Open Source Programming
"Open source is a set of principles and practices that promote access to the production and design process for various goods, products, resources and technical conclusions or advice. The term is most commonly applied to the source code of software that is made available to the general public with relaxed or non-existent intellectual property restrictions. This allows users to create user-generated software content through incremental individual effort or through collaboration."
1.0 Introduction Open source software (OSS) is defined as computer software for which the source code and certain other rights normally reserved for copyright holders are provided under a software license that meets the Open Source Definition or that is in the public domain. This permits users to use, change, and improve the software, and to redistribute it in modified or unmodified forms. It is very often developed in a public, collaborative manner. Open source software is the most prominent example of open source development and often compared to user-generated content. The term open source software originated as part of a marketing campaign for free software. Hardware is a general term that refers to the physical artifacts of a technology. It may also mean the physical components of a computer system, in the form of computer hardware. Software is a general term used to describe a collection of computer programs, procedures and documentation that perform some tasks on a computer system. Software includes websites, programs, etc. that are coded by programming languages. 2.0 The Latest Open Source Operating System (OS) 2.1 Meanings of open source OS (OSOS) OSOS is operating system that provided for use, modification and redistribution. It can be download from the Internet for free and modify with suggested improvements. 2.2 Examples of open source OS a) Haiku (operating system) Haiku is an open source operating system currently in development designed from the ground up for desktop computing. Inspired by the Be Operating System, Haiku aims to provide users of all levels with a personal computing experience that is simple yet powerful, and void of any unnecessary complexities.Haiku is developed mostly by volunteers around the world in their spare time. Besides the project admins and core members, Haiku also exists thanks to the dedicated support of a fervent and friendly community, and that of Haiku Inc., a non-profit founded by project leader Michael Phipps with the purpose of supporting the development of Haiku. Haiku, formerly known as OpenBeOS, is an open source project dedicated to the re-creation and continuation of the Be Operating System on x86 and PowerPC based computers. Haiku is an open-source operating system currently in development designed from the ground up for desktop computing. Inspired by the BeOS, Haiku aims to provide users of all levels with a personal computing experience that is simple yet powerful, and free of any unnecessary complexities. b) Syllable A free and open source operating system for Intel x86 Pentium and compatible processors. Its purpose is to create an easy-to-use desktop operating system for the home and small office user. It was forked from the stagnant AtheOS in July 2002. It has a native web browser (ABrowse), email client (Whisper), media player, IDE, and many more applications. Features include: - Native 64-bit journaled file system, the AtheOS File System (usually called AFS, which is not the same as the Andrew File System) - C++ oriented API - Legacy-free, object-oriented graphical desktop environment on a native GUI architecture - POSIX compliance is 99% - Many software ports (Emacs, Vim, Perl, Python, Apache etc.) - GNU toolchain (GCC, Glibc, Binutils, Make) - Pre-emptive multitasking with multithreading - Symmetric multiprocessing (multiple processor) support - Device drivers for most common hardware (video, sound, network chips) - File system drivers for FAT (read/write), NTFS (read) and ext2 (read).3.0 3.1 The Latest Open Source Application Software Meaning of open source application software(OSAS) OSAS is an application software (is a computer program or a suite of computer programs that performs a particular function for the user) that is its source codes are available to users and they have the rights to modify it which also means that it is free to download and use. 3.2 Examples of open source application software(OSAS) a)GNOME GNOME Office empowers you with three "best in class" productivity applications available as GNU Free Software. The times of wrestling with file formats, compatibility, and 'halfway-there' features is over. The AbiWord word processor, Gnumeric spreadsheet, and Gnome-DB data access components allow you to get it done now. b) NeoOffice NeoOffice is a fork of the free/open source OpenOffice.org office suite that is ported to Mac OS X. It implements nearly all of the features of the corresponding OpenOffice.org version, including a word processor, spreadsheet, presentation program, and graphics program. It is developed by Planamesa Software, and uses Java technology to integrate OpenOffice.org 'originally developed for Solaris and Linux' with the Aqua interface of Mac OS X. OpenOffice.org was originally released under both the LGPL and SISSL; it is now released solely under the LGPL. 4.0 4.1 Latest Development in ICT Hardware (state specification OR special features of ONE hardware and compare it to previous model.a) Canon Pixma MP280 b) Canon Pixma MX360 -The Canon Pixma MP280 is an entry level -The Canon Pixma MX360 was first all-in-one printer, scanner, and copier with introduced by Canon in January during enhanced photo printing capabilities. It was CES 2011. It is an entry level model the budget-friendly model out of its line of designed for small office/home office use, eight photo printers released by Canon in alongside the Pixma MX410. We have 2010. Taking on the new Pixma photo printer already reviewed the leading flagship inkjet look, it features a simple glossy black design out of the bunch, the Pixma MX882, and with silver accents just like the previously the inkjet that is one step down from it, reviewed sister product, the Canon Pixma the Pixma MX420. Now we will take a MP495. Canon has included Full HD Movie look at the MX360. This four-in-one can Print and photo editing software, as well as the print, scan, copy, and fax and connects to a Easy Photo Print app for Android smartphones computer via HighSpeed USB 2.0 (note in the package.Moreover, this photo all-in-one that the MX410 has wireless connectivity). offers high color resolution color photo It has an automatic document feeder that capabilities with a maximum of 4800 x 1200 can fit up to 30 sheets and a 100-sheet rear dpi and is Energy Star certified. It is currently feed tray. We tested the MX360 and found selling for only $70 from Canon's website; so that it can print up to 8 black and white keep reading to find out if this is the right pages per minute under the default settings. printer for you. Our reviews include an The MX360 has a list price of $79.99; overview of specifications, testing results, a check out our full review below to find outsummary of the build and design, and more. if this is the suitable inkjet for your office at that price. 4.2 Software(state year/date of release, special features of ONE software and compare it to previous versions) Name File Size VLC Media Player 2.0.6 VLC Media Player 2.0.0 21.88 MB Requirement Windows 20.99MB XP / Vista Windows7 / Windows8 / Windows 2000 / XP / Vista / Windows7 / XP64 / Vista64 / Windows7 64 / Windows8 / Windows8 64 Date April 12, 2013 February 20, 2012 License Open source Open source Author VideoLAN.org VideoLAN.org Release Features Can play: Can play: MPEG-1,MPEG-2 and MPEG-1,MPEG-2 and MPEG-4 MPEG-4 DVDs, VCDs, and Audio CDs DVDs, VCDs, and Audio Several types of network streams such CDs as HTTP,RTSP,MS and etc. Several types of network From satellite cards (DVB-S) streams such as HTTP,RTSP,MS and etc. 5.0 5.1 Pervasive Computing Meaning of pervasive computingRefers to the use of computers in everyday life, including PDAs, smart phones and other mobile devices. It also refers to computers contained in commonplace objects such as cars and appliances and implies that people are unaware of their presence. One of the Holy Grails of this environment is that all these devices communicate with each other over wireless networks without any interaction required by the user. See pervasive workplace. 5.2 Examples of pervasive computing a)Smart TV *Samsung Smart TV Smart TV, which is also sometimes referred to as "Connected TV" or "Hybrid TV", (not to be confused with Internet TV, Web TV, or LG Electronics's upcoming "SMART TV" branded NetCast Entertainment Access devices), is the phrase used to describe the current trend of integration of the internet and Web 2.0 features into modern television sets and set-top boxes, as well as the technological convergence between computers and these television sets /set-top boxes. These new devices most often also have a much higher focus on online interactive media, Internet TV, over-the-top content, as well as on-demand streaming media, and less focus on traditional broadcast media like previous generations of television sets and set-top boxes always have had. The technology that enables Smart TVs is not only incorporated into television sets, but also devices such as set-top boxes, Blu-ray players, game consoles, and other companion devices. These devices allow viewers to search and find videos, movies, photos and other content on the web, on a local cable TV channel, on a satellite TV channel, or stored on a local hard drive. b) GPS*Garmin GPS The Global Positioning System (GPS) is a space-based global navigation satellite system (GNSS) that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely accessible by anyone with a GPS receiver. The GPS project was developed in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors, including a number of classified engineering design studies from the 1960s. GPS was created and realized by the U.S. Department of Defense (USDOD) and was originally run with 24 satellites. It became fully operational in 1994. 6.0 Conclusion Open Source can be used by anyone and because it has no copyright claims, so users are free to use, change, and improve the software, and to redistribute it in modified or unmodified forms. Pervasive Computing is to make our lives easier because we can interact with computers. Besides that, we can easily give the computer commands and the computer will grant your wish.
