Purpose of Routing Algorithms
Many telecommunications networks, including the public switched telephone network, mobile phone networks, local area networks and the Internet, consist of separate addressable devices, or nodes, that need to communicate with each other. The purpose of a routing algorithm is to define a set of rules for transferring units of data, known as packets, from one node to another.
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Routing Criteria
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Typically, not all the nodes in a network -- file servers, workstations and peripherals -- are connected directly to each other, so a routing algorithm must choose some criteria on which to base routing decisions. Typical criteria include the number of point-to-point connections forming part of the route between two nodes, known as hops, the time taken for a packet to cross a network connection, known as latency, and the transmission capacity of the network, known as bandwidth.
Objective
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The objective of a routing algorithm is to maintain a network configuration in which each network node advances, or forwards, transmissions from other nodes to the correct destination, so that any two nodes can communicate with each other. The process of determining where to forward packets, and actually forwarding them, is known as routing”. A typical routing algorithm employs a database or look-up table, known as a routing table, on each machine on the network, in which it stores details of each possible destination and how to reach it. If a network has only a small set of local addresses and just one connection to the Internet, the information in the routing table may be consolidated into a default entry.
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Delivery
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All packets must reach their destination -- unless prevented from doing so by other factors, such as the load on the network exceeding its capacity, known as congestion -- so a routing algorithm must find a route between the source and destination. Without such a route, data packets would need to randomly circulate around the entire network in search of their destination.
Best Path
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Not only must a routing algorithm find a route between source and destination, but, often, it must also choose the shortest or fastest route, known as the best path. To maintain network performance, routing calculations need to be as fast and simple as possible. Most telecommunications networks are dynamic -- or, in other words, nodes are added or removed on a regular basis -- so routing algorithms must be flexible enough to recalculate the best route between nodes if the network topology or the load on the network, or both, changes.
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References
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