ECE544: Communication Networks-II, Spring 2010Today’s LectureEthernet HubBridges/LAN switchesEthernet Hubs vs. Ethernet SwitchesA Switched Enterprise NetworkNeed for RoutingTransparent BridgesSlide 9(1) Frame Forwarding(2) Address Learning (Learning Bridges)ExampleDanger of LoopsSpanning Trees / Transparent BridgesATM OverviewATM Basic ConceptsNegotiated Service ConnectionThe ATM CellATM VisionATM System ArchitectureATM Adaptation LayerATM LayerPhysical LayerSlide 24Private UNI PHYPublic UNI PHYATM PHY: Two Sublayers155 Mbps, SONET STS-3c/SDH STM-1HEC Cell Delineation (For SONET, etc...)1.5 Mbps, DS125.6 Mbps UTP-3ATM UNI CellWhy 53 Bytes?Packetization Delay Advantage of Small CellsQueuing Advantage of Small CellsVirtual ConnectionsVirtual Paths and Virtual ChannelsSlide 38Cell Loss PriorityGeneric Flow ControlHeader Error CheckPermanent Virtual CircuitsSwitched Virtual CircuitsPoint-to-Point ConnectionPoint-to-Multipoint ConnectionWhy SVCs?Call Control SignallingSignalling 4.0Signalling Protocol StackSetting Up a Call - 1Setting Up a Call - 2Setting Up a Call - 3Setting Up a Call - 4Setting Up a Call - 5ATM AddressingAddress to EndstationATM End System AddressPrivate Address FormatsAddress RegistrationSubaddress UseMessages and Information ElementsAAL1: Adaptive Clock MethodAAL2AAL3/4AAL 5Quality-of-ServiceATM Service CategoriesQuality of Service ParametersGeneric Cell Rate AlgorithmPayload Type IdentifierABR FeedbackExample Source Cell Rate ProfileBandwidth NegotiationOther ATM InterfacesNNIB-ICIATM Network ManagementToday’s HomeworkECE544: Communication Networks-II, Spring 2010D. RaychaudhuriLecture 3Includes tutorial materials from the ATM Forum & U VAToday’s Lecture•Switched Networks–Switched Ethernet•Concepts•Learning bridge, spanning tree–ATM networks•Overview•Signaling•PNNI Routing (basics)Ethernet Hub•Used to connect hosts to Ethernet LAN and to connect multiple Ethernet LANs•Collisions are propagatedBridges/LAN switches •We will use the terms bridge and LAN switch (or Ethernet switch in the context of Ethernet) interchangeably. Interconnect multiple LAN, possibly with different type•Bridges operate at the Data Link Layer (Layer 2)Ethernet 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•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 SwitchInternetA Switched Enterprise NetworkRouterSwitchNeed for Routing•What do bridges do if some LANs are reachable only in multiple hops ? •What do bridges do if the path between two LANs is not unique ? LAN 2Bridge 2LAN 5LAN 3LAN 1LAN 4Bridge 5Bridge 4Bridge 3dBridge 1Transparent Bridges•Three principal approaches can be found:–Fixed Routing–Source Routing–Spanning Tree Routing (IEEE 802.1d)•We only discuss the last one in detail.•Bridges that execute the spanning tree algorithm are called transparent bridgesTransparent Bridges Three parts to transparent bridges:(1) Forwarding of Frames(2) Learning of Addresses(3) Spanning Tree Algorithm(1) Frame Forwarding•Each bridge maintains a forwarding database with entries< MAC address, port, age> MAC address: host name or group addressport: port number of bridgeage: aging time of entrywith interpretation: •a machine with MAC address lies in direction of the port number from the bridge. The entry is age time units old.•Routing tables entries are set automatically with a simple heuristic: The source field of a frame that arrives on a port tells which hosts are reachable from this port.(2) Address Learning (Learning Bridges)Port 1Port 2Port 3Port 4Port 5Port 6Src=x, Dest=ySrc=x, Dest=yx is at Port 1y is at Port 5ExampleBridge 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 FSpanning Trees / Transparent Bridges•A solution is to prevent loops in the topology •IEEE 802.1d has an algorithm that organizes the bridges as spanning tree in a dynamic environment–Note: Trees don’t have loops•Bridges that run 802.1d are called transparent bridges•Bridges exchange messages to configure the bridge (Configuration Bridge Protocol Data Unit, Configuration BPDUs) to build the tree.LAN 2Bridge 2LAN 5LAN 3LAN 1LAN 4Bridge 5Bridge 4Bridge 3dBridge 1•Introduction•Physical Layers•ATM Layer•ATM Adaptation Layer•Interfaces•ManagementATM OverviewATM OverviewATM Basic ConceptsATM Basic Concepts•Negotiated Service Connection–End-to-end connections, called virtual circuits–Traffic contract•Switched Based–Dedicated capacity•Cell Based–Small, fixed lengthAANegotiated Service ConnectionNegotiated Service ConnectionParametersTraffic CharacteristicsPeak Cell RateSustainableCell RateQuality of ServiceDelayCell LossTraffic ContractVirtual Connection 1-QOS AVirtual Connection 1-QOS BVirtual Connection 1-QOS bThe ATM CellThe ATM Cell•Small Size–5 Byte Header–48 Byte Payload•Fixed Size•Header contains virtual circuit information•Payload can be voice, video or other data typesHeaderHeader5 Bytes48 Bytes48 BytesPayloadPayloadAAATM VisionATM Vision•ATM network moves cells (fixed length packets) with low delay and low delay variation at high speeds•Devices at ends translate (e.g., segment and reassemble) between cells and original trafficThe Ultimate Integrated Services The Ultimate Integrated Services NetworkNetworkThe Ultimate Integrated Services The Ultimate Integrated Services NetworkNetworkDataData VoiceVideoVideoVoiceVoiceDataDataDataDataVideoVideoVideoVideoATMATMNetworkNetworkATM System ArchitectureATM System ArchitectureDataDataCellCellVideoVideoCellCellVoiceVoiceCellCellAAATM Adaptation LayerATM Adaptation Layer•Provides Mapping Of Applications To ATM