Computer networkFrom Wikipedia, the free encyclopediaNetwork science
Theory
Graph Complex network Contagion Small-world Scale-free Community structure Percolation Evolution Controllability Graph drawing Social capital Link analysis Optimization Reciprocity Closure Homophily Transitivity Preferential attachment Balance theory Network effect Social influence
Network types
Informational (computing) Telecommunication Social Biological Artificial neural Interdependent Semantic Random graph Dependency Flow
Graphs
Features Clique Component Cut Cycle Data structure Edge Loop Neighborhood Path Vertex Adjacency list/matrix Incidence list/matrixTypes Bipartite Complete Directed Hyper Multi Random Weighted
Metrics Algorithms
Centrality Degree Betweenness Closeness PageRank Motif Clustering Degree distribution Assortativity Distance Modularity
Models
Random graph ErdsRnyi BarabsiAlbert WattsStrogatz Exponential random (ERGM) Epidemic Hierarchical
Lists
Topics Software Network scientists
Categories
Graph theory Network theory
v t e
Acomputer networkordata networkis atelecommunications networkthat allowscomputersto exchangedata. In computer networks, networked computing devices pass data to each other along data connections. The connections (network links) between nodes are established using eithercable mediaorwireless media. The best-known computer network is theInternet.Network computer devices that originate, route and terminate the data are callednetwork nodes.[1]Nodes can includehostssuch aspersonal computers,phones,serversas well asnetworking hardware. Two such devices are said to be networked together when one device is able to exchange information with the other device, whether or not they have a direct connection to each other.Computer networks supportapplicationssuch as access to theWorld Wide Web, shared use ofapplication and storage servers,printers, and fax machines, and use ofemailandinstant messagingapplications. Computer networks differ in the physical media used to transmit their signals, thecommunications protocolsto organize network traffic, the network's size,topologyand organizational intent.Contents[hide] 1History 2Properties 3Network topology 3.1Network links 3.2Network nodes 3.3Network structure 4Communications protocols 4.1Ethernet 4.2Internet Protocol Suite 4.3SONET/SDH 4.4Asynchronous Transfer Mode 5Geographic scale 6Organizational scope 6.1Intranets 6.2Extranet 6.3Internetwork 6.4Internet 6.5Darknet 7Routing 8Network service 9Network performance 9.1Quality of service 9.2Network congestion 9.3Network resilience 10Security 10.1Network security 10.2Network surveillance 10.3End to end encryption 11Views of networks 12See also 13References 14Further reading 15External linksHistory[edit] In the late 1950s, early networks of communicating computers included the military radar systemSemi-Automatic Ground Environment(SAGE). In 1960, the commercial airline reservation systemsemi-automatic business research environment(SABRE) went online with two connected mainframes. In 1962,J.C.R. Lickliderdeveloped a working group he called the "Intergalactic Computer Network", a precursor to theARPANET, at theAdvanced Research Projects Agency(ARPA). In 1964, researchers at Dartmouth developed theDartmouth Time Sharing Systemfor distributed users of large computer systems. The same year, atMassachusetts Institute of Technology, a research group supported byGeneral ElectricandBell Labsused a computer to route and manage telephone connections. Throughout the 1960s,Leonard Kleinrock,Paul Baran, andDonald Daviesindependently developed network systems that usedpacketsto transfer information between computers over a network. In 1965, Thomas Marill andLawrence G. Robertscreated the firstwide area network(WAN). This was an immediate precursor to theARPANET, of which Roberts became program manager. Also in 1965, the first widely usedtelephone switchthat implemented true computer control was introduced byWestern Electric. In 1969, theUniversity of California at Los Angeles, theStanford Research Institute, theUniversity of California at Santa Barbara, and theUniversity of Utahwere connected as the beginning of theARPANETnetwork using 50 kbit/s circuits.[2] In 1972, commercial services usingX.25were deployed, and later used as an underlying infrastructure for expandingTCP/IPnetworks. In 1973,Robert Metcalfewrote a formal memo atXerox PARCdescribingEthernet, a networking system that was based on theAloha network, developed in the 1960s byNorman Abramsonand colleagues at theUniversity of Hawaii. In July 1976,Robert MetcalfeandDavid Boggspublished their paper "Ethernet: Distributed Packet Switching for Local Computer Networks"[3]and collaborated on several patents received in 1977 and 1978. In 1979, Robert Metcalfe pursued making Ethernet an open standard.[4] In 1976, John Murphy ofDatapoint CorporationcreatedARCNET, a token-passing network first used to share storage devices. In 1995, the transmission speed capacity for Ethernet was increased from 10 Mbit/s to 100 Mbit/s. By 1998, Ethernet supported transmission speeds of a Gigabit. The ability of Ethernet to scale easily (such as quickly adapting to support new fiber optic cable speeds) is a contributing factor to its continued use today.[4]Today, computer networks are the core of modern communication. All modern aspects of thepublic switched telephone network(PSTN) are computer-controlled. Telephony increasingly runs over the Internet Protocol, although not necessarily the public Internet. The scope of communication has increased significantly in the past decade. This boom in communications would not have been possible without the progressively advancing computer network. Computer networks, and the technologies that make communication between networked computers possible, continue to drive computer hardware, software, and peripherals industries. The expansion of related industries is mirrored by growth in the numbers and types of people using networks, from the researcher to the home user.Properties[edit]Computer networking may be considered a branch ofelectrical engineering,telecommunications,computer science,information technologyorcomputer engineering, since it relies upon the theoretical and practical application of the related disciplines.A computer network has the following properties:Facilitates interpersonal communicationsPeople can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.Allows sharing of files, data, and other types of informationAuthorized users may access information stored on other computers on the network. Providing access to information on shared storage devices is an important feature of many networks.Allows sharing of network and computing resourcesUsers may access and use resources provided by devices on the network, such as printing a document on a shared network printer.Distributed computinguses computing resources across a network to accomplish tasks.May be insecureA computer network may be used bycomputer Crackersto deploycomputer virusesorcomputer wormson devices connected to the network, or to prevent these devices from accessing the network (denial of service).May interfere with other technologiesPower line communicationstrongly disturbs certain[5]forms of radio communication, e.g., amateur radio. It may also interfere withlast mileaccess technologies such asADSLandVDSL.May be difficult to set upA complex computer network may be difficult to set up. It may be costly to set up an effective computer network in a large organization.Network topology[edit]Main article:Network topologyThe physical layout of a network is usually less important than the topology that connects network nodes. Most diagrams that describe a physical network are therefore topological, rather than geographic. The symbols on these diagrams usually denote network links and network nodes.Network links[edit]The communication media used to link devices to form a computer network includeelectrical cable(HomePNA,power line communication,G.hn),optical fiber(fiber-optic communication), andradio waves(wireless networking). In theOSI model, these are defined at layers 1 and 2 the physical layer and the data link layer.A widely adoptedfamilyof communication media used in local area network (LAN) technology is collectively known asEthernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined byIEEE 802.3. Ethernet transmit data over both copper and fiber cables. Wireless LAN standards (e.g. those defined byIEEE 802.11) useradio waves, or others useinfraredsignals as a transmission medium.Power line communicationuses a building's power cabling to transmit data.Wired technologies[edit]
Fiber optic cables are used to transmit light from one computer/network node to anotherThe orders of the following wired technologies are, roughly, from slowest to fastest transmission speed. Twisted pairwireis the most widely used medium for all telecommunication. Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer network cabling (wiredEthernetas defined byIEEE 802.3) consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reducecrosstalkandelectromagnetic induction. The transmission speed ranges from 2 million bits per second to 10 billion bits per second. Twisted pair cabling comes in two forms: unshielded twisted pair (UTP) and shielded twisted-pair (STP). Each form comes in several category ratings, designed for use in various scenarios. Coaxial cableis widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire surrounded by an insulating layer (typically a flexible material with a high dielectric constant), which itself is surrounded by a conductive layer. The insulation helps minimize interference and distortion. Transmission speed ranges from 200 million bits per second to more than 500 million bits per second. ITU-TG.hntechnology uses existinghome wiring(coaxial cable, phone lines andpower lines) to create a high-speed (up to 1 Gigabit/s) local area network. Anoptical fiberis a glass fiber. It carries pulses of light that represent data. Some advantages of optical fibers over metal wires are very low transmission loss and immunity from electrical interference. Optical fibers can simultaneously carry multiple wavelengths of light, which greatly increases the rate that data can be sent, and helps enable data rates of up to trillions of bits per second. Optic fibers can be used for long runs of cable carrying very high data rates, and are used forundersea cablesto interconnect continents.Wireless technologies[edit]
