Business Data Communications and Networking - Chapter 8: Backbone Networks

Business Data Communications and Networking 8th Edition Jerry Fitzgerald and Alan DennisJohn Wiley & Sons, Inc Prof. M. UlemaManhattan CollegeComputer Information Systems1Copyright 2005 John Wiley & Sons, IncChapter 8Backbone Networks 2Copyright 2005 John Wiley & Sons, IncOutlineComponents of Backbone networksBridges, Routers, GatewaysBackbone network architecturesBackbone technologiesBest practice backbone designImproving backbone performance3Copyright 2005 John Wiley & Sons, IncBackbone NetworksHigh speed networks linking an organization’s LANsMaking information transfer possible between departmentsUse high speed circuits to connect LANsProvide connections to other backbones, MANs, and WANsSometimes referred to as An enterprise networkA campus-wide network4Copyright 2005 John Wiley & Sons, IncBackbone Network ComponentsNetwork cableFunctions in the same way as in LANsOptical fiber - more commonly chosen (provides higher data rates)Hardware devicesComputers or special purpose devices used for interconnecting networksBridgesRouters Gateways5Copyright 2005 John Wiley & Sons, Inc DeviceOperates atPacketsPhysicalLayerData Link LayerNetworkLayer BridgeData Link LayerFiltered using data link layer addressesSame or Different Same Same RouterNetwork LayerRouted using network layer addressesSame or DifferentSame or Different Same GatewayNetwork LayerRouted using network layer addressesSame or DifferentSame or DifferentSame or Different Backbone Network Devices6Copyright 2005 John Wiley & Sons, IncBridgesData link layer devicesConnect LANs with the same Data Link and same Network layersOperate in a similar way to layer 2 switches (learning bridges)Allows different types of cabling7Copyright 2005 John Wiley & Sons, IncLearning BridgesOperate in a similar way to layer 2 switches: Learn which computers are on each side of the bridgeBy reading the source addresses on incoming frames and recording this information in forwarding tablesData link layer devices Connecting similar type of networksBut they can connect different types of cableNot popular anymore Losing market share to layer 2 switches as the latter become cheaper and more powerful8Copyright 2005 John Wiley & Sons, IncRoutersOperate at the network layer Connect LANS with different data link layer, but the same network layer protocolPerform more processing than bridges or layer 2 switchesAllows different types of cabling9Copyright 2005 John Wiley & Sons, IncRouters (Cont.)Operations Strip off the header and trailer of the incoming L2 frameExamine the destination address of the network layer Build a new frame around the packetChoose the “best” route for a packet (via routing tables)Send it out onto another network segmentCompared to BridgesPerform more processingProcess L3 messages (no changes made)Form new L2 messages for outgoing packetsProcesses only messages specifically addressed to it10Copyright 2005 John Wiley & Sons, IncGatewaysAlso operate at network layer (like routers)Connect LANS with different data link layer and different network layer protocolsSome operate at the application layer as well11Copyright 2005 John Wiley & Sons, IncOther BB Network DevicesMultiprotocol routersCan handle several different protocols (no translation)In and out protocols must be the sameBroutersCombine bridge and router functionsExamine L2 addresses of all messagesCan also process directly addressed (L2) messages Layer-3 switchesSimilar to L2 switches, but switch messages based on L3 addressesCan support many more simultaneous ports than routers12Copyright 2005 John Wiley & Sons, IncBackbone Network ArchitecturesIdentifies the way backbone interconnects LANsDefines how it manages packets moving through BBFundamental architecturesBridged BackbonesRouted BackbonesCollapsed BackbonesRack-basedChassis-basedVirtual LANsSingle-switch VLANMultiswitch VLAN13Copyright 2005 John Wiley & Sons, IncBackbone Architecture LayersAccess Layer (not part of BB)Closest to the users; Backbone Design LayersDistribution LayerConnects the LANs together (often in one buildingCore Layer (for large campus/enterprise networks)Connects different BNs together (building to building)>>> Figure 8.10 goes here23Copyright 2005 John Wiley & Sons, IncChassis-Based Collapsed BackbonesUse a “chassis” switch instead of a rackA collection of modulesNumber of hubs with different speedsL2 switchesExample of a chassis switch with 710 Mbps capacity5 10Base-T hubs, 2 10Base-T switches (8 ports each)1 100Base-T switch (4 ports), 100Base-T router ( 5 x 10) + (2 x 10 x 8) + (4 x 100) + 100 = 710 MbpsFlexibleEnables users to plug modules directly into the