Motivated by the needs and success of projects such as SETI@home and genome@home, we propose an architecture for a sustainable large-scale peer-to-peer environment for distributed cycle sharing among Internet hosts. Such networks are characterized by highly dynamic state due to high arrival and departure rates. This makes it difficult to build and maintain structured networks and to use state-based resource allocation techniques. We build our system to work in an environment similar to current file-sharing networks such as Gnutella and Freenet. In doing so, we are able to leverage vast network resources while providing resilience to random failures, low network overhead, and an open architecture for resource brokering. This paper describes the underlying analytical and algorithmic substrates based on randomization for job distribution, replication, monitoring, aggregation and oblivious resource sharing and communication between participating hosts. We support our claims of robustness and scalability analytically with high probabilistic guarantees. Our algorithms do not introduce any state dependencies, and hence are resilient to dynamic node arrivals, departures, and failures. We support all analytical claims with a detailed simulation-based evaluation of our distributed framework.

Simulation and control are two critical elements of Dynamic Data-Driven Application Systems (DDDAS). Simulation of dynamical systems such as weather phenomena, when augmented with real-time data, can yield precise forecasts. In other applications such as structural control, the presence of real-time data relating to system state can enable robust active control. In each case, there is an ever increasing need for improved accuracy, which leads to models of higher complexity. The basic motivation for system approximation is the need, in many instances, for a simplified model of a dynamical system, which captures the main features of the original complex model. This need arises from limited computational capability, accuracy of measured data, and storage capacity. The simplified model may then be used in place of the original complex model, either for simulation and prediction, or active control. As sensor networks and embedded processors proliferate our environment, technologies for such approximations and real-time control emerge as the next major technical challenge. This paper outlines the state of the art and outstanding challenges in the development of efficient and robust methods for producing reduced order models of large state-space systems.

Node clustering in sensor networks increases scalability, robustness, and energy-efficiency. In hostile environments, unexpected failures or attacks on cluster heads (through which communication takes place) may partition the network or degrade application performance. We propose REED (Robust Energy-Efficient Distributed clustering), for clustering sensors deployed in hostile environments in an interleaved manner with low complexity. Our primary objective is to construct a k-fault-tolerant (i.e., k-connected) clustered network, where k is a constant determined by the application. Fault tolerance is achieved by selecting k independent sets of cluster heads (i.e., cluster head overlays) on top of the physical network, so that each node can quickly switch to other cluster heads in case of failures. The independent cluster head overlays also give multiple vertex-disjoint routing paths for load balancing and security. Network lifetime is prolonged by selecting cluster heads with high residual energy and low communication cost, and periodically re-clustering the network. We prove that REED asymptotically achieves k-connectivity if certain conditions on node density are met. We also discuss inter-cluster routing and MAC layer considerations, and investigate REED clustering properties via extensive simulations.

We study the sleep/wake scheduling problem in the context of clustered sensor networks. We conclude that the design of any sleep/wake scheduling algorithm must take into account the impact of the synchronization error. Our work includes two parts. In the first part, we show that there is an inherent tradeoff between energy consumption and message delivery performance (defined as the message capture probability in this work). We formulate an optimization problem to minimize the expected energy consumption, with the constraint that the message capture probability should be no less than a threshold. In the first part, we assume the threshold is already given. However, by investigating the unique structure of the problem, we transform the non-convex problem into a convex equivalent, and solve it using an efficient search method. In the second part, we remove the assumption that the capture probability threshold is already given, and study how to decide it to meet the quality of services (QoS) requirement of the application. We observe that in many sensor network applications, a group of sensors collaborate to perform common task(s). Therefore, the QoS is usually not decided by the performance of any individual node, but by the collective performance of all the related nodes. To achieve the collective performance with minimum energy consumption, intuitively we should provide differentiated services for the nodes and favor more important ones. We thus formulate an optimization problem, which aims to set the capture probability threshold for messages from each individual node such that the expected energy consumption is minimized, while the collective performance is guaranteed. The problem turns out to be non-convex and hard to solve exactly. Therefore, we use approximation techniques to obtain a suboptimal solution that approximates the optimum. Simulations show that our approximate solution significantly outperforms a scheme without differentiated treatment of the nodes.

