Communications And Networks

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Communications and Networks

CommunicationsComputer communications describe aprocess in which two or more computersor devices transfer data, instructions andinformation. Even the smallest computers and devicescan communicate directly with oneanother, often via the Internet.

Communications A sending device initiates an instruction totransmit data, instructions, or information.A communications device connects the sendingdevice to a communications channel.A communications channel, or transmissionmedia, is where the data, instructions, orinformation travel.A communications device connects thecommunications channel to a receiving device.A receiving device accepts the transmission ofdata, instructions, or information.

Communications

Uses of Computer Communications BlogsChat RoomsE-MailFaxFTP (file transfer protocol)Instant MessagingInternetNewsgroupsRSSVideo ConferencingVoIPWebWeb 2.0Web FoldersWikis

Wireless Messaging Services Users can send and receive wirelessmessages to and from smart phones, cellphones, handheld game consoles, andother mobile devices through textmessaging, picture/video messaging, andwireless instant messaging.

Text Messaging A mobile device with text messaging,also called SMS (short message service),capability allows users to send andreceive short text messages on a phoneor other mobile device or computer. Mobile to MobileMobile to E-MailWeb to MobileMobile to Provider

Picture/Video MessagingWith picture messaging, users can sendpictures and sound files as well as short textmessages to a phone or other mobile device, or acomputer. With video messaging, users can send shortvideo clips, usually about 30 seconds in length, inaddition to all picture messaging services. Mobile devices with picture/video messaging, alsocalled MMS (multimedia message service), typicallyhave a digital camera built in. Mobile to Mobile Mobile to E-Mail

Wireless Instant Messaging Wireless instant messaging (IM) is a realtime Internet communications servicethat allows wireless mobile devices toexchange messages with one or moremobile devices or online users. Mobile to Mobile Mobile to Personal Computer Web to Mobile

Wireless Internet Access PointsA wireless Internet access point is used athome, work, school, or in public locations, forpeople to connect wirelessly to the Internet usingmobile computers and devices. A hot spot is a wireless network that providesInternet connections o mobile computers anddevices. Wi-Fi hot spots provide wireless networkconnections to users in public locations, such asairports. WiMAX hot spots are wider than Wi-Fi, oftencovering entire cities. Bluetooth hot spots provide location-based services,such as coupons or menus.

CybercafésA cybercafé, or Internet café, is acoffeehouse, restaurant, or other locationthat provides personal computers withInternet access to its customers. Some are free, some are by the hour. Some are also wireless hot spots.

Global Positioning SystemA global positioning system (GPS) is anavigation system that consists of one ormore earth-based receivers that accept andanalyze signals sent by satellites in order todetermine the receiver’s geographic location. A GPS receiver is a handheld, mountable, orembedded device that contains an antenna, aradio receiver, and a processor. Many smart phones have GPS capability. The most used application of GPS is to assistpeople with determining their location andgiving directions to a destination.

GroupwareGroupware is a software that helpsgroups of people work together onprojects and share information. It is a common component of workgroupcomputing, which includes networkhardware and software that enables groupmembers to communicate.

Voice MailVoice Mail functions much like ananswering machine and allows someoneto leave a voice message for one or morepeople. A voice mailbox is a storage location on ahard disk in the voice mail system. With visual voice mail users can viewmessage details such as the length of themessage and message contents.

CollaborationMany programs provide a means tocollaborate, or work online, with otherusers connected to a server. Collaborative software includes tools thatenable users to share documents via onlinemeetings and communicate with otherconnected users. When an online meeting takes place on the Web, itis called a Web conference. A document management system, provides forstorage and management of a company’sdocuments.

Web ServicesWeb services describe standardized softwarethat enables programmers to createapplications that communicate with otherremote computers of the Internet. Used by businesses to provide a means fordepartments to communicate with eachother, suppliers, and venders. A mashup is a Web application that combinesservices from two or more sources, creatinga new application.

