Lecture 5 - Introduc9on to Computer Networks Rou9ng...

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10/29/13’ 1’ Computer’Science’&’Engineering’ Introduc±on’to’Computer’Networks’ Rou±ng’Overview’ Improving’on’the’Spanning’Tree’ Spanning’tree’provides’ basic’connec±vity’ e.g.,’some’path’B à C’ Rou±ng’uses’all’links’to’ fnd’“best”’paths’ e.g.,’use’BC,’BE,’and’CE’ 3’ A’ B’ C’ D’ E’ F’ A’ B’ C’ D’ E’ F’ Unused’
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10/29/13’ 2’ Perspec±ve’on’Bandwidth’Alloca±on’ Rou±ng’allocates’network’bandwidth’adap±ng’to’ failures;’other’mechanisms’used’at’other’±mescales’ 4’ Mechanism Timescale / Adaptation Load-sensitive routing Seconds / Traffic hotspots Routing Minutes / Equipment failures Traffic Engineering Hours / Network load Provisioning Months / Network customers 6’ Goals’of’Rou±ng’Algorithms’ What’are’the’proper±es’we’want’of’ any’rou±ng’scheme?’
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10/29/13’ 3’ 7’ Rules’of’Rou±ng’Algorithms’ Decentralized,’distributed’se[ng’ All’nodes’are’alike;’no’controller’ Nodes’only’know’what’they’learn’by’ exchanging’messages’with’neighbors’ Nodes’operate’concurrently’ May’be’node/link/message’failures’ Who²s’there?’ Delivery’Models’ DiFerent’rou±ng’used’for’diFerent’delivery’models’ 8’ Unicast’ (§5.2)’ Mul±cast’ (§5.2.8)’ Anycast’ (§5.2.9)’ Broadcast’ (§5.2.7)’
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10/29/13’ 4’ Computer’Science’&’Engineering’ Introduc±on’to’Computer’Networks’ Shortest’Path’Rou±ng’ (§5.2.1-5.2.2)’ 11’ What’are’“Best”’paths’anyhow?’ Many’possibili±es:’ Latency,’avoid’circuitous’paths’ Bandwidth,’avoid’slow’links’ Money,’avoid’expensive’links’ Hops,’to’reduce’switching’ But’only’consider’topology’ Ignore’workload,’e.g.,’hotspots’ A’ B’ C’ D’ E’ F’ G’ H’
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10/29/13’ 5’ 12’ Shortest’Paths’ We±ll’approximate’“best”’by’a’cost’ func²on’that’captures’the’factors’ OIen’call’lowest’“shortest”’ 1. Assign’each’link’a’cost’(distance)’ 2. DeFne’best’path’between’each’ pair’of’nodes’as’the’path’that’has’ the’lowest’total’cost’(or’is’shortest)’ 3. Pick’randomly’to’break’²es’ 16’ Sink’Trees’ Sink’tree’for’a’des²na²on’is’ the’union’of’all’shortest’paths’ towards’the’des²na²on’ Similarly’source’tree’ A’ B’ C’ D’ E’ ³’ G’ H’ 2’ 1’ 10’ 2’ 2’ 4’ 2’ 4’ 4’ 3’ 3’ 3’
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10/29/13’ 6’ 17’ Sink’Trees’(2)’ Implica±ons:’ Only’need’to’use’des±na±on’ to’follow’shortest’paths’ Each’node’only’need’to’send’ to’the’next’hop’ Forwarding’table’ at’a’node’
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Lecture 5 - Introduc9on to Computer Networks Rou9ng...

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