Computers are very often connected to networks using wireless linksMain article:Wireless network Terrestrialmicrowave Terrestrial microwave communication uses Earth-based transmitters and receivers resembling satellite dishes. Terrestrial microwaves are in the low-gigahertz range, which limits all communications to line-of-sight. Relay stations are spaced approximately 48km (30mi) apart. Communicationssatellites Satellites communicate via microwave radio waves, which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically in geosynchronous orbit 35,400km (22,000mi) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals. Cellular and PCS systemsuse several radio communications technologies. The systems divide the region covered into multiple geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area. Radio andspread spectrumtechnologies Wireless local area networks use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area.IEEE 802.11defines a common flavor of open-standards wireless radio-wave technology known asWifi. Free-space optical communicationuses visible or invisible light for communications. In most cases,line-of-sight propagationis used, which limits the physical positioning of communicating devices.Exotic technologies[edit]There have been various attempts at transporting data over exotic media: IP over Avian Carrierswas a humorous April fool'sRequest for Comments, issued asRFC 1149. It was implemented in real life in 2001.[6] Extending the Internet to interplanetary dimensions via radio waves.[7]Both cases have a largeround-trip delay time, which gives slow two-way communication, but doesn't prevent sending large amounts of information.Network nodes[edit]Main article:Node (networking)Apart from the physical communications media described above, networks comprise additional basicsystembuilding blocks, such asnetwork interface controller(NICs),repeaters,hubs,bridges,switches,routers,modems, andfirewalls.Network interfaces[edit]
AnATMnetwork interface in the form of an accessory card. Very many network interfaces are built-in.Anetwork interface controller(NIC) iscomputer hardwarethat provides a computer with the ability to access the transmission media, and has the ability to process low-level network information. For example the NIC may have a connector for accepting a cable, or an aerial for wireless transmission and reception, and the associated circuitry.The NIC respond to traffic addressed to anetwork addressfor either the NIC or the computer as a whole.InEthernetnetworks, each network interface controller has a uniqueMedia Access Control(MAC) addressusually stored in the controller's permanent memory. To avoid address conflicts between network devices, theInstitute of Electrical and Electronics Engineers(IEEE) maintains and administers MAC address uniqueness. The size of an Ethernet MAC address is sixoctets. The three most significant octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce.Repeaters and hubs[edit]Arepeateris anelectronicdevice that receives a networksignal, cleans it of unnecessary noise, and regenerates it. The signal isretransmittedat a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. With fiber optics, repeaters can be tens of even hundreds of kilometers apart.A repeater with multiple ports is known as ahub. Repeaters work on the physical layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause apropagation delaythat affects network performance. As a result, many network architectures limit the number of repeaters that can be used in a row, e.g., the Ethernet5-4-3 rule.Hubs have been mostly obsoleted by modern switches; but repeaters are used for long distance links, notably undersea cabling.Bridges[edit]Anetwork bridgeconnects and filters traffic between twonetwork segmentsat thedata link layer(layer 2) of theOSI modelto form a single network. This breaks the network's collision domain but maintains a unified broadcast domain. Network segmentation breaks down a large, congested network into an aggregation of smaller, more efficient networks.Bridges come in three basic types: Local bridges: Directly connect LANs Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers. Wireless bridges: Can be used to join LANs or connect remote devices to LANs.Switches[edit]Anetwork switchis a device that forwards and filtersOSI layer 2datagramsbetweenportsbased on the MAC addresses in the packets.[8]A switch is distinct from a hub in that it only forwards the frames to the physical ports involved in the communication rather than all ports connected. It can be thought of as a multi-port bridge.[9]It learns to associate physical ports to MAC addresses by examining the source addresses of received frames. If an unknown destination is targeted, the switch broadcasts to all ports but the source. Switches normally have numerous ports, facilitating a star topology for devices, and cascading additional switches.Multi-layer switchesare capable of routing based on layer 3 addressing or additional logical levels. The termswitchis often used loosely to include devices such as routers and bridges, as well as devices that may distribute traffic based on load or based on application content (e.g., a WebURLidentifier).Routers[edit]
A typical home or small office router showing theADSLtelephone line andEthernetnetwork cable connectionsArouteris an internetworking device that forwardspacketsbetween networks by processing the routing information included in the packet or datagram (Internet protocol information from layer 3). The routing information is often processed in conjunction with the routing table (or forwarding table). A router uses its routing table to determine where to forward packets. (A destination in a routing table can include a "null" interface, also known as the "black hole" interface because data can go into it, however, no further processing is done for said data.)Modems[edit]Modems(MOdulator-DEModulator) are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless. To do this one or more frequencies are modulated by the digital signal to produce an analog signal that can be tailored to give the required properties for transmission. Modems are commonly used for telephone lines, using aDigital Subscriber Linetechnology.Firewalls[edit]Afirewallis a network device for controlling network security and access rules. Firewalls are typically configured to reject access requests from unrecognized sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase incyber attacks.Network structure[edit]Network topologyis the layout or organizational hierarchy of interconnected nodes of a computer network. Different network topologies can affect throughput, but reliability is often more critical. With many technologies, such as bus networks, a single failure can cause the network to fail entirely. In general the more interconnections there are, the more robust the network is; but the more expensive it is to install.Common layouts[edit]
Common network topologiesCommon layouts are: Abus network: all nodes are connected to a common medium along this medium. This was the layout used in the originalEthernet, called10BASE5and10BASE2. Astar network: all nodes are connected to a special central node. This is the typical layout found in aWireless LAN, where each wireless client connects to the centralWireless access point. Aring network: each node is connected to its left and right neighbour node, such that all nodes are connected and that each node can reach each other node by traversing nodes left- or rightwards. TheFiber Distributed Data Interface(FDDI) made use of such a topology. Amesh network: each node is connected to an arbitrary number of neighbours in such a way that there is at least one traversal from any node to any other. Afully connected network: each node is connected to every other node in the network. Atree network: nodes are arranged hierarchically.Note that the physical layout of the nodes in a network may not necessarily reflect the network topology. As an example, withFDDI, the network topology is a ring (actually two counter-rotating rings), but the physical topology is often a star, because all neighboring connections can be routed via a central physical location.Overlay network[edit]
A sample overlay networkAnoverlay networkis a virtual computer network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from that of the underlying one. For example, manypeer-to-peernetworks are overlay networks. They are organized as nodes of a virtual system of links that run on top of the Internet.[10]Overlay networks have been around since the invention of networking when computer systems were connected over telephone lines usingmodems, before any data network existed.The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on thetelephone network.[10]Even today, at the network layer, each node can reach any other by a direct connection to the desired IP address, thereby creating a fully connected network. The underlying network, however, is composed of a mesh-like interconnect of sub-networks of varying topologies (and technologies).Address resolutionandroutingare the means that allow mapping of a fully connected IP overlay network to its underlying network.Another example of an overlay network is adistributed hash table, which maps keys to nodes in the network. In this case, the underlying network is an IP network, and the overlay network is a table (actually amap) indexed by keys.Overlay networks have also been proposed as a way to improve Internet routing, such as throughquality of serviceguarantees to achieve higher-qualitystreaming media. Previous proposals such asIntServ,DiffServ, andIP Multicasthave not seen wide acceptance largely because they require modification of allroutersin the network.[citation needed]On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation fromInternet service providers. The overlay network has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes that a message traverses before it reaches its destination.For example,Akamai Technologiesmanages an overlay network that provides reliable, efficient content delivery (a kind ofmulticast). Academic research includes end system multicast,[11]resilient routing and quality of service studies, among others.Communications protocols[edit]
The TCP/IP model or Internet layering scheme and its relation to common protocols often layered on top of it.Acommunications protocolis a set of rules for exchanging information over network links. In aprotocol stack(also see theOSI model), each protocol leverages the services of the protocol below it. An important example of a protocol stack isHTTPrunning overTCPoverIPoverIEEE 802.11. (TCP and IP are members of theInternet Protocol Suite. IEEE 802.11 is a member of theEthernetprotocol suite.) This stack is used between thewireless routerand the home user's personal computer when the user is surfing the web.Whilst the use of protocol layering is today ubiquitous across the field of computer networking, it has been historically criticized by many researchers[12]for two principle reasons. Firstly, abstracting the protocol stack in this way may cause a higher layer to duplicate functionality of a lower layer, a prime example being error recovery on both a per-link basis and an end-to-end basis.