switchSimple to add new modules24Copyright 2005 John Wiley & Sons, IncVirtual LANs (VLANs)A new type of LAN-BN architectureMade possible by high-speed intelligent switchesComputers assigned to LAN segments by softwareOften faster and provide more flexible network managementMuch easier to assign computers to different segmentsMore complex and so far usually used for larger networksBasic VLAN designs: Single switch VLANs Multi-switch VLANs25Copyright 2005 John Wiley & Sons, IncSingle Switch VLAN Collapsed BackboneSwitchacting as a large physical switchComputers assigned to different LANs by software26Copyright 2005 John Wiley & Sons, IncTypes of Single Switch VLANsPort-based VLANs (Layer 1 VLANs)Use physical layer port numbers on the front of the VLAN switch to assign computers to VLAN segmentsUse a special software to tell the switch about the computer - port number mappingMAC-based VLANs (Layer 2 VLANs)Use MAC addresses to form VLANsUse a special software to tell the switch about the computer - MAC address mappingSimpler to manageEven if a computer is moved and connected to another port, its MAC address determines which LAN it is on27Copyright 2005 John Wiley & Sons, IncTypes of Single Switch VLANsIP-based VLANs (Layer 3 VLANs, protocol based VLANs)Use IP addresses of the computers to form VLANsSimilar to MAC based approach (use of IP instead of MAC address)Application-based VLANs (Layer 4 VLANs, policy-based VLANs)Use a combination of the type of application (Indicated by the port number in TCP packet) and The IP address to form VLANsComplex process to make assignmentsAllow precise allocation of network capacity28Copyright 2005 John Wiley & Sons, IncMulti-switch VLAN-Collapsed BackboneSwitchSwitchSwitchSwitch29Copyright 2005 John Wiley & Sons, IncMulti-switch VLAN OperationsInter-switch protocolsMust be able to identify the VLAN to which the packet belongsUse IEEE 802.1q (an emerging standard)When a packet needs to go from one switch to another16-byte VLAN tag inserted into the 802.3 packet by the sending switchWhen the IEEE 802.1q packet reaches its destination switchIts header (VLAN tag) stripped off and Ethernet packet inside is sent to its destination computer30Copyright 2005 John Wiley & Sons, IncVLAN Operating CharacteristicsAdvantages of VLANsFaster performancePrecise management of traffic flowAbility to allocate resources to different type of applicationsTraffic prioritization (via 802.1q VLAN tag)Include in the tag: a priority code based on 802.1pCan have QoS capability at MAC levelSimilar to RSVP and QoS capabilities at network and transport layersDrawbacksCostManagement complexity31Copyright 2005 John Wiley & Sons, IncBackbone TechnologiesGigabit EthernetFiber Distributed Data Interface (FDDI)Asynchronous Transfer Mode (ATM)32Copyright 2005 John Wiley & Sons, IncFDDIA set of standards designed in 80’s for MANs (ANSI X3T9.5)Also used as BB and LAN technologiesLimited futureGigabit Ethernet’s strong presenceA ring network operating at 100 Mbps over fiber cablesAssumes a mix of 1,000 stations and 200 Km pathWith repeaters at every 2 KmUses 2 counter rotating rings: primary and secondaryData on the primary; secondary used as backup33Copyright 2005 John Wiley & Sons, IncFDDI Topology>>>> Figure 8.15Two types of FDDI computerssecondary ring flows in opposite direction 34Copyright 2005 John Wiley & Sons, IncManaging a Broken Ring in FDDI>>>> Figure 8.16If a ring is broken, the ring can still operate in a limited fashion 35Copyright 2005 John Wiley & Sons, IncFDDI Media Access ControlUses a controlled access token passing schemeSending computerWait for the token, when receive itAttach the packet to the token and transmit themReceiving computerSee if there is a packet attached to the tokenIf there is  process the packetIf it needs to transmit a packet  follow the steps aboveIf no packet to send  simply transmit the token to the next computerVery reliable and provide adequate response time until it almost reaches saturation at 100 Mbps36Copyright 2005 John Wiley & Sons, IncATMOriginally designed for use in WANOften used now in BNs Standardized; simple to connect BNs and WANsAlso called cell relayIncludes Layer 3, Layer 2 and Layer 1 technologies in the specificationsCompatible with TCP/IP and Ethernet as if ATM was Layer 2 technologyA connection oriented technologyATM switchesProvide point-to-point full duplex circuits at 155 Mbps (622 Mbps for switch-to-switch)37Copyright 2005 John Wiley & Sons, IncATM vs. EthernetPacket format:Uses fixed-length packets (cells) of 53 bytes: 5-byte header, 48 byte dataDesigned to make switching faster (in hardware)Error CheckingError checking done for header only (not on data)If