Presentation on theme: "Telecommunications and Networks"— Presentation transcript:
1Telecommunications and Networks Chapter 6Telecommunications and Networks
2Communications Communications The message (data and information) is communicated via the signalThe transmission medium “carries” the signalTransmission mediumSenderReceiverSignal
3Communications ‘Discussion’ The transmission of data from one computer to another, or from onedevice to another. A communications device, therefore, is anymachine that assists data transmission. For example, modems,cables, and ports are all communications devices. Communicationssoftware refers to programs that make it possible to transmit data.
4Telecommunications Telecommunications Telecommunication medium The electronic transmission of signals for communications, including such means as:TelephoneRadioTelevisionTelecommunication mediumAnything that carries an electronic signal and interfaces between a sending device and a receiving device
5Communications and Telecommunications In human speech, the sender transmits a signal through the transmission medium of the airIn telecommunications, the sender transmits a signal through the transmission medium of a cableSchematic
7Data Communications Data communications A specialized subset of telecommunications that refers to the electronic collection, processing, and distribution of data -- typically between computer system hardware devices
8Elements of a Telecommunications System Telecommunication devicesRelay signals between computer systems and transmission mediaSchematic
10Computer Network Computer network… The communications media, devices, and software needed to connect two or more computer systems and/or devicesUsed to share hardware, programs, and databases across the organizationFosters teamwork, innovative ideas, and new business strategies
11Types of Telecommunications Media (1) Twisted pair wire cableInsulated pairs of wires historically used in telephone service and to connect computer devicesCoaxial cableConsists of an inner conductor wire surrounded by insulation, called the dielectricThe dielectric is surrounded by a conductive shield, which is surrounded by a non-conductive jacket. Coaxial cable has better data transmission rate than twisted pair
12Twisted-pair ‘Discussion’ A type of cable that consists of two independently insulated wirestwisted around one another. One wire carries the signal while theother wire is grounded and absorbs signal interference. Twisted-paircable is used by older telephone networks and is the least expensivetype of local-area network (LAN) cable. Other types of cables usedfor LANs include coaxial cables and fiber optic cables.
13Coaxial Cable ‘Discussion’ A type of wire that consists of a centre wire surrounded byinsulation and then a grounded shield of braided wire. The shieldminimizes electrical and radio frequency interference.Coaxial cabling is the primary type of cabling used by the cabletelevision industry and is also widely used for computer networks.Although more expensive than standard telephone wire, it is muchless susceptible to interference and can carry much more data.Because the cable television industry has already connected millionsof homes with coaxial cable, many analysts believe that they arethe best positioned to capitalize on the much-heralded informationhighway.
14Types of Telecommunications Media (2) Fiber-optic CableMany extremely thin strands of glass or plastic bound together in a sheathing which transmits signals with light beamsCan be used for voice, data, and video
15Fiber Optic ‘Discussion’ (1) A technology that uses glass (or plastic) threads (fibers) to transmitdata. A fiber optic cable consists of a bundle of glass threads, eachof which is capable of transmitting messages modulated onto lightwaves.Fiber optics has several advantages over traditional metalcommunications lines:Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry more dataFiber optic cables are less susceptible than metal cables to interferenceFiber optic cables are much thinner and lighter than metal wiresData can be transmitted digitally (the natural form for computer data) rather than analogically.
16Fiber Optic ‘Discussion’ (2) The main disadvantage of fiber optics is that the cables areexpensive to install. In addition, they are more fragile than wire andare difficult to split.Fiber optics is a particularly popular technology for local-areanetworks. In addition, telephone companies are steadily replacingtraditional telephone lines with fiber optic cables. In the future,almost all communications will employ fiber optics.
17Types of Telecommunications Media (3) Microwave CommunicationsLine-of-sight devices which must be placed in relatively high locationsMicrowave usageInformation is converted to a microwave signal, sent through the air to a receiver, and recoveredPretty picture
19Types of Telecommunications Media (4) Satellite transmissionCommunications satellites are relay stations that receive signals from one earth station and rebroadcast them to anotherThey use microwave signalsPretty picture
23Cellular ‘Discussion’ Refers to communications systems, especially the Advance MobilePhone Service (AMPS), that divide a geographic region into sections,called cells. The purpose of this division is to make the most use outof a limited number of transmission frequencies. Each connection, orconversation, requires its own dedicated frequency, and the totalnumber of available frequencies is about 1,000. To support morethan 1,000 simultaneous conversations, cellular systems allocate aset number of frequencies for each cell. Two cells can use the samefrequency for different conversations so long as the cells are notadjacent to each other.For digital communications, several competing cellular systems exist,including GSM and CDMA.
24Types of Telecommunications Media (6) Infrared transmissionInvolves sending signals through the air via light wavesRequires line-of-sight and short distances (a few hundred yards)Used to connect various computing devices such as handheld computersSorry, no pretty picture!
