04-07-2013, 02:03 PM
Performance Comparison of Wireless Mobile Ad-Hoc Network Routing Protocols
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Summary
The Efficient routing protocols can provide significant benefits to mobile ad hoc networks, in terms of both performance and reliability. Many routing protocols for such networks have been proposed so far. Amongst the most popular ones are Ad hoc On-demand Distance Vector (AODV), Destination-Sequenced Distance-Vector Routing protocol (DSDV), Dynamic Source Routing Protocol (DSR), and Optimum Link State Routing (OLSR). Despite the popularity of those protocols, research efforts have not focused much in evaluating their performance when applied to variable bit rate (VBR). In this paper we present our observations regarding the performance comparison of the above protocols for VBR in mobile ad hoc networks (MANETs). We perform extensive simulations, using NS-2 simulator. Our studies have shown that reactive protocols perform better than proactive protocols. Further DSR has performed well for the performance parameters namely delivery ratio and routing overload while AODV performed better in terms of average delay.
Introduction
Mobile Ad Hoc Networks are wireless networks which do not require any infrastructure support for transferring data packet between two nodes [1]. In these networks nodes also work as a router that is they also route packet for other nodes. Nodes are free to move, independent of each other, topology of such networks keep on changing dynamically which makes routing much difficult. Therefore routing is one of the most concerns areas in these networks. Normal routing protocol which works well in fixed networks does not show same performance in Mobile Ad Hoc Networks. In these networks routing protocols should be more dynamic so that they quickly respond to topological changes [2].
DSR Protocol
The DSR is a simple and efficient routing protocol designed specifically for use in multi-hop wireless ad hoc networks of mobile nodes [7][8][9]. DSR allows the network to be completely self-organizing and self-configuring, without the need for any existing network infrastructure or administration. The protocol is composed of the two main mechanisms of “Route Discovery” and “Route Maintenance’, which work together to allow nodes to discover and maintain routes to arbitrary destinations in the ad hoc network All aspects of the protocol operate entirely on DSR protocol include easily guaranteed loop-free routing, operation in networks containing unidirectional links, use of only “soft state” in routing, and very rapid recovery when routes in the network change. In DSR, Route Discovery and Route Maintenance each operate entirely “on demand”. In particular, unlike other protocols, DSR requires no periodic packets of any kind at any layer within the network. For example, DSR does not use any periodic routing advertisement, link status sensing, or neighbor detection packets, and does not rely on these functions from any underlying protocols in the network. This entirely on demand behavior and lack of periodic activity allows the number of overhead packets caused by DSR to scale all the way down to zero, when all nodes are approximately stationary with respect to each other and all routes needed for current communication have already been discovered.
AODV Protocol
The AODV algorithm is an improvement of DSDV protocol described above. It reduces number of broadcast by creating routes on demand basis, as against DSDV that maintains mutes to each known destination [4] [5] [6] [20]. When source requires sending data to a destination and if route to that destination is not known then it initiates route discovery. AODV allows nodes to respond to link breakages and changes in network topology in a timely manner. Routes, which are not in use for long time, are deleted from the table. Also AODV uses Destination Sequence Numbers to avoid loop formation and Count to Infinity Problem.
Simulation Result And Observations
In this section we present our simulation efforts to evaluate and observations that compare the performance of the protocols that we described previously in Section 2.
Effect of Varying Pause Time
Pause time can be defined as time for which nodes waits on a destination before moving to other destination. We used this as a parameter as it is measure of mobility of nodes. Low pause time means node will wait for less time thus giving rise to high mobility scenario. Figure 1 (1a, 1b, 1c) shows various performance parameters v/s pause time when other parameters were constant. From figure we can observe that normalized overload for DSDV and OLSR is almost constant. This is because of their proactive nature due to which they offer constant routing overhead in all cases. While for reactive protocols considered here as we increased pause time routing overload has decreased .This is because as routing pause time increases mobility decreases and thus link breakage become rare which in turn will decrease number of route request from sources and hence decreasing overhead. Also DSR outperformed AODV as it maintains multiple routes to a destination. In case of failure in one route other route will be used rather than initiating route request.
Effect of Varying Burst Time
Burst Time may be another varying parameter. Burst time is the time for which source generates packets in a go. It plays important role in performance. Figure 3(3a, 3b, and 3c) shows various performance parameters versus Burst Time. From figure we can observe that routing overload for all protocols decreased with increase in burst time with DSR performing better than others. For reactive protocols route expiry has become less common thus reducing routing overload while for proactive which give constant overload irrespective of load, increasing burst increased data packet thus reduced normalized overhead. Also from graph it can be seen that
Conclusion
We have presented a detailed performance comparison of important routing protocols for mobile ad hoc wireless networks. AODV and DSR are reactive protocol while DSDV and OLSR are proactive protocols. Both reactive protocols performed well in high mobility scenarios than proactive protocol. High mobility result in highly dynamic topology i.e. frequent route failures and changes. Both proactive protocols fail to respond fast enough to changing topology. Routing overhead in Proactive protocols remain almost constant and OLSR being winner irrespective of mobility while in AODV it increases with increase in mobility.