1.
Communications protocol
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These are the rules or standard that defines the syntax, semantics and synchronization of communication and possible error recovery methods. Protocols may be implemented by hardware, software, or a combination of both, Communicating systems use well-defined formats for exchanging various messages. Each message has a meaning intended to elicit a response from a range of possible responses pre-determined for that particular situation. The specified behavior is independent of how it is to be implemented. Communications protocols have to be agreed upon by the parties involved, to reach agreement, a protocol may be developed into a technical standard. Multiple protocols often describe different aspects of a single communication, a group of protocols designed to work together are known as a protocol suite, when implemented in software they are a protocol stack. Most recent protocols are assigned by the IETF for Internet communication, the ITU-T handles telecommunications protocols and formats for the PSTN. As the PSTN and Internet converge, the two sets of standards are also being driven towards convergence, the nature of a communication, the actual data exchanged and any state-dependent behaviors, is defined by these specifications. In digital computing systems, the rules can be expressed by algorithms, expressing the algorithms in a portable programming language makes the protocol software operating-system independent. Operating systems usually contain a set of cooperating processes that manipulate shared data to communicate each other. This communication is governed by protocols, which can be embedded in the process code itself. In contrast, because there is no memory, communicating systems have to communicate with each other using a shared transmission medium. Transmission is not necessarily reliable, and individual systems may use different hardware or operating systems, to implement a networking protocol, the protocol software modules are interfaced with a framework implemented on the machines operating system. This framework implements the functionality of the operating system. The best known frameworks are the TCP/IP model and the OSI model and this gave rise to the concept of layered protocols which nowadays forms the basis of protocol design. Systems typically do not use a protocol to handle a transmission. Instead they use a set of cooperating protocols, sometimes called a family or protocol suite. Some of the best known protocol suites are TCP/IP, IPX/SPX, X.25, AX.25, the protocols can be arranged based on functionality in groups, for instance there is a group of transport protocols
2.
Protocol stack
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The protocol stack is an implementation of a computer networking protocol suite. The terms are used interchangeably. Strictly speaking, the suite is the definition of the protocols, individual protocols within a suite are often designed with a single purpose in mind. This modularization makes design and evaluation easier, because each protocol module usually communicates with two others, they are commonly imagined as layers in a stack of protocols. The lowest protocol always deals with low-level, physical interaction of the hardware, every higher layer adds more features. User applications usually deal only with the topmost layers, in practical implementation, protocol stacks are often divided into three major sections, media, transport, and applications. A particular operating system or platform will often have two well-defined software interfaces, one between the media and transport layers, and one between the layers and applications. The media-to-transport interface defines how transport protocol software makes use of particular media, for example, this interface level would define how TCP/IP transport software would talk to Ethernet hardware. Examples of these interfaces include ODI and NDIS in the Microsoft Windows, the application-to-transport interface defines how application programs make use of the transport layers. For example, this level would define how a web browser program would talk to TCP/IP transport software. Examples of these interfaces include Berkeley sockets and System V STREAMS in the Unix world, T ~ ~ ~ T _____ Imagine three computers, A, B, and C. A and B both have radio equipment, and can communicate via the airwaves using a network protocol B and C are connected via a cable. However, neither of two protocols will be able to transport information from A to C, because these computers are conceptually on different networks. One, therefore, needs an inter-network protocol to connect them and it is easier to leave the base protocols alone, and design a protocol that can work on top of any of them This will make two stacks of two protocols each. The inter-network protocol will communicate with each of the protocol in their simpler language. A request on computer A to send a chunk of data to C is taken by the upper protocol and it, therefore, instructs the wireless protocol to transmit the data packet to B. On this computer, the lower layer handlers will pass the packet up to the inter-network protocol and this time, the cable protocol is used to send the data to C. There, the packet is again passed to the upper protocol
3.
Novell
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/noʊˈvɛl/ was a software and services company headquartered in Provo, Utah. It had been instrumental in making Utah Valley a focus for technology, Novell technology contributed to the emergence of local area networks, which displaced the dominant mainframe computing model and changed computing worldwide. The company began in 1979 in Orem, Utah as Novell Data Systems Inc. a hardware manufacturer producing CP/M-based systems, former Eyring Research Institute employee Dennis Fairclough was the member of the original team that started Novell Data Systems. It was co-founded by George Canova, Darin Field, and Jack Davis, victor V. Vurpillat brought the deal to Pete Musser, chairman of the board of Safeguard Scientifics, Inc. who provided the seed funding. The company initially did not do well, the microcomputer produced by the company was comparatively weak against performance by competitors. In order to compete on systems sales Novell Data Systems planned a program to more than one microcomputer to operate together. The former ERI employees Drew Major, Dale Neibaur and Kyle Powell, the Safeguard board then ordered Musser to shut Novell down. Davis left Novell Data Systems in November 1981, followed by Canova in March 1982, rubinstein and Dolin, along with Jack Messman, interviewed and hired Raymond Noorda. The required funding was obtained through an offering to Safeguard shareholders, managed by the Cleveland brokerage house, Prescott, Ball and Turben. Major, Neibaur and Powell continued to support Novell through their SuperSet Software Group, in January 1983, the companys name was shortened to Novell, Inc. and Raymond Noorda became the head of the firm. Later that same year, the company introduced its most significant product, a network interface card was developed for the IBM PC industry standard architecture bus. The server was using the first network operating system called ShareNet, later, ShareNet was ported to run on the Intel platform and renamed NetWare. The first commercial release of NetWare was version 1.5, Novell based its network protocol on Xerox Network Systems, and created its own standards from IDP and SPP, which it named Internetwork Packet Exchange and Sequenced Packet Exchange. File and print services ran on the NetWare Core Protocol over IPX, as did Routing Information Protocol, NetWare uses Novell DOS as a boot loader. Novell DOS is similar to MS-DOS and IBM PC DOS, but no license for DOS is required. Novell had already acquired Kanwal Rekhis company Excelan, which manufactured smart Ethernet cards and commercialized the Internet protocol TCP/IP, Novell did extremely well throughout the 1980s. It aggressively expanded its share by selling its expensive Ethernet cards at cost. By 1990, Novell had an almost monopolistic position in NOS for any business requiring a network, with this market leadership, Novell began to acquire and build services on top of its NetWare operating platform
4.
