We empirically study the effect of mobility on the performance of protocols designed for wireless adhoc networks. An important ohjective is to study the interaction of the Routing and MAC layer protocols under different mobility parameters. We use three basic mobility models: grid mobility model, random waypoint model, and exponential correlated random model. The performance of protocols was measured in terms of (i) latency, (ii) throughput, (iii) number of packels received, (iv) long term fairness and (v) number of control packets at the MAC layer level. Three different commonly studied routing protocols were used: AODV, DSR and LAR1. Similarly three well known MAC protocols were used: MACA, 802.1 1 and CSMA. The inair1 conclusion of our study include the following: 1. 'I'he performance of the: network varies widely with varying mobility models, packet injection rates and speeds; and can ba in fact characterized as fair to poor depending on the specific situation. Nevertheless, in general, it appears that the combination of AODV and 802.1 I is far better than other combination of routing and MAC protocols. 2. MAC layer protocols interact with routing layer protocols. This concept which is formalized using statistics implies that in general it is not meaningful to speak about a MAC or a routing protocol in isolation. Such an interaction leads to trade-offs between the amount of control packets generated by each layer. More interestingly, the results wise the possibility of improving the performance of a particular MAC layer protocol by using a cleverly designed routing protocol or vice-versa. 3. Routing prolocols with distributed knowledge about routes are more suitable for networks with mobility. This is seen by comparing the performance of AODV with DSR or LAR scheme 1. In DSli and IAR scheme 1, information about a computed path is being stored in the route query control packct. 4. MAC layer protocols have varying performance with varying mobility models. It is not only speed that influences the performance but also node degree and connectivity of the dynamic network that affects the protocol performance. 'The main implication of OUI' work is that performance analysis of protocols at a given level in the protocol stack need to be studied not locally in isolation but as a part of the complete protocol stack. The results suggest that in order to improve the pcrlormance of a communication network, it will be important to study the entire protocol stack as a single algorithmic construct; optimizing individual layers in the 7 layer OS1 stilck will not yield performance improvements beyond a point. A methodological contribution of this paper is the use of statistical methods such as design of experinierits arzd aiialysis qf variance methods to characterize the interaction between the protocols, mobility patterns and speed. This allows us to mako much more informed conclusions about the performance of thc protocols than would have been possible by merely running these experiments and observing the data. These ideas are of independtmt interest and are applicable in other contexts wherein one experimentally analyzes algorithms
