TOC: Switching & ForwardingWhy?Switching TechniquesSwitch CharacteristicsSwitch ExamplesSwitch ArchitecturesSummaryTOC – Switching Direct 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 RoutingComparisonTechniquesTOC – Switching – Techniques Mechanism:Circuit-Switching !"#"$$%& ' (!) )#%& & * (#Features:TOC – Switching – Techniques – Circuit Mechanism:Packet-Switching )( '& & #!% & # ( )! #%Features:TOC – Switching – Techniques – Packet PS - 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 port to use for each destinationTwo types of addressing:Layer 2 or Layer 3TOC – Switching – Techniques – Packet - Datagram Layer 2 (e.g., Ethernet)Flat address space (no structure)Forwarding table:Exact match of destination L2 address)+,+,),+)+,-)-.TOC – Switching – Techniques – Packet – Datagram – L2 Layer 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 .///////#///////////////////////////////01213323//////////////Layer 3 (e.g., IP)"#"/// ,)12+ 14'$,)13 13 4$TOC – Switching – Techniques – Packet – Datagram – L3 .///////#///////////////////////////////01213323/////////////////Layer 3 (e.g., IP)"#"//// 5)126 4'$TOC – Switching – Techniques – Packet – Datagram – L3 ////.///////#///////////////////////////////01213323//////////////Layer 3 (e.g., IP)"#"+//// /)13 23/)2/ 4'$TOC – Switching – Techniques – Packet – Datagram – L3 .///////#///////////////////////////////01213323//////////////////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+,+,77777777+78707,,+,9"TOC – Switching – Techniques – Packet – VC Source Routing1234123412341234123412344source3 44 3 44 3 4:!%TOC – Switching – Techniques – Source RoutingComparisonlowlowhighRobustness*yesflexiblenoneResource reservationslowflexiblehighBandwidth
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