[13]Secondly, it is common that a protocol implementation at one layer may require data, state or addressing information that is only present at another layer, thus defeating the point of separating the layers in the first place. For example,TCPuses the ECN field in theIPv4 headeras an indication of congestion; IP is anetwork layerprotocol whereas TCP is atransport layerprotocol.Communication protocols have various characteristics. They may beconnection-orientedorconnectionless, they may usecircuit modeorpacket switching, and they may use hierarchical addressing or flat addressing.There are many communication protocols, a few of which are described below.Ethernet[edit]Ethernetis a family of protocols used in LANs, described by a set of standards together calledIEEE 802published by theInstitute of Electrical and Electronics Engineers. It has a flat addressing scheme. It operates mostly at levels 1 and 2 of theOSI model. For home users today, the most well-known member of this protocol family isIEEE 802.11, otherwise known asWireless LAN(WLAN). The completeIEEE 802protocol suite provides a diverse set of networking capabilities. For example,MACbridging(IEEE 802.1D) deals with the routing of Ethernet packets using aSpanning Tree Protocol,IEEE 802.1QdescribesVLANs, andIEEE 802.1Xdefines a port-basedNetwork Access Controlprotocol, which forms the basis for the authentication mechanisms used in VLANs (but it is also found in WLANs) it is what the home user sees when the user has to enter a "wireless access key".Internet Protocol Suite[edit]TheInternet Protocol Suite, also called TCP/IP, is the foundation of all modern internetworking. It offers connection-less as well as connection-oriented services over an inherently unreliable network traversed by datagram transmission at theInternet protocol(IP) level. At its core, the protocol suite defines the addressing, identification, and routing specifications forInternet Protocol Version 4(IPv4) and for IPv6, the next generation of the protocol with a much enlarged addressing capability.SONET/SDH[edit]Synchronous optical networking(SONET) and Synchronous Digital Hierarchy (SDH) are standardizedmultiplexingprotocols that transfer multiple digital bit streams over optical fiber using lasers. They were originally designed to transport circuit mode communications from a variety of different sources, primarily to support real-time, uncompressed,circuit-switchedvoice encoded inPCM(Pulse-Code Modulation) format. However, due to its protocol neutrality and transport-oriented features, SONET/SDH also was the obvious choice for transportingAsynchronous Transfer Mode(ATM) frames.Asynchronous Transfer Mode[edit]Asynchronous Transfer Mode(ATM) is a switching technique for telecommunication networks. It uses asynchronoustime-division multiplexingand encodes data into small, fixed-sizedcells. This differs from other protocols such as theInternet Protocol SuiteorEthernetthat use variable sized packets orframes. ATM has similarity with bothcircuitandpacketswitched networking. This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time,low-latencycontent such as voice and video. ATM uses aconnection-orientedmodel in which avirtual circuitmust be established between two endpoints before the actual data exchange begins.While the role of ATM is diminishing in favor ofnext-generation networks, it still plays a role in thelast mile, which is the connection between anInternet service providerand the home user. For an interesting write-up of the technologies involved, including the deep stacking of communications protocols used, see.[14]Geographic scale[edit]A network can be characterized by its physical capacity or its organizational purpose. Use of the network, including user authorization and access rights, differ accordingly.Personal area networkApersonal area network(PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters.[15]A wired PAN is usually constructed with USB and FireWire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.Local area networkAlocal area network(LAN) is a network that connects computers and devices in a limited geographical area such as a home, school, office building, or closely positioned group of buildings. Each computer or device on the network is anode. Wired LANs are most likely based onEthernettechnology. Newer standards such asITU-TG.hnalso provide a way to create a wired LAN using existing wiring, such as coaxial cables, telephone lines, and power lines.[16]A LAN is depicted in the accompanying diagram. All interconnected devices use thenetwork layer(layer 3) to handle multiplesubnets(represented by different colors). Those inside the library have 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the centralrouter. They could be calledLayer 3 switches, because they only have Ethernet interfaces and support theInternet Protocol. It might be more correct to call them access routers, where the router at the top is a distribution router that connects to theInternetand to the academic networks' customer access routers.The defining characteristics of a LAN, in contrast to awide area network(WAN), include higherdata transfer rates, limited geographic range, and lack of reliance onleased linesto provide connectivity. Current Ethernet or otherIEEE 802.3LAN technologies operate at data transfer rates up to 10 Gbit/s. TheIEEEinvestigates the standardization of 40 and 100 Gbit/s rates.[17]A LAN can be connected to a WAN using arouter.Home area networkAhome area network(HAN) is a residential LAN used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a cable TV ordigital subscriber line(DSL) provider.Storage area networkAstorage area network(SAN) is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium sized business environments.Campus area networkAcampus area network(CAN) is made up of an interconnection of LANs within a limited geographical area. The networking equipment (switches, routers) and transmission media (optical fiber, copper plant,Cat5cabling, etc.) are almost entirely owned by the campus tenant / owner (an enterprise, university, government, etc.).For example, a university campus network is likely to link a variety of campus buildings to connect academic colleges or departments, the library, and student residence halls.Backbone networkAbackbone networkis part of a computer network infrastructure that provides a path for the exchange of information between different LANs or sub-networks. A backbone can tie together diverse networks within the same building, across different buildings, or over a wide area.For example, a large company might implement a backbone network to connect departments that are located around the world. The equipment that ties together the departmental networks constitutes the network backbone. When designing a network backbone,network performanceandnetwork congestionare critical factors to take into account. Normally, the backbone network's capacity is greater than that of the individual networks connected to it.Another example of a backbone network is theInternet backbone, which is the set ofwide area networks(WANs) andcore routersthat tie together all networks connected to theInternet.Metropolitan area networkAMetropolitan area network(MAN) is a large computer network that usually spans a city or a large campus.Wide area networkAwide area network(WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances. A WAN uses a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often makes use of transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of theOSI reference model: thephysical layer, thedata link layer, and thenetwork layer.Enterprise private networkAnenterprise private networkis a network that a single organization builds to interconnect its office locations (e.g., production sites, head offices, remote offices, shops) so they can share computer resources.Virtual private networkAvirtual private network(VPN) is an overlay network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point.Global area networkAglobal area network(GAN) is a network used for supporting mobile across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrialwireless LANs.[18]Organizational scope[edit]Networks are typically managed by the organizations that own them. Private enterprise networks may use a combination of intranets and extranets. They may also provide network access to theInternet, which has no single owner and permits virtually unlimited global connectivity.Intranets[edit]Anintranetis a set of networks that are under the control of a single administrative entity. The intranet uses theIPprotocol and IP-based tools such as web browsers and file transfer applications. The administrative entity limits use of the intranet to its authorized users. Most commonly, an intranet is the internal LAN of an organization. A large intranet typically has at least one web server to provide users with organizational information. An intranet is also anything behind the router on a local area network.Extranet[edit]Anextranetis a network that is also under the administrative control of a single organization, but supports a limited connection to a specific external network. For example, an organization may provide access to some aspects of its intranet to share data with its business partners or customers. These other entities are not necessarily trusted from a security standpoint. Network connection to an extranet is often, but not always, implemented via WAN technology.Internetwork[edit]Aninternetworkis the connection of multiple computer networks via a common routing technology using routers.Internet[edit]
Partial map of the Internet based on the January 15, 2005 data found onopte.org. Each line is drawn between two nodes, representing twoIP addresses. The length of the lines are indicative of the delay between those two nodes. This graph represents less than 30% of theClass Cnetworks reachable.TheInternetis the largest example of an internetwork. It is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is based on the networking technologies of theInternet Protocol Suite. It is the successor of theAdvanced Research Projects Agency Network(ARPANET) developed byDARPAof theUnited States Department of Defense. The Internet is also the communications backbone underlying theWorld Wide Web(WWW).Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP addresses) administered by theInternet Assigned Numbers Authorityandaddress registries. Service providers and large enterprises exchange information about thereachabilityof their address spaces through theBorder Gateway Protocol(BGP), forming a redundant worldwide mesh of transmission paths.Darknet[edit]ADarknetis an overlay network, typically running on the internet, that is only accessible through specialized software. A darknet is an anonymizing network where connections are made only between trusted peers sometimes called "friends" (F2F)[19] using non-standardprotocolsandports.Darknets are distinct from other distributedpeer-to-peernetworks assharingis anonymous (that is,IP addressesare not publicly shared), and therefore users can communicate with little fear of governmental or corporate interference.[20]Routing[edit]
