Routing algorithm

Routing algorithm

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  By K.Sivapriya Msc(IT) Nadar Saraswathi CollegeOf Arts & Science Theni
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  Routing algorithm  Inorder to transfer the packets from source to the destination, the network layer must determine the best route through which packets can be transmitted.  Whether the network layer provides datagram service or virtual circuit service, the main job of the network layer is to provide the best route. The routing protocol provides this job.
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  Cont…  The routingprotocol is a routing algorithm that provides the best path from the source to the destination. The best path is the path that has the "least-cost path" from source to the destination.  Routing is the process of forwarding the packets from source to the destination but the best route to send the packets is determined by the routing algorithm.
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  Classification of aRouting algorithm  The Routing algorithm is divided into two categories:  Adaptive Routing algorithm  Non-adaptive Routing algorithm
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  Adaptive Routing algorithm An adaptive routing algorithm is also known as dynamic routing algorithm.  This algorithm makes the routing decisions based on the topology and network traffic.  The main parameters related to this algorithm are hop count, distance and estimated transit time.
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  Non-Adaptive Routing algorithm Non Adaptive routing algorithm is also known as a static routing algorithm.  When booting up the network, the routing information stores to the routers.  Non Adaptive routing algorithms do not take the routing decision based on the network topology or network traffic.
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  Distance Vector RoutingAlgorithm  A distance-vector routing (DVR) protocol requires that a router inform its neighbors of topology changes periodically. Historically known as the old ARPANET routing algorithm (or known as Bellman-Ford algorithm). ... Distances,based on a chosen metric, are computed using information from the neighbors' distance vectors.
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  Cont…  Distributed: Itis distributed in that each node receives information from one or more of its directly attached neighbors, performs calculation and then distributes the result back to its neighbors.  Iterative: It is iterative in that its process continues until no more information is available to be exchanged between neighbors.  Asynchronous: It does not require that all of its nodes operate in the lock step with each other.
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  working of DistanceVector Routing Algorithm  Knowledge about the whole network: Each router shares its knowledge through the entire network. The Router sends its collected knowledge about the network to its neighbors.  Routing only to neighbors: The router sends its knowledge about the network to only those routers which have direct links. The router sends whatever it has about the network through the ports.
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  Cont… The information isreceived by the router and uses the information to update its own routing table.  Information sharing at regular intervals: Within 30 seconds, the router sends the information to the neighboring routers.
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  Link State Routing In link-state routing, each router shares its knowledge of its neighbourhood with all routers in the network. Link-state protocols implement an algorithm called the shortest path first (SPF, also known as Dijkstra's Algorithm) to determine the path to a remote destination
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  Link State Routingalgorithm  Knowledge about the neighborhood: Instead of sending its routing table, a router sends the information about its neighborhood only. A router broadcast its identities and cost of the directly attached links to other routers.  Flooding: Each router sends the information to every other router on the internetwork except its neighbors. This process is known as Flooding.
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  Cont… Every router thatreceives the packet sends the copies to all its neighbors. Finally, each and every router receives a copy of the same information.  Information sharing: A router sends the information to every other router only when the change occurs in the information.
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  Link State Routinghas two phases  Reliable Flooding  Initial state: Each node knows the cost of its neighbors.  Final state: Each node knows the entire graph.  Route Calculation  Each node uses Dijkstra's algorithm on the graph to calculate the optimal routes to all nodes.
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  Cont…  The Linkstate routing algorithm is also known as Dijkstra's algorithm which is used to find the shortest path from one node to every other node in the network.  The Dijkstra's algorithm is an iterative, and it has the property that after kth iteration of the algorithm, the least cost paths are well known for k destination nodes.