Gugrajah_Yuvaan_ Ramesh_2003.pdf
Gugrajah_Yuvaan_ Ramesh_2003.pdf
Gugrajah_Yuvaan_ Ramesh_2003.pdf
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Routing Protocols for Ad Hoc Networks<br />
2.2. Unicast Routing Protocols<br />
Chapter 2<br />
Unicast protocols for ad hoc networks are derived from the two fundamental types of<br />
routing strategies: distance vector routing and link-state routing. Link state<br />
algorithms flood routing information to all nodes in the network. Each router,<br />
however, only sends the portion of its routing table that describes the state of it's<br />
own links. This information is then used to construct an overview of the entire<br />
network topology and calculate routes to each node. Distance vector algorithms are<br />
based on every router sending its entire routing table to its neighbours. Nodes<br />
compute the shortest path and next hop towards a destination. Each node then<br />
compares the routes its neighbours has to its own routes, and updates its routing table<br />
if a more efficient route is found.<br />
The unicast protocols are divided into proactive or table-drive routing protocols and<br />
reactive or on-demand routing protocols, determined by the manner in which routing<br />
information is obtained and maintained. Hybrid protocols and protocols with special<br />
adaptations have also been developed in order to take advantage of technological<br />
developments as well try to overcome problems unique to ad hoc networking. These<br />
include location aided routing protocols, routing based on network stability, routing<br />
with a virtual backbone and the mUlti-scope routing protocols which include<br />
clustering and hierarchical algorithms. Attempts have also been made to develop<br />
protocols to maintain a certain degree of Quality of Service (QoS) since most of the<br />
routing protocols for ad hoc networks only consider shortest path as the main routing<br />
metric.<br />
2.2.1. Proactive Protocols<br />
The proactive routing protocols are also referred to as table-driven protocols. This is<br />
because they attempt to maintain complete routes from each node to every other node<br />
in the network by maintaining one or more tables to record the route information. In<br />
order to maintain a consistent network view, updates of topological changes are<br />
continuously propagated throughout the network to all nodes. Information is<br />
therefore immediately available when a route is required. The earliest protocols that<br />
2-2
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