Routing calculates good paths through a network for information to take. For example from node 1 to node 6 the best routes are likely to be 1-8-7-6 or 1-8-10-6, as this has the thickest routes.Routingis the process of selecting network paths to carry network traffic. Routing is performed for many kinds of networks, includingcircuit switchingnetworks andpacket switched networks.In packet switched networks, routing directspacket forwarding(the transit of logically addressednetwork packetsfrom their source toward their ultimate destination) through intermediatenodes. Intermediate nodes are typically network hardware devices such asrouters,bridges,gateways,firewalls, orswitches. General-purposecomputerscan also forward packets and perform routing, though they are not specialized hardware and may suffer from limited performance. The routing process usually directs forwarding on the basis ofrouting tables, which maintain a record of the routes to various network destinations. Thus, constructing routing tables, which are held in the router'smemory, is very important for efficient routing. Most routing algorithms use only one network path at a time.Multipath routingtechniques enable the use of multiple alternative paths.There are usually multiple routes that can be taken, and to choose between them, different elements can be considered to decide which routes get installed into the routing table, such as (sorted by priority):1. Prefix-Length: where longer subnet masks are preferred (independent if it is within a routing protocol or over different routing protocol)2. Metric: where a lower metric/cost is preferred (only valid within one and the same routing protocol)3. Administrative distance: where a lower distance is preferred (only valid between different routing protocols)Routing, in a more narrow sense of the term, is often contrasted withbridgingin its assumption thatnetwork addressesare structured and that similar addresses imply proximity within the network. Structured addresses allow a single routing table entry to represent the route to a group of devices. In large networks, structured addressing (routing, in the narrow sense) outperforms unstructured addressing (bridging). Routing has become the dominant form of addressing on the Internet. Bridging is still widely used within localized environments.Network service[edit]Network servicesare applications hosted byserverson a computer network, toprovide some functionalityfor members or users of the network, or to help the network itself to operate.TheWorld Wide Web,E-mail,[21]printingandnetwork file sharingare examples of well-known network services. Network services such as DNS (Domain Name System) give names forIPandMAC addresses(people remember names like nm.lan better than numbers like 210.121.67.18),[22]andDHCPto ensure that the equipment on the network has a valid IP address.[23]Services are usually based on aservice protocolthat defines the format and sequencing of messages between clients and servers of that network service.Network performance[edit]Quality of service[edit]Depending on the installation requirements,network performanceis usually measured by thequality of serviceof a telecommunications product. The parameters that affect this typically can includethroughput,jitter,bit error rateandlatency.The following list gives examples of network performance measures for a circuit-switched network and one type ofpacket-switched network, viz. ATM: Circuit-switched networks: Incircuit switchednetworks, network performance is synonymous with thegrade of service. The number of rejected calls is a measure of how well the network is performing under heavy traffic loads.[24]Other types of performance measures can include the level of noise and echo. ATM: In anAsynchronous Transfer Mode(ATM) network, performance can be measured by line rate,quality of service(QoS), data throughput, connect time, stability, technology, modulation technique and modem enhancements.[25]There are many ways to measure the performance of a network, as each network is different in nature and design. Performance can also be modelled instead of measured. For example, state transition diagrams are often used to model queuing performance in a circuit-switched network. The network planner uses these diagrams to analyze how the network performs in each state, ensuring that the network is optimally designed.[26]Network congestion[edit]Network congestionoccurs when a link or node is carrying so much data that itsquality of servicedeteriorates. Typical effects includequeueing delay,packet lossor theblockingof new connections. A consequence of these latter two is that incremental increases inoffered loadlead either only to small increase in networkthroughput, or to an actual reduction in network throughput.Network protocolsthat use aggressiveretransmissionsto compensate for packet loss tend to keep systems in a state of network congestioneven after the initial load is reduced to a level that would not normally induce network congestion. Thus, networks using these protocols can exhibit two stable states under the same level of load. The stable state with low throughput is known ascongestive collapse.Modern networks usecongestion controlandcongestion avoidancetechniques to try to avoid congestion collapse. These include:exponential backoffin protocols such as802.11'sCSMA/CAand the originalEthernet,windowreduction inTCP, andfair queueingin devices such asrouters. Another method to avoid the negative effects of network congestion is implementing priority schemes, so that some packets are transmitted with higher priority than others. Priority schemes do not solve network congestion by themselves, but they help to alleviate the effects of congestion for some services. An example of this is802.1p. A third method to avoid network congestion is the explicit allocation of network resources to specific flows. One example of this is the use of Contention-Free Transmission Opportunities (CFTXOPs) in theITU-TG.hnstandard, which provides high-speed (up to 1 Gbit/s)Local area networkingover existing home wires (power lines, phone lines and coaxial cables).For the InternetRFC 2914addresses the subject of congestion control in detail.Network resilience[edit]Network resilienceis "the ability to provide and maintain an acceptable level ofservicein the face offaultsand challenges to normal operation.[27]Security[edit]Network security[edit]Network securityconsists of provisions andpoliciesadopted by thenetwork administratorto prevent and monitorunauthorizedaccess, misuse, modification, or denial of the computer network and its network-accessible resources.[28]Network security is the authorization of access to data in a network, which is controlled by the network administrator. Users are assigned an ID and password that allows them access to information and programs within their authority. Network security is used on a variety of computer networks, both public and private, to secure daily transactions and communications among businesses, government agencies and individuals.Network surveillance[edit]Network surveillanceis the monitoring of data being transferred over computer networks such as theInternet. The monitoring is often done surreptitiously and may be done by or at the behest of governments, by corporations, criminal organizations, or individuals. It may or may not be legal and may or may not require authorization from a court or other independent agency.Computer and network surveillance programs are widespread today, and almost all Internet traffic is or could potentially be monitored for clues to illegal activity.Surveillance is very useful to governments and law enforcement to maintainsocial control, recognize and monitor threats, and prevent/investigatecriminalactivity. With the advent of programs such as theTotal Information Awarenessprogram, technologies such ashigh speed surveillance computersandbiometricssoftware, and laws such as theCommunications Assistance For Law Enforcement Act, governments now possess an unprecedented ability to monitor the activities of citizens.[29]However, manycivil rightsandprivacygroupssuch asReporters Without Borders, theElectronic Frontier Foundation, and theAmerican Civil Liberties Unionhave expressed concern that increasing surveillance of citizens may lead to amass surveillancesociety, with limited political and personal freedoms. Fears such as this have led to numerous lawsuits such asHepting v. AT&T.[29][30]ThehacktivistgroupAnonymoushas hacked into government websites in protest of what it considers "draconian surveillance".[31][32]End to end encryption[edit]End-to-end encryption(E2EE) is adigital communicationsparadigm of uninterrupted protection of data traveling between two communicating parties. It involves the originating partyencryptingdata so only the intended recipient can decrypt it, with no dependency on third parties. End-to-end encryption prevents intermediaries, such asInternet providersorapplication service providers, from discovering or tampering with communications. End-to-end encryption generally protects bothconfidentialityandintegrity.Examples of end-to-end encryption includePGPforemail,OTRforinstant messaging,ZRTPfortelephony, andTETRAfor radio.Typicalserver-based communications systems do not include end-to-end encryption. These systems can only guarantee protection of communications betweenclientsandservers, not between the communicating parties themselves. Examples of non-E2EE systems areGoogle Talk,Yahoo Messenger,Facebook, andDropbox. Some such systems, for example LavaBit and SecretInk, have even described themselves as offering "end-to-end" encryption when they do not. Some systems that normally offer end-to-end encryption have turned out to contain aback doorthatsubverts negotiation of theencryption keybetween the communicating parties, for exampleSkype.The end-to-end encryption paradigm does not directly address risks at the communications endpoints themselves, such as thetechnical exploitationofclients, poor qualityrandom number generators, orkey escrow. E2EE also does not addresstraffic analysis, which relates to things such as the identities of the end points and the times and quantities of messages that are sent.Views of networks[edit]Users and network administrators typically have different views of their networks. Users can share printers and some servers from a workgroup, which usually means they are in the same geographic location and are on the same LAN, whereas a Network Administrator is responsible to keep that network up and running. Acommunity of interesthas less of a connection of being in a local area, and should be thought of as a set of arbitrarily located users who share a set of servers, and possibly also communicate viapeer-to-peertechnologies.Network administrators can see networks from both physical and logical perspectives. The physical perspective involves geographic locations, physical cabling, and the network elements (e.g.,routers,bridgesandapplication layer gateways) that interconnect the physical media. Logical networks, called, in the TCP/IP architecture,subnets, map onto one or more physical media. For example, a common practice in a campus of buildings is to make a set of LAN cables in each building appear to be a common subnet, usingvirtual LAN (VLAN)technology.Both users and administrators are aware, to varying extents, of the trust and scope characteristics of a network. Again using TCP/IP architectural terminology, anintranetis a community of interest under private administration usually by an enterprise, and is only accessible by authorized users (e.g. employees).[33]Intranets do not have to be connected to the Internet, but generally have a limited connection. Anextranetis an extension of an intranet that allows secure communications to users outside of the intranet (e.g. business partners, customers).[33]Unofficially, the Internet is the set of users, enterprises, and content providers that are interconnected byInternet Service Providers(ISP). From an engineering viewpoint, theInternetis the set of subnets, and aggregates of subnets, which share the registeredIP addressspace and exchange information about the reachability of those IP addresses using theBorder Gateway Protocol. Typically, thehuman-readablenames of servers are translated to IP addresses, transparently to users, via the directory function of theDomain Name System(DNS).Over the Internet, there can bebusiness-to-business (B2B),business-to-consumer (B2C)andconsumer-to-consumer (C2C)communications. When money or sensitive information is exchanged, the communications are apt to be protected by some form ofcommunications securitymechanism. Intranets and extranets can be securely superimposed onto the Internet, without any access by general Internet users and administrators, using secureVirtual Private Network(VPN) technology.
