Gateway nodes are important elements in a sensor network since they provide the ability to establish long-range reach-back communication in order to retrieve critical data to remote locations. The gateways are however prone to failures just like any sensor nodes, and they consume significantly more energy since they transmit over longer distances compared with sensor-to-sensor links. We introduce an adaptive and fault-tolerant method for gateway assignment in sensor networks. Our approach is fully distributed and achieves the following objectives: (i) it allows surviving gateways to recover for other failed gateways; (ii) it distributes energy usage and traffic load between several gateway nodes within the sensor network. Each gateway adaptively controls its region of influence based on local conditions such as remaining energy level and traffic load. Our methodology was evaluated via simulation using a network model containing 400 sensor nodes with virtual targets. The simulation results indicate that our scheme is robust to gateway failures. Moreover, our scheme successfully balances the energy consumption and traffic load among the gateways.

In this paper we investigate the performance of multicast routing protocols in wireless mobile ad hoc networks. An ad hoc network is composed of mobile nodes without the presence of a wired support infrastructure. In this environment, routing/multicasting protocols are faced with the challenge of producing multihop routes under host mobility and bandwidth constraints. In recent years, a number of new multicast protocols of different styles have been proposed for ad hoc networks. However, systematic performance evaluations and comparative analysis of these protocols in a common realistic environment has not yet been performed. In this study, we simulate a set of representative wireless ad hoc multicast protocols and evaluate them in various network scenarios. The relative strengths, weaknesses, and applicability of each multicast protocol to diverse situations are studied and discussed.

An ad hoc wireless network is composed of mobile hosts without any wired infrastructure support. In mobile ad hoc networks, unicast and multicast routing protocols are faced with the challenge of producing multihop routes because of limited radio propagation range. In addition, routing protocols must manage mobility and be bandwidth and power efficient. The on-demand multicast routing protocol (ODMRP) is a protocol designed for ad hoc networks with multicast purposes. Two unique features of ODMRP are its unicast capability and its utilization of a mobility prediction scheme to perform rerouting in anticipation of route disconnection. We describe ODMRP unicast routing functionality and assess the mobility prediction effectiveness and efficiency. We evaluate the ODMRP performance via detailed simulation and compare it with other ad hoc routing schemes.

An ad hoc wireless network is an infrastructureless network composed of mobile hosts. The primary concerns in ad hoc networks are bandwidth limitations and unpredictable topology changes. Thus, efficient utilization of routing packets and immediate recovery of route breaks are critical in routing and multicasting protocols. A multicast scheme, on-demand multicast routing protocol (ODMRP), has been recently proposed for mobile ad hoc networks. ODMRP is a reactive (on-demand) protocol that delivers packets to destinations on a mesh topology using scoped flooding of data. A number of enhancements can be applied to improve the performance of ODMRP. In this paper, we propose a mobility prediction scheme to help select stable routes and to perform rerouting in anticipation of topology changes. We also introduce techniques to improve transmission reliability and eliminate route acquisition latency. The impact of our improvements is evaluated via simulation.