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  • Easy to add extra computers . If computer goes down it doesn’t affect rest of network
  • If central host goes doewn affects rest of network
  • LAN local area network
  • Contention occurs on star and bus networks.
  • Devives that connect local area networks If a BUS or ring then a Gateway needs to be used
  • Communications

    1. 1. Graham BettsCommunicationsSystemsThe topics within this unit are:Characteristics of communication systems.Examples of communication systems.Transmitting and receiving in communicationsystems.Other information processes in communicationsystems.Issues related to communication systems.
    2. 2. Graham BettsTOPICS MENUCharacteristics of CommunicationSystemsExamples of Communication SystemsTransmitting and ReceivingOther Information ProcessesIssues Related To CommunicationSystemsClick on the topic of your choice
    3. 3. Graham BettsCommunications GlossaryCommunications Networking GlossaryGlossary of Networking terms at Clock.orgCommunicationsTerms
    4. 4. Graham BettsCharacteristics ofCommunication SystemsProtocolsHandshakingSpeed of TransmissionError CheckingCommunication Settings
    5. 5. Graham BettsMore Informationmust be a Sender and ReceiverA protocol is a set of rules which governs the transfer ofdata between computers. Protocols allow communicationbetween computers and networks.Handshaking is used to establish which protocols to use.Handshaking controls the flow of data between computersprotocols will determine the speed of transmission, errorchecking method, size of bytes, and whether synchronousor asynchronousExamples of protocols are: token ring, CSMA/CD, X.25,TCP/IPCharacteristics ofCommunicationSystems
    6. 6. Graham Betts5 Basic ComponentsEvery communication system has 5 basic requirements•Data Source (where the data originates)•Transmitter (device used to transmit data)•Transmission Medium (cables or non cable)•Receiver (device used to receive data)•Destination (where the data will be placed)
    7. 7. Graham Betts5 Basic Components
    8. 8. Graham Betts•Bandwidth:The amount of data which can betransmitted on a medium over a fixed amount of time(second). It is measured on Bits per Second or Baud•Bits per Second (bps): A measure oftransmission speed. The number of bits (0 0r 1) whichcan be transmitted in a second (more)•Baud Rate: Is a measure of how fast a change ofstate occurs (i.e. a change from 0 to 1) (more)Transmission Media Speed
    9. 9. Graham BettsThis file has now been broken into four packetsPACKETPacketsTransmissions are broken up intosmaller units or data transmissionscalled packetsPACKET PACKET PACKETExampleA data file is divided into packets.It does not matter what the transmission is. It could be Worddocument, a PowerPoint or an MP3. Imagine this Green boxis a file for transfer
    10. 10. Graham BettsPackets and OSIAfter the file is divided into packetsextra information is required to makesure it all goes back together correctly.The OSI model helps to look after this.The OSI model also provides muchmore information which is included witheach package.
    11. 11. Graham BettsMore Information on OSIOSI 7 Layer Model•OSI “Open System Interconnection”•OSI is not a protocol but a list of protocolsdivided between 7 layers with each layer havinga different set of functions.•Each packet is layered/packaged withprotocols from each of the layers as it isprocessed.•The process of layering the protocols aroundeach package is called encapsulation. The finalencapsulated data packet is called a frame.Originally Created by Bob BakerModified 2006Graham Betts
    12. 12. Graham BettsFileOSI Reference modelLayer 7 applicationLayer 6 presentationLayer 5 sessionLayer 4 transportLayer 3 networkLayer 2 data linkLayer 1 physicalTransmission MediumFileSender ReceiverFileEach fileis dividedintopacketsThe receivedframe is thenunpackedin theopposite orderOpen SystemsInterconnectionOriginally Created by Bob BakerModified 2006Graham BettsEach Packetwillthen beEncapsulatedwithPROTOCOLSThe protocolsWill be addedsystematicallyLayerBy layerThe encapsulatedPacket is calleda frame
    13. 13. Graham Betts Layer 7 application Layer 6 presentation Layer 5 session Layer 4 transport Layer 3 network Layer 2 data link Layer 1 physical Identification, authentication Format conversion Set-up coordinate conversation Ensures error-free transfer Routing of data through network Error control and synchronisation Placing signals on the carrierOriginally Created by Bob BakerModified 2006Graham BettsServices Performed atEach Layer
    14. 14. Graham BettsExamples of protocols Layer 7 application Layer 6 presentation Layer 5 session Layer 4 transport Layer 3 network Layer 2 data link Layer 1 physical E-mail, Web browser, Directory POP, SMTP, FTP, HTTP, DNS Sockets TCP IP PPP, Ethernet, Token ring 100baseTMore on ProtocolsOriginally Created by Bob BakerModified 2006Graham Betts
