Routing table updates are periodically
transmitted through the network to keep the nodes updated with the same
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Chapter 15 Information Forwarding and Tra?±c Engineering
information. The Link State Routing (LSR) is another example of proactive
protocol. Every node floods the network with the cost of all the links to which
it is connected. Upon receiving the flooded information, every node calculates
the shortest distance to every other node.
A general advantage of proactive protocols is that they can give QoS guarantees
related to latency, connection setup, and other real-time requirements.
The routing tables are updated frequently and therefore, as long as the topology
does not change very fast, they reflect the current topology with a certain
confidence. On the other hand, proactive protocols have a big disadvantage
which is related to excessive signaling overhead in lightly loaded networks.
In a light load scenario, the frequent updates on the routing tables still take
place, regardless of the actual need for communication, resulting in critical
energy being wasted.
2.2 Reactive (On-demand) Routing
One way of dealing with routing in the presence of a fast changing topology of
an ad hoc network is by using a reactive protocol or on-demand routing. Unlike
proactive routing, on-demand routing waits for a data packet before the node
attempts to find the next hop. This allows for the path to be calculated step
by step.
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