Mobile communications technologies have reached a significant penetration today and the development of technologies and applications is still emerging. The Internet has become the major core network around which several wireless access networks are inter-connected. These access networks are not just single wireless links, but are becoming diverse and complex. For example, sensors are connected via sensor networks, cars connect via mobile ad hoc networks, and users in areas without GSM/UMTS coverage might only be reached via satellites. Moreover, the requirements to mobile communications are increasing. Security is a major concern in such networks and small wireless/mobile devices need to save as much power as possible to ensure long lifetimes. The 4th International Conference on Wired/Wireless Internet Communications (WWIC 2006) took place at University of Bern (Switzerland) from May 10 to 12, 2006. WWIC 2006 addressed relevant research issues such wireless networks, UMTS and OFDM, mobile ad hoc networks, power saving and sensor networks, voice and video over wireless networks, mobility, transport protocol issues as well as signalling, charging, and security. The goal of the conference was to present high-quality results in the field. The international conference program committee selected 29 papers out of 142 submissions for conference presentation. Finally, five papers from the ones presented at the conference have been selected for this special issue. The selected papers have been improved based on the conference reviews and extended in order to present latest research results in more detail.

Fair bandwidth allocation is critical in wireless communication networks, since the wireless channel is often shared by a number of stations in the same neighborhood. With fair scheduling, bandwidth can be shared by competing flows in proportion to their assigned weights. In this paper, we propose a credit-based distributed protocol for fair allocation of bandwidth in IEEE 802.11 wireless LANs. Our protocol is derived from the distributed coordination function in the IEEE 802.11 medium access control (MAC) protocol. Analytical and simulation results demonstrate that the protocol achieves the desired bandwidth allocations. An important feature of our protocol is its backward compatibility, which allows legacy IEEE 802.11 stations to coexist with stations adopting the new MAC protocol.

The authors develop a simulation model for asynchronous transfer mode available bit rate (ATM ABR) service and use it to engineer ABR congestion control behavior. Although significant work has been performed on ABR rate allocation algorithms at network switches, little work has focused on the end system behavior, which is examined in this article. The effect of (1) the speed of the links on the path from the source to the destination and (2) the connection round trip time on the selection of ABR parameter values is studied. Simulation results illustrate the impact of the key parameters that control rate reduction in the absence of network feedback on performance, in terms of connection throughputs, queue lengths at the switches, and link utilizations. These results have been incorporated into the ABR standards and can be generalized to cooperative congestion control with explicit congestion notification in the Internet.

This paper proposes an algorithm for aggregating virtual channel connections (VCCs) onto virtual path connections (VPSs) in asynchronous transfer mode (ATM) networks. We focus on the interesting problem of multiplexing onto an available bit rate (ABR) VPC. ABR VPCs are particularly useful for connecting enterprise sites over the Internet, providing a virtual private network (VPN). The VPC/VCC hierarchy is also important for supporting Internet differentiated services over ATM. The coupling between the flow control mechanisms for VCCs and VPCs is not standardized. We propose fairness definitions for VPC bandwidth allocation, and describe an algorithm for allocating the VPC capacity to the multiplexed VCCs. Preliminary simulation results indicate that the algorithm achieves the required fair allocations, while controlling queue sizes

The unprecedented increase in the number of Internet users, routers, and service providers has introduced significant challenges to the design of scalable network architectures and end-to-end protocols. Web driven demand and traffic can exhibit extreme variability; providing predictable quality of service (QoS) without resorting to major over-provisioning is a difficult problem; facilitating dynamic group communication and multicast has spurred a multitude of proposals, each with its own idiosyncrasies and trade-offs; QoS routing faces the computational complexity barrier; congestion control is asked to be fair, efficient, and stable in a complex environment; mobility and wireless channels impose new control dimensions and constraints; and faults in software and hardware introduce disruptions that may persist in time and spread in space. A common denominator to many of these examples is scalability, which, to varying degrees, plays an important role when designing and evaluating feasible solutions.

While the DETER testbed provides a safe environment and basic tools for security experimentation, researchers face a significant challenge in assembling the testbed pieces and tools into realistic and complete experimental scenarios. In this paper, we describe our work on developing a set of sampled and comprehensive benchmark scenarios, and a workbench for experiments involving denial-of-service (DoS) attacks. The benchmark scenarios are developed by sampling features of attacks, legitimate traffic and topologies from the real Internet. We have also developed a measure of DoS impact on network services to evaluate the severity of an attack and the effectiveness of a proposed defense. The benchmarks are integrated with the testbed via the experimenter’s workbench - a collection of traffic generation tools, topology and defense library, experiment control scripts and a graphical user interface. Benchmark scenarios provide inputs to the workbench, bypassing the user’s selection of topology and traffic settings, and leaving her only with the task of selecting a defense, its configuration and deployment points. Jointly, the benchmarks and the experimenter’s workbench provide an easy, point-and-click environment for DoS experimentation and defense testing.