Efficient flooding using relay routing in on-demand Routing protocol for Mobile Adhoc Networks

In this paper an enhancement technique for Dynamic Source Routing protocol (DSR) using relay routing and flooding alternately is proposed. DSR is a popular on demand reactive routing protocol in Mobile Adhoc Networks (MANET) which uses flooding for route discovery and route maintenance when only a node has data to be transmitted. Flooding causes serious redundancy, contention and collision in the network which increases the overhead of transmission in a dynamic network where the nodes have different mobilities. In order to reduce this routing overhead we have used relay routing technique which selects only a small number of nodes in the neighbourhood of the source node for route discovery and route maintenance. Selection of the nodes is done based on the mobility of the neighbourhood nodes at that instant of time. Simulation results on DSR have shown that this technique can reduce redundant flooding to a great extent thus making DSR more efficient.

I. Introduction

Mobile Adhoc Networks (MANETs) have recently been the subject of active research because of their unique advantages. MANETs [3], [11], [12] are self-creating, self-organizing, self administrating and do not require deployment of any kind of fixed infrastructure. They offer special benefits and versatility for wide range of applications in military (e.g., battlefields, sensor networks etc.), commercial (e.g., distributed mobile computing, disaster discovery systems, etc.), and educational environments (e.g., conferences, conventions, etc.), where fixed infrastructure is not easily acquired. With the absence of pre-established infrastructure (e.g., no router, no access point, etc.), two nodes communicate with one another in a peer-to-peer fashion. Two nodes communicate directly if they are within the transmission range of each other. Otherwise, the nodes communicate via a multihop route. To find such a multi-hop route, MANETs commonly employ on demand routing algorithms that use flooding or broadcast messages. Many ad hoc routing protocols [14], [20], [21], multicast schemes [18], or service discovery programs depend on massive flooding. In flooding, a node transmits a message to all of its neighbours. The neighbours in turn relay to their NEIGHBOURS and so on until the message has been propagated to the entire network. In this paper, we will refer to such flooding as blind flooding. As one can easily see, the performance of blind flooding is closely related to the average number of NEIGHBOURS (NEIGHBOUR degree) in the Carrier Sense Multiple Access/Collision Avoidance network. As the NEIGHBOUR degree gets higher, blind flooding suffers from the increase of (1) redundant and superfluous packets, (2)probability of collision, and (3) congestion of wireless medium [1]. Performance of blind flooding is severely impaired especially in large and dense networks [2], [30]. When topology or NEIGHBOURHOOD information is available, only subsets of NEIGHBOURS are required to participate in flooding to guarantee the complete flooding. We call such flooding efficient flooding. The characteristics of MANETs (e.g., node mobility, the limited bandwidth and resource), however, make the periodic collection of topology information difficult and costly (in terms of overhead). For that reason many on-demand ad hoc routing schemes and service discovery protocols simply use blind flooding [14], [18]. In contrast with on-demand routing methods, the proactive ad hoc routing schemes by virtue of periodic route table exchange, can gather topological information without much extra overhead. Thus, the leading MANET proactive ad hoc routing schemes use route aggregation methods to forward routing packets through only a subset of the neighbours [20], [21].