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Wednesday, August 7, 2013

Difference between adaptive and non - adaptive algorithms?

- Routing is the process of sending information from one point of network to another. 
- The originating point is called the source and the last point is called the destination. 
- Through the way a number of intermediate nodes might or might not be encountered. 
- Routing is sometimes compared with bridging. 
- Both of these accomplish the same purpose for the casual observer. But it is not so. 
- The basic difference between the two is that the routing is done at the layer 3 i.e., the network layer of the OSI model and the bridging takes place at the layer 2 i.e., data link layer of the OSI model. 
- Because of this distinction, the input supplied to the two processes is different and thus the task of path selection occurs in different ways. 
The routing algorithm is included as a part of the network layer software. 
- The primary responsibility of this software is to decide on which line the incoming traffic must be forwarded i.e., what will be the next node. 
- Certain metrics are used by the routing protocols for the evaluation of the path that is most appropriate for the transmission of a packet. 
- These metrics include reliability, path bandwidth, current load, delay and so on. 
- These metrics help in determining the optimal path towards a destination. 
Routing tables are created and maintained by the routing algorithms in order to aid the path determination process.
- The tables will contain what routing information is entirely based up on the routing algorithm that is being used. 
- The routing tables are filled by a variety of information by the routing algorithms. 
- If the internal subnet used is the datagram subnet, then for every datagram that arrives, a new decision has to be taken since the routes keep changing in this case after every transmission.
- On the other hand in virtual circuit subnet, all the decisions are taken with the setting up of the virtual circuit. 
- Once the connection or the links are established, the same path is followed by all the packets. 

The routing algorithms can be classified in to two major categories namely:
  1. Non – adaptive algorithms and
  2. Adaptive algorithms
- Another name for non – adaptive algorithms is the static algorithms. 
- Here the computation regarding the various routes is done in advance and the same routes are followed by all the packets. 
- The adaptive algorithms are better known as the dynamic algorithms. 
- In this type of algorithms, the routes are not computed in advance, rather the route is decided up on the arrival of a particular packet depending up on the traffic and the topology of the network. 

We have three different types of algorithms under the category of non – adaptive algorithms as mentioned below:
  1. Shortest path routing: This algorithm makes use of the Dijkstra’s algorithm for computing the shortest path where nodes and communication links are represented by vertices and edges of the graph respectively.
  2. Flooding: Here, the arriving data packet is transmitted on all the outgoing lines save the one on which it arrived. Its selective flooding variation is commonly used.
  3. Flow based routing: This algorithm takes in to consideration the present flow of the network before deciding on which line the packet must be transmitted.
And following are some of the adaptive algorithms:

  1. Distance vector routing: It requires knowledge about the whole network and is associated with the count  to infinity problem.
  2. Link state routing: It requires knowledge about neighborhood.
  3. Hierarchical routing: It is used for very large networks.
  4. Optimized link state routing: It is used for mobile hosts. 

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