Mobile Intelligence

1.4 REACTIVE ROUTING PROTOCOLS

The main design aim of reactive routing protocols is to reduce the control packet overhead of proactive protocols. These protocols do not maintain routing tables proactively and, as a result, cannot find routes as soon as they are required. There is usually a delay or latency in finding routes. This results in high throughput in packet delivery as the available bandwidth is utilized for delivery of data packets rather than regular flooding of control packets as in the proactive protocols. However, reactive protocols also need flooding or broadcasting of packets, which occurs on-demand. We will discuss below two of the most important reactive protocols, namely, the DSR and the AODV protocol.

1.4.1 The Dynamic Source Routing Protocol

The DSR protocol [9, 10] has two distinct phases, route discovery and route maintenance. The route discovery phase starts when a source node, say S, wants to find a route to a destination node D. Once a route to D has been found, the route maintenance phase starts while S transfers its data packets to D using the discovered route. We discuss these two phases in detail below.

A source node S starts route discovery by sending a route request (RREQ) packet to its neighbors. A RREQ packet has an identifier that includes a source node, a destination node, and a sequential ID that is an integer. If an intermediate node I receives a RREQ packet and it does not know a route to the destination node D, it takes one of the two actions. ...