MS-DOS
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MS-DOS is a discontinued operating system for x86-based personal computers mostly developed by Microsoft. MS-DOS resulted from a request in 1981 by IBM for a system to use in its IBM PC range of personal computers. Microsoft quickly bought the rights to 86-DOS from Seattle Computer Products, IBM licensed and released it in August 1981 as PC DOS1.0 for use in their PCs. During its life, several competing products were released for the x86 platform and it was also the underlying basic operating system on which early versions of Windows ran as a GUI. It is a operating system, and consumes negligible installation space. MS-DOS was a form of 86-DOS – owned by Seattle Computer Products. This first version was shipped in August 1980, Microsoft, which needed an operating system for the IBM Personal Computer hired Tim Paterson in May 1981 and bought 86-DOS1.10 for $75,000 in July of the same year. Microsoft kept the number, but renamed it MS-DOS. They also licensed MS-DOS1. 10/1.14 to IBM, within a year Microsoft licensed MS-DOS to over 70 other companies. It was designed to be an OS that could run on any 8086-family computer, thus, there were many different versions of MS-DOS for different hardware, and there is a major distinction between an IBM-compatible machine and an MS-DOS machine. This design would have worked well for compatibility, if application programs had only used MS-DOS services to perform device I/O, Microsoft omitted multi-user support from MS-DOS because Microsofts Unix-based operating system, Xenix, was fully multi-user. After the breakup of the Bell System, however, AT&T Computer Systems started selling UNIX System V, believing that it could not compete with AT&T in the Unix market, Microsoft abandoned Xenix, and in 1987 transferred ownership of Xenix to the Santa Cruz Operation. On 25 March 2014, Microsoft made the code to SCP MS-DOS1.25, as an April Fools joke in 2015, Microsoft Mobile launched a Windows Phone application called MS-DOS Mobile which was presented as a new mobile operating system and worked similar to MS-DOS. Version 3.1 – Support for Microsoft Networks Version 3.2 – First version to support 3.5 inch,720 kB floppy drives and diskettes. Version 3.21 Version 3.22 – Version 3.25 Version 3.3 – First version to support 3.5 inch,1.44 MB floppy drives and diskettes, Version 3. 3a Version 3.31 – supports FAT16B and larger drives. MS-DOS4.0 and MS-DOS4.1 – A separate branch of development with additional multitasking features and it is unrelated to any later versions, including versions 4.00 and 4.01 listed below MS-DOS4. x – includes a graphical/mouse interface. It had many bugs and compatibility issues. Version 4.00 – First version to support a hard disk partition that is greater than 32 MiB. Version 4.01 – Microsoft rewritten Version 4.00 released under MS-DOS label, First version to introduce volume serial number when formatting hard disks and floppy disks
5.
Microsoft Windows
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Microsoft Windows is a metafamily of graphical operating systems developed, marketed, and sold by Microsoft. It consists of families of operating systems, each of which cater to a certain sector of the computing industry with the OS typically associated with IBM PC compatible architecture. Active Windows families include Windows NT, Windows Embedded and Windows Phone, defunct Windows families include Windows 9x, Windows 10 Mobile is an active product, unrelated to the defunct family Windows Mobile. Microsoft introduced an operating environment named Windows on November 20,1985, Microsoft Windows came to dominate the worlds personal computer market with over 90% market share, overtaking Mac OS, which had been introduced in 1984. Apple came to see Windows as an encroachment on their innovation in GUI development as implemented on products such as the Lisa. On PCs, Windows is still the most popular operating system, however, in 2014, Microsoft admitted losing the majority of the overall operating system market to Android, because of the massive growth in sales of Android smartphones. In 2014, the number of Windows devices sold was less than 25% that of Android devices sold and this comparison however may not be fully relevant, as the two operating systems traditionally target different platforms. As of September 2016, the most recent version of Windows for PCs, tablets, smartphones, the most recent versions for server computers is Windows Server 2016. A specialized version of Windows runs on the Xbox One game console, Microsoft, the developer of Windows, has registered several trademarks each of which denote a family of Windows operating systems that target a specific sector of the computing industry. It now consists of three operating system subfamilies that are released almost at the time and share the same kernel. Windows, The operating system for personal computers, tablets. The latest version is Windows 10, the main competitor of this family is macOS by Apple Inc. for personal computers and Android for mobile devices. Windows Server, The operating system for server computers, the latest version is Windows Server 2016. Unlike its clients sibling, it has adopted a strong naming scheme, the main competitor of this family is Linux. Windows PE, A lightweight version of its Windows sibling meant to operate as an operating system, used for installing Windows on bare-metal computers. The latest version is Windows PE10.0.10586.0, Windows Embedded, Initially, Microsoft developed Windows CE as a general-purpose operating system for every device that was too resource-limited to be called a full-fledged computer. The following Windows families are no longer being developed, Windows 9x, Microsoft now caters to the consumers market with Windows NT. Windows Mobile, The predecessor to Windows Phone, it was a mobile operating system
6.
