Communications systems

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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


  • 1. Communications Systems The 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. Graham Betts
  • 2. TOPICS MENU Click on the topic of your choiceCharacteristics of Communication SystemsExamples of Communication SystemsTransmitting and ReceivingOther Information ProcessesIssues Related To Communication Systems Graham Betts
  • 3. CommunicationsCommunicationsTerms GlossaryCommunications Networking GlossaryGlossary of Networking terms at Graham Betts
  • 4. Characteristics ofCommunication Systems Protocols Handshaking Speed of Transmission Error Checking Communication Settings Graham Betts
  • 5. Characteristics of Communication Systems More Information must be a Sender and Receiver A 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 computers protocols will determine the speed of transmission, errorchecking method, size of bytes, and whether synchronousor asynchronous Examples of protocols are: token ring, CSMA/CD, X.25,TCP/IP Graham Betts
  • 6. 5 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) Graham Betts
  • 7. 5 Basic Components Graham Betts
  • 8. Transmission Media Speed•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) Graham Betts
  • 9. Packets Transmissions are broken up into smaller units or data transmissions called packetsExampleA This file is divided intobroken into four packets data has now been packets.It does not matter what the transmission is. It could be Word PACKET PACKET PACKET PACKETdocument, a PowerPoint or an MP3. Imagine this Green boxis a file for transfer Graham Betts
  • 10. Packets 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. Graham Betts
  • 11. OSI 7 Layer ModelOriginally Created by Bob BakerModified 2006 More Information on OSIGraham Betts •OSI “Open System Interconnection” •OSI is not a protocol but a list of protocols divided between 7 layers with each layer having a different set of functions. •Each packet is layered/packaged with protocols from each of the layers as it is processed. •The process of layering the protocols around each package is called encapsulation. The final encapsulated data packet is called a frame. Graham Betts
  • 12. Originally Created by Bob Baker Open SystemsModified 2006Graham Betts Interconnection OSI Reference model Sender Receiver  Layer 7 application Each Packet Each file  Layer 6 presentation The protocols will is divided The encapsulated Will be added  Layer 5 session then be into Packet is called systematically The received File Encapsulated packets File File  Layer 4 transport aLayer frame frame is then with By layer unpacked  Layer 3 network PROTOCOLS in the  Layer 2 data link opposite order  Layer 1 physical Transmission Medium Graham Betts
  • 13. Originally Created by Bob Baker Services Performed atModified 2006Graham Betts Each Layer Layer 7 application  Identification, authentication Layer 6 presentation  Format conversion Layer 5 session  Set-up coordinate conversation Layer 4 transport  Ensures error-free transfer Layer 3 network  Routing of data through network Layer 2 data link  Error control and synchronisation Layer 1 physical  Placing signals on the carrier Graham Betts
  • 14. Originally Created by Bob BakerModified 2006Graham Betts Examples of protocols More on Protocols  Layer 7 application  E-mail, Web browser, Directory  Layer 6 presentation  POP, SMTP, FTP, HTTP, DNS  Layer 5 session  Sockets  Layer 4 transport  TCP  Layer 3 network  IP  Layer 2 data link  PPP, Ethernet, Token ring  Layer 1 physical  100baseT Graham Betts
  • 15. Originally Created by Bob Baker Modified 2006 Graham Betts Encapsulation Device 1 Device 2 Application data Application Presentation H6 data T6 Presentation Session H5 data T5 Session Transport H4 data T4 (Packet) Transport Network H3 data T3 (packet) Network Data Link H2 data T2 Data Link Physical H1 data T1 Physical carrier FRAME FRAME FRAME FRAME Destination SourceA typical frame Preamble Address Address Data Padding CRC Graham Betts
  • 16. Error Checking Methods More on internet• Parity bit check• Check sum * data transmitted in blocks, each block added to give a total – checksum * used in X Modem protocol• Cycle redundancy check Graham Betts
  • 17. HSC Topic 3.3Examples ofCommunication Systems Graham Betts
  • 18. Examples 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 Graham Betts
  • 19. HSC 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 Graham Betts
  • 20. Communication ConceptsAny transmission May be:•analog or digital•Serial or parallel Graham Betts
  • 21. Serial TransmissionData is transmitted, on a single channel, one bit at a time one after another- Much faster than parallel because of way bits processed (e.g. USB and SATA drives) 1 0 0 1 1 0 0 1 Sender transmitted Receiver received Graham Betts
