42047029
The effect of multiplexing, switching and other factors on the performance of broadband networks
A network model is developed for studying the effect of multiplexing and switching on broadband network performance. Emphasis is placed on the queuing behavior in the network and the impact of multiplexing and switching on the burstiness of the various traffic streams. The three parameters commonly used to characterize traffic (peak bit rate, mean bit rate, and mean burst length) are also considered, and the dependence of the queuing behavior on these parameters is investigated. The performance of three congestion control schemes based on the leaky bucket algorithm is evaluated. The results provide insight into how call acceptance, bandwidth allocation, and bandwidth enforcement should be implemented in a broadband integrated services digital network (BISDN).<<ETX>>
969658
Performance Analysis of Secure Web Server Based on SSL
In recent years, protocols have been developed to ensure secure communications over the Internet, e.g., the secure sockets layer (SSL) and secure electronic transaction (SET). Deployment of these protocols incurs additional resource requirements at the client and server. This may have a negative impact on system performance. In this paper, we consider a scenario where users request information pages stored on a web server, and some of the requests require secure communication. An analytic model is developed to study the performance of a web server based on SSL. In our model, the details of the client-server interactions found in a typical SSL session are represented explicitly. Input parameters to this model are obtained by measuring an existing SSL implementation. Numerical examples on the performance characteristics of SSL are presented.
17359298
Queueing Network Modeling of Computer Communication Networks
The application of queueing network models to the performance analysis of messageswitched (or packet-switched) commumcatmn networks m surveyed. The main topics covered are the analysis of end-to-end delay and the analysis of buffer management schemes. A brief discussmn on flow control is also included. A queueing network model is developed for a simple user-resource network. The mean response time of a host computer m this network is illustrated by a numerical example.
8690187
Distributed Simulation Using a Network of Processors
Abstract Simulation, particulary of networks of queues, is an application with a high degree of inherent parallelism and is of great practical interest. We hope to exploit this parallelism by performing simulations using a network of cheap, but slow, micro-processors. We define a taxonomy by which we classify a number of parameters of a distributed simulation method, and seek solutions to problems of synchronization, deadlock prevention and inter-process communication arising with various methods in each class of the taxonomy. We concentrate in particular on the class (loose, event-driven) which seems to possess the greatest potential parallelism, and on the class (scaled, tight, time-driven) which allows mock-up studies of real systems. We give algorithms for deadlock prevention and detection, and briefly discuss the design of a distributed operating system to support the simulation application. This research forms part of a joint program with the Dept. of Computer Sciences, University of Texas at Austin, directed by Prof. K.M. Chandy.
3873642
On staleness and the delivery of web pages
A popular technique to improve the scalability of a web based system is caching at proxy servers. Caching has the drawback that a cached page becomes stale when the page is updated at the web server. In some cases, staleness may not be completely avoided because the server may not wish to expend the processing and communication resources required to transmit all the updates immediately. In general, if updates are transmitted less frequently, the staleness will tend to increase, but the amount of resources consumed will be reduced. The tradeoff between resource consumption and staleness is investigated. A measure of staleness is defined and optimization problems are formulated. The solutions to these problems allow one to come up with an optimal strategy for transmitting page updates. Numerical examples showing the resource consumption/staleness tradeoff are presented.
7414504
Performance Modeling of a Channel Reservation Service
Certