7679474
Delay Reduction Techniques for Playout Buffering
Receiver synchronization of continuous media streams is required to deal with delay differences and variations resulting from delivery over packet networks such as the Internet. This function is commonly provided using per-stream playout buffers which introduce additional delay in order to produce a playout schedule which meets the synchronization requirements. Packets which arrive after their scheduled playout time are considered late and are discarded. In this paper, we present the Concord algorithm, which provides a delay-sensitive solution for playout buffering. It records historical information and uses it to make short-term predictions about network delay with the aim of not reacting too quickly to short-lived delay variations. This allows an application-controlled tradeoff of packet lateness against buffering delay, suitable for applications which demand low delay but can tolerate or conceal a small amount of late packets. We present a selection of results from an extensive evaluation of Concord using Internet traffic traces. We explore the use of aging techniques to improve the effectiveness of the historical information and hence, the delay predictions. The results show that Concord can produce significant reductions in buffering delay and delay variations at the expense of packet lateness values of less than 1%.
17385246
Challenges for Mobile Voice-over-IP
The use of IP to transport voice is receiving significant attention in the telecommunications and data networking industries. Commonly known as Voice-over-IP (VoIP), this technology has the potential to allow user communication involving multiple media types, and between terminals that offer improved capabilities and user interfaces. Meanwhile there has been explosive growth in the demand for wireless connectivity, raising the question of how VoIP can be extended to situations where users and terminals can be mobile. In this paper we survey the technologies necessary to provide mobile VoIP, and identify relevant technical challenges.
1250825
Enhancing Training Set for Face Detection
We present a novel method to enhance training set for face detection with nonlinearly generated examples from the original data. The motivation is from support vector machines (SVM) that, for classification problems, examples lying close to class boundary usually have more influence and thus are more informative than those far from the boundary. We utilize a nonlinear technique - reduced set (RS) method and a new image distance metric to generate new examples, and then add them to the original collected database to enhance it. Extensive experiments show that the proposed approach has an encouraging performance
691108
Utilization-based admission control for real-time applications
In this paper, we present a methodology to use utilization-based admission control in guaranteed real-time communication in a scalable fashion. We make admission control scalable by using a configuration-time test to determine a safe utilization level of servers. Admission control at run-time then is reduced to simple utilization tests on the servers along the path of the new flow. Furthermore, we discuss how appropriate route selection improve utilization levels, design a safe route selection heuristic algorithm to achieve high utilization of resources, and derive two bounds on the maximum utilization level for given traffic in a network. We compare the results of our route selection heuristics with that of a shortest-path based algorithm, and find that our heuristics can achieve a much higher maximum utilization level than that of the shortest-path based algorithm.
44957022
Separability and Topology Control of Quasi Unit Disk Graphs
A deep understanding of the structural properties of wireless networks is critical for evaluating the performance of network protocols and improving their designs. Many protocols for wireless networks - routing, topology control, information storage/retrieval and numerous other applications - have been based on the idealized unit-disk graph (UDG) network model. The significant deviation of the UDG model from many real wireless networks is substantially limiting the applicability of such protocols. A more general network model, the quasi unit-disk graph (quasi-UDG) model, captures much better the characteristics of wireless networks. However, the understanding of the properties of general quasi-UDGs has been very limited, which is impeding the designs of key network protocols and algorithms. In this paper, we present results on two important properties of quasi-UDGs: separability and the existence of power efficient spanners. Network separability is a fundamental property leading to efficient network algorithms and fast parallel computation. We prove that every quasi-UDG has a corresponding grid graph with small balanced separators that captures its connectivity properties. We also study the problem of constructing an energy-efficient backbone for a quasi-UDG. We present a distributed localized algorithm that, given a quasi-UDG, constructs a nearly planar backbone with a constant stretch factor and a bounded degree. We demonstrate the excellent performance of these auxiliary graphs through simulations and show their applications in efficient routing.
9663015
Customizing a geographical routing protocol for wireless sensor networks
Several problems are required to be fixed in order to apply geographical routing protocol greedy perimeter stateless routing (GPSR) in wireless sensor networks. First, GPSR is designed under the assumption of symmetric links (i.e., bidirectional reachability), which is not realistic for many practical sensor networks, since wireless links in sensor networks often are asymmetric. Second, in sensor networks, packet destinations are often marked with locations instead of identifiers like IP address. Therefore, packets are routed to the home node, which is the node geographically closest to the destined location. Under GPSR, when the target location is outside the exterior perimeter of the sensor network, each packet has to visit all nodes on the boundary of the sensor network topology before it identifies the home node, which results in energy inefficiency. Third, due to the dynamic nature of sensor networks, maintaining data consistency, that is, data retrieved from the home node for a location should be consistent with the data sent to the same location, becomes a challenge when home nodes change. We propose on-demand GPSR (OD-GPSR), a data driven geographical routing protocol customized for sensor networks with solutions to the above three problems. Simulation results show that OD-GPSR performs well in terms of energy efficiency and packet delivery rate at the cost of a little bit more packet delivery delay.
27587317
An executable specification language for specification understanding in object-oriented specification reuse
System analysis time can be reduced through specification reuse which, however, requires specification understanding. This paper presents an object-oriented executable specification language which reduces understanding time through executing specifications. In addition to being executable, the specification language hides as many classes as possible within subsystems, and explicitly specifies relationships between specification components. This facilitates specification modification. Moreover, the language explicitly specifies interface parameters of specification components. This facilitates specification composition.