the workings of the internet

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The Workings of the Internet. CECS 5030 with Cathie Norris, Jennifer Smolka & Gerald Knezek. Overview. Layered Organization Topologies Network Transports Access Methods Routing. ISO/OSI Model. Developed by International Organization for Standardization in 1974 Consists of seven layers - PowerPoint PPT Presentation


  • The Workings of the InternetCECS 5030with Cathie Norris, Jennifer Smolka & Gerald Knezek

  • OverviewLayered OrganizationTopologiesNetwork TransportsAccess MethodsRouting

  • ISO/OSI Model Developed by International Organization for Standardization in 1974Consists of seven layersEach with unique functionEach hands off functions to adjacent layerModules (layers) may be replaced with another of equal functionality (Xerox vs. Novell, for example)

  • OSI Model LayersPhysicalData LinkNetworkTransportSessionPresentationApplicationTransmission of binary signalTransfer of units of information, framing, and error checkingDelivery of packets of information, which includes routingProvision for end-to-end reliable and unreliable deliveryEstablishment and maintenance of sessionsData formatting and encryptionNetwork applications such as file transfer and terminal emulationOSI LayerFunction Provided

  • Network TopologiesArchitectural drawings that show the overall physical configuration for a given communications systemDetermine access methods and rules used to design and implement a communication systemRepresent the drawing of your network cable plantThree main types: star, ring, and bus

  • Network TopologiesLinear Bus - Ethernet/IEEE 802.3 10Base2 and 10Base5Star Wired Bus - Ethernet/IEEE 802.3i 10BaseT Star Wired Ring - Token Ring/IEEE 802.5Dual Counter Rotating Ring - FDDI/ANSI X3T9.5Wireless - Product Specific

  • Star TopologyFirst used with the telephone switchesCentralized hub with all stations connectedNo single point of failure effects the whole network, except the hubOldest and most popular topologyBetter network management

  • Ring TopologyAll stations (repeaters) are enclosed in a loopEach receives the signal and repeats it on the other side to its downstream neighborData is transmitted in one direction onlySingle point of failure when one station quits repeatingManagement processes invoked that dynamically remove a station allowing the ring to return to an operational state

  • Ring TopologyNodeNodeNodeNodeData DirectionReceiverTransmitterRepeater

  • Bus TopologyAlso known as linear busUses a single length of cable with all stations attached to itThe network is terminated at its endpoints (not a closed loop)A break on the single cable will bring down all attachments on the networkThe bus topology is most commonly used for Ethernet networks

  • Bus TopologyNodeNodeNode

  • Star-Wired Bus TopologyEach node is attached to hubWhen one node fails, it doesnt affect the other nodesThe hub is a single point of failure for all nodesHub failure causes all nodes to lose connectivity

  • Physical MediaPhysical media provide the connections between network devices that make networking possibleThere are four main types of physical media in widespread use today:Coaxial CableTwisted PairFiber Optic CableWireless Media

  • Thick Coaxial CableUsed in the first Ethernet networksType RG-11 / 10Base5 Usually orange/blackThickness of a small garden hose Very expensive and heavy cableTwo strands along the axisConductor down the center Insulator surrounds conductorShielded mesh serves as outside

  • Thin Coaxial CableAlternative to Thick Ethernet CableType RG-58 / 10Base2 / CheapnetUsually blackThickness of a pencilMore flexible than thick Ethernet Reduced the cost of the cablingFlexible

  • Twisted Pair CablePhone Systems

    Twisted Pair Cable consists of two copper wires, usually twisted around each other to cancel out any noise in the circuit

    Two main type of Twisted Pair CablingShielded Twisted Pair (STP)Unshielded Twisted Pair (UTP)

  • Shielded Twisted Pair (STP)Shielded twisted pair is the original media used for token ring networks

    STP can be used for high-speed networks, such as FDDI or ATM, where shielding is important

  • Unshielded Twisted Pair (UTP)Most commonly used twisted pair cableUses common telephone wire UTP was standardized by the IEEE 802.3 committee in October of 1990UTP for LANs is now classified as:Category 3 - used for LANs up to 10 MbpsCategory 4 - used for LANs up to 16 MbpsCategory 5 - used for LANs up to 100 Mbps

  • Fiber Optic CableUses light signals transmitted over a very thin filament, usually made of glass

    Advantage over other types of mediasecurity against eavesdroppingimmunity to interferencemaximum length of a single segment

    Most expensive of all media

  • Wireless MediaConnect your computer to your cell phone?

