the workings of the internet cecs 5030 with cathie norris, jennifer smolka & gerald knezek cecs 5030...

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  • 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 combine networks and form internets

  • Routers - OperationNetwork 1Network 2BCDestination network address is localtransmit packet directly to the end stationDestinationnetwork numberis differentFind routerand give packetto the routerRouter sendspacket directlyto the end stationMAC address for the routerRouter ZNode PNode ANode D

  • Routing DiagramNetwork 1Network 2Network 3Network 4ABCDEFGHMAC AddressesRouter ZRouter YRouter X

  • Multiprotocol RoutersLANs currently operate with many different types of protocolsApple Computers can use AppleTalkUNIX workstations use TCP/IPClient/Server applications could use Novell NetWareTo require one router for each protocol on the LAN is not efficientMultiprotocol routers were invented to handle thisArrived around 1986Routes not only based on the network IDs but are able to pass the packet to the correct protocol processor by examining the Type of packet

  • GatewaysComplex devices that provide for a protocol translation during data forwardingExamples are:TCP/IP to SNAasynchronous to synchronous serial streamGateways differ from bridges and routersPerform protocol translation of the incoming packet to match the outgoing stream

  • References

    From Networking 101 Jim Cabral, Puget Technology Group, Inc. & Tammy Ruth, Childrens Hospital and Medical Center [email protected] [email protected]

    HIMSHIMSHIMSHIMSA topology is the physical configuration of a network. The term is used to describe a network layout.

    A topology can easily describe a particular type of network. This drawing should show a companys layout of their network.

    There are three main types of topologies: star, ring, and bus.HIMSHIMSStar TopologyHIMSRing TopologyHIMSRing TopologyAll stations are considered repeaters and are enclosed in a loop.Each active attachment receives the signal at one end of the repeater and repeats it on the other side to its downstream neighbor.Data is transmitted in one direction only.There may be a single point of failure in that one station could quit repeating.There are usually management processes invoked in the attachment that are able to dynamically remove a station that has quit repeating, allowing the ring to return to an operational state.A ring topology usually have a centralized control mechanism for cable access.HIMSBus TopologyHIMSBus TopologyThe bus topology is also known as the linear bus topology.It uses a single length of cable with all stations attached to it.All stations share this single cable.The network is terminated at its endpoints (not a closed loop).A break on the single cable will bring down all attachments on the network.The bus topology is most commonly used for Ethernet networks.HIMSHIMS

    HIMSThick Ethernet cable:is a specially manufactured cable to be used only in certain Ethernet environments

    provides many layers of shielding.

    HIMSThin Ethernet cable: was designed in 1984 as an alternative to thick Ethernet cable.provides a simplification of the Ethernet cabling scheme. uses a commonly manufactured cable type.reduces installation time from about 5 minutes to around 1minute.eliminated or moved certain thick coaxial components whichintroduced new connectors

    HIMSHIMSHIMSUnshielded Twisted Pair (UTP) cable:provides an alternative, easy to use, less expensive cable type for Ethernet networks..implements the star topology on Ethernet which allows for better network managementintroduced a new component called the concentrator which allows for network cabling to be collapsed into one entity.

    HIMSFiber is used for Ethernet in proprietary systems. It is not standardized.HIMSHIMSThis device was introduced around 1985 after UTP wire began being used.It is usually called a concentrator although it can be called a hub.It houses repeater modules that slide into the chassis.Concentrators house all repeater types into one unit using repeater modules that are connected together with a common backplane.It allows the concentrator to act as one repeater.It reduces the number of repeaters on a network.Concentrators usually have connections for fiber, 10BASET, 10BASE2 and one connector for 10BASE5 (connection to external cable plant).It added life to the Ethernet standard by providing a physical star topology.The concentrator allows for better network managementHIMSHIMSHIMSHIMSNode A needs to transmit data to Node D.Node A builds a packet.Node A checks to see if the cable plant is clear (no one else is currently transmitting).Node A transmits the packet while listening to the cable. If there were no collisions, node A returns to listen mode.Another station wishing to transmit should detect the cable plant is busy when node A is transmitting and enter into defer mode.That station will try again later.There is no priority scheme used with Ethernet.All stations have equal access to the cable plant.An Ethernet station is allowed to transmit a packet as small as 64 bytes, as large as 1518 bytes (18 bytes of MAC header or trailer information) or any size in between.HIMSHIMSHIMSHIMSHIMSHIMSInternetworking and the OSI ModelRepeaters work at the physical layer.They simply repeat any signal from one cable plant to the next.Concentrators are repeaters but offer more fault isolation than normal repeaters.Bridges work at the data link layer. Specifically, they forward based on the MAC address of the packet.Routers work at the network layer.They forward based on a network identification inside the packet, not on the MAC address.Gateways operate the the session, presentation and application layer.They provide protocol translation between different communication types.HIMSHIMSHIMSCascadedCommon network design that is used for small to medium sized office networks.Cannot cascade through more than seven bridges Not a strict standard; it is based on network delays.This is not a recognized standard but usually leads to better design.Generally, when more than three bridges are to be cascaded, a backbone should be installed.HIMSBackboneThis is commonly used in building configurations to interconnect many cable segments.The backbone cable plant runs up the riser of a building.The speed capacity of the access method should be 5 to 10 times faster than its fastest interconnection link.Bridges from each floor are attached to this backbone.HIMSHub and SpokeThis can be used for local and remote configurations, but is usually found in remote (serial line interconnection) configurations.It usually has one site that acts as a hub for all the other sites.It allows redundancy between sites by providing shortest path to any location.This reduces the amount of bridges that network stations will communicate through.The topology contains a single point of failure; if the hub site becomes disabled all other sites lose communication.Most bridges and routers are fault-resilient in that they contain redundancy options in the event of a failure.HIMSHIMSHIMSRouters - OperationRouters forward packets based not on the MAC address of the packet but on the network number inside the packet.Each network separated by a router is assigned a unique network number. End stations know only of the network number of the network to which they are attached.Before an end station transmits a packet, it compares the network number of the destination to its network number.If the network numbers are the same, the packet is simply transmitted on the cable, addressed to the destination station.The destination station is local.If the network numbers do not match, the end station must find a router that it can send the packet to so that it can be forwarded to the proper network.The requesting station submits a special type of packet to the network requesting information from the routers.The requesting station acquires the routers MAC address by some means specific to the protocol.HIMSRouting DiagramEach of the four above LANs have unique network numbers 1 through 4.Each station has its own unique MAC address.Example:Station A wants to transmit a packet to station H.Those stations reside on different network numbers.Station A requests information about network 4.Router Z responds with that information.Station A transmits the packet to router Z .The MAC source address is A and the MAC destination address is B.Router Z receives the packet.The destination network is not local.Router Z transmits the packet to router Y with the MAC source address is C and MAC destination is address D.The destination network is not local to router Y and router Y gives the packet to router X.The destination network number is local to router X and it transmits the packet to end station H.Router X extracts the destination end stations MAC address from network header.Router X transmits the packet to station H with the MAC source address is G.HIMSHIMSHIMS