of the routers u All routers avoid the busy links u Routers may send packets on

Of the routers u all routers avoid the busy links u

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of the routers u All routers avoid the busy links u Routers may send packets on longer paths 30 CSE 222A – Lecture 12: WAN Routing Alternatives
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Over - Reacting to Congestion Routers make decisions based on old information u Propagation delay in flooding link metrics u Thresholds applied to limit number of updates Old information leads to bad decisions u All routers avoid the congested links u … leading to congestion on other links u … and the whole things repeats I-5 US-101 UCSD ± SigAlert on the 5 ² on radio triggers back-up in Del Mar 31 Swami’s CSE 222A – Lecture 12: WAN Routing Alternatives
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Newer ARPAnet Metric (1987) Prevent over-reacting u Shed traffic from a congested link gradually u Starting with alternate paths that are just slightly longer u Through weighted average in computing the metric, and limits on the change from one period to the next Limit path length u Bound the value of the link metric u “This link is busy enough to go two extra hops” New algorithm u New way of computing the link weights u No change to link-state routing or shortest-path algorithm 32 CSE 222A – Lecture 12: WAN Routing Alternatives
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Today: ± Static ² Link Weights Routers flood information to learn topology u Determine “next hop” to reach other routers… u Compute shortest paths based on link weights Link weights configured by network operator 3 2 2 1 1 3 1 4 5 3 33 CSE 222A – Lecture 12: WAN Routing Alternatives
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Setting the Link Weights How to set the weights u Inversely proportional to link capacity? u Proportional to propagation delay? u Network-wide optimization based on traffic? 3 2 2 1 3 1 4 5 3 3 34 CSE 222A – Lecture 12: WAN Routing Alternatives
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Measure, Model, and Control Topology/ Configuration Offered traffic Changes to the network Operational network Network-wide ± what if ² model measure control 35 CSE 222A – Lecture 12: WAN Routing Alternatives
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For Next Class… Read the Entact paper Keep moving on term projects! 36 CSE 222A – Lecture 12: WAN Routing Alternatives
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  • Fall '08
  • Vahdat,A
  • routing protocol

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