# lec23 - ECE 333 Introduction to Communication Networks Fall...

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1 ECE 333: Introduction to Communication Networks Fall 2002 Lecture 23: Routing and Addressing II Link state routing Hierarchical routing 2 Link state Routing In Lecture 22, we considered distance vector routing. In distance vector routing, each node maintains a list of the distance to each destination and periodically broadcasts this list to its neighbors. Each node uses the Bellman- Ford algorithm to calculate shortest paths. Next we consider another type of shortest-path routing algorithm - Link state routing. In link state routing, each router must: 1. Discover its neighbors and learn their addresses. 2. Measure cost to each neighbor, this is called the “link state”. 3. Broadcast (e.g. flood) a packet containing the link state to all other routers 4. Use the information it receives to compute the shortest path to all other routers. Each node will receive a link state packet from every other node in the network. Thus, each node can reconstruct a graph of the entire network topology and use this to calculate the shortest paths to every node. Each node will individually calculate the shortest paths, based on this common information. To calculate shortest paths, Dijkstra’s Algorithm is used.

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3 Dijkstra’s Algorithm Given a graph for the entire network, Dijkstra's Algorithm can be used to find the shortest paths from a given node to every other node. The basic idea of Dijkstra's algorithm is to first find the closest node, then the second closest node, etc. For a given node, s
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