Windows 95
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Windows 95 is a consumer-oriented operating system developed by Microsoft. It was released on August 24,1995, and was a significant improvement over the companys previous DOS-based Windows products, Windows 95 merged Microsofts formerly separate MS-DOS and Windows products. It featured significant improvements over its predecessor, Windows 3.1, most notably in the user interface. It was also suggested that Windows 95 had an effect of driving other major out of business. Three years after its introduction, Windows 95 was succeeded by Windows 98, Microsoft ended support for Windows 95 on December 31,2001. The initial design and planning of Windows 95 can be traced back to around March 1992, at this time, Windows for Workgroups 3.11 and Windows NT3.1 were still in development and Microsofts plan for the future was focused on Cairo. Cairo would be Microsofts next-generation operating system based on Windows NT and featuring a new interface and an object-based file system. However, Cairo would partially ship in July 1996 in the form of Windows NT4.0, but without the object-based file system, simultaneously with Windows 3. 1s release, IBM started shipping OS/22.0. Microsoft realized they were in need of a version of Windows that could support 32-bit applications and preemptive multitasking. So the development of Windows Chicago was started and, as it was planned for a late 1993 release, became known as Windows 93. Initially, the decision was not to include a new user interface, as this was planned for Cairo, and only focus on making installation, configuration. Windows 93 would ship together with MS-DOS7.0, offering an integrated experience to the user. The first version of Chicagos feature specification was finished on September 30,1992, cougar was to become Chicagos kernel. Prior to Windows 95s official release, users in the United States had an opportunity to preview it in the Windows 95 Preview Program. For US$19.95, users would receive several 3. 5-inch floppy disks that would be used to install Windows 95 either as an upgrade from Windows 3. 1x or as a fresh installation. Participants were also given a preview of The Microsoft Network. The preview versions expired in November 1995, after which the user would have to purchase their own copy of the version of Windows 95. Windows 95 was designed to be compatible with existing MS-DOS and 16-bit Windows programs and device drivers, while offering a more stable
7.
Conventional memory
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In DOS memory management, conventional memory, also called base memory, is the first 640 kilobytes of the memory on IBM PC or compatible systems. It is the memory directly addressable by the processor for use by the operating system. As memory prices declined, this design decision became a limitation in the use of large memory capacities until the introduction of operating systems. The 640 KB barrier is a limitation of IBM and IBM PC compatible PCs. The Intel 8088 CPU, used in the original IBM PC, was able to address 1 MB, the first memory segment of the conventional memory area is named low memory. In the design of the PC, the memory below 640 KB was for random-access memory on the motherboard or on expansion boards, the 384 KB above was reserved for system use and optional devices. The design of the original IBM PC placed the Color Graphics Adapter memory map and this introduced a reserved hole into the set of addresses occupied by hardware that could be used for arbitrary data. Avoiding such a hole was difficult and ugly and not supported by MS-DOS or most programs that could run on it, later, space between the holes would be used as upper memory blocks. It is still present in IBM PC compatibles today if they are running in Real mode such as used by MS-DOS, even the most modern Intel PCs still have the area between 640 and 1024 KB reserved. This however is invisible to programs on newer operating systems that use virtual memory, instead they operate within a virtual address space, which is defined independently of available RAM addresses. Some motherboards feature a Memory Hole at 15 Megabytes option required for certain VGA video cards that require access to one particular megabyte for video memory. Newer video cards on AGP bus can have 256 MB memory with 1 GB aperture size, one technique used on early IBM XT computers was to install additional RAM into the video memory address range and push the limit up to the start of the Monochrome Display Adapter. Sometimes software or an address decoder was required for this to work. This moved the barrier to 704 KB or 736 KB, Memory managers on 386-based systems could achieve the same effect, adding conventional memory at 640 KB and moving the barrier to 704 KB or 736 KB. The AllCard, a memory management unit for XT-class computers, allowed normal memory to be mapped into the A0000-EFFFF address range. Programs such as Lotus 1-2-3, which accessed video memory directly, therefore, the 640 KB barrier was removed at the cost of hardware compatibility. It was also possible to use console redirection to direct output to, most standard programs written for DOS did not necessarily need 640kb or more of memory. Instead, driver software and utilities referred to as Terminate and Stay Resident programs could be used in addition to the standard DOS software and these drivers and utilities typically permanently used some conventional memory, reducing the total available for standard DOS programs
8.
Internet
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The Internet is the global system of interconnected computer networks that use the Internet protocol suite to link devices worldwide. The origins of the Internet date back to research commissioned by the United States federal government in the 1960s to build robust, the primary precursor network, the ARPANET, initially served as a backbone for interconnection of regional academic and military networks in the 1980s. Although the Internet was widely used by academia since the 1980s, Internet use grew rapidly in the West from the mid-1990s and from the late 1990s in the developing world. In the two decades since then, Internet use has grown 100-times, measured for the period of one year, newspaper, book, and other print publishing are adapting to website technology, or are reshaped into blogging, web feeds and online news aggregators. The entertainment industry was initially the fastest growing segment on the Internet, the Internet has enabled and accelerated new forms of personal interactions through instant messaging, Internet forums, and social networking. Business-to-business and financial services on the Internet affect supply chains across entire industries, the Internet has no centralized governance in either technological implementation or policies for access and usage, each constituent network sets its own policies. The term Internet, when used to refer to the global system of interconnected Internet Protocol networks, is a proper noun. In common use and the media, it is not capitalized. Some guides specify that the word should be capitalized when used as a noun, the Internet is also often referred to as the Net, as a short form of network. Historically, as early as 1849, the word internetted was used uncapitalized as an adjective, the designers of early computer networks used internet both as a noun and as a verb in shorthand form of internetwork or internetworking, meaning interconnecting computer networks. The terms Internet and World Wide Web are often used interchangeably in everyday speech, however, the World Wide Web or the Web is only one of a large number of Internet services. The Web is a collection of interconnected documents and other web resources, linked by hyperlinks, the term Interweb is a portmanteau of Internet and World Wide Web typically used sarcastically to parody a technically unsavvy user. The ARPANET project led to the development of protocols for internetworking, the third site was the Culler-Fried Interactive Mathematics Center at the University of California, Santa Barbara, followed by the University of Utah Graphics Department. In an early sign of growth, fifteen sites were connected to the young ARPANET by the end of 1971. These early years were documented in the 1972 film Computer Networks, early international collaborations on the ARPANET were rare. European developers were concerned with developing the X.25 networks, in December 1974, RFC675, by Vinton Cerf, Yogen Dalal, and Carl Sunshine, used the term internet as a shorthand for internetworking and later RFCs repeated this use. Access to the ARPANET was expanded in 1981 when the National Science Foundation funded the Computer Science Network, in 1982, the Internet Protocol Suite was standardized, which permitted worldwide proliferation of interconnected networks.5 Mbit/s and 45 Mbit/s. Commercial Internet service providers emerged in the late 1980s and early 1990s, the ARPANET was decommissioned in 1990
9.
