Routing AlgorithmRoutingRouting Algorithm classificationA Link-State Routing AlgorithmDijsktra’s AlgorithmDijkstra’s algorithm: exampleRouting Lab Project 3Slide 8Slide 9Slide 10Slide 11Routing AlgorithmMarch 3rd, 2006RoutingGraph abstraction for routing algorithms:graph nodes are routersgraph edges are physical linkslink cost: delay, $ cost, or congestion levelGoal: determine “good” path(sequence of routers) thru network from source to dest.Routing protocolAEDCBF2213112535“good” path:typically means minimum cost pathother def’s possibleRouting Algorithm classificationGlobal or decentralized information?Global:all routers have complete topology, link cost info“link state” algorithmsDecentralized: router knows physically-connected neighbors, link costs to neighborsiterative process of computation, exchange of info with neighbors“distance vector” algorithmsStatic or dynamic?Static: routes change slowly over timeDynamic: routes change more quicklyperiodic updatein response to link cost changesA Link-State Routing AlgorithmDijkstra’s algorithmnet topology, link costs known to all nodesaccomplished via “link state broadcast” all nodes have same infocomputes least cost paths from one node (‘source”) to all other nodesgives routing table for that nodeiterative: after k iterations, know least cost path to k dest.’sNotation:c(i,j): link cost from node i to j. cost infinite if not direct neighborsD(v): current value of least cost of path from source to destination Vp(v): previous node along the current least-cost path from source to v, that is neighbor of vN: set of nodes whose least cost path definitively knownDijsktra’s Algorithm1 Initialization: 2 N = {A} 3 for all nodes v 4 if v adjacent to A 5 then D(v) = c(A,v) 6 else D(v) = infinity 7 8 Loop 9 find w not in N such that D(w) is a minimum 10 add w to N 11 update D(v) for all v adjacent to w and not in N: 12 D(v) = min( D(v), D(w) + c(w,v) ) 13 /* new cost to v is either old cost to v or known 14 shortest path cost to w plus cost from w to v */ 15 until all nodes in NDijkstra’s algorithm: exampleStep012345start NAADADEADEBADEBCADEBCFD(B),p(B)2,A2,A2,AD(C),p(C)5,A4,D3,E3,ED(D),p(D)1,AD(E),p(E)infinity2,DD(F),p(F)infinityinfinity4,E4,E4,EAEDCBF2213112535Routing LabProject 3A link-state algorithm in the context of a simple routing simulator Event-driven Simulation main loop repeatedly pulls the earliest event from a queue and passes it to a handler until there are no more events in the queue.make TYPE=GENERIC” will build a single executable “routesim”, which contains no routing algorithm. You will do TYPE=LINKSTATETo run: ./routesim topologyfile eventfile [singlestep]Events in routesim come from the topology file, the event file, and from handlers that are executed in response to events. The topology file generally only contains events that construct the network topology (the graph) arrival_time ADD_NODE node_num latency bandwidtharrival_time DELETE_NODE node_num latency bandwidtharrival_time ADD_LINK src_node_num dest_node_num latency bandwidtharrival_time DELETE_LINK src_node_num dest_node_num latency bandwidthThe event file generally only contains events that modify link characteristics in the graph, or draw the graph, a path and etc. arrival_time CHANGE_NODE node_num latency bandwidtharrival_time CHANGE_LINK src_node_num dest_node_num latency bandwidtharrival_time DRAW_TOPOLOGYarrival_time DRAW_TREE src_node_numNote that although each link event contains both bandwidth and latency numbers, your algorithms will determine shortest paths using only the link
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