Mobile computingishumancomputer interactionby which acomputeris expected to be transported during normal usage. Mobile computing involvesmobile communication, mobile hardware, and mobile software. Communication issues include ad hoc and infrastructure networks as well as communication properties,protocols, data formats and concrete technologies. Hardware includesmobile devicesor device components.Mobile softwaredeals with the characteristics and requirements of mobile applications.Contents[hide] 1Definitions 2Devices 3Limitations 4In-vehicle computing and fleet computing 5Security issues involved in mobile computing 6Portable computing devices 7Mobile data communication 8See also 9References 9.1Citations 9.2Bibliography 10Further readingDefinitions[edit]Mobile Computing is "taking a computer and all necessary files and software out into the field".[1]Mobile computing is any type of computing which use Internet or intranet and respective communications links, as WAN, LAN, WLAN etc. Mobile computers may form awireless personal networkor apiconet.There are at least three different classes of mobile computing items: portable computers, compacted lightweight units including a full character set keyboard and primarily intended ashostsfor software that may be parametrized, as laptops, notebooks, notepads, etc. mobile phonesincluding a restricted key set primarily intended but not restricted to for vocal communications, as cell phones, smart phones, phonepads, etc. wearable computers, mostly limited to functional keys and primarily intended as incorporation ofsoftware agents, as watches, wristbands, necklaces, keyless implants, etc.The existence of these classes is expected to be long lasting, and complementary in personal usage, none replacing one the other in all features of convenience..Devices[edit]Many types of mobile computers have been introduced since the 1990s including the: Personal digital assistant/enterprise digital assistant Smartphone Tablet computer Ultra-Mobile PC Wearable computerLimitations[edit] Range & Bandwidth: Mobile Internet access is generally slower than direct cable connections, using technologies such asGPRSandEDGE, and more recentlyHSDPAandHSUPA3Gand4Gnetworks. These networks are usually available within range of commercial cell phone towers. Higher speedwireless LANsare inexpensive but have very limited range. Security standards: When working mobile, one is dependent on public networks, requiring careful use ofVPN. Security is a major concern while concerning the mobile computing standards on the fleet. One can easily attack the VPN through a huge number of networks interconnected through the line. Power consumption: When a power outlet or portable generator is not available, mobile computers must rely entirely on battery power. Combined with the compact size of many mobile devices, this often means unusually expensive batteries must be used to obtain the necessary battery life. Transmission interferences: Weather, terrain, and the range from the nearest signal point can all interfere with signal reception. Reception in tunnels, some buildings, and rural areas is often poor. Potential health hazards: People who use mobile devices while driving are often distracted from driving and are thus assumed more likely to be involved in traffic accidents.[2](While this may seem obvious, there is considerable discussion about whether banning mobile device use while driving reduces accidents or not.[3][4]) Cell phones may interfere with sensitive medical devices. Questions concerningmobile phone radiation and healthhave been raised. Human interface with device: Screens and keyboards tend to be small, which may make them hard to use. Alternate input methods such as speech or handwriting recognition require training.In-vehicle computing and fleet computing[edit]Many commercial and government field forces deploy a ruggedized portable computer with their fleet of vehicles. This requires the units to be anchored to the vehicle for driver safety, device security, andergonomics.Rugged computersare rated for severe vibration associated with large service vehicles and off-road driving and the harsh environmental conditions of constant professional use such as inemergency medical services, fire, and public safety.
TheCompaq Portable- Circa 1982 pre-laptopOther elements affecting function in vehicle: Operating temperature: A vehicle cabin can often experience temperature swings from -20F to +140F. Computers typically must be able to withstand these temperatures while operating. Typical fan-based cooling has stated limits of 95F-100F of ambient temperature, and temperatures below freezing require localized heaters to bring components up to operating temperature (based on independent studies by the SRI Group and by Panasonic R&D). Vibration can decrease the life expectancy of computer components, notably rotational storage such asHDDs. Visibility of standard screens becomes an issue in bright sunlight. Touchscreen users easily interact with the units in the field without removing gloves. High-temperature battery settings: Lithium ion batteries are sensitive to high temperature conditions for charging. A computer designed for the mobile environment should be designed with a high-temperature charging function that limits the charge to 85% or less of capacity. External antenna connections go through the typical metal cabins of vehicles which would block wireless reception, and take advantage of much more capable external communication and navigation equipment.Several specialized manufacturers such as First Mobile Technologies, National Products Inc (Ram Mounts), Gamber Johnson and LedCo build mounts for vehicle mounting of computer equipment for a wide range of vehicles. The mounts are built to withstand the harsh conditions and maintain ergonomics.Specialized installation companies design the mount design, assembling the parts, and installing them in a safe and consistent manner away fromairbags, vehicle HVAC controls, and driver controls. Frequently installations will include aWWANmodem, power conditioning equipment, transceiver antennae mounted external to the vehicle, and WWAN/WLAN/GPS/etc.Security issues involved in mobile computing[edit]Main article:Mobile securityMobile securityormobile phone securityhas become increasingly important in mobile computing. It is of particular concern as it relates to thesecurityof personal information now stored on thesmartphone.More and more users and businesses use smartphones as communication tools but also as a means of planning and organizing their work and private life. Within companies, these technologies are causing profound changes in the organization ofinformation systemsand therefore they have become the source of new risks. Indeed, smartphones collect and compile an increasing amount of sensitive information to which access must be controlled to protect theprivacyof the user and theintellectual propertyof the company.All smartphones, as computers, are preferred targets of attacks. These attacks exploit weaknesses related to smartphones that can come from means of communication likeSMS,MMS,wifi networks, andGSM. There are also attacks that exploit software vulnerabilities from both the web browser and operating system. Finally, there are forms ofmalicious softwarethat rely on the weak knowledge of average users.Different security counter-measures are being developed and applied to smartphones, from security in different layers of software to the dissemination of information to end users. There are good practices to be observed at all levels, from design to use, through the development ofoperating systems, software layers, and downloadable apps.Portable computing devices[edit]Main articles:Mobile deviceandPortable computerThis sectionmay requirecleanupto meet Wikipedia'squality standards.Nocleanup reasonhas been specified. Please helpimprove this sectionif you can.(February 2009)
Several categories of portable computing devices can run on batteries but are not usually classified as laptops: portable computers, keyboardless tablet PCs, Internet tablets, PDAs, ultra mobile PCs (UMPCs) and smartphones. Aportable computeris a general-purpose computer that can be easily moved from place to place, but cannot be used while in transit, usually because it requires some "setting-up" and an AC power source. The most famous example is theOsborne 1. Portable computers are also called a "transportable" or a "luggable" PC. Atablet computerthat lacks a keyboard (also known as a non-convertible tablet) is shaped like a slate or a paper notebook. Instead a physical keyboard it has atouchscreenwith some combination ofvirtual keyboard, stylus and/orhandwriting recognitionsoftware. Tablets may not be best suited for applications requiring a physical keyboard for typing, but are otherwise capable of carrying out most of the tasks of an ordinary laptop. Apersonal digital assistant(PDA) is a small, usually pocket-sized, computer with limited functionality. It is intended to supplement and to synchronize with a desktop computer, giving access to contacts, address book, notes, e-mail and other features.
