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Rutgers University ECE 544 - Network Hardware and Software

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L6: Network Hardware and SoftwareECE 544: Computer Networks IISpring 2011Network Hardware BasicsStandards Availability of interoperable equipment from multiple vendors Prevents a “Tower of Babel” situation Equipment from different vendors will interoperate if it complies with the standard Alliances and certification bodies assure interoperability Wi-Fi for 802.11 WiMax for 802.16  Lowers costs to consumers Both through competition and economies of scale Promotes advancement of technology Vendors constantly strive for competitive advantage through improved technology and featuresIEEE 802 StandardsMaintained by IEEE 802 LAN/MAN Standards Committee (LMSC): 802.1 Overview, Architecture, Internetworking and Management 802.2 Logical Link Control 802.3 Ethernet (CSMA/CD PHY and MAC) 802.5 Token Ring PHY and MAC 802.11 Wireless LAN 802.12 Demand Priority Access 802.15 Wireless PAN 802.16 Broadband Wireless Access 802.17 Resilient Packet Ring 802.18 Radio Regulatory 802.19 Coexistence 802.20 Mobile Broadband Wireless Access 802.21 Media Independent Handoff 802.22 Wireless Regional Area NetworkIEEE 802 Naming Conventions Standalone documents either get no letter (IEEE 802.3) or gets a capital letter (IEEE 802.1D) Document that supplements a standalone document gets a lower-case letter (IEEE 802.11b) Letters are assigned in sequential order (a,B,C,d,e …) and uniquely identify both the Working Group Task Force and the actual document Approved standards have IEEE in front while drafts have P only designation followed by the draft number (P802.1p/D9)802.1 802.1B Management 802.1D MAC Bridges 802.1E System Load Protocol 802.1F Common Definitions for Management 802.1G Remote MAC Bridging 802.1H Bridging of Ethernet 802.1Q Virtual Bridged LANsTerminologyPHY LayerHeaderEthernetHeaderIPHeaderTCPHeaderDataEthernetTrailerPHY LayerTrailerTCP SegmentEthernet FrameIP PacketFast Ethernet Symbol StreamSource: Seifert “The switch Book”PDU Interconn. DeviceApplicationGatewayPresentationSessionTransport Segment or MessageFirewall Network PacketRouter Data Link FrameBridgePhysical Symbol StreamRepeaterRouter Hardware History Mid 1980s (early days): Shared LANs interconnected by bridges Two port software based routers Late 1980s – early 1990s (rapid expansion for router market) Slower than bridges but have much more functions “Route when you can, bridge when you must” Early – mid 1990s (routers as necessary evils) Hardware based bridges (switches) with wire-speed performance “Switch when you can, route when you must” Late 1990s Hardware based routers become practical Wire-speed routing Perception that all traffic can be switchedDevices Repeaters/Hubs Bridges (Layer 2 Switches?) Routers (Layer 3 Switches?) Core Edge Firewalls, Network Address Translators (Layer 4 Switches?) Gateways, Load Balancers (Layer 7 Switches?)Basic Building BlocksSwitchingForwardingTableRoutingTableRouting ProtocolsManagement& CLISoftwareHardwareExceptionProcessingControl PlaneData Plane(per-packet processing)Generic Datapath ArchitectureLookupIP AddressUpdateHeaderHeader ProcessingData Hdr Data HdrForwardingTableIP Address Next HopQueuePacketBufferMemorySwitch/Router HardwareMediaInterfaceLink ProtocolControllerHeaderProcessingPort 1 (Line Card)Port N (Line Card)…Port 2Switch FabricProcessor{s}Requirements Distributed Data Plane Packet Processing: Examine L2-L7 protocol information (Determine QoS, VPN ID, policy, etc.) Packet Forwarding: Make appropriate routing, switching, and queuing decisions Performance: At least sum of external BW Distributed Control Plane Up to 106 entries in various tables (forwarding addresses, routing information etc.) Performance: on the order of 100 MIPSSwitch Fabric Connects inputs and outputs Fabric types: Shared Bus – shared backplane with or without DMA (first and second generation routers) – arbitration problem Shared Memory – single common memory is shared between multiple input outputs (typically used in low-cost devices) – memory bandwidth problem Shared Interconnect (Crossbar) – switching fabric provides parallel paths. Scheduler is centralized; routing tables are kept in the line cards (third generation routers) – multicast problemQueuingOutput queuePros: Simple algorithms Single congestion pointCons: N inputs may send to the same output; requires N times speedupInput queuePros: Simple algorithms Single congestion pointCons: Must implement flow control Low utilization due to HoL BlockingModern routersCombine input buffering with virtual output queues (separate input queue per output) and use output buffering Solves blocking problem Resolves contention and simplifies scheduling Can achieve utilization of 1 Scales to > 1 TbpsCrossbar switch for distributed forwardingIncreases complexity (as well as introduces multiple congestion points)Table SRAMFwd/Class TCAMsRTT Buffer Mem (1GB)+ pointer SRAMDistributed Memory Router Line CardInputQueuingReceiveFwdEngineControlCPU MemControlLinecardControlCPUFabricRe-Assem.TransmitFwdEngineOutputQueuingL2 BufferingOpticsToFabricFromFabricFramerRTT Buffer Mem (1GB)+ pointer SRAMTable SRAMFwd/Class TCAMs512+MB DRAMFrom CISCOSwitched LAN Modern switches - LAN Segmentation taken to the extreme (microsegmentation): No access contention No collisions (full-duplex) Dedicated bandwidth for each station No distance reduction per segment Best case capacity (non-blocking switch)nportportDataRateCapacity1Store-and-forwardThe frame (packet,message) is received completely before decision is madeCut-troughTable lookup and forwarding decision is made as soon as “Destination” has been receivedCut-Trough vs. Store-and-Forward Absolute latency (not that much affected by the lookup process) Problem with output port availability Cut-trough is generally not possible for multicast or unknown destination (all output ports have to be available simultaneously)Performance Requirements•In general header inspection and packet forwarding require complex look-ups on a per packet basis resulting in up to 500 instructions per packet•At 40Gbps processing requirements are > 100 MPPSRate[Mbps]OverheadPeak packet rate [Kpps]Time per packet [µs]small large10Base-T10.00 38 [Bytes] 19.5 51.20


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