    15. 15. Graham BettsEncapsulationApplicationPresentationSessionTransportNetworkData LinkPhysicaldataDevice 1 Device 2dataH6 T6dataH5 T5dataH4 T4(packet)H3 data T3H2 data T2H1 data T1carrier FRAMEApplicationPresentationSessionTransportNetworkData LinkPhysicalA typical frameDestinationAddressSourceAddressData Padding CRCPreambleFRAME FRAME FRAME(Packet)Originally Created by Bob BakerModified 2006Graham Betts
    16. 16. Graham Betts• Parity bit check• Check sum* data transmitted in blocks, each block addedto give a total – checksum* used in X Modem protocol• Cycle redundancy checkError Checking MethodsMore on internet
    17. 17. Graham BettsHSC Topic 3.3Examples ofCommunication Systems
    18. 18. Graham BettsExamples of Communication Systems- E-mail- Voice Mail - Fax- Smart Phone - Instant Messaging- Telecommuting - Video-conferencing- Groupware - Telephony- E-Commerce - The Internet- Bulletin board system - The Web- Global positioning system
    19. 19. Graham BettsHSC Topic 3.4Transmitting andReceiving inCommunication SystemsCommunication concepts(transmission of data, protocols and handshaking, networks, LANs andWANs,Topologies, Network Access Methods)Network Hardware(NICs, Servers, Routers and Switches, Bridges and gateways, Hubs,Transmission mediaNetwork SoftwareNOSs, Network Operating System Tasks, Logon and Logoff Procedures,Intranets and Extranets
    20. 20. Graham BettsAny transmission May be:•analog or digital•Serial or parallelCommunicationConcepts
    21. 21. Graham BettsSender transmittedData is transmitted, on a single channel, one bit at atime one after another- Much faster than parallel because of way bitsprocessed (e.g. USB and SATA drives)Receiver receivedSerial Transmission101 0 0 1 1 0
    22. 22. Graham Betts Receiverreceived-each bit has it’s own piece of wire along which it travels- often used to send data to a printerParallel TransmissionSendertransmittedAll bits are sent simultaneously10011001
    23. 23. Graham BettsWhy Not use ParallelInstead of serial?Due to inconsistencies on channels dataarrives at different timesBecause of the way it is transmitted packetswitching cannot be usedThe above two points makes parallel slowerthan serial and requires higher bandwidth.Parallel transmissions are rarely usedanymore
    24. 24. Graham BettsSynchronous Transmissionall data sent at once and no packet switchingAsynchronous Transmission•Uses stop/ start bits•most common type of serial data transfer•Allows packet switching•Allows sharing of bandwidth (i.e. talk on phonewhile another person is using internet)Synchronous VsAsynchronousTransmissions
    25. 25. Graham Betts- simplex: One direction onlyTransmission Direction
    26. 26. Graham BettsHalf DuplexTransmissionhalf duplex: Bothdirections butonly onedirection at atime
    27. 27. Graham BettsFull DuplexTransmissionfull duplex:send andreceive bothdirections atonce
    28. 28. Graham Betts•Ethernet (Ethernet Network)-Carrier Sense Multiple Access/Collision Detection(CSMA/CD)-TCP/IP3 Common Protocols
    29. 29. Graham BettsEthernetDeveloped at Xerox in 1976.First protocol approved as an industrystandard protocol 1983LAN protocol used on bus and starMost popular LAN protocolInexpensive
    30. 30. Graham BettsCarrier Sense MultipleAccess/CollisionDetection (CSMA/CD)- Used on bus networks to avoid datacollisions.
    31. 31. Graham Betts• Developed in 1973 for use on theARPANET which was a defense forceresearch network.-Adopted in 1983 as the Internet standard.all hosts on the Internet are required to useTCP/IP.- Allows transfer of data using packetswitchingTCP/IP
    32. 32. Graham BettsLANs Vs WANsLAN is “local Area network” which is anetwork confined to a small geographicarea which is a building or a group ofbuildings.WAN is “wide area network” which is anetwork spread over a large geographicarea. The largest WAN is the internet.
    33. 33. Graham BettsExamples of LANS3 different types of LANS are:RingBusStar
    34. 34. Graham BettsUses an empty datapacket called a tokenand a special protocolcalled “token ring”.Packets travel aroundthe ring in a clockwisedirection. Clientsrequire an empty tokento transmit data.Advantages- no collisionsbecause all data travelsin same direction.Disadvantages- fails if an individualnode in the networkfailsRing
    35. 35. Graham BettsA bus is a form of Ethernet. Nodes linked by a cable known as thebus. Bus transmits in both directions and uses CSMA/CD protocolBUS TOPOLOGYAdvantages- Easy to set up and maintainfailure of one node does not affectnetworkDisadvantages-Higher rate of data collision thanwith a bus network-fails if there is any damage to thebus
    36. 36. Graham BettsAll data is sent fromone client to anotherthrough the server.Advantages- If one client fails noother clients areaffected.Disadvantages- If central file serverfails the network fails.Star
    37. 37. Graham BettsNetwork Hardware
    38. 38. Graham BettsA network is a number of computers andperipheral devices connected together so asto be able to communicate (i.e. transferdata)Each device in a network is called anode.Terminals are data entry points whichcan also display.What is a Network?
    39. 39. Graham BettsLAN – a network that connects computers in a limitedgeographical area.MAN – a backbone that connects LANs in a metropolitanarea such as a city and handles the bulk of communicationsactivity across that region.WAN – covers a large geographical area such as a city orcountry. Communication channels include telephone lines,Microwave, satellites, etc.NETWORKS: categorizedby size
    40. 40. Graham BettsNETWORK TOPOLOGIES(categorizing by shape)
    41. 41. Graham BettsLarge networks can be separated into two or more smallernetworks using a bridge. This is done to increase speed andefficiency. This type of network is called a segmented LAN andhas largely been superseded by the use of switches which cantransfer data straight to a computer and thus avoid bottleneck jamswhich bridges were designed to fix.BridgeBridge
    42. 42. Graham BettsOften used to connect a LAN with a WAN. Gateways join two orMore different networks together.GatewayGateway
    43. 43. Graham BettsInternetpublic/international network which is used to accessinformation, e-shopping, e-banking, emailIntranetprivate network (LAN or WAN) used to share resources in secureenvironmentuses web pages (HTML to view) and TCP/IP protocols (to makeconnection)Extranetintranet that has been extended to include access to or from selectedexternal organizations such as customers, but not general public.Note: Connections via leased lines, or network interconnections.Internet, Intranet, Extranet
    44. 44. Graham BettsTransmission Mediatwisted pair – telephone cablecoaxial cable –Thick black cable used forhigher bandwidth communications thantwisted pair (i.e. Optus cable)fibre optic – data transferred throughpulses of light. Extremely fast.Non cable methods such as satelite,microwave, wireless and bluetoothMore on internet
    45. 45. Graham BettsSERVERS: Help to manage the network and the resourcesof that network. On larger networks servers commonly havespecialised tasks such as: File Servers: stores and managesfiles, Print Servers: manages printers and print jobs, MailServer: Manages email, Web Server: manages web access.Routers: connects multiple networks and are protocolindependent. can be used in place of a switch or bridge.Switches: smart hubs which transmit packets to thedestination port onlyHubs: like double adapters /power boards in the homeexcept instead of plugging in extension cords we are pluggingin computers to allow them to communicate.Network HardwareMore on Internet
    46. 46. Graham Betts- adding/removing users- assigning users to printers- giving users file access rights- installation of software and sharing with users- client installation and protocol assignment- logon and logoff procedures- network based applicationsSome NetworkAdministration Tasks
    47. 47. Graham BettsOther InformationProcesses inCommunicationSystemsCollecting: phone as collection device with voice mail,EFTPOS terminal as a collection device for electronicbankingprocessing: sending of attachments with e-mail,encoding and decoding methods, including: analog datato analog signal, digital data to analog signal, digitaldata to digital signal, analog data to digital signal, client-server architecture: the client controls the user interfaceand the application logic server controls access to thedatabase
    48. 48. Graham BettsCollecting: The following are collection devices:ATMs for internet banking, EFTPOS for stores,microphone and video camera for video conferencing.Data can be analog or digitalCollecting
    49. 49. Graham BettsProcessingProcessing: Is the manipulation orchanging the data into a more useableformat. The processing may includechanging the appearance of the data,the file type or storage options.
    50. 50. Graham BettsDisplayingDisplaying: How the informationis made available for the user tosee
    51. 51. Graham BettsIssues related toCommunication SystemsMessaging Systems (social context, Danger of Misinterpretation, PowerRelationships, Privacy and confidentiality, power relationships, electronic junkmail, information overload)Internet (Internet trading, taxation, employment, nature of business, tradebarriers, censorship, child protection, internet banking, security, changingnature of work, branch closures and job losses, radio and video)Telecommuting (work from home), blurring between work and home,more stress, advantagesand disadvantages)
    52. 52. Graham Betts•‘netiquette’ is etiquette/ manners on net•Many people rely on messaging systems morethan spoken or face to face communication.•written word only recipient miss out on (e.g. bodylanguage and voice inflection)•privacy (employers have right to read e-mail atwork)•Spam is overloading mailboxes•Work/ information overload from ever growingnumber of emailsIssues relating tomessaging systems
    53. 53. Graham BettsIssues relating tointernet tradingemployment ramificationsEffect on trade barriers andtaxation lawsPhishing and security
    54. 54. Graham Betts•branch closures and job losses•decreasing number of bank branches•job losses•changing nature of work•security of banking detailsIssues relating tointernet banking
    55. 55. Graham BettsPhysical boundariestelecommuting is working from homevirtual organisationsnational trade barriers
    56. 56. Graham BettsAcknowledgementsSlides 11-15 were originally created byBob Baker and have been modified byGraham BettsA number of slides have been adaptedfrom a slide show by Loretta Kocovskaaround 2001 especially the illustrationson slides 18,39,40, 41, 42 and 43