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
10.
Dynamic Host Configuration Protocol
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The Dynamic Host Configuration Protocol is a standardized network protocol used on Internet Protocol networks. The DHCP is controlled by a DHCP server that dynamically distributes network configuration parameters, such as IP addresses, a router or a residential gateway can be enabled to act as a DHCP server. A DHCP server enables computers to request IP addresses and networking parameters automatically, in the absence of a DHCP server, each computer or other device on the network needs to be statically assigned to an IP address. TCP/IP defines how devices on one network communicate with devices on another network, a DHCP server can manage TCP/IP settings for devices on a network, by automatically or dynamically assigning Internet Protocol addresses to the devices. As of 2011, networks ranging in size from home networks to large campus networks, most residential network routers receive a globally unique IP address within the provider network. Within a local network, a DHCP server assigns a local IP address to each device connected to the network, the DHCP operates based on the client–server model. When a computer or other device connects to a network, the DHCP client software sends a broadcast query requesting the necessary information, any DHCP server on the network may service the request. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as default gateway, domain name, the name servers, a client typically queries for this information immediately after booting, and periodically thereafter before the expiration of the information. When a DHCP client refreshes an assignment, it requests the same parameter values. On large networks that consist of links, a single DHCP server may service the entire network when aided by DHCP relay agents located on the interconnecting routers. Such agents relay messages between DHCP clients and DHCP servers located on different subnets, the request-and-grant process uses a lease concept with a controllable time period, allowing the DHCP server to reclaim IP addresses that are not renewed. Automatic allocation The DHCP server permanently assigns an IP address to a client from the range defined by the administrator. This is like dynamic allocation, but the DHCP server keeps a table of past IP address assignments, manual allocation The DHCP server issues a private IP address dependent upon each clients MAC address, based on a predefined mapping by the administrator. If no match for the clients MAC address is found, the server may or may not optionally fall back to either Dynamic or Automatic allocation, DHCP is used for Internet Protocol version 4, as well as for IPv6. While both versions serve the purpose, the details of the protocol for IPv4 and IPv6 differ sufficiently that they may be considered separate protocols. For the IPv6 operation, devices may alternatively use stateless address autoconfiguration, IPv6 hosts may also use link-local addressing to achieve operations restricted to the local network link. In 1984, the Reverse Address Resolution Protocol, defined in RFC903, was introduced to allow simple devices such as diskless workstations to dynamically obtain a suitable IP address. However, because it acted at the link layer it made implementation difficult on many server platforms
11.
Router (computing)
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A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet, a data packet is typically forwarded from one router to another router through the networks that constitute the internetwork until it reaches its destination node. A router is connected to two or more lines from different networks. When a data packet comes in on one of the lines, then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. The most familiar type of routers are home and small office routers that simply pass IP packets between the computers and the Internet. An example of a router would be the cable or DSL router. Though routers are typically dedicated hardware devices, software-based routers also exist, when multiple routers are used in interconnected networks, the routers can exchange information about destination addresses using a dynamic routing protocol. Each router builds up a table listing the preferred routes between any two systems on the interconnected networks. A router may have interfaces for different physical types of connections, such as copper cables, fibre optic. Its firmware can also support different networking communications protocol standards, each network interface is used by this specialized computer software to enable data packets to be forwarded from one protocol transmission system to another. Routers may also be used to two or more logical groups of computer devices known as subnets, each with a different network prefix. The network prefixes recorded in the table do not necessarily map directly to the physical interface connections. It does this using internal pre-configured directives, called static routes, static and dynamic routes are stored in the Routing Information Base. The control-plane logic then strips non-essential directives from the RIB and builds a Forwarding Information Base to be used by the forwarding-plane, Forwarding plane, The router forwards data packets between incoming and outgoing interface connections. It routes them to the network type using information that the packet header contains. It uses data recorded in the routing control plane. Routers may provide connectivity within enterprises, between enterprises and the Internet, or between internet service providers networks, the largest routers interconnect the various ISPs, or may be used in large enterprise networks. Smaller routers usually provide connectivity for typical home and office networks, other networking solutions may be provided by a backbone Wireless Distribution System, which avoids the costs of introducing networking cables into buildings
12.