APalm TXPDA A PDA with a web browser is anInternet tablet, anInternet appliancein tablet form. It does not have as much computing power as a full tablet computer and its applications suite is limited, and it can not replace a general purpose computer. Internet tablets typically feature an MP3 and video player, a web browser, a chat application and a picture viewer. Anultra mobile PCis a full-featured, PDA-sized computer running a general-purpose operating system. Asmartphonehas a wide range of features and installable applications. Acarputeris installed in an automobile. It operates as a wireless computer, sound system, GPS, and DVD player. It also contains word processing software and is bluetooth compatible.[5] AFly Fusion Pentop Computeris a computing device the size and shape of a pen. It functions as a writing utensil, MP3 player, language translator, digital storage device, and calculator.[6]Boundaries that separate these categories are blurry at times. For example, theOQOUMPC is also a PDA-sized tablet PC; theApple eMatehad the clamshell form factor of a laptop, but ran PDA software. TheHP Omnibookline of laptops included some devices small more enough to be called ultra mobile PCs. The hardware of theNokia 770internet tablet is essentially the same as that of a PDA such as theZaurus6000; the only reason it's not called a PDA is that it does not havePIMsoftware. On the other hand, both the 770 and the Zaurus can run some desktop Linux software, usually with modifications.Mobile data communication[edit]Wirelessdata connections used in mobile computing take three general forms so.[7]Cellulardata service uses technologies such asGSM,CDMAorGPRS,3Gnetworks such asW-CDMA,EDGEorCDMA2000.[8][9]and more recently4Gnetworks such asLTE,LTE-Advanced.[10]These networks are usually available within range of commercialcell towers.Wi-Ficonnections offer higher performance,[11]may be either on a private business network or accessed through publichotspots, and have a typical range of 100 feet indoors and up to 1000 feet outdoors.[12]Satellite Internet accesscovers areas where cellular and Wi-Fi are not available[13]and may be set up anywhere the user has aline of sightto the satellite's location,[14]which for satellites ingeostationaryorbit means having an unobstructed view of the southern sky.[7]Some enterprise deployments combine networks from multiple cellular networks or use a mix of cellular, Wi-Fi and satellite.[15]When using a mix of networks, amobile virtual private network(mobile VPN) not only handles thesecurityconcerns, but also performs the multiple networkloginsautomatically and keeps theapplicationconnections alive to preventcrashesor data loss during network transitions or coverage loss
NEWS
Samsung announces Galaxy ACE Style smartphone
4 mins ago,comments (0)This new budget smartphone comes with a 4.0-inch display, dual-core processor and Android KitKat.
Verizon buys Cincinatti Bell for $210 million
3 hours ago,comments (3)Verizon has acquired Cincinnati Bell for $210 million. The transition will be made final in the 2nd half of 2014.
New Sharp Aquos flagship offers unparalleled screen-to-body ratio
15 hours ago,comments (74)The Sharp Aquos Xx 302Sh provides a 5.2" 1080p display and still measures smaller than most flagships.
Qualcomm unveils Snapdragon 810 and 808 64-bit chipsets
16 hours ago,comments (65)The Snapdragon 810 is an octa-core, while the 808 is a hexa-core. Both come with new Adreno GPUs.
HTC Q1 2014 results: net loss, missed revenue forecast
18 hours ago,comments (31)HTC published unaudited financial results for the first quarter of 2014 and it's another one in the red.
Major Asha update hits now with Mix Radio and new camera
18 hours ago,comments (18)The second major update to the Asha line is coming over the air now with a bunch of new features.
LAVA introduces midrange Iris Pro 20 smartphone
19 hours ago,comments (15)The latest 4.7" smartphone from Indian manufacturer LAVA will be impressively compact and light.
Octa-core Galaxy S5 tops S801-packing model in AnTuTu
19 hours ago,comments (37)The Exynos chipsets is showing better CPU performance and has a slight lead in 3D too.Oppo Find 7a is now on pre-order for 39921 hours ago,comments (15)Google Play Edition treatment available for HTC One (M8)21 hours ago,comments (14)Mysterious Moto X+1 branding leaks out on Twitter1 day ago,comments (21)Sony Mobile rises to number 2 phone maker in India2 days ago,comments (76)Samsung Galaxy Note 4 rumors alert2 days ago,comments (129)Nokia Lumia 630 will be priced at 150 in Europe2 days ago,comments (29)
REVIEWS
Samsung Galaxy S5 reviewFab Five
Every time the Samsung Galaxy S counter flips a digit, the world is getting ready to be amazed. The lineup that stood up to the iPhone and has been pulling Android to the very top of the food chain, is under new leadership effective last month...ElementalSony Xperia Z2 Tablet review
Thinnest, lightest, highest water resistance there are plenty of superlatives you can throw at the Sony Xperia Z2 Tablet prettiest is another, though that one's more subjective. What is certain is that Sony has crafted one of the best tablets of 2014...One and onlyHTC One (M8) review
To say there are great expectations of the freshly announced HTC One (M8) would be a massive understatement. This is, after all, one of the flagships to shape the entire season....Updated with display and loudspeaker tests.
Perfect frameNokia Lumia Icon review
The Nokia Lumia Icon for Verizon Wireless is the most capable smartphone to come out of the Finnish manufacturer to date. A successor to the Nokia Lumia 928, the carrier-exclusive Windows...March 2014GSMArena smartphone shopping guide
We're back with our latest smartphone shopper's guide, and our first for 2014! In this edition we'll see which new devices announced at the MWC made the cut as good buys, next to some...
Royal duelLG G Pro 2 vs Samsung Galaxy Note 3
March 2014The GSMArena tablet shopping guide
By the dozenSamsung Galaxy Note Pro 12.2 review
Double visionSamsung Galaxy Grand 2 review
See you 2morrowLG G Pro 2 review
MWC 2014Nokia X, X+ and XL hands-on
MWC 2014Various brands overview
MWC 2014Samsung Galaxy S5, Gear 2, 2 Neo, Fit hands-on
HTC Desire 816 hands-onMWC 2014
Lenovo S860, S850 and S660, Yoga 10 HD+ hands-onMWC 2014
Sony Xperia Z2, Tablet Z2, M2 hands-onMWC 2014
LG G Pro 2, G2 mini and L III seriesMWC 2014
Huawei MediaPad and Ascend hands-onMWC 2014
Alcatel One Touch Idol 2, Mini 2, Mini 2 S, PopFitMWC 2014
BLOG Samsung Galaxy S5 battery life test2 hours ago LatentSense security learns how you touch your phone3 hours ago Alleged specs of Samsung SM-T800 slate with 10.5 inch AMOLED display leak out4 hours ago Sony Xperia Z2 tops the DxOMark mobile photography rankings6 hours ago
LATEST PHONESSamsung Galaxy S5 G9009DNokia Lumia 930
Huawei Ascend Y600 Samsung ATIV SE Nokia Lumia 635 Nokia Lumia 630 Dual SIM Nokia Lumia 630 Samsung Galaxy Tab 4 8.0 LTELATEST ADDITIONS Nokia X 360 view Sony Xperia E1 gallery Sony Xperia E1 360 view Nokia X gallery Sony Xperia Z2 Tablet gallery HTC One (M8) 360 view HTC One (M8) gallery LG G Pro 2 360 viewIN STORES NOWSony Xperia T2 Ultra dualLG G2 mini LTE
HTC One (M8) Sony Xperia Z2 Tablet LTE Sony Xperia Z2 Tablet Wi-Fi HTC Desire 816 Samsung Galaxy Tab Pro 8.4 3G/LTE Samsung Galaxy Tab Pro 10.1
htc one x$500.00Right now on eBay
CURRENT RANKINGSDeviceDaily hits
1.Samsung Galaxy S5112,398
2.Nokia X83,659
3.Samsung Galaxy Grand 250,790
4.Motorola Moto G47,415
5.Samsung Galaxy Note 346,915
6.Samsung I9500 Galaxy S446,264
7.HTC One (M8)44,947
8.Nokia Lumia 93037,683
By daily interest
DeviceRateVotes
1.Sony Xperia Z8.5735,722
2.Sony Xperia Z1 Compact8.5551,080
3.Sony Xperia Z18.5302,499
4.LG Nexus 58.3781,855
5.HTC One (M8)8.346629
6.Sony Xperia Z2 Tablet LTE8.288229
7.Sony Xperia Z Ultra8.2351,559
8.HTC One8.2273,648
By user ratings
Voice over IPFrom Wikipedia, the free encyclopedia(Redirected fromVoice over Internet Protocol)It has been suggested thatWeb-based VoIPbemergedinto this article. (Discuss)Proposed since February 2013.
