Many techniques used by routing protocols for ad hoc networks assume that links in the network can be used equally well in both directions between the two endpoint nodes of the link. However, there are many real-world situations in which wireless links may physically work in only one direction, resulting in degradation of routing performance in the network. In this paper, we present the first study of the effect of unidirectional links on the performance of on-demand multicast routing protocols for ad hoc networks and present mechanisms that enable such protocols to route efficiently over unidirectional links. We evaluate these mechanisms in the context of the Adaptive Demand-Driven Multicast Routing protocol (ADMR), and simulate the extended protocol, ADMR-U, in a wide range of mobile and static network scenarios with unidirectional links. In networks with only bidirectional links, the unidirectional extensions do not get activated and cause no overhead; in networks with unidirectional links, ADMR-U matches or outperforms ADMR in terms of packet delivery ratio, and lowers ADMR s packet overhead.

24 pages

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