Hexadecimal
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In mathematics and computing, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, Hexadecimal numerals are widely used by computer system designers and programmers. As each hexadecimal digit represents four binary digits, it allows a more human-friendly representation of binary-coded values, one hexadecimal digit represents a nibble, which is half of an octet or byte. For example, a byte can have values ranging from 00000000 to 11111111 in binary form. In a non-programming context, a subscript is typically used to give the radix, several notations are used to support hexadecimal representation of constants in programming languages, usually involving a prefix or suffix. The prefix 0x is used in C and related languages, where this value might be denoted as 0x2AF3, in contexts where the base is not clear, hexadecimal numbers can be ambiguous and confused with numbers expressed in other bases. There are several conventions for expressing values unambiguously, a numerical subscript can give the base explicitly,15910 is decimal 159,15916 is hexadecimal 159, which is equal to 34510. Some authors prefer a text subscript, such as 159decimal and 159hex, or 159d and 159h. example. com/name%20with%20spaces where %20 is the space character, thus ’, represents the right single quotation mark, Unicode code point number 2019 in hex,8217. In the Unicode standard, a value is represented with U+ followed by the hex value. Color references in HTML, CSS and X Window can be expressed with six hexadecimal digits prefixed with #, white, CSS allows 3-hexdigit abbreviations with one hexdigit per component, #FA3 abbreviates #FFAA33. *nix shells, AT&T assembly language and likewise the C programming language, to output an integer as hexadecimal with the printf function family, the format conversion code %X or %x is used. In Intel-derived assembly languages and Modula-2, hexadecimal is denoted with a suffixed H or h, some assembly languages use the notation HABCD. Ada and VHDL enclose hexadecimal numerals in based numeric quotes, 16#5A3#, for bit vector constants VHDL uses the notation x5A3. Verilog represents hexadecimal constants in the form 8hFF, where 8 is the number of bits in the value, the Smalltalk language uses the prefix 16r, 16r5A3 PostScript and the Bourne shell and its derivatives denote hex with prefix 16#, 16#5A3. For PostScript, binary data can be expressed as unprefixed consecutive hexadecimal pairs, in early systems when a Macintosh crashed, one or two lines of hexadecimal code would be displayed under the Sad Mac to tell the user what went wrong. Common Lisp uses the prefixes #x and #16r, setting the variables *read-base* and *print-base* to 16 can also used to switch the reader and printer of a Common Lisp system to Hexadecimal number representation for reading and printing numbers. Thus Hexadecimal numbers can be represented without the #x or #16r prefix code, MSX BASIC, QuickBASIC, FreeBASIC and Visual Basic prefix hexadecimal numbers with &H, &H5A3 BBC BASIC and Locomotive BASIC use & for hex. TI-89 and 92 series uses a 0h prefix, 0h5A3 ALGOL68 uses the prefix 16r to denote hexadecimal numbers, binary, quaternary and octal numbers can be specified similarly
13.
MAC address
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A media access control address of a computer is a unique identifier assigned to network interfaces for communications at the data link layer of a network segment. MAC addresses are used as an address for most IEEE802 network technologies, including Ethernet. Logically, MAC addresses are used in the access control protocol sublayer of the OSI reference model. MAC addresses are most often assigned by the manufacturer of a network interface controller and are stored in its hardware, if assigned by the manufacturer, a MAC address usually encodes the manufacturers registered identification number and may be referred to as the burned-in address. It may also be known as an Ethernet hardware address, hardware address or physical address and this can be contrasted to a programmed address, where the host device issues commands to the NIC to use an arbitrary address. A network node may have multiple NICs and each NIC must have a unique MAC address, sophisticated network equipment such as a multilayer switch or router may require one or more permanently assigned MAC addresses. MAC addresses are formed according to the rules of one of three numbering name spaces managed by the Institute of Electrical and Electronics Engineers, MAC-48, EUI-48, the IEEE claims trademarks on the names EUI-48 and EUI-64, in which EUI is an abbreviation for Extended Unique Identifier. The original IEEE802 MAC address comes from the original Xerox Ethernet addressing scheme and this 48-bit address space contains potentially 248 or 281,474,976,710,656 possible MAC addresses. The distinction between EUI-48 and MAC-48 identifiers is purely nominal, MAC-48 is used for hardware, EUI-48 is used to identify other devices. Instead, the proprietary term EUI-48 should be used for this purpose, in addition, the EUI-64 numbering system encompasses both MAC-48 and EUI-48 identifiers by a simple translation mechanism. To convert a MAC-48 into an EUI-64, copy the OUI, to convert an EUI-48 into an EUI-64, the same process is used, but the sequence inserted is FF-FE. In both cases, the process can be reversed when necessary. Organizations issuing EUI-64s are cautioned against issuing identifiers that could be confused with these forms, the IEEE has a target lifetime of 100 years for applications using MAC-48 space, but encourages adoption of EUI-64s instead. IPv6 — one of the most prominent standards that uses a Modified EUI-64 — treats MAC-48 as EUI-48 instead and this results in extending MAC addresses to Modified EUI-64 using only FF-FE and with the U/L bit inverted. An Individual Address Block was a 24-bit OUI managed by the IEEE Registration Authority, followed by 12 IEEE-provided bits, an IAB is ideal for organizations requiring fewer than 4097 unique 48-bit numbers. IABs have been replaced with 12-bit MA-S address blocks, addresses can either be universally administered addresses or locally administered addresses. A universally administered address is assigned to a device by its manufacturer. The first three octets identify the organization issued the identifier and are known as the Organizationally Unique Identifier
14.