Voice over Internet Protocol(VoIP) is a methodology and group of technologies for the delivery ofvoice communicationsandmultimediasessions overInternet Protocol(IP) networks, such as the Internet. Other terms commonly associated with VoIP areIP telephony,Internet telephony,voice over broadband(VoBB),broadband telephony,IP communications, andbroadband phone service.The termInternet telephonyspecifically refers to the provisioning of communications services (voice,fax, SMS, voice-messaging) over the publicInternet, rather than via thepublic switched telephone network(PSTN). The steps and principles involved in originating VoIP telephone calls are similar to traditional digitaltelephonyand involve signaling, channel setup, digitization of the analog voice signals, and encoding. Instead of being transmitted over a circuit-switched network, however, the digital information is packetized, and transmission occurs asInternet Protocol(IP) packets over apacket-switched network. Such transmission entails careful considerations about resource management different fromtime-division multiplexing(TDM) networks.Early providers of voice over IP services offered business models and technical solutions that mirrored the architecture of the legacy telephone network. Second-generation providers, such asSkype, have built closed networks for private user bases, offering the benefit of free calls and convenience while potentially charging for access to other communication networks, such as the PSTN. This has limited the freedom of users to mix-and-match third-party hardware and software. Third-generation providers, such asGoogle Talk, have adopted[1]the concept offederated VoIPwhich is a departure from the architecture of the legacy networks. These solutions typically allow dynamic interconnection between users on any two domains on the Internet when a user wishes to place a call.VoIP systems employ session control and signaling protocols to control the signaling, set-up, and tear-down of calls. They transport audio streams over IP networks using special media delivery protocols that encode voice, audio, video withaudio codecs, and video codecs asDigital audiobystreaming media. Various codecs exist that optimize the media stream based on application requirements and network bandwidth; some implementations rely onnarrowbandandcompressed speech, while others supporthigh fidelitystereo codecs. Some popular codecs include-lawanda-lawversions ofG.711,G.722, which is a high-fidelity codec marketed as HD Voice byPolycom, a popular open source voice codec known asiLBC, a codec that only uses 8kbit/s each way calledG.729, and many others.VoIP is available on manysmartphones, personal computers, and on Internet access devices. Calls and SMS text messages may be sent over3GorWi-Fi.[2]Contents[hide] 1Pronunciation 2Protocols 3Adoption 3.1Consumer market 3.2PSTN and mobile network providers 3.3Corporate use 4Quality of service 4.1Layer 2 5PSTN integration 5.1Number portability 5.2Emergency calls 6Fax support 7Power requirements 8Redundancy 9Security 10Caller ID 11Compatibility with traditional analog telephone sets 12Support for other telephony devices 13User and administrative interfaces 14Operational cost 15Regulatory and legal issues 15.1European Union 15.2India 15.3Middle East 15.4South Korea 15.5United States 16Historical milestones 17See also 18References 19External linksPronunciation[edit]The acronym "VoIP" has been pronounced variably since the inception of the term. Apart from spelling out the acronym letter by letter, /vioapi/ (vee-oh-eye-pee), there are three likely possible pronunciations: /voapi/ (vo-eye-pee) and /voip/ (vo-ipp), have been used, but generally, the single syllable /vjp/ (voyp, as invoice) may be the most common within the industry.[3]Protocols[edit]Voice over IP has been implemented in various ways using bothproprietary protocolsand protocols based onopen standards. Examples of the VoIP protocols are: H.323 Media Gateway Control Protocol (MGCP) Session Initiation Protocol(SIP) H.248(also known as Media Gateway Control (Megaco)) Real-time Transport Protocol(RTP) Real-time Transport Control Protocol(RTCP) Secure Real-time Transport Protocol(SRTP) Session Description Protocol(SDP) Inter-Asterisk eXchange(IAX) JingleXMPPVoIP extensions Skype protocol TeamspeakThe H.323 protocol was one of the first VoIP protocols that found widespread implementation for long-distance traffic, as well aslocal area networkservices. However, since the development of newer, less complex protocols such as MGCP and SIP, H.323 deployments are increasingly limited to carrying existing long-haul network traffic. In particular, the Session Initiation Protocol (SIP) has gained widespread VoIP market penetration.These protocols can be used by special-purpose software, such asJitsi, or integrated into a web page (web-based VoIP), likeGoogle Talk.Adoption[edit]Consumer market[edit]
Example of residential network including VoIPA major development that started in 2004 was the introduction of mass-market VoIP services that utilize existingbroadband Internet access, by which subscribers place and receive telephone calls in much the same manner as they would via thepublic switched telephone network(PSTN). Full-service VoIP phone companies provide inbound and outbound service withdirect inbound dialing. Many offer unlimited domestic calling for a flat monthly subscription fee. This sometimes includes international calls to certain countries. Phone calls between subscribers of the same provider are usually free when flat-fee service is not available. AVoIP phoneis necessary to connect to a VoIP service provider. This can be implemented in several ways: Dedicated VoIP phones connect directly to the IP network using technologies such as wiredEthernetor wirelessWi-Fi. They are typically designed in the style of traditional digital business telephones. Ananalog telephone adapteris a device that connects to the network and implements the electronics and firmware to operate a conventional analog telephone attached through a modular phone jack. Some residential Internet gateways andcablemodemshave this function built in. Asoftphoneis application software installed on a networked computer that is equipped with a microphone and speaker, or headset. The application typically presents a dial pad and display field to the user to operate the application by mouse clicks or keyboard input.PSTN and mobile network providers[edit]It is becoming increasingly common for telecommunications providers to use VoIP telephony over dedicated and public IP networks to connect switching centers and to interconnect with other telephony network providers; this is often referred to as "IPbackhaul."[4][5]SmartphonesandWi-Fi-enabled mobile phones may have SIP clients built into the firmware or available as an application download.Corporate use[edit]Because of the bandwidth efficiency and low costs that VoIP technology can provide, businesses are migrating from traditional copper-wire telephone systems to VoIP systems to reduce their monthly phone costs. In 2008, 80% of all newPrivate branch exchange(PBX) lines installed internationally were VoIP.[6]VoIP solutions aimed at businesses have evolved intounified communicationsservices that treat all communicationsphone calls, faxes, voice mail, e-mail, Web conferences, and moreas discrete units that can all be delivered via any means and to any handset, including cellphones. Two kinds of competitors are competing in this space: one set is focused on VoIP for medium to large enterprises, while another is targeting the small-to-medium business (SMB) market.[7]VoIP allows both voice and data communications to be run over a single network, which can significantly reduce infrastructure costs.[8]The prices of extensions on VoIP are lower than for PBX and key systems. VoIP switches may run on commodity hardware, such aspersonal computers. Rather than closed architectures, these devices rely on standard interfaces.[8]VoIP devices have simple, intuitive user interfaces, so users can often make simple system configuration changes. Dual-mode phones enable users to continue their conversations as they move between an outside cellular service and an internalWi-Finetwork, so that it is no longer necessary to carry both a desktop phone and a cellphone. Maintenance becomes simpler as there are fewer devices to oversee.[8]Skype, which originally marketed itself as a service among friends, has begun to cater to businesses, providing free-of-charge connections between any users on the Skype network and connecting to and from ordinaryPSTNtelephones for a charge.[9]In the United States the Social Security Administration (SSA) is converting its field offices of 63,000 workers from traditional phone installations to a VoIP infrastructure carried over its existing data network.[10][11]Quality of service[edit]Communication on the IP network is perceived as less reliable in contrast to the circuit-switched public telephone network because it does not provide a network-based mechanism to ensure that data packets are not lost, and are delivered in sequential order.[citation needed]It is a best-effort network without fundamentalQuality of Service(QoS) guarantees. Therefore, VoIP implementations may face problems withlatency, packet loss, andjitter.[12][13]By default, network routers handle traffic on a first-come, first-served basis. Network routers on high volume traffic links may introduce latency that exceeds permissible thresholds for VoIP. Fixed delays cannot be controlled, as they are caused by the physical distance the packets travel; however, latency can be minimized by marking voice packets as being delay-sensitive with methods such asDiffServ.[12]VoIP endpoints usually have to wait for completion of transmission of previous packets, before new data may be sent. Although it is possible to preempt (abort) a less important packet in mid-transmission, this is not commonly done, especially on high-speed links where transmission times are short even for maximum-sized packets.[14]An alternative to preemption on slower links, such as dialup anddigital subscriber line(DSL), is to reduce the maximum transmission time by reducing themaximum transmission unit. But every packet must contain protocol headers, so this increases relative header overhead on every link traversed, not just the bottleneck (usually Internet access) link.[14]DSL modems provide Ethernet (or Ethernet overUSB) connections to local equipment, but inside they are actuallyAsynchronous Transfer Mode(ATM) modems. They useATM Adaptation Layer 5(AAL5) to segment each Ethernet packet in
