to a single mechanical typebar, which sacrificed a key that was felt to be less important, usually the 1⁄2— 1⁄4 key. Portuguese, however, uses not ñ but nh and it uses the tilde on the vowels a and o
23.
GSM
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As of 2014 it has become the de facto global standard for mobile communications – with over 90% market share, operating in over 219 countries and territories. This expanded over time to include communications, first by circuit-switched transport, then by packet data transport via GPRS. Subsequently, the 3GPP developed third-generation UMTS standards followed by fourth-generation LTE Advanced standards, GSM is a trademark owned by the GSM Association. It may also refer to the most common voice codec used, the decision to develop a continental standard eventually resulted in a unified, open, standard-based network which was larger than that in the United States. In February 1987 Europe produced the very first agreed GSM Technical Specification, the MoU drew-in mobile operators from across Europe to pledge to invest in new GSM networks to an ambitious common date. In 1989, the Groupe Spécial Mobile committee was transferred from CEPT to the European Telecommunications Standards Institute, in parallel, France and Germany signed a joint development agreement in 1984 and were joined by Italy and the UK in 1986. In 1986 the European Commission proposed reserving the 900 MHz spectrum band for GSM, the former Finnish prime minister Harri Holkeri made the worlds first GSM call on July 1,1991, calling Kaarina Suonio using a network built by Telenokia and Siemens and operated by Radiolinja. In the following year,1992, saw the sending of the first short messaging service message, work began in 1991 to expand the GSM standard to the 1800 MHz frequency band and the first 1800 MHz network became operational in the UK by 1993 called and DCS1800. Also that year, Telecom Australia became the first network operator to deploy a GSM network outside Europe and the first practical hand-held GSM mobile phone became available. In 1995, fax, data and SMS messaging services were launched commercially, in the same year, the GSM Association formed. Pre-paid GSM SIM cards were launched in 1996 and worldwide GSM subscribers passed 100 million in 1998, in 2000 the first commercial GPRS services were launched and the first GPRS-compatible handsets became available for sale. In 2001 the first UMTS network was launched, a 3G technology that is not part of GSM, worldwide GSM subscribers exceeded 500 million. In 2002 the first Multimedia Messaging Service were introduced and the first GSM network in the 800 MHz frequency band became operational, EDGE services first became operational in a network in 2003 and the number of worldwide GSM subscribers exceeded 1 billion in 2004. By 2005, GSM networks accounted for more than 75% of the cellular network market. In 2005 the first HSDPA-capable network also became operational, the first HSUPA network launched in 2007. Worldwide GSM subscribers exceeded three billion in 2008, GSM is a second-generation standard employing time-division multiple-Access spectrum-sharing, issued by the European Telecommunications Standards Institute. GSM, for the first time, set a standard for Europe for wireless networks. It was also adopted by many countries outside Europe and this allowed subscribers to use other GSM networks that have roaming agreements with each other
24.
SMS
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Short Message Service is a text messaging service component of most telephone, World Wide Web, and mobile telephony systems. It uses standardized protocols to enable mobile phone devices to exchange short text messages. SMS, as used on modern handsets, originated from radio telegraphy in radio memo pagers that used standardized phone protocols and these were defined in 1985 as part of the Global System for Mobile Communications series of standards. The protocols allowed users to send and receive messages of up to 160 alpha-numeric characters to, though most SMS messages are mobile-to-mobile text messages, support for the service has expanded to include other mobile technologies, such as ANSI CDMA networks and Digital AMPS. SMS is also employed in marketing, a type of direct marketing. Adding text messaging functionality to mobile devices began in the early 1980s, the first action plan of the CEPT Group GSM was approved in December 1982, requesting that, The services and facilities offered in the public switched telephone networks and public data networks. Should be available in the mobile system and this plan included the exchange of text messages either directly between mobile stations, or transmitted via message handling systems in use at that time. The SMS concept was developed in the Franco-German GSM cooperation in 1984 by Friedhelm Hillebrand, the GSM is optimized for telephony, since this was identified as its main application. In this way, unused resources in the system could be used to transport messages at minimal cost, however, it was necessary to limit the length of the messages to 128 bytes so that the messages could fit into the existing signalling formats. Based on his observations and on analysis of the typical lengths of postcard and Telex messages. SMS could be implemented in every mobile station by updating its software, hence, a large base of SMS-capable terminals and networks existed when people began to use SMS. The technical development of SMS was a multinational collaboration supporting the framework of standards bodies, through these organizations the technology was made freely available to the whole world. The first proposal which initiated the development of SMS was made by a contribution of Germany and this proposal was further elaborated in GSM subgroup WP1 Services based on a contribution from Germany. There were also discussions in the subgroup WP3 network aspects chaired by Jan Audestad. The result was approved by the main GSM group in a June 85 document which was distributed to industry, the input documents on SMS had been prepared by Friedhelm Hillebrand with contributions from Bernard Ghillebaert. The last three words transformed SMS into something more useful than the prevailing messaging paging that some in GSM might have had in mind. SMS was considered in the main GSM group as a service for the new digital cellular system. In GSM document Services and Facilities to be provided in the GSM System, the discussions on the GSM services were concluded in the recommendation GSM02.03 TeleServices supported by a GSM PLMN
25.
Personal identification number
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A personal identification number is a numeric password used to authenticate a user to a system. PINs may be used with banking systems to authenticate the identity of the cardholder, usually, both a private PIN and public user identifier is required to authenticate a user to the system. In these situations, typically the user is required to provide a user identifier or token. Upon receiving the user ID and PIN, the system looks up the PIN based upon the user ID, the user is granted access only when the number entered matches with the number stored in the system. Hence, despite the name, a PIN does not personally identify the user, PINs may also be used in contexts other than ATM or POS transactions, such as door access, Internet transactions, or to log in to a restricted website. In such cases, the PIN may simply be a password, the PIN originated with the introduction of the ATM in 1967, as an efficient way for banks to dispense cash to their customers. The first ATM system was that of Barclays in London, in 1967, it accepted cheques with machine-readable encoding, rather than cards,1972, Lloyds Bank issued the first bank card to feature an information-encoding magnetic strip, using a PIN for security. In 2006, James Goodfellow, the inventor who patented the first personal identification number, was awarded an OBE in the Queens Birthday Honours, there are several main methods of validating PINs. The operations discussed below are usually performed within a security module. One of the earliest ATM models was the IBM3624, which used the IBM method to generate what is termed a natural PIN, the natural PIN is generated by encrypting the primary account number, using an encryption key generated specifically for the purpose. This key is sometimes referred to as the PIN generation key and this PIN is directly related to the primary account number. To validate the PIN, the issuing bank regenerates the PIN using the above method, natural PINs can not be user selectable because they are derived from the PAN. If the card is reissued with a new PAN, a new PIN must be generated, natural PINs allow banks to issue PIN reminder letters as the PIN can be generated. To allow user selectable PINs it is possible to store a PIN offset value, the offset is found by subtracting natural PIN from the customer selected PIN using modulo 10. For example, if the natural PIN is 1234, and the wishes to have a PIN of 2345. The offset can be stored either on the track data. To validate the PIN, the issuing bank calculates the natural PIN as in the method, then adds the offset. The VISA method is used by many card schemes and is not VISA-specific, the VISA method generates a PIN verification value
26.
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
