2983275
The interrelation of TCP responsiveness and smoothness in heterogeneous networks
TCP(/spl alpha/,/spl beta/) protocols trade the congestion window increase value /spl alpha/ for the decrease ratio /spl beta/, to generate smoother traffic patterns and to maintain a friendly behavior. We study the design assumptions of TCP(/spl alpha/,/spl beta/) protocols and discuss the impact of equation-based modulation of /spl alpha/ and /spl beta/ on application efficiency. We confirm experimentally that, in general, smoothness and responsiveness constitute a tradeoff; however, we uncover undesirable dynamics of the protocols when the network or flow characteristics do not follow a prescribed and static behavior. For example, we show that smooth backward adjustments confine the protocol's capability to exploit resources that become available rapidly, and embarrass the fair and efficient growth of incoming flows. Furthermore, we show that in the context of wireless networks with high error rate, a low /spl alpha/ dictates a conservative behavior that degrades the protocol performance with both delay-tolerant and delay-sensitive applications; and in the context of high contention of heterogeneous flows, a low /spl alpha/ does not contribute to efficiency and friendliness.
1830896
A Communication Virtual Machine
The convergence of data, voice and multimedia communication over digital networks, coupled with continuous improvement in network capacity and reliability has significantly enriched the ways we communicate. However, the stovepipe approach used to develop today's communication applications and tools results in rigid technology, limited utility, lengthy and costly development cycle, difficulty in integration, and hinders innovation. In this paper, we present a fundamentally different approach, which we call communication virtual machine (CVM) to address these problems. CVM provides a user-centric, model-driven approach for conceiving, synthesizing and delivering communication solutions across application domains. We argue that CVM represents a far more effective paradigm for engineering communication solutions. The concept, architecture, modeling language, prototypical design and implementation of CVM are discussed
3978452
The Interaction Between Window Adjustment Strategies and Queue Management Schemes
In this paper, we investigate extensively the joint network dynamics with different AIMD window-adjustment parameters on end-hosts, and different queue management schemes (i.e. DropTail vs. RED) in routers. We reveal that with DropTail buffer, although smooth TCPs causes less queuing-delay jitter, its average queuing delay is significantly higher than that of responsive TCPs. The direct implication of this discovery is that when mobile users of media-streaming and short messages share a bottleneck link, the energy consumption for sending short messages can increase severely if media-streaming users adopt smooth TCPs. With RED, on the other hand, smooth TCPs not only lead to smaller queue oscillation, the average/max queue length is smaller as well.
1383951
Improving TCP smoothness by synchronized and measurement-based congestion avoidance
In this paper, we observe that although multiplicative decrease is necessary to accomplish fairness in congestion control, it does not inevitably sacrifice system throughput, as long as the system operates between the knee and the cliff, according to an equation. However, even when the system throughput is relatively stable, end users of real-time applications do not necessarily experience a smooth traffic, mainly caused by the unsynchronized window adjustments due to random congestion indications. We analyzed and evaluated the negative impact of random window adjustments on smoothness, short-term fairness, and even long-term fairness measured by a novel fairness metric defined in this paper. Therefore, we propose an experimental congestion avoidance mechanism to improve TCP smoothness for media-streaming applications. The mechanism relies on a fine-grained RTT estimation to measure the network condition, and coordinates the upward and backward window adjustments to abolish the damage of unsynchronized window control. Congestive packet drops are reduced by a new control parameter g, and the bottleneck queue length can also be controlled in an end-to-end way. Simulation results confirm that the new mechanism enhance significantly the smoothness and fairness, without a cost of responsiveness. In fact, by enabling a new parameter d, the responsiveness can be even enhanced when the bandwidth is under-utilized.
