TOC: Switching & ForwardingWhy?Switching TechniquesSwitch CharacteristicsSwitch ExamplesSwitch ArchitecturesSummaryTOC – SwitchingDirect vs. Switched Networks:Direct Network Limitations:Distance (coordination delay; propagation limitation)Number of hosts (collisions; shared bandwidth; address tables)Single link technology (cannot mix optical, wireless, …)Internetworking: Externality gain at low costWhy?Single linkn linksSwitches TOC – Switching – Why?Circuit-Switching (e.g., Telephone net.)Packet-SwitchingDatagram (e.g., IP, Ethernet)Virtual Circuits (e.g., MPLS, ATM)Source Routing ComparisonTechniquesTOC – Switching – TechniquesMechanism:Circuit-Switching ! "# $%& & "# # '% Features:TOC – Switching – Techniques – CircuitMechanism:Packet-Switching! &%$# # " # %&"Features:TOC – Switching – Techniques – PacketPS - DatagramGeneral idea: no connection establishment, but each packet contains enough info to specify destinationSwitches contain forwarding tables (but no per-connection “state”)Forwarding tables contain info on which outgoing portto use for each destinationTwo types of addressing:Layer 2 or Layer 3TOC – Switching – Techniques – Packet - DatagramLayer 2 (e.g., Ethernet)Flat address space (no structure)Forwarding table:Exact match of destination L2 address&()*+()*+(&+*)))(&(()*+,&,- TOC – Switching – Techniques – Packet – Datagram – L2Layer 3 (e.g., IP)L3-network (e.g., IP)Topological structure – match prefixEither fixed prefix length or longest match.(.).*TOC – Switching – Techniques – Packet – Datagram – L3 -((/(///(((//((/(((//(//((/(//(((((/(////((//(///(/(//////(//////((/(0 1213323((/(/(/(((//(((((/////((//((//Layer 3 (e.g., IP).(((/((//( +&1(2* 14$ +&13 13 4. TOC – Switching – Techniques – Packet – Datagram – L3 -((/(///(((//((/(((//(//((/(//(((((/(////((//(///(/(//////(//////((/(0 1213323((/(/(/(((//(((((/////((/((//(((//((//Layer 3 (e.g., IP).)((//(//( 5&1(26 4$ TOC – Switching – Techniques – Packet – Datagram – L3 ((//(//(-((/(///(((//((/(((//(//((/(//(((((/(////((//(///(/(//////(//////((/(0 1213323((/(/(/(((//(((((/////((//((//Layer 3 (e.g., IP).*/((//(/( /&13 23/&2/) 4$ TOC – Switching – Techniques – Packet – Datagram – L3 -((/(///(((//((/(((//(//((/(//(((((/(////((//(///(/(//////(//////((/(0 1213323((/(/(/(((//(((((//////((//(/(((//((//PS – Virtual CircuitConnection setup establishes a path through switchesA virtual circuit ID (VCI) identifies pathUses packet switching, with packets containing VCIVCIs are often indices into per-switch connection tables; change at each hop()*+()*+7(7(7(7(7)7(7)7*7)8707((+(()+*)(+)9TOC – Switching – Techniques – Packet – VCSource Routing1234123412341234123412344source3 44 3 44 3 4.: " TOC – Switching – Techniques – Source RoutingComparisonlowlowhighRobustness*yesflexiblenoneResource reservationslowflexiblehighBandwidth utilizationnonelowhighForwarding costCircuit switchingVirtual circuit switchingDatagram; 7 ' 9TOC – Switching – Techniques – ComparisonCharacteristicsPortsFast Ethernet, OC-3, ATM, …ProtocolsST, Link Agg., VLAN, OSPF, RIP, BGP, VPN, Load Balancing, WRED, WFQPerformanceThroughput, Reliability, Power, …TOC – Switching – CharacteristicsExamples Juniper M160 Cisco “GSR” Cisco “7600” Cisco “catalyst
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