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ECE 333: Introduction to Communication Networks
Fall 2002
Lecture 23: Routing and Addressing II
Link state routing
Hierarchical routing
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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 shortestpath 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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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
, notice the first closest node must be a neighbor
of
s
and the second closest node must either be a neighbor of
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 Fall '02
 RandallBerry

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