33105882
CyberBridges A Model Collaboration Infrastructure for e-Science
The "CyberBridges" pilot project is an innovative model for creating a new generation of scientists and engineers who are capable of fully integrating cyberinfrastructure into the whole educational, professional, and creative process of their respective disciplines. CyberBridges augments graduate student education to include a foundation of understanding in advanced networking and grid infrastructure for high performance computing, and bridges the divide between the information technology community and diverse science and engineering disciplines. We demonstrate the effectiveness of CyberBridges by providing four case studies. Groundwork has begun to extend the outreach of CyberBridges for international research and education collaborations.
3967435
Experimental Evaluation of Red in Heterogeneous Environments
206924421
Classification of access network types: Ethernet wireless LAN, ADSL, cable modem or dialup?
Ethernet, wireless LAN, ADSL, cable modem and dialup are common access networks, but have dramatically different characteristics. Fast and accurate classification of access network type can improve protocol or application performance significantly. In this paper, we propose a simple and efficient end-end scheme to classify the type of an access network into three categories: Ethernet, wireless LAN and low-bandwidth connection. Our scheme is based on the intrinsic characteristics of the various access networks and utilizes the median and entropy of packet pair inter-arrival times. Extensive experiments show that our scheme obtains accurate classification results in a very short time (10 to 100 seconds).
28540558
A Serving Agent for Integrating Soft Computing and Software Agents
This paper discusses the design and implementation of a serving agent for integrating soft computing and software agents.
36530209
Determination of the star valency of a graph
The star valency of a graph G is the minimum, over all star decompositions π, of the maximum number of elements in π incident with a vertex. The maximum average degree of G, denoted by dmax-ave(G), is the maximum average degree of all subgraphs of G. In this paper, we prove that the star valency of G is either ⌈dmax-ave(G)/2⌉ or ⌈dmax-ave(G)/2⌉ + 1, and provide a polynomial time algorithm for determining the star valency of a graph.
2272663
Refactoring Middleware with Aspects
Middleware platforms, such as Web services, J2EE, CORBA, and DCOM, have become increasingly popular during the last decade. They have been very successful in solving distributed computing problems for a large family of application domains. The architecture of middleware systems have gone through many significant cycles of evolution, both in terms of the completeness of functionality and the range of adoptions for different types of platforms. However, at the same time, it is getting increasingly difficult to achieve and to maintain a high level of adaptability and configurability because the structure of the middleware architecture is becoming overly complicated and rigid. We attribute that problem to the limitations of traditional software decomposition methods. Aspect-oriented programming, on the contrary, has introduced new design perspectives that permit the superimpositions of different abstraction models on top of one another. This is a very powerful technique for separating and simplifying design concerns. In our effort of applying principles of aspect orientation to the middleware architecture, we first pragmatically analyze the use of aspects in the middleware architecture. We then show that aspects are the correct remedy for the above outlined middleware problems by quantifying crosscutting concerns in the legacy implementations of several prominent middleware systems. Our aspect analysis results strongly indicate that modularity of middleware architecture is greatly hindered by the wide existence of tangled logic. To go one step further, we factor out a number of crosscutting concerns identified in the mining process, reimplement them as aspects, and superimpose them back into the refactored architecture. This allows us to use a set of software engineering metrics to quantify the refactorization in terms of changes in the structural complexity, modularity, and performance of the resulting system. This aspect-oriented refactoring proves that aspect orientation is capable of composing orthogonal design requirements. The final "woven" system is able to correctly provide both the fundamental functionality and the "aspectized" functionality with negligible overhead and an overall leaner architecture. Furthermore, the "aspectized" feature can be configured in and out during compile-time, which greatly enhances the configurability of the architecture.
16103789
A flexible image retrieval and multimedia presentation management system for multimedia databases
In today's fast-growing information age, multimedia data is becoming more and more common in daily applications, however this data is nearly useless if there is no computer-aided browsing, searching, and retrieving mechanism to obtain the desired contents. In this demonstration, we present a multimedia query and presentation management system for multimedia databases. It uses an unsupervised segmentation method for image and video feature extraction. A presentation design interface systems is provided that allows query results to be used to create multimedia presentations.