Xerox
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Xerox Corporation /ˈzɪərɒks/ is an American global corporation that sells document solutions and services, and document technology products in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut, though its largest population of employees is based around Rochester, New York, the company purchased Affiliated Computer Services for $6.4 billion in early 2010. As a large developed company, it is placed in the list of Fortune 500 companies. Xerox completed the separation of Conduent Incorporated effective on Dec.31,2016, creating two market-leading, publicly- traded companies. In connection with the spin-off, Xerox received a transfer from Conduent of $1.8 billion. Xerox continues to trade on the NYSE under the ticker symbol “XRX”, researchers at Xerox and its Palo Alto Research Center invented several important elements of personal computing, such as the desktop metaphor GUI, the computer mouse and desktop computing. These concepts were frowned upon by the board of directors. The concepts were adopted by Apple and, later, Microsoft, with the help of these innovations, Apple and Microsoft came to dominate the personal computing revolution of the 1980s, whereas Xerox was not a major player. Xerox was founded in 1906 in Rochester as The Haloid Photographic Company, in 1938 Chester Carlson, a physicist working independently, invented a process for printing images using an electrically charged photoconductor-coated metal plate and dry powder toner. However, it would more than 20 years of refinement before the first automated machine to make copies was commercialized, using a document feeder, scanning light. Wilson, credited as the founder of Xerox, took over Haloid from his father and he saw the promise of Carlsons invention and, in 1946, signed an agreement to develop it as a commercial product. Wilson remained as President/CEO of Xerox until 1967 and served as Chairman until his death in 1971, looking for a term to differentiate its new system, Haloid coined the term Xerography from two Greek roots meaning dry writing. Haloid subsequently changed its name to Haloid Xerox in 1958 and then Xerox Corporation in 1961, before releasing the 914, Xerox tested the market by introducing a developed version of the prototype hand-operated equipment known as the Flat-plate 1385. The 1385 was not actually a viable copier because of its speed of operation and it was little more than a high quality, commercially available plate camera mounted as a horizontal rostrum camera, complete with photo-flood lighting and timer. The glass film/plate had been replaced with an aluminum plate. Clever electrics turned this into a developing and reusable substitute for film. A skilled user could produce fast, paper and metal printing plates of a higher quality than almost any other method, having started as a supplier to the offset lithography duplicating industry, Xerox now set its sights on capturing some of offsets market share. The 1385 was followed by the first automatic xerographic printer, the Copyflo, the Copyflo was a large microfilm printer which could produce positive prints on roll paper from any type of microfilm negative
15.
Transmission Control Protocol
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The Transmission Control Protocol is one of the main protocols of the Internet protocol suite. It originated in the initial implementation in which it complemented the Internet Protocol. Therefore, the suite is commonly referred to as TCP/IP. TCP provides reliable, ordered, and error-checked delivery of a stream of octets between applications running on hosts communicating by an IP network, major Internet applications such as the World Wide Web, email, remote administration, and file transfer rely on TCP. Applications that do not require reliable data stream service may use the User Datagram Protocol, during May 1974, the Institute of Electrical and Electronic Engineers published a paper titled A Protocol for Packet Network Intercommunication. The papers authors, Vint Cerf and Bob Kahn, described a protocol for sharing resources using packet-switching among the nodes. A central control component of this model was the Transmission Control Program that incorporated both connection-oriented links and datagram services between hosts, the model became known informally as TCP/IP, although formally it was henceforth termed the Internet Protocol Suite. The Transmission Control Protocol provides a service at an intermediate level between an application program and the Internet Protocol. It provides host-to-host connectivity at the Transport Layer of the Internet model, an application does not need to know the particular mechanisms for sending data via a link to another host, such as the required packet fragmentation on the transmission medium. At the transport layer, the protocol handles all handshaking and transmission details, at the lower levels of the protocol stack, due to network congestion, traffic load balancing, or other unpredictable network behaviour, IP packets may be lost, duplicated, or delivered out of order. TCP detects these problems, requests re-transmission of lost data, rearranges out-of-order data, If the data still remains undelivered, the source is notified of this failure. Once the TCP receiver has reassembled the sequence of octets originally transmitted, thus, TCP abstracts the applications communication from the underlying networking details. TCP is optimized for accurate delivery rather than timely delivery and can incur relatively long delays while waiting for messages or re-transmissions of lost messages. Therefore, it is not particularly suitable for applications such as Voice over IP. For such applications, protocols like the Real-time Transport Protocol operating over the User Datagram Protocol are usually recommended instead, TCP is a reliable stream delivery service which guarantees that all bytes received will be identical with bytes sent and in the correct order. Since packet transfer by many networks is not reliable, a known as positive acknowledgement with re-transmission is used to guarantee reliability. This fundamental technique requires the receiver to respond with an acknowledgement message as it receives the data, the sender keeps a record of each packet it sends and maintains a timer from when the packet was sent. The sender re-transmits a packet if the timer expires before receiving the message acknowledgement, the timer is needed in case a packet gets lost or corrupted
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IP address
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An IP address is an identifier assigned to each computer and other device connected to a TCP/IP network that is used to locate and identify the node in communications with other nodes on the network. IP addresses are written and displayed in human-readable notations, such as 172.16.254.1 in IPv4. Version 4 of the Internet Protocol defines an IP address as a 32-bit number and its deployment commenced in the mid-2000s and is ongoing. Addresses have been distributed by IANA to the RIRs in blocks of approximately 16.8 million addresses each, each ISP or private network administrator assigns an IP address to each device connected to its network. Such assignments may be on a static or dynamic basis, depending on its software, an IP address serves two principal functions, host or network interface identification and location addressing. Its role has been characterized as follows, A name indicates what we seek, an address indicates where it is. A route indicates how to get there, the header of each IP packet sent over the Internet must contain the IP address of both the destination server or website and of the sender. The Domain Name System translates domain names to the corresponding destination IP address, both the source address and the destination address may be changed in transit by a network address translation device. The senders IP address is available to the server and becomes the destination address when the server responds to a client request. A sender wanting to remain anonymous to the server may use a proxy server, when the destination server responds to the proxy server, it would forward it on to the true client—ie. Change the IP address to that of the originator of the request, a reverse DNS lookup involves the querying of DNS to determine the domain name associated with an IP address. There are two versions of the Internet Protocol, IP version 4 and IP version 6, each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of number 5 to the experimental Internet Stream Protocol in 1979, an IP address in IPv4 is 32-bits in size, which limits the address space to 4294967296 IP addresses. Of this number, IPv4 reserves some addresses for special purposes such as private networks or multicast addresses. IPv4 addresses are usually represented in dot-decimal notation, consisting of four numbers, each ranging from 0 to 255, separated by dots. Each part represents a group of 8 bits of the address, in some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations. In the early stages of development of the Internet Protocol, network administrators interpreted an IP address in two parts, network number portion and host number portion
17.
