Abstract-In this article, we present CodeCast, a network coding based ad hoc multicast protocol. CodeCast well-suited especially for multimedia applications with low loss, low latency constraints such as audio/video streaming. The key ingredient of CodeCast is random network coding which transparently implements both localized loss recovery and path diversity with very low overhead. Simulation results show that in a typical setting, CodeCast yields near 100% delivery ratio as compared to 94% delivery ratio by traditional multicast. More importantly, the overhead is reduced by as much as 50%.

Mobile ad hoc networks (MANETs) are vulnerable to routing attacks, especially attacks launched by non-cooperative (selfish or compromised) network members and appear to be protocol compliant. For instance, since packet loss is common in mobile wireless networks, the adversary can exploit this fact by hiding its malicious intents using compliant packet losses that appear to be caused by environmental reasons.In this paper we study two routing attacks that use non-cooperative network members and disguised packet losses to deplete ad hoc network resources and to reduce ad hoc routing performance. These two routing attacks have not been fully addressed in previous research. We propose the design of "self-healing community" to counter these two attacks. Our design exploits the redundancy in deployment which is typical of most ad hoc networks; Namely, it counters non-cooperative attacks using the probabilistic presence of nearby cooperative network members.To realize the new paradigm, we devise localized simple schemes to (re-)configure self-healing communities in spite of random node mobility. We develop a general analytic model to prove the effectiveness of our design. Then we implement our secure ad hoc routing protocols in simulation to verify the cost and overhead incurred by maintaining the communities. Our study confirms that the community-based security is a cost-effective strategy to make off-the-shelf ad hoc routing protocols secure.

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Abstract-In wireless ad-hoc networks, unidirectional links occur for several reasons: non uniform transmit power, non uniform background noise, and external interference. Several researchers have addressed unidirectional links and the associated unidirectional routing problem. The main focus has been so far on "unicast" routing; the consensus is that unidirectional links should be detected and avoided. In this paper, we consider the multicast case and derive a different conclusion: namely, it pays to exploit unidirectional links rather then avoid them. To prove the point, we select a popular ad hoc multicast protocol, On-Demand Multicast Routing Protocol (ODMRP) and introduce a slightly modified version, ODMRP-ASYM, that can handle unidirectional links. Specifically, ODMRP-ASYM reroutes the Join Reply packet when a unidirectional link is detected on the Join Query path. The option is invoked only when a unidirectional link is detected. The main advantages are: control overhead comparable with ODMRP even in highly asymmetric topologies; virtually no performance degradation in presence of unidirectional links (while ODMRP typically suffers up to 15% drop in delivery performance), and; 2-connectivity maintenance even if no bidirectional path exists between sender and receiver (in this case, unidirectional link avoidance strategies fail). Extensive simulation experiments demonstrate ODMRP-ASYM robustness to unidirectional links and superiority over conventional ODMRP.

Hardware/Software cosimulation is the key process to shorten the design turn around time. We have proposed a novel technique, called virtual synchronization, for fast and time accurate cosimulation that involves interacting component simulators. In this paper, we further extend the virtual synchronization technique with OS modeling for the case where multiple software tasks are executed under the supervision of a real-time operating system. The OS modeler models the RTOS overheads of context switching and tick interrupt handling as well as preemption behavior. While maintaining the timing accuracy to an acceptable level below a few percents, we could reduce the simulation time drastically compared with existent conservative approach by removing the need of time synchronization between simulators. It is confirmed with a preliminary experiment with a multimedia example that consists of four real-life tasks.

Abstract. This paper proposes a novel reliable multicast transport protocol for multi-hop, wireless ad hoc networks (or MANETs) . To recover from the different types of Iosses that may occur in MANETs, our Reliable Adaptive Congestion-controlled Transport protocol, or Re-ACT, combines source-based congestion-and error control with receiverinitiated localized recovery. While the latter attempts to recover localized Iosses ( e.g., caused by transmission errors), the former is invoked only for Iosses and congestion that could not be recovered locally ( e.g., caused by global congestion) . Loss differentiation is an important component of ReACT and uses medium access control (MAC) layer information to distinguish between different types of losses. Through extensive simulations, we evaJuate ReACT's performance under a variety of MANET scenarios, including different affered Ioad and mobility conditions, and compare it agairrst a strictly end-to-end (i.e., no localized recovery) scheme. Our results show that ReACT is the best performer in terms of reliability. Our results also showcase the effect of ReACT's local recovery mechanism which quickly corrects error-and path breakage induced Iosses and thus manages to prevent the source from reducing its rate unnecessarily , t hus achieving significant throughput improvement with lower overhead when compared to the strictly end-to-end protocol.