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.
3967435
Experimental Evaluation of Red in Heterogeneous Environments
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.
1874082
TCP-real: improving real-time capabilities of TCP over heterogeneous networks
We present a TCP-compatible and -friendly protocol which abolishes thr ee major shortfalls of TCP for reliable multimedia applications over heterogeneous networks: (i) ineffective bandwidth utilization, (ii) unnecessary congestion-oriented responses to wireless link errors (e.g., fading channels) and operations (e.g. handoffs), and (iii) wasteful window adjustments over asymmetric, low-bandwidth reverse paths. We propose TCP-Real, a high-throughput transport protocol that minimizes transmission-rate gaps, thereby enabling better performance and reasonable playback timers. In TCP-Real, the receiver decides with better accuracy about the appropriate size of the congestion window. Slow Start and timeout adjustments are used whenever congestion avoidance fails; however, rate and timeout adjustments are cancelled whenever the receiving rate indicates sufficient availability of bandwidth. We detail the protocol design and we report significant improvement on the performance of the protocol with time-constrained traffic, wireless link errors and asymmetric paths.
7030276
Adaptive Query-Caching in Peer-to-Peer Systems
Peer-to-Peer (P2P) architectures are very prevalent in today’s Internet. Lots of P2P file sharing systems using Gnutella protocol emerge out and draw attractions of millions of people. The “flooding” search mechanism of Gnutella makes it easy to be deployed, but also spawns numerous messages which leads to serious scalability problems. However, the locality discovered in both user’s share files and queries, enables us to use query-caching to shorten the search length and reduce the messages traffic. This paper makes an extensive study of query-caching in P2P systems and proposes an adaptive query-caching mechanism to manage the cached query reply messages according to the heterogeneity of the uptime of different peers. Along with several other techniques we proposed, our approach achieves a 30% reduction of average search length and a 61% reduction of query message traffic comparing with the previous query-caching mechanisms in the simulation, which indicates that our approach makes Gnutella more scalable.
14748826
QoS-Aware Optimization of Composite-Service Fulfillment Policy
In a service-oriented IT infrastructure, functional capabilities of a computing component are externalized via one or more service interfaces. Driven by the demand for business agility and return-on-investment optimization, various dynamic service discovery and composition technologies have been proposed and developed with a common goal of enabling business-aligned fulfillment of customer requests. However, from the viewpoint of capacity planning and IT optimization, much work is still needed in helping an enterprise decide the "optimal" IT resources necessary for deploying the atomic services in support of those composite ones. The service deployment decision must be integrated with the request fulfillment policy so that the differentiated quality-of-service (QoS) requirements of service requests can be met, for instance, with minimum hardware/software cost. In this paper, we propose an approach for QoS-aware optimization of composite-service fulfillment policy. Without loss of generality, we assume that the optimization goal is to minimize the number of machines subject to response time and throughput requirements. After presenting our approach to the optimization problem using the assumption, we show that an NP-hard throughput optimization problem must be attacked. We then illustrate how we attack the problem via an efficient heuristic algorithm. The algorithm decomposes the end-to-end response time requirement for each type of composite service into atomic-service level response time assurance, and co-locate atomic services with similar response time assurance on machines with similar utilization characteristics. The algorithm exemplifies an integrated approach to optimizing service deployment and service composition. We demonstrate that the algorithm achieves a substantially higher throughput than a common baseline algorithm.
10539713
On optimal routing with multiple traffic matrices
Routing optimization is used to find a set of routes that minimizes cost (delay, utilization). Previous work has addressed this problem for the case of a known, static end-to-end traffic matrix. In the Internet, it is difficult to accurately estimate a traffic matrix, and the constantly changing nature of Internet traffic makes it costly to maintain optimal routing by responding to traffic changes. Thus, it is of interest to maintain a set of routes that are "good" for a number of different possible traffic scenarios. In this paper, we explore ways to find an optimal set of routes with multiple traffic matrices to minimize expected cost. We focus on two general approaches, source-destination routing and destination routing. In the case of source-destination routing, we extend existing methods with a single traffic matrix to solve the optimization problem with multiple traffic matrices: we extend the convex optimization solution methods for a single traffic matrix to the multiple traffic matrix case; we also extend the gradient-based solution methods for a single traffic matrix to the multiple traffic matrix case. However, the multiple traffic matrix case requires many more control variables. In the case of destination routing, we encounter many more differences from the single traffic matrix case. The loop-free property, which is valid for the single traffic matrix case, is no longer valid for the multiple traffic matrix case, and it is difficult to extend existing methods for a single traffic matrix to solve the optimization problem with multiple traffic matrices. We show that it is NP-complete even to determine the feasibility of multiple traffic matrices. We thus propose and evaluate a heuristic algorithm for this case.
2023360
A reliable Web-based system for hurricane analysis and simulation
In this paper, we present our research and development efforts toward a reliable, large-scale, Web-based system for hurricane analysis and simulation. The major contributions of this system lie in the following three aspects: (1) it supports the multidisciplinary research efforts in predicting and simulating the hurricane damages and insured losses; (2) it is a large-scale, distributed, Web-based system, which allows both the professional and general users to conduct computational intensive on-line analysis simultaneously and to share and exchange the information; and (3) database management techniques are employed in our system to manage the huge amount of hurricane-related historical and simulated data.
23191981
Cycles of all lengths in arc-3-cyclic semicomplete digraphs
Abstract Let D be an arc-3-cyclic, semicomplete digraph and uv be an arc of D contained in a cycle of length r . If vu ∉ A ( D ) then the arc uv is contained in cycles of length h : 3 ⩽ h ⩽ r , or if δ + ( D ), δ − ( D ) ⩾ 3 then the arc uv is contained in cycles of length h : 6 ⩽ h ⩽ r . Also included in this paper is a very useful crossing arc theorem .