Yunhao Liu

In large-scale wireless sensor networks, faulty link detection plays a critical role in network diagnosis and management. Most potential network bottlenecks such as network partition and routing errors can be detected by link scan. Since sequentially checking all potential links incurs high transmission and storage cost, we propose a passive scheme Link Scanner (LS) for monitoring wireless links. As we know, to maintain a sensor network running in a normal condition, many applications in flooding manner are necessary, such as time synchronization, reprogramming, protocol update, etc. During such regular flooding processes that for other purposes originally, LS passively collects hop counts of received probe messages at sensor nodes. Based on the observation that faulty links can result in mismatch between received hop counts and network topology, LS deduces all links' status with a probabilistic model. We evaluate our scheme by carrying out experiments on a testbed with 60 TelosB motes and conducting extensive simulation tests. A real outdoor system is also deployed to verify that LS can be reliably applied to surveillance networks.

A typical multicast network consists of a single tree, in which only a few internal nodes contribute most resources and are involved in performing the multicast functionality. This leads to an uneven and inefficient utilization of network resources. The problem is more pronounced in mobile ad hoc networks (MANETs), where network resources are limited. One solution is to split the multicast content over a number of trees. This provides several paths for the multicast content and would involve more nodes in implementing multicast functionality. Although this approach improves network utilization, overall multicast latency increases. This paper presents a distributed algorithm to construct multiple edge-sharing trees (MESTs) for small group multicast. MESTs balance the resource allocation and delay constraints by choosing to overlap certain edges that have low weight. Simulation results show that MESTs can generate multicast networks that have low delays and fair resource utilization. MESTs are designed to work with any form of multicast in both wired and wireless networks.

In order to maximize resource utilization as well as providing trust management in grid, we propose a novel framework - Trust-Incentive Resource Management (TIM). Having child model, club model, bid model and trust model, TIM dynamically manages grid resource by integrating values of prices, trust, and incentive. In this mechanism, providers set the price according to demand and supply, and consumers maximize the surplus upon budget and deadline. A weighted voting scheme is also proposed to secure the grid system by declining the join request from malicious nodes. A TIM prototype has been successfully implemented in a real grid system, CROWN grid. We evaluate the proposed approach through comprehensive experiments and achieve improved results in resource allocation efficiency, system completion time, and aggregated resource utilization.

The newly emerging wireless backhaul network has fundamental difficulties in supporting Voice over IP (VoIP) applications due to the MAC overheads introduced by huge amounts of small packets. Packet aggregation is a promising approach to mitigate these overheads. However, previous approaches to such problems are often stringent, not adaptive to the change of channel conditions. They are operated by each TAP (Transit Access Point) separately without any coordination in the use of shared channels. As a result, they fail to ensure the VoIP quality in terms of delay and loss. The major contribution of this paper is the proposal of a coordinated aggregation algorithm, which is adaptive and distributed. By coordinating with neighboring TAPs, the proposed algorithm is able to assign an appropriate aggregation rate to each TAP, aiming at better channel utilization and lower packet loss and delay. We evaluate this design by comprehensive analysis and simulations. The simulation results show that our algorithm significantly improves the VoIP capacity in wireless backhaul networks and outperforms existing aggregation algorithms.

Overlay networks have made it easy to implement multicast functionality in wireless ad hoc networks. Their flexibility to adapt to different environments has helped in their steady growth. In MANET, the position of nodes constantly changes; as a result, overlay multicast trees that are built using location information to account for node movement would certainly have a low latency. However, the performance gains of such a tree are offset by the overhead involved in maintaining precise location information. As the degree of (location) accuracy increases, the performance improves but the overhead required to store and broadcast this information also increases. In this paper, we present SOLONet, a design to build a sub-optimal location aided overlay multicast tree, where location updates of each member node are event based. Our simulation results indicate that such a sub-optimal tree does not compromise the performance gains of a location aided overlay multicast tree.

Inter-organizational business processes usually require complex and time-consuming interactions between partners than simple interactions supported by WSDL. Automated reconciliation is essential to enable dynamic inter-organizational business collaboration. To the best of our knowledge, however, there is not a practical automated reconciliation algorithm available. In this paper, we propose a practical automated reconciliation algorithm, called IPR (interaction process reconciliation) based on Petri net, which is able to effectively facilitate dynamic interactions among trading partners in a peer-to-peer fashion. We implement a prototype IPR server in our lab, and evaluate our design by comprehensive experiments. Results show that IPR significantly outperforms existing approaches in terms of matching success rate, response time, and matching efficiency.