    Problems with stability of connection

    Have wireless for a long time

    Commercial SatelliteGeostationary OrbitMicrowave WavelengthExpensive

  • Wireless MediaA number of wireless media are used in internetworking, e.g.:


    Commercial Radio wave

    Infrared signaling (Palm Synching)

  • Concentrators/HubsHubs allow multiple users to be connected to a single network as a shared device

    The more users on a hub the slower the response time

  • Network TransportsEthernet / Fast Ethernet / IEEE 802.3

    Token Ring / IEEE 802.5


    Wireless/IEEE 802.11

  • Ethernet Cable Names


    NameThick CoaxialThin CoaxialUnshieldedTwisted PairFiber

    Wire TypeRG-8RG-5822 - 26 AWG62.5/125 micron


    Standard NumberIEEE 802.3IEEE 802.3aIEEE 802.3iNA

    Other NamesThick netThin netUTP



  • How Ethernet WorksSent the message and listens for a response

    An access method based on the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) algorithm

    Cooperative effort between Digital, Intel, and Xerox produced Ethernet version 1.0 in 1980

  • How Ethernet WorksEthernet was adopted with modifications by the standards committees IEEE 802.3 and ANSI 8802/3

    Most widely used network system today

  • Normal Ethernet OperationDataAddress mismatchpacket discardedAddress mismatchpacket discardedAddress matchpacket processedSend datato node DTransmitted packet seenby all stations on the LAN(broadcast medium)ACBD

  • Final Ethernet IssuesEthernet is an access method that strictly adheres to the CSMA/CD algorithm

    Ethernet is a multiprotocol solution

    Ethernet is usually hardware (firmware), not software

  • How Token Ring WorksToken Ring controls which PC can send messages by passing a token from station to station around the ring

    When a PC wants to transmit it will replace the token with a frame (message)

    The frame is passed from PC to PC until it reaches its destination

  • How Token Ring WorksThe destination PC makes a copy of the frame (message) and marks the frame to indicate that it got the message

    The frame circulates around the network until it gets back to the sender

    The sender, seeing that the message has been received, replaces it with a new token

  • Wide Area Network (WAN) TopologiesDedicated Circuits56KbT-1DS-3

    Frame-Relay56Kb to T-1 speeds

    Integrated Services Digital Network (ISDN)

  • Inter-networkingNetworks have their restrictions

    Thick coaxial cable maximum length is 500 meters

    LANs are broadcast-oriented

    Proper network design is impossible using repeaters

  • Inter-networkingProperly extending the LAN requires special devices known as bridges and routers

    A LAN that uses bridges is called an extended LAN

    A LAN that uses routers is called an internet or inter-network

    A gateway between dissimilar networks

  • Inter-networkingBridges and routers are data-forwarding devices that forward packets to one or more LANs

    They allow for more efficient networks to be designed

  • Inter-networking CategoriesPhysicalData LinkNetworkTransportSessionPresentationApplicationRepeatersBridgesRoutersGateways

  • RepeatersExtend the network by interconnecting multiple segmentsHave transformed into wiring concentrators (hubs)Low costCan be used to interconnect different wiring types but not different access methodse.g. Coax to twisted pair

  • Bridge DesignsCascadedLocates on bridge next to another in a pillar fashionBackboneFor networks with many LANsBackbone cable is run vertically in buildings riserLAN ribs run on each floorStarUsed in wide area networks or remote bridged networks

  • CascadedCable segment 1Cable segment 2Cable segment 3Terminal ServerTerminalWorkstationFile ServerHost

  • Backbone FiberbackboneFloor 1Floor 20TerminalWorkstationHostWorkstation

  • StarCaliforniaVirginiaNorth CarolinaTexasSerial lineSerial lineSerial line

  • Introduction to RoutersRouters are data forwarding devices but operate differently than a bridgeRouters separate networks into regions.Each region is assigned a unique network numberThese network numbers are unique for each network they are assigned toPacket forwarding is based on these network IdsRouters route packets based on a protocol as well as a network IDMost routers today are multiprotocol in that one box can forward different protocol packetsRouters, like bridges, can be used locally or remotely

  • RoutingMost network protocols were designed with network-layer routingRouters base forwarding decisions on an embedded network number in the network layer header of the packetNetwork numbers can be thought of as area codes in the phone systemMust use the area code to call different areasAny number of end stations may be assigned to one network numberMost routers do not keep track of individual end stations addressesNetwork numbers group network stations into one or more network numbersTaken as a whole, routers com