Subnetwork
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A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting, computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. This results in the division of an IP address into two fields, a network or routing prefix and the rest field or host identifier. The rest field is an identifier for a specific host or network interface, the routing prefix may be expressed in CIDR notation written as the first address of a network, followed by a slash character, and ending with the bit-length of the prefix. The IPv6 address specification 2001, db8, /32 is an address block with 296 addresses. For IPv4, a network may also be characterized by its subnet mask, subnet masks are also expressed in dot-decimal notation like an address. For example,255.255.255.0 is the mask for the 192.168.1. 0/24 prefix. Traffic is exchanged between subnetworks with special gateways when the routing prefixes of the address and the destination address differ. A router constitutes the logical or physical boundary between the subnets, the benefits of subnetting an existing network vary with each deployment scenario. In the address allocation architecture of the Internet using Classless Inter-Domain Routing and in large organizations and it may also enhance routing efficiency, or have advantages in network management when subnetworks are administratively controlled by different entities in a larger organization. Subnets may be arranged logically in an architecture, partitioning an organizations network address space into a tree-like routing structure. Computers participating in a such as the Internet each have at least one logical address. An address fulfills the functions of identifying the host and locating it on the network, the most common network addressing architecture is Internet Protocol version 4, but its successor, IPv6, has been increasingly deployed since approximately 2006. An IPv4 address consists of 32 bits, for readability written in a form consisting of four decimal octets separated by dots, an IPv6 address consists of 128 bits written in a hexadecimal notation and grouping 16 bits separated by colons. For the purpose of management, an IP address is divided into two logical parts, the network prefix and the host identifier or rest field. All hosts on a subnetwork have the network prefix. This routing prefix occupies the most-significant bits of the address, the number of bits allocated within a network to the internal routing prefix may vary between subnets, depending on the network architecture. While in IPv6 the prefix must consist of a set of contiguous 1-bits, in IPv4 this is not enforced, the host part is a unique local identification and is either a host number on the local network or an interface identifier
18.
Address Resolution Protocol
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The Address Resolution Protocol is a telecommunication protocol used for resolution of Internet layer addresses into link layer addresses, a critical function in computer networks. ARP was defined by RFC826 in 1982, is Internet Standard STD37, ARP is used for mapping a network address to a physical address like an Ethernet address. IPv4 over IEEE802.3 and IEEE802.11 is the most common usage, in Internet Protocol Version 6 networks, the functionality of ARP is provided by the Neighbor Discovery Protocol. The Address Resolution Protocol is a request and response protocol whose messages are encapsulated by a link layer protocol and it is communicated within the boundaries of a single network, never routed across internetwork nodes. However, ARP was not developed in the OSI networking framework, the Address Resolution Protocol uses a simple message format containing one address resolution request or response. The message header specifies these types, as well as the size of addresses of each, the message header is completed with the operation code for request and reply. The payload of the consists of four addresses, the hardware. The principal packet structure of ARP packets is shown in the table which illustrates the case of IPv4 networks running on Ethernet. In this scenario, the packet has 48-bit fields for the hardware address and target hardware address. Thus, the ARP packet size in this case is 28 bytes, the EtherType for ARP is 0x0806. Hardware type This field specifies the network protocol type, Protocol type This field specifies the internetwork protocol for which the ARP request is intended. For IPv4, this has the value 0x0800, the permitted PTYPE values share a numbering space with those for EtherType. Hardware length Length of a hardware address, Protocol length Length of addresses used in the upper layer protocol. Operation Specifies the operation that the sender is performing,1 for request,2 for reply, sender hardware address Media address of the sender. In an ARP request this field is used to indicate the address of the host sending the request, in an ARP reply this field is used to indicate the address of the host that the request was looking for. Note that switches do not pay attention to field, particularly in learning MAC addresses. The ARP PDU is encapsulated in Ethernet frame, and that is what Layer 2 devices examine, sender protocol address Internetwork address of the sender. Target hardware address Media address of the intended receiver, in an ARP request this field is ignored
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Internet Protocol
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The Internet Protocol is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet, IP has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered and it also defines addressing methods that are used to label the datagram with source and destination information. The Internet protocol suite is often referred to as TCP/IP. The first major version of IP, Internet Protocol Version 4, is the dominant protocol of the Internet and its successor is Internet Protocol Version 6. The Internet Protocol is responsible for addressing hosts and for routing datagrams from a source host to a destination host across one or more IP networks. For this purpose, the Internet Protocol defines the format of packets, each datagram has two components, a header and a payload. The IP header is tagged with the source IP address, the destination IP address, the payload is the data that is transported. This method of nesting the data payload in a packet with a header is called encapsulation, IP addressing entails the assignment of IP addresses and associated parameters to host interfaces. The address space is divided into networks and subnetworks, involving the designation of network or routing prefixes, IP routing is performed by all hosts, as well as routers, whose main function is to transport packets across network boundaries. Routers communicate with one another via specially designed routing protocols, either interior gateway protocols or exterior gateway protocols, IP routing is also common in local networks. For example, many Ethernet switches support IP multicast operations and these switches use IP addresses and Internet Group Management Protocol to control multicast routing but use MAC addresses for the actual routing. The versions currently relevant are IPv4 and IPv6, in May 1974, the Institute of Electrical and Electronic Engineers published a paper entitled A Protocol for Packet Network Intercommunication. The papers authors, Vint Cerf and Bob Kahn, described a protocol for sharing resources using packet switching among network nodes. A central control component of this model was the Transmission Control Program that incorporated both connection-oriented links and datagram services between hosts, the model became known as the Department of Defense Internet Model and Internet protocol suite, and informally as TCP/IP. IP versions 0 to 3 were experimental versions, used between 1977 and 1979, IEN26, dated February 1978 describes a version of the IP header that uses a 1-bit version field. IEN28, dated February 1978 describes IPv2, IEN41, dated June 1978 describes the first protocol to be called IPv4. The IP header is different from the modern IPv4 header, IEN44, dated June 1978 describes another version of IPv4, also with a header different from the modern IPv4 header