NetworksA network is a collection of computersand devices connected together viacommunications devices and transmissionmedia. A network can be internal to anorganization or span the world byconnecting to the Internet.

Networks

Networks Facilitating communications People can communicate efficiently via e-mail,IM, chat rooms, blogs, wikis, social networks,and so on. Sharing hardware Each computer on the network has access tonetwork hardware. Sharing data and information Any authorized computer can access datastored on other computers on the network.

Networks Sharing software Users on a network have access to software onthat network. A network license is a legal agreement that allowsmultiple users to access the software on a serversimultaneously. A site license is a legal agreement that permitsusers to install the software on multiplecomputers. Transferring funds Electronic funds transfer allows users connected toa network to transfer money from one bankaccount to another.

LANs, MANs, and WANsA local area network (LAN) is a networkthat connects computers and devices in alimited geographical area, such as a home. Each computer or device on the network,called a node, often shares resources such asprinter, hard disks, and programs. A wireless LAN (WLAN) is a LAN thatuses no physical wires. Very often, a WLAN communicates with aLAN for access to its resources.

LANs, MANs, and WANs

LANs, MANs, and WANsA metropolitan area network (MAN) is a highspeed network that connects local areanetworks in a metropolitan area such as acity or town and handles the bulk ofcommunications activity across that region. A wide area network (WAN) is anetwork that covers a large geographic areausing a communications channel thatcombines many types of media. The Internet is the world’s largest WAN.

Network Architectures Network architecture is the design ofcomputers, devices, and media in anetwork and is categorized as eitherclient/server or peer-to-peer.

Client/ServerOn a client/server network, one or morecomputers act as a server, and the othercomputers on the network request servicesfrom the server. A server, sometimes called a host computer,controls access to the hardware, software,and other resources on the network andprovides centralized storage for data. The clients are other computers andmobile devices on the network that rely onthe server for its resources.

Peer-to-Peer A peer-to-peer network is a simple,inexpensive network that connectscomputers, called peers, that have equalresponsibilities and capabilities, sharinghardware and data over the network.

Internet Peer-to-PeerP2P describes an Internet network onwhich users access each other’s harddisks and exchange files directly over theInternet, usually called a file sharingnetwork. BitTorrent, Gnutella, Kazaa, and LimeWire

Network Topologies A network topology refers to thelayout of the computers and devices in acommunications network.

Star NetworkOn a star network, all of the computersand devices connect to a central device (ahub or a switch), thus forming a star. Easy to set up and maintain. If one node fails, only that node isaffected.

Bus NetworkA bus network consists of a single centralcable, to which all computers and devicesconnect. The bus is the physical cable that connectsthe computers and other devices. Easy to install. Failure of one devices does not affect the restof the network

Ring NetworkOn a ring network, a cable forms aclosed loop with all computers anddeviecs arranged along the ring. When one node sends data, ittravels to each computer until itreaches its destination.

IntranetsAn intranet is an internal network thatuses Internet technologies. It is a small version of the Internet thatexists within an organization.

Network CommunicationsStandardsA network standard defines guidelines thatspecify the way computers access themedium to which they are attached, types ofmedium used, the speeds used on differenttypes of networks, and the types of physicalcable and/or wireless technology used. A standard that outlines characteristics ofhow two network devices communicate iscalled a protocol, which defines data format,coding schemes, error handling, andsequencing techniques.

EthernetEthernet is a network standard thatspecifies no central computer or deviceon the network should control when datacan be transmitted. Based on a bus topology, but can be wiredin a star pattern.

Token RingThe token ring standard specifies thatcomputers and devices on the networkshare or pass a special signal, called a token,in a unidirectional manner and in a presentorder. A token is a special series of bits thatfunction like a ticket. Only one token existsper network and only the holder haspermission to transmit data. Based on ring topology, but can be used instar.

