Routing Algorithms-old

Routing Algorithms-old - February 13, 2012 Veton Kpuska 1...

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Unformatted text preview: February 13, 2012 Veton Kpuska 1 Computer Networks 2 ROUTING ALGORITHMS February 13, 2012 Veton Kpuska 2 Routing Algorithms Main function of Network Layer: Routing of packets form the source machine to the destination machine. Routing Algorithm: Network Layer Software responsible for deciding which output line an incoming packed should be transmitted on. Datagrams: require computation of decision making tables for each packed Virtual Circuit: routing decision are made only when a new virtual circuit is being set up. Session Routing: data packets follow the same routing for the entire session. Routing vs. Forwarding: Routing: Filling and Updating routing tables Forwarding: making the decision which routes to use based on routing tables. Adaptive vs. Non-Adaptive Algorithms. Non-Adaptive Algorithms: Routing decision is based on pre-computed measurements or estimates and do not update the table based on current traffic and topology Adaptive Algorithms: Change their routing decisions to reflect changes in the topology and traffic. February 13, 2012 Veton Kpuska 3 Optimality Principle If router J is on the optimal path from router I to router K, then the optimal path form J to K also falls along the same (optimal path) route. February 13, 2012 Veton Kpuska 4 Shortest Path Routing Optimization criterion: Distance, Bandwidth, Average Traffic Communication cost, Mean Queue Length, Measured Delay, Algorithms: Dijkstra Flooding Selective Flooding February 13, 2012 Veton Kpuska 5 Distance Vector Routing Static Routing Algorithms Do not take into account actual network load. Dynamic Routing Algorithms Taking into account actual network load Distance Vector Routing: Each router maintain a table with the best known distance to each destination and which line to use to get there. Tables updated by exchanging information with the neighbors. Link State Routing February 13, 2012 Veton Kpuska 6 Countto-Infinity Problem Slow Convergence to the correct answer. Good news Propagate fast Bad news Propagate slowly: The core of the problem is that when X tells Y that I has a path somewhere, Y has no way of knowing whether it itself is on the path. February 13, 2012 Veton Kpuska 7 Link State Routing Distance Vector Routing was used in the ARPANET until 1979 when it was replaced by link state routing....
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Routing Algorithms-old - February 13, 2012 Veton Kpuska 1...

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