25Terminology Analog Signal Digital Signal Modems A continuous, curving signalDigital SignalA signal represented by bitsModemsDevices that translate data from digital to analog and analog to digital
26Analog ‘Discussion’ (1) Almost everything in the world can be described or represented inone of two forms: analog or digital. The principal feature of analogrepresentations is that they are continuous. In contrast, digitalrepresentations consist of values measured at discrete intervals.Digital watches are called digital because they go from one value tothe next without displaying all intermediate values. Consequently,they can display only a finite number of times of the day. Incontrast, watches with hands are analog, because the hands movecontinuously around the clock face. As the minute hand goes
27Analog ‘Discussion’ (1) around, it not only touches the numbers 1 through 12, but also theinfinite number of points in between.Early attempts at building computers used analog techniques, butaccuracy and reliability were not good enough. Today, almost allcomputers are digital.
28Digital ‘Discussion’ (1) Describes any system based on discontinuous data or events.Computers are digital machines because at their most basic levelthey can distinguish between just two values, 0 and 1, or off andon. There is no simple way to represent all the values in between,such as All data that a computer processes must be encodeddigitally, as a series of zeroes and ones.The opposite of digital is analog. A typical analog device is a clock inwhich the hands move continuously around the face. Such a clock iscapable of indicating every possible time of day. In contrast, a
29Digital ‘Discussion’ (2) digital clock is capable of representing only a finite number of times(every tenth of a second, for example).In general, humans experience the world analogically. Vision, forexample, is an analog experience because we perceive infinitelysmooth gradations of shapes and colors. Most analog events,however, can be simulated digitally. Photographs in newspapers, forinstance, consist of an array of dots that are either black or white.From afar, the viewer does not see the dots (the digital form), butonly lines and shading, which appear to be continuous. Although
30Digital ‘Discussion’ (3) digital representations are approximations of analog events, they areuseful because they are relatively easy to store and manipulateelectronically. The trick is in converting from analog to digital, andback again.This is the principle behind compact discs (CDs). The music itselfexists in an analog form, as waves in the air, but these sounds arethen translated into a digital form that is encoded onto the disk.When you play a compact disc, the CD player reads the digital data,translates it back into its original analog form, and sends it to the
31Digital ‘Discussion’ (4) amplifier and eventually the speakers.Internally, computers are digital because they consist of discreteunits called bits that are either on or off. But by combining manybits in complex ways, computers simulate analog events. In onesense, this is what computer science is all about.
32How a Modem WorksModemModulates a digital signal into an analog signal for transmission via analog medium, then demodulates the signal into digital for receivingPretty picture
34Modem ‘Discussion’ (1)Acronym for modulator-demodulator. A modem is a device orprogram that enables a computer to transmit data over telephonelines. Computer information is stored digitally, whereas informationtransmitted over telephone lines is transmitted in the form of analogwaves. A modem converts between these two forms.Fortunately, there is one standard interface for connecting externalmodems to computers called RS-232. Consequently, any externalmodem can be attached to any computer that has an RS-232 port,which almost all personal computers have. There are also modems
35Modem ‘Discussion’ (2)that come as an expansion board that you can insert into a vacantexpansion slot. These are sometimes called onboard or internalmodems.
36Multiplexer Multiplexer Allows several telecommunications signals to be transmitted over a single communications medium at the same timePretty picture
38Multiplexor ‘Discussion’ A communications device that multiplexes (combines) several signalsfor transmission over a single medium. A demultiplexor completesthe process by separating multiplexed signals from a transmissionline. Frequently a multiplexor and demultiplexor are combined into asingle device capable of processing both outgoing and incomingsignals.A multiplexor is sometimes called a mux.
