18232832
Tree-assisted gossiping for overlay video distribution
Given its readily deployable nature and broad applications for digital entertainment, video streaming through overlay networks has received much attention recently. While a tree topology is often advocated due to its scalability, it suffers from discontinuous playback under highly dynamic network environments. For on-demand streaming, the asynchronicity among client requests further aggravates the problem. On the other hand, gossip protocols using random message dissemination, though robust, fail to meet the real-time constraints for streaming applications. In this paper, we propose TAG, a Tree-Assisted Gossip protocol that addresses the above issues. TAG adopts a tree structure with time indexing to accommodate asynchronous requests, and an efficient pull-based gossip algorithm to mitigate the impact of network dynamicity. It seamlessly integrates these two approaches and realizes their best features, namely, low delay with a regular tree topology, and robust delivery with smart switching among multiple paths, thus making effective use of the available bandwidth in the network. We evaluate the performance of TAG under various settings, and the results demonstrate that it is quite robust in the presence of local and global bandwidth fluctuations. As compared to pure tree-based overlay VOD system, it achieves much lower and stable segment missing rates, even under highly dynamic network conditions.
46541251
Trustworthy Distributed Algorithm Design to Defend Distance Cheating in Link-Weighted ALM
In link-weighted Application Layer Multicast (ALM), each selfish and strategic end-host receiver may cheat in distance measurement to obtain a better position in the ALM tree. Distance cheating of ALM receivers might lead the ALM tree to be sub-optimal and unstable. We proposed a VCG-based cheat-proof mechanism to defend this kind of cheating behavior in previous work. Based on the theoretical framework, a practical algorithm is designed in this paper, which runs distributedly on ALM receivers. The primary characteristic of the distributed algorithm lies in that it is trustworthy to enforce each selfish receiver to fulfill the algorithm truthfully, which is not considered in other similar studies. Simulations results further suggest that the algorithm is effective in defending distance cheating in link-weighted ALM.
1037858
Power-Aware Task Motion for Enhancing Dynamic Range of Embedded Systems with Renewable Energy Sources
In this paper we propose a novel scheduling framework for a dynamic real-time environment that experiences power consumption constraints. This framework is capable of dynamically adjusting the voltage/ speed of the system, such that no task in the system misses its deadline and the total energy savings of the system are maximized. 
 
Each task in the system consumes a certain amount of energy, which depends on a speed chosen for execution. The process of selecting speeds for execution while maximizing the energy savings of the system requires the exploration of a large number of combinations, which is too time consuming to be computed on-line. Thus, we propose an integrated heuristic methodology which executes an optimization procedure and an approximate greedy algorithm in a low computation time. This scheme allows the scheduler to handle power-aware real-time tasks with low cost while maximizing the use of the available resources and without jeopardizing the temporal constraints of the system. Simulation results show that our heuristic methodology achieves a performance with near-optimal results.
5434773
Simulation validation using direct execution of wireless ad-hoc routing protocols
Computer simulation is the most common approach to studying wireless ad-hoc routing algorithms. The results, however, are only as good as the models the simulation uses. One should not underestimate the importance of validation, as inaccurate models can lead to wrong conclusions. In this paper, we use direct-execution simulation to validate radio models used by ad-hoc routing protocols, against real-world experiments. This paper documents a common testbed that supports direct execution of a set of ad-hoc routing protocol implementations in a wireless network simulator. The testbed reads traces generated from real experiments, and uses them to drive direct-execution implementations of the routing protocols. Doing so we reproduce the same network conditions as in real experiments. By comparing routing behavior measured in real experiments with behavior computed by the simulation, we are able to validate the models of radio behavior upon which protocol behavior depends. We conclude that it is possible to have fairly accurate results using a simple radio model, but the routing behavior is quite sensitive to one of this model's parameters. The implication is that one should: i) use a more complex radio model that explicitly models point-to-point path loss; or ii) use measurements from an environment typical of the one of interest; or iii) study behavior over a range of environments to identify sensitivities.
33842812
Anycast-Based Cooperative Proxy Caching
As one of the most popular applications currently running on the Internet, the World Wide Web is of an exponential growth in size, which results in the network congestion and server overloading. Web caching as an important technique aims at reducing network traffic, server load, and user-perceived retrieval delays by replicating popular contents on proxy caches. In our paper, we develop an anycast-based cooperative web proxy caching mechanism. It puts response time, hop counts, self-organized load balancing, adaption, and self-configuration as primary concerns. In our scheme, anycast is used to bring a server “nearest” to a client to improve overall performance, all proxies in a local network consists an anycast group. The object placement and replacement problems are formulated as an optimization problem and the solution is obtained by using an anycast-based cooperative proxy caching algorithm. Some simulation experiments have been conduced to evaluate the proposed scheme in terms of a wide range of performance metrics. Analytical and experimental results show that our algorithm outperforms some existing algorithms in response time, hop counts.
5135154
Linking UML models of design and requirement
Both a UML model of requirement and a UML model of a design are defined as a pair of class diagram and a family of sequence diagrams. We then give an unified semantics for models of requirements and designs. We define the consistency between a design class diagram and the interaction diagrams and show how the removal of inconsistency can be treated as a model refinement. We then formally define the correctness of UML model of design with respect to the model of requirement.
9720054
Anycast-Based Cooperative Proxy Caching: Preliminary Results
The World Wide Web is one of the most popular applications currently running on the Internet, and its size is growing exponentially. Web caching is an important technique that aims to reduce network traffic, server load, and user-perceived retrieval delays by replicating popular contents on proxy servers. Anycast is a new network service widely used for providing auto-configuration and load-balancing. We present an anycast-based cooperative proxy algorithm (ACPA) that brings a server ienearestle to a client to improve overall performance by selective allowing duplicates and migrate objects to other proxies based on request pattern. Analytical and experimental results show that the algorithm outperforms a hash-based algorithm in response time and hop counts.