  • 22. Parallel Transmission-each bit has it’s own piece of wire along which it travels- often used to send data to a printer 1 Sender transmitted 0 Receiver received 0 1 1 0 0 1 All bits are sent simultaneously Graham Betts
  • 23. Why Not use Parallel Instead 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 Graham Betts
  • 24. Synchronous VsAsynchronousTransmissionsSynchronous 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) Graham Betts
  • 25. Transmission Direction- simplex: One direction only Graham Betts
  • 26. Half Duplex Transmissionhalf duplex: Both directions but only one direction at a time Graham Betts
  • 27. Full Duplex Transmissionfull duplex: send and receive both directions at once Graham Betts
  • 28. 3 Common Protocols•Ethernet (Ethernet Network)-Carrier Sense Multiple Access/Collision Detection(CSMA/CD)-TCP/IP Graham Betts
  • 29. EthernetDeveloped at Xerox in 1976.First protocol approved as an industrystandard protocol 1983 LAN protocol used on bus and starMost popular LAN protocolInexpensive Graham Betts
  • 30. Carrier Sense Multiple Access/Collision Detection (CSMA/CD)- Used on bus networks to avoid data collisions. Graham Betts
  • 31. TCP/IP• 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 packetswitching Graham Betts
  • 32. LANs 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. Graham Betts
  • 33. Examples of LANS3 different types of LANS are: Ring Bus Star Graham Betts
  • 34. Uses an empty dataRing packet called a token and a special protocol called “token ring”. Packets travel around the ring in a clockwise direction. Clients require an empty token to transmit data. Advantages - no collisions because all data travels in same direction. Disadvantages - fails if an individual node in the network Graham Betts fails
  • 35. BUS TOPOLOGYA bus is a form of Ethernet. Nodes linked by a cable known as thebus. Bus transmits in both directions and uses CSMA/CD protocol Advantages Disadvantages - Easy to set up and maintain -Higher rate of data collision than failure of one node does not affect with a bus network network -fails if there is any damage to the bus Graham Betts
  • 36. Star All data is sent from one client to another through the server. Advantages - If one client fails no other clients are affected. Disadvantages - If central file server fails the network fails. Graham Betts
  • 37. Network Hardware Graham Betts
  • 38. What is a Network? A 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. Graham Betts
  • 39. NETWORKS: categorized by sizeLAN – 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. Graham Betts
  • 40. NETWORK TOPOLOGIES(categorizing by shape) Graham Betts
  • 41. BridgeLarge 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. Bridge Graham Betts
  • 42. GatewayOften used to connect a LAN with a WAN. Gateways join two orMore different networks together. Gateway Graham Betts
  • 43. Internet, Intranet, ExtranetInternet public/international network which is used to accessinformation, e-shopping, e-banking, emailIntranet private network (LAN or WAN) used to share resources in secureenvironment uses web pages (HTML to view) and TCP/IP protocols (to makeconnection)Extranet intranet 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. Graham Betts
  • 44. Transmission Media More on internettwisted 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 bluetooth Graham Betts
  • 45. Network Hardware More on InternetSERVERS : 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. Graham Betts
  • 46. Some Network Administration Tasks- 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 applications Graham Betts
  • 47. Other Infor mationProcesses 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 Graham Betts
  • 48. CollectingCollecting : The following are collection devices:ATMs for internet banking, EFTPOS for stores,microphone and video camera for video conferencing.Data can be analog or digital Graham Betts
  • 49. ProcessingProcessing: 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. Graham Betts
  • 50. DisplayingDisplaying: How the information is made available for the user to see Graham Betts
  • 51. Issues related to Communication 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) Graham Betts
  • 52. Issues relating to messaging systems•‘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 emails Graham Betts
  • 53. Issues relating to internet tradingemployment ramificationsEffect on trade barriers andtaxation lawsPhishing and security Graham Betts
  • 54. Issues relating to internet banking•branch closures and job losses•decreasing number of bank branches•job losses•changing nature of work•security of banking details Graham Betts
  • 55. Physical boundariestelecommuting is working from home virtual organisations national trade barriers Graham Betts
  • 56. AcknowledgementsSlides 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 Graham Betts