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Cisco Systems
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Through its numerous acquired subsidiaries, such as OpenDNS, WebEx, and Jasper, Cisco specializes into specific tech markets, such as Internet of Things, domain security, and energy management. Cisco is the largest networking company in the world, the stock was added to the Dow Jones Industrial Average on June 8,2009, and is also included in the S&P500 Index, the Russell 1000 Index, NASDAQ-100 Index and the Russell 1000 Growth Stock Index. By the time the company went public in 1990, when it was listed on the NASDAQ, Cisco was the most valuable company in the world by 2000, with a more than $500 billion market capitalization. Despite founding Cisco in 1984, Bosack, along with Kirk Lougheed, continued to work at Stanford on Ciscos first product and it consisted of exact replicas of Stanfords Blue Box router and a stolen copy of the Universitys multiple-protocol router software. The software was written some years earlier at Stanford medical school by research engineer William Yeager. Bosack and Lougheed adapted it into what became the foundation for Cisco IOS, in 1987, Stanford licensed the router software and two computer boards to Cisco. In addition to Bosack, Lerner and Lougheed, Greg Satz, a programmer, and Richard Troiano, the companys first CEO was Bill Graves, who held the position from 1987 to 1988. In 1988, John Morgridge was appointed CEO, the name Cisco was derived from the city name San Francisco, which is why the companys engineers insisted on using the lower case cisco in its early years. The logo is intended to depict the two towers of the Golden Gate Bridge, on February 16,1990, Cisco Systems went public and was listed on the NASDAQ stock exchange. On August 28,1990, Lerner was fired, upon hearing the news, her husband Bosack resigned in protest. The couple walked away from Cisco with $170 million, 70% of which was committed to their own charity, although Cisco was not the first company to develop and sell dedicated network nodes, it was one of the first to sell commercially successful routers supporting multiple network protocols. Classical, CPU-based architecture of early Cisco devices coupled with flexibility of operating system IOS allowed for keeping up with evolving technology needs by means of frequent software upgrades, some popular models of that time managed to stay in production for almost a decade virtually unchanged—a rarity in high-tech industry. This philosophy dominated the companys product lines throughout the 1990s, in 1995, John Morgridge was succeeded by John Chambers. The phenomenal growth of the Internet in mid-to-late 1990s quickly changed the telecom landspe, as the Internet Protocol became widely adopted, the importance of multi-protocol routing declined. In late March 2000, at the height of the bubble, Cisco became the most valuable company in the world. In July 2014, with a cap of about US$129 billion. One of them, Juniper Networks, shipped their first product in 1999, Cisco answered the challenge with homegrown ASICs and fast processing cards for GSR routers and Catalyst 6500 switches. In 2004, Cisco also started migration to new high-end hardware CRS-1, as part of a massive rebranding campaign in 2006, Cisco Systems adopted the shortened name Cisco and created The Human Network advertising campaign
21.
Ethernet frame
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A data packet on an Ethernet link is called an Ethernet packet, which transports an Ethernet frame as its payload. An Ethernet frame is preceded by a preamble and start frame delimiter, each Ethernet frame starts with an Ethernet header, which contains destination and source MAC addresses as its first two fields. The middle section of the frame is payload data including any headers for other protocols carried in the frame, the frame ends with a frame check sequence, which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data. A data packet on the wire and the frame as its payload consist of binary data, Ethernet transmits data with the most-significant octet first, within each octet, however, the least-significant bit is transmitted first. The internal structure of an Ethernet frame is specified in IEEE802.3, the table below shows the complete Ethernet packet and the frame inside, as transmitted, for the payload size up to the MTU of 1500 octets. Some implementations of Gigabit Ethernet and other higher-speed variants of Ethernet support larger frames, the optional 802. 1Q tag consumes additional space in the frame. Field sizes for this option are indicated parenthetically in the table above, IEEE802. 1ad allows for multiple tags in each frame. This option is not illustrated here, an Ethernet packet starts with a seven-octet preamble and one-octet start frame delimiter. The preamble consists of a 56-bit pattern of alternating 1 and 0 bits, allowing devices on the network to easily synchronize their receiver clocks and it is followed by the SFD to provide byte-level synchronization and to mark a new incoming frame. The SFD is the value that marks the end of the preamble, which is the first field of an Ethernet packet. The SFD is designed to break the bit pattern of the preamble, the SFD is immediately followed by the destination MAC address, which is the first field in an Ethernet frame. SFD has the value of 171, which is transmitted with least-significant bit first as 213, physical layer transceiver circuitry is required to connect the Ethernet MAC to the physical medium. The connection between a PHY and MAC is independent of the medium and uses a bus from the media independent interface family. Fast Ethernet transceiver chips utilize the MII bus, which is a wide bus, therefore the preamble is represented as 14 instances of 0x5. Gigabit Ethernet transceiver chips use the GMII bus, which is a wide interface. The header features destination and source MAC addresses, the EtherType field and, optionally, the EtherType field is two octets long and it can be used for two different purposes. When used as EtherType, the length of the frame is determined by the location of the interpacket gap, the IEEE802. 1Q tag, if present, is a four-octet field that indicates virtual LAN membership and IEEE802. 1p priority. The minimum payload is 42 octets when an 802. 1Q tag is present and 46 octets when absent, the maximum payload is 1500 octets
