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Rutgers University ECE 544 - Communication Networks II

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ECE544: Communication Networks-II, Spring 2009Today’s LectureIntro to SwitchingEthernet HubBridges/LAN switchesBridges/LAN switches (Cont.)Ethernet Hubs vs. Ethernet SwitchesA Switched Enterprise NetworkForwardingRoutingTransparent BridgesSelf Learning (Learning Bridges)Frame Forwarding/FilteringExampleDanger of LoopsSpanning Trees / Transparent BridgesSpanning Tree Protocol (STP)Spanning Tree Protocol (Cont.)Slide 19STP ExampleBroadcast and MulticastVirtual LANAsynchronous Transfer Mode (ATM) NetworkATM IntroductionATM Basic ConceptsNegotiated Service ConnectionThe ATM CellATM VisionATM System ArchitectureATM Adaptation Layer (AAL)ATM LayerPhysical LayerATM PHY: Two SublayersATM Physical Layer (Cont.)155 Mbps, SONET STS-3c/SDH STM-1Slide 36ATM: network or link layer?ATM InterfacesATM UNI CellATM NNI CellGeneric Flow ControlPayload Type Identifier (PTI)Cell Loss PriorityHeader Error CheckWhy 53 Bytes?Queuing Delay Advantage of Small CellsPacketization Delay Advantage of Small CellsVirtual Circuit SwitchingVirtual Circuit Switching (Cont)Permanent Virtual CircuitsSwitched Virtual CircuitsCall Control SignallingSetting Up a Call - 1Setting Up a Call - 2Setting Up a Call - 3Setting Up a Call - 4Setting Up a Call - 5Bandwidth NegotiationVirtual Paths and Virtual ChannelsATM VCsNNIAddress to End StationATM AddressingATM End System Address (AESA)Address RegistrationPoint-to-Point ConnectionPoint-to-Multipoint ConnectionAAL1: Adaptive Clock MethodAAL2AAL3/4AAL 5Quality-of-ServiceATM Service CategoriesQuality of Service ParametersLeaky Bucket AlgorithmLeaky Bucket Algorithm (Cont)Generic Cell Rate Algorithm (GCRA)Slide 78ATM Network ManagementVirtual ConnectionsSwitch Implementation (1)Switch Implementation (2)Switch Implementation (3)IP over ATMIP-over-ATM (Cont)Ethernet Switching vs. Virtual Circuit SwitchingToday’s HomeworkECE544: Communication Networks-II, Spring 2009H. LiuLecture 3Includes teaching materials from D. Raychaudhuri, J. Kurose, and ATM Forum tutorialsToday’s Lecture•Switched Networks–Switching Concepts–Ethernet Switches•Learning bridge•Spanning tree•Multicast–Asynchronous Transfer Mode (ATM) Network•Overview•Virtual Circuit Switching•Virtual Circuit and Virtual Path•ATM AAL•ATM Quality of Service (QoS) •Leaky Bucket Algorithm•Switch ImplementationIntro to Switching•Build a large network by interconnecting a number of switches•Easily add new hosts•Switching Techniques–Datagram or connectionless (Ethernet)•Unique address•No need to setup connection–Virtual circuit or connection-oriented (ATM)•Set up connection and maintain connection state–Source routing•Source specify the whole or partial route to the destinationEthernet Hub•Hub is just a repeater–Receive signal from one port and broadcast to all other ports•Extends max distance between nodes, but collisions are propagated –Individual segment collision domains become one large collision domain•Cannot interconnect different LAN technologies, e.g. 10BaseT & 100BaseThubhubhubhubBridges/LAN switches •Bridge = LAN switch = Ethernet switch •Link layer device–stores and forwards frames–examines frame header and selectively forwards frame based on MAC dest address–when frame is to be forwarded on segment, uses the corresponding MAC to access segment (e.g. CSMA/CD for Ethernet) hubhubhubSwitchBridges/LAN switches (Cont.) •Interconnect multiple LANs, possibly even support different IEEE 802.x types, e.g. 802.3 and 802.5, 802.11, but NOT 802.x with ATMToken-ringBridgeEthernet Hubs vs. Ethernet Switches•An Ethernet switch is a packet switch for Ethernet frames •Buffering of frames prevents collisions •Each port is isolated and builds its own collision domain –Break subnet into LAN segments•Host can directly connect to switch, no collision, full duplex•An Ethernet Hub does not perform buffering:•Collisions occur if two frames arrive at the same time.HighSpeedBackplaneCSMA/CDCSMA/CDCSMA/CDCSMA/CDCSMA/CDCSMA/CDCSMA/CDCSMA/CDOutputBuffersInputBuffersCSMA/CDCSMA/CDCSMA/CDCSMA/CDCSMA/CDCSMA/CDCSMA/CDCSMA/CDHub SwitchA Switched Enterprise NetworkInternetRouterSwitchForwarding•Which port to forward a frame?–Use forwarding database/table< MAC address, port, Time-to-Live (TTL)>•How to build the forwarding table???–A routing problemForwarding TableDestinationPort Time-to-Live (TTL)A 3 2B 0 4C 3 2D 3 4E 2 5F 1 1G 0 4H 0 5013022213301Host AHost BHost HHost FHost GHost EHost DHost CSwitch 1Switch 2Switch 3Routing•Three principal approaches for routing:–Fixed Routing•Manually setup–Source Routing•Somehow the sender knows the path and includes the routing info in the frame header–Possibly only include partial route•Bridges read the routing info to determine if they should forward the frame–Automatically learning (Transparent Bridges)Transparent Bridges Three parts to transparent bridges:(1) Learning of Addresses(2) Forwarding of Frames(3) Spanning Tree Algorithm•Forwarding tables entries are set automatically with a simple heuristic: The source address field of a frame that arrives on a port tells which host is reachable from this port.–When a frame received, switch “learns” location of sender–records sender/location pair in forwarding table with TTL = MAX_TTL•TTL reset to MAX_TTL every time a frame with the same source addr is received to refresh the existing table entry•Entry removed when TTL counts down to 0 Self Learning (Learning Bridges)Port 1Port 2Port 3Port 4Port 5Port 6Src=x, Dest=ySrc=x, Dest=yx is at Port 1y is at Port 5Frame Forwarding/FilteringWhen switch receives a frame:index forwarding table using MAC dest addressif entry found for destinationthen{ if dest on the same port from which frame arrived then drop the frame (filtering) else forward the frame on port indicated }else floodForward on all but the port on which the frame arrivedExampleBridge 2Port1LAN 1ALAN 2CB DLAN 3E FPort2Bridge 2Port1Port2•Consider the following packets: (Src=A, Dest=F), (Src=C, Dest=A), (Src=E, Dest=C)•What have the bridges learned?•Consider the two LANs that are connected by two bridges.•Assume host n is transmitting a frame F with unknown destination.What is happening?•Bridges A and B flood the frame to LAN 2.•Bridge B sees F on LAN 2 (with unknown destination), and copies the frame back to LAN 1•Bridge A does the same. •The copying continuesDanger of LoopsLAN 2LAN 1Bridge BBridge Ahost nFF FFFF


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