39Front-End Processor Front-end processor… Special purpose computers that manage communication to and from a computer systemPretty picture
40Incoming and outgoing jobs Front-end processorMain systemJob 4
41Carriers and Services (1) Organizations that take the responsibility of ensuring telecommunications can effectively take place between enterprisesCommon carriersLong-distance telephone companiesValue-added carriersCompanies that have developed private telecommunications systems and offer their services for a feeSwitched linesLines that use switching equipment to allow one transmission device to be connected to other transmission devices (e.g., standard telephone line)Dedicated lineA line that provides constant connection between two points. No switching or dialing is needed
42Carriers and Services (2) Private branch exchange (PBX)Communication system that can manage both voice and data transfer within a location (e.g. a building) and to outside linesWide area telecommunication service (WATS)Billing method for heavy users of voice servicesPhone and dialing servicesIncludes automatic number identification (a.k.a. caller ID)Integration of telephones and personal computersAccess code screeningCall prioritiesOne number portability (use anywhere)Intelligent dialing (auto re-dial for a busy number)
43Carriers and Services (3) ISDNISDN = Integrated Services Digital NetworkTechnology that uses existing common-carrier lines to simultaneously transmit voice, video, and image data in digital formPretty picture
45Carriers and Services (4) T1 carriersAn expensive service developed by AT&T to increase the number of voice calls that could be handled through existing cablesDigital subscriber lines (DSL)Uses existing phone wires going into today’s homes and businesses to provide transmission speeds exceeding 500 Kbps at a cost of $100 - $300 per month
46Networks and Distributed Processing Centralized processingData processing that occurs in a single location or facilityDecentralized processingData processing that occurs when devices are placed at various remote locationsDistributed processingData processing that occurs when computers are placed at remote locations but are connected to each other via telecommunications devices
47Network Concepts and Considerations Network TopologyA logical model that describes how networks are structured or configuredTopologies…Ring (see chapter 1)Bus (see chapter 1)Star (see chapter 1)HierarchicalHybrid
48HierarchicalUses treelike structures with messages passed along the branches of the hierarchyHybridNetwork made up of various types of topologies
49Network Types Local area network (LAN) Wide area network (WAN) Connects computer systems and devices in the same geographic area (can be Ring, Bus, Hierarchical, Star, Hybrid)Wide area network (WAN)Ties together large geographic regions using microwave and satellite transmission or telephone linesInternational networkLinks systems between countries
50Terminal-to-Host Connection Applications and databases reside on the same host computerUser interacts with the application using a “dumb terminal”Target PC“dumb terminal”Host computer
51File Server Connection Applications and databases reside on the same host computerFile server transfers data and programs to PCs on the network, where these target PCs perform most of the processingTarget PCFile downloaded to userFile serverHost computer
52Client/Server Connection Applications and databases reside on specialized host computersServers do most or all of the processing and transmit the results to the clientClientServerServerClientServer
53Advantages & Disadvantages of Client/Server Reduced cost potentialImproved PerformanceIncreased SecurityDisadvantagesIncreased cost potentialLoss of controlComplex multi-vendor environment
54Communications Software and Protocols (1) Provides error checking, message formatting, communications logs, data security and privacy, and translation capabilities for networksNetwork operating system (NOS)Systems software that controls the computer systems and devices on a network and allows them to communicate with each otherNetwork management softwareEnables a manager on a networked desktop to monitor the use of individual computers and shared hardware, scan for viruses, and ensure compliance with software licenses
55Communications Software and Protocols (2) Rules that ensure communications among computers of different types and from different manufacturers.
56Communications Software and Protocols (3) Open Systems Interconnection (OSI) ModelServes as a standard model for network architectures and is endorsed by the International Standards CommitteeCommunication functions are represented in seven layers to promote the development of modular networks. Designed to permit communication among different computers from different operating systemsSeven layers (see figure 6.20)
57Communications Software and Protocols (4) TCP/IPTCP/IP = Transmission Control Protocol/Internet Protocol Standard originally developed by the U.S. government to link defense research agencies; it is the primary communication protocol of the InternetSystems Network Architecture (SNA)IBM communication protocolEthernetProtocol standard developed forLANs using a bus topologyX.400 and X.500An international standard for message handling and network directories
58Bridges, Routers, Gateways and Switches Connects two or more networks, with the same protocol, at the media control portions of the data link layerRouterOperates at the network level of the OSI model and features more sophisticated addressing software than bridges. Can determine preferred pathsGatewayOperates at or above the OSI transport layer and links LANs or networks that employ different architectures and use dissimilar protocolsSwitchRoutes or switches data to its destinationSchematic
60Telecommunications Applications (1) Linking personal computers to mainframe computersDownload and upload informationVoice mailEnables users to leave, receive, and store verbal messages for and from other usersElectronic mail ( )Enables a sender to connect a computer to a network, type messages, and send it to another person on the network
61Telecommunications Applications (2) Electronic software distributionInvolves installing software on a file server for users to share by signing onto the network and requesting that the software be downloaded onto their computers over a networkElectronic document distributionTransporting documents -- such as sales reports, policy manuals, and advertising brochures -- over communications lines and networksTelecommutingEnables employees to work away from the office using personal computers and networks to communicate via electronic mail with other workers and to pick up and deliver results
62Telecommunications Applications (3) VideoconferencingAllows participants to conduct long-distance meetings “face to face” while eliminatingPretty picture
64Telecommunications Applications (4) Electronic Data Interchange (EDI)Uses network systems and follows standards and procedures that allow output from one system to be processed directly as input to other systems, without human interventionPretty picture
65Third-party clearing house EDI linkVendorCustomer(a)EDI linkEDI linkThird-party clearing houseVendorCustomer(b)
66Telecommunications Applications (5) Public network servicesServices that give personal computer users access to vast databases and other services, usually for an initial fee plus usage feesSpecialized and regional information servicesSpecialized electronic bulletin boards and services targeting particular interests.Distance learningUse of telecommunications to extend the classroom