TCP/IPTransmission Control Protocol/InternetProtocol (TCP/IP) is a network standard,specifically a protocol that defines howmessages are routed from one end of anetwork to the other, ensuring data arrivescorrectly. The messages are divided into small pieces,called packets, providing addresses for eachpacket, checking for errors, sequencing andregulating the flow of messages along thenetwork.

Wi-FiComputers with wireless capability cancommunicate via radio waves using Wi-Fi(wireless fidelity), which identifies anynetwork based on the 802.11 standards. 802.11 is a series of network standardsthat specifies how two wireless devicescommunicate over the air.

BluetoothBluetooth is a network standard,specifically a protocol, that defines howtwo Bluetooth devices use short-rangeradio waves to transmit data. Rates up to 3 Mbps. Range from 10 meters and up to 100meters with additional equipment. Examples: desktops, mobile computers,smart phones, keyboards, mice, printers.

UWBUWB, which stands for ultra-wideband, isa network standard that specifies how twoUWB devices use short-range radio wavesto communicate at high speeds. At distances of 10 meters, transfer rate is110 Mbps. Examples: transferring video from a digitalvideo camera, printing from a digital camera,and downloading media to a portable mediaplayer.

IrDAThe IrDA standard is used by devices totransmit data wirelessly to each other viainfrared (IR) light waves. Rates of 115 Kbps to 4 Mbps. Requires a line-of-sight transmission,meaning the sending devices and thereceiving device must be in line with eachother so that nothing obstructs the pathof the light wave.

RFIDRFID (radio frequency identification) is astandard, specifically a protocol, thatdefines how a network uses radio signalsto communicate with a tag placed in orattached to an object, animal, or person. The RFID tag (transponder) is an antennaand a memory chip with information tobe transmitted via radio waves. Can be passive or active. Range from 5 inches to 15 feet.

WiMAXWiMAX (Worldwide Interoperability forMicrowave Access), or 802.16, is anetwork standard that specifies howwireless devices communicate over theair in a wide area. Properly equipped devices cancommunicate with the WiMAX tower, upto 30 miles away. Similar to Wi-Fi, it connects users tointernet hot spots.

WAP The Wireless Application Protocol(WAP) is a standard, specifically aprotocol, that specifies how some mobiledevices such as smart phones can displaythe content of Internet services such asthe Web, e-mail, and chat rooms.

Communications Software Communications software consists ofprograms that Help users establish a connection to anothercomputer or network Manage the transmission of data Provide an interface for users tocommunicate with one another

Communications Over theTelephone NetowrkThe public switched telephone netowrk(PSTN) is the worldwide telephonesystem that handles voice-orientedtelephone calls. This mostly digital network is an integralpart of computer communications.

Dial-Up Lines A dial-up line is a temporary connectionthat uses one or more analog telephonelines for communications.

Dedicated LinesA dedicated line is a type of always-onconnection that is established betweentwo communication devices. ISDN, DSL, FTTP, T-carrier, and ATM

ISDN Lines ISDN (Integrated Services Digital Network) isa set of standards for digital transmissionof data over standard copper telephonelines.

DSLDSL (Digital Subscriber Line) transmitsat fast speeds on existing standard coppertelephone wiring. ADSL (Asymmetric digital subscriber line) is atype of DSL that supports faster transferrates when receiving than sending.

FTTPFTTP, or Fiber to the Premises, usesfiber-optic cable to provide extremelyhigh-speed Internet access to a user’sphysical permanent location. As the cost of installing fiber decreases, itis becoming more popular.

T-Carrier LinesA T-carrier line is any of several types oflong-distance digital telephone lines thatcarry multiple signals over a singlecommunications line. The most popular is the T1 line. A T3 line is equal to the speed of 28 T1lines and are quite expensive.

ATM ATM (Asynchronous Transfer Mode) is aservice that carries voice, data, video, andmultimedia at very high speeds.

Communications Devices A communications device is any typeof hardware capable of transmitting databetween a sending and receiving device.