error detected, cell is discardedAddressingUses a virtual channel(VC) between sender and receiverAll cells use VC Identifier as addressesQoS (prioritized transmissions)Each VC assigned a specific class of service with a priority38Copyright 2005 John Wiley & Sons, IncVirtual Channels in ATMIdentified by a two-part numberPath numberCircuit number within that pathA physical port on a switch may have many pathsA path may have many circuitsA switch may have thousands of VCsA VC table is used to map the connections which can be established either:Permanently: Permanent Virtual Circuit (PVC)Temporarily: Switched Virtual Circuit (SVC)Deleted when the connection is not needed39Copyright 2005 John Wiley & Sons, IncAddressing and Forwarding in ATM>>>Figure 8.17 goes hereWhen a cell arrives, switch checks the cell’s VC identifier at the table and determines where to send it .40Copyright 2005 John Wiley & Sons, IncApproaches of Using ATM in BackboneLAN Emulation (LANE)Breaking LAN frame into 48-byte long blocks and transmit them in an ATM cellCalled encapsulation and done by edge switchesReassembling done at the destination edge switch and LAN frame is sent to the LANRequires translating of MAC addresses to VC Identifiers (assuming VCs are setup already)Performance suffers due to encapsulation and connection managementMultiprotocol over ATM (MPOA)- LANE extensionUses IP addresses in addition to MAC addressesIf same subnet, use MAC address; otherwise use IPATM backbone operating like a network of brouters41Copyright 2005 John Wiley & Sons, IncBest Practice Backbone DesignArchitecturesPerformance and cost  Collapsed backboneVLANs closer; but not mature enoughEfficiency of data ratesData Link Protocol EfficiencyFDDI with 99%: Overhead 29 bytes; up to 4500 byte dataATM with about 87%: Overhead: 5 bytes over 53 byte cellMAC Efficiency42Copyright 2005 John Wiley & Sons, IncFDDI MAC EfficiencyUses token passing controlled accessImposes more fixed-cost delays initially in low trafficIncreases response times only slowly up to 90-95% nominal capacityTotal effective data rate = 89 Mbps99% efficiency x 90% capacity x 100 Mbps>>>> Fig 8.19 goes here43Copyright 2005 John Wiley & Sons, IncATM MAC EfficiencyUses full duplex transmissionEfficiency ~ 100% of capacityEffective data rate = 135 Mbps each direction simultaneously87% efficiency x 100% capacity x 155 MbpsTotal for both directions: 270 MbpsAn ATM network with 622 Mbps circuitsProvides 540 Mbps capacity each direction 1080 Mbps total44Copyright 2005 John Wiley & Sons, IncConversion between ProtocolsBoth requires conversion from/to Ethernet frames FDDI uses translationRemove Ethernet frame; replace it with FDDI frameDecreases efficiency 10-20%Actual total effective rate of FDDI  70 MbpsATM uses encapsulationSegment and surround Ethernet frames with ATM cell headers  Generally fasterMAC Addresses must be translated to VC Identifiers and VC management  30-40% decreased efficiencyActual total effective rate of ATM  80 Mbps each direction (160 Mbps total)45Copyright 2005 John Wiley & Sons, IncEffective Data Rates of BB Technologies>>>Fig 8-20 goes here46Copyright 2005 John Wiley & Sons, IncRecommendations for BB DesignBest architectureCollapsed backbone or VLANBest technologyGigabit EthernetIdeal designA mixture of layer-2 and layer-3 Ethernet switchesAccess Layer10/100Base-T Later 2 switches with cat5e or cat6Distribution Layer100base-T or 1000BaseT/F Layer 3 switchesCore LayerLayer 3 switches running 10GbE or 40GBe47Copyright 2005 John Wiley & Sons, IncBest Practice BB Design>>>>>Fig 8-21 goes here48Copyright 2005 John Wiley & Sons, IncImproving Backbone PerformanceImprove computer and device performanceUpgrade them to faster devicesUse faster routing protocolsStatic routing is faster for small networksUse gigabit Ethernet as BB (eliminate translations)Increase memory in devicesImprove circuit capacityUpgrade to a faster circuit; Add additional circuitsReplace shared circuit BB with a switched BBReduce network demandRestrict applications that use a lot of network capacityReduce broadcast messages (placing filters at switches)49Copyright 2005 John Wiley & Sons, IncImplications for ManagementIncreased traffic at backbone due to faster technologiesMay requires that BN be replaced Design BN to be easily upgradeableFDDI and ATM becoming as legacy technologiesVendors stopping the production of these Begin to invest more funds to replace theseEthernet moving into Backbone extensivelyOne standard technology used for both LANs and BN Cheaper equipment; Easier management50Copyright 2005 John Wiley & Sons, IncCopyright 2005 John Wiley & Sons, Inc. 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