A New Solution to Improve the Link Failure Tolerance in Mobile Ad hoc Networks

Abstract

An ad hoc network is a mobile wireless network that has no fixed access point or centralized infrastructure. Each node in the network also functions as a mobile router of data packets for other nodes. However, due to node mobility, link failures in such networks are very frequent and render certain standard protocols inefficient resulting in wastage of power and loss in throughput We propose two solutions based on two different approaches to alleviate the problems caused by link failures. The first solution, the Network-Link scheme, deals with preventing ‘false’ link failures and in avoiding actual link failures. The scheme involves predicting a failure in advance by monitoring the power levels of all nodes in communication. On the other hand, the Transport-Link scheme deals with the inability of Transmission Control Protocol (TCP) to distinguish between link failures and congestion. TCP, as such, assumes that a packet loss is due to network congestion and invokes congestion control measures. However, in ad hoc networks, packet loss is most often due to link failures, and the congestion control methods invoked only reduce the throughput. Our second solution informs TCP of a link failure thus allowing it to treat such cases differently. In both cases, we observed an improvement in throughput and power utilization efficiency when compared to standard cases: the Network-Link scheme resulted in an average throughput increase of 1.74 times and the Transport-Network scheme, an average increase of 1.71 times. Both schemes also resulted in a reduction in the percentage of Network layer control packets transmitted, thereby improving power utilization.