Dial-Up ModemsA dial-up modem is a communicationsdevice that can convert digital signals toanalog signals, and back, so that data cantravel along an analog phone line. Usually the form of an adapter card thatyou insert into the motherboard.

Digital Modems: ISDN, DSL, andCableA digital modem is a communications devicethat sends and receives data to and from adigital line. An ISDN modem sends digital data from acomputer to an ISDN line and back. A DSL modem sends digital data from acomputer to a DSL line and back. A cable modem, or broadband modem, is adigital modem that sends and receives digitaldata over the cable television network.

Wireless ModemsA wireless modem uses the cell phonenetwork to connect to the Internetwirelessly from a notebook computer,smart phone, or mobile device. Some smart phones can function as awireless modem when connected to acomputer.

Network CardsA network card, sometimes called anetwork interface card (NIC), is acommunications device that enables acomputer or device that does not have builtin networking capability to access a network. Wireless network cards often have an antennaand provide wireless data transmission.

Wireless Access Points A wireless access point is a centralcommunications device that allowscomputers and devices to transfer datawirelessly among themselves or to awired network.

RouterA router is a communications device thatconnects multiple computers or otherrouters together. Can be used on any size network. To prevent unauthorized users fromaccessing files, many routers areprotected by a built-in hardware firewall. Some support wireless communication,eliminating the need for a separatewireless access point.

Router

Hubs and SwitchesA hub or switch is a device that providesa central point for cables in a network. They receive data from many directionand forward to the correct destination. Hubs are generally used in largernetworks, while switches are used forsmaller ones.

Home Networks Many home users are connecting multiplecomputers and devices together in ahome network. Connect to the InternetShare a single Internet connectionAccess files on other computersShare peripheralsPlay gamesConnect game consoles to the InternetVoIP

Wired Home Networks Ethernet This may involve running cables through walls. Powerline Cable Network A network that uses the same lines that bringelectricity into the house. Phoneline Network An easy-to-install and inexpensive networkthat uses existing telephone lines in thehouse.

Wireless Home NetworksMost home networks use a Wi-Finetwork to send signals through the air atdistances of up to 1,500 feet. Good for mobility. Don’t need to run cables through walls.

Communications ChannelThe transmission media on which datatravels in a communications system. The amount of data that can travel over acommunications channel is calledbandwidth. (higher better) Latency is the time it takes a signal totravel from one location to another on anetwork. (lower better) Transmission media consist of materialsor substances capable of carrying one ormore signals.

Communications Channel Broadband media transmit multiplesignals simultaneously. DSL and Cable are examples.Physical transmission media use wire, cable,or other tangible materials. Wireless transmission media send signalsthrough the air using radio, microwave,and infrared signals.

Physical Transmission MediaTwisted-pair cable consists of one ormore twisted-pair wires (to reduce noise,or electrical disturbance) bundled together. Coaxial cable, often referred to as coax,consists of a single copper wire surroundedby at least three layers: insulation, braidedmetal, plastic coating. Fiber-optic cable consists of dozens orhundreds of thin strands of glass or plastic(optical fiber) that use light to transmitsignals.

Physical Transmission Media

Wireless Transmission MediaInfrared uses IR light waves. Broadcast radio is a wireless transmissionmedium that distributes radio signalsthrough the air over long distances, such asbetween cities, and short distances such aswithin an office. Includes Bluetooth, UWB, Wi-Fi, and WiMAX. Cellular radio is a form of broadcast radiothat is used widely for mobilecommunications, specifically wirelessmodems and cell phones.

Wireless Transmission Media Microwaves are radio waves thatprovide a high-speed signal transmission. Fixed wireless involves sending signals from onemicrowave station to another. Communications Satellite is a spacestation that receives microwave signalsfrom an earth-based station, amplifies thesignals, and broadcasts the signals over awide area to earth-based stations.

networks in a metropolitan area such as a city or town and handles the bulk of communications activity across that region. A wide area network (WAN) is a network that covers a large geographic area using a communications channel that combines many types o

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