- Administrative distance: This basis is valid when different routing protocols are being used. It prefers a lower distance.
- Metric: This basis is valid when only one routing protocol is being used throughout the networks. It prefers a low cost route.
- Prefix-length: This basis does not depends on whether the same protocol is being used or there are many different protocols involved. It prefers the longer subnet masks.
Thursday, July 18, 2013
- The process of path selection in the network along which the data and the network traffic could be send is termed as routing.
- Routing is a common process carried out in a number of networks such as the transportation networks, telephone networks (in circuit switching), electronic data networks (for example, internet).
- The main purpose of routing is to direct the packet forwarding from source to its destination via the intermediate nodes.
- These nodes are nothing but hardware devices namely gateways, bridges, switches, firewalls, routers and so on.
- A general purpose system which does not have any of these specialized routing components can also participate in routing but only to a limited extent.
But how to know where the packets have to be routed?
- This information about the source and the destination address is found in a table called the routing table which is stored in the memory of the routers.
- These tables store the records of routers to a number of destinations over the network.
- Therefore, construction of the routing tables is also an important part of efficient routing process.
- Routing algorithms are used to construct this table and for selecting the optimal path or route to a particular destination.
- A majority of the routing algorithms are based on single path routing techniques while few others use multi-path routing techniques.
- This allows for the use of other alternative paths if one is not available.
- In some, the algorithm may discover equal or overlapping routes.
- In such cases the following 3 basis are considered for deciding up on which route is to be used:
Types of Routing Algorithms
Distance Vector Algorithms:
- In these algorithms, the basic algorithm used is the “Bellman – Ford algorithm”.
- In this approach, a cost number is assigned to all the links that exist between the nodes of a network.
- The information is send by the links from point A to point B through the route that results in the lowest total cost.
- The total cost is the sum of the costs of all the individual links in the route.
- The manner of operation of this algorithm is quite simple.
- It checks from its immediate neighboring nodes that can be reached with the minimum cost and proceeds.
- This algorithm works based up on the graphical map of the network which is supplied as input to it.
- For producing this map, each of the nodes assembles the information regarding to which all nodes it can connect to in the network.
- Then the router can itself determine which path has the lowest cost and proceed accordingly.
- The path is selected using standard path selection algorithms such as the Dijkstra’s algorithm.
- This algorithm results in a tree graph whose root is the current node.
- This tree is then used for the construction of the routing tables.
Optimized link state Routing Algorithm:
- This is the algorithm that has been optimized to be used in the mobile ad-hoc networks.
- This algorithm is often abbreviated to OLSR (optimized link state routing).
- This algorithm is proactive and makes used of topology control messages for discovering and disseminating the information of the link’s state via mobile ad-hoc network.