14690444
Fluid-flow analysis of TCP Westwood with RED
This paper concerns TCP Westwood (TCPW), a recently developed modification of TCP, in combination with RED queue management. We develop a fluid-flow model of TCPW with RED and use it to study both equilibrium and dynamic features. On the equilibrium side, we identify the scaling of window with loss-probability, and compare it to TCP NewReno. We also use the model to find the boundary of stability, beyond which we see large oscillations; we find that the stable region of TCPW is enhanced with respect to TCP NewReno. Furthermore we show preliminary evidence that oscillations, when they occur, have a limited impact on network throughput. Fairness and friendliness of TCPW is also analyzed and compared with NewReno. Our results show that TCPW is more fair than NewReno for flows with heterogenous round trip time. We also found that TCPW friendliness to NewReno is dependent on the difference between equilibrium queue size and the product of bandwidth and delay.
11672412
Dealing with Node Mobility in Ad Hoc Wireless Network
A Mobile “Ad hoc” wireless NETwork (MANET) is a network established for a special, often extemporaneous service customized to applications. The ad hoc network is typically set up for a limited period of time, in an environment that may change from application to application. As a difference from the Internet where the TCP/IP protocol suite supports a vast range of applications, in the MANET the protocols are tuned to a specific customer and application (eg, send a video stream across the battlefield; find out if there is a fire in the forest; establish a videoconference among several teams engaged in a rescue effort, etc). The customers move and the environment may change dynamically and unpredictably. For the MANET to retain its efficiency, the ad hoc protocols at various layers may need to self-tune to adjust to environment, traffic and mission changes. From these properties emerges the vision of the MANET as an extremely flexible, malleable and yet robust and formidable network architecture. Indeed, an architecture that can be deployed to monitor the habits of birds in their natural habitat, and which, in other circumstances, can be organized to interconnect rescue crews after a Tsunami disaster, or yet can be structured to launch deadly attacks onto unsuspecting enemies.
14793234
On the Amount of Nondeterminism and the Power of Verifying
The relationship between nondeterminism and other computational resources is investigated based on the "guess-then-check" model GC. Systematic techniques are developed to construct natural complete languages for the classes defined by this model. This improves a number of previous results in the study of limited nondeterminism. Connections of the model GC to computational optimization problems are exhibited.
10195041
PFED: a prediction-based fair active queue management algorithm
In this paper, we propose a novel active queue management algorithm PFED, which is based on network traffic prediction. The main properties of PFED are: (1) stabilizing queue length at a desirable level with consideration of future traffic, and using a MMSE (minimum mean square error) predictor to predict future network traffic; (2) imposing effective punishment upon misbehaving flow with a full stateless method; (3) maintaining queue arrival rate bounded by queue service rate through more reasonable calculation of packet drop probability. To verify the performance of PFED, PFED is implemented in NS2 and is compared with RED and CHOKe with respect to different performance metrics. Simulation results show that PFED outperforms RED and CHOKe in stabling instantaneous queue length and in fairness. It is also shown that PFED enables the link capacity to be fully utilized by stabilizing the queue length at a desirable level, while not incurring excessive packet loss ratio.
193728
Feedback-based Scheduling for Back-end Databases in Shared Dynamic Content Server Clusters
This paper introduces a self-configuring architecture for scaling the database tier of dynamic content Web servers. We use a unified approach to load and fault management based on dynamic data replication and feedback-based scheduling. While replication provides scaling and high availability, feedback scheduling dynamically allocates tasks to commodity databases across workloads in response to peak loads or failure conditions thus providing quality of service. By augmenting the feedback loop with state awareness, we avoid oscillations in resource allocation. We investigate our transparent provisioning mechanisms in the database tier using the TPC-W e-commerce and the on-line auction Rubis benchmarks. We demonstrate that our techniques provide quality of service under load bursts and failure scenarios
14245135
Automatic Correlation and Calibration of Noisy Sensor Readings Using Elite Genetic Algorithms
This paper explores an image processing application of optimization techniques which entails interpreting noisy sensor data. The application is a generalization of image correlation; we attempt to find the optimal gruence which matches two overlapping gray scale images corrupted with noise. Both tabu search and genetic algorithms are used to find the parameters which match the two images. A genetic algorithm approach using an elitist reproduction scheme is found to provide significantly superior results.
10823490
Specification-based Testing for Gui-based Applications
The development of GUI-based applications has raised a lot of new issues, one of them being how to automate effective testing for applications with complicated graphical user interactions. In this paper, we discuss the architectural issues and the implementation concerns of our approach to an automated specification-based testing technique for GUI-based applications. This approach is carried out by enriching existing architecture for automated specification-based testing. An essential part of our work is a visual environment to obtain test specifications. This environment pre-runs the Application Under Test (AUT) under its own control, with two prominent characteristics: First, testers can edit test specifications within the true GUI environment of the AUT. Second, the recorded input and output contain the same references as those in the AUT, so that the test cases generated from the edited specification can be used directly by test oracles during the automated testing procedure.We present our running prototype of a visual specification editor that allows users to graphically manipulate test specifications when these specifications are given in term of Finite State Machines (FSM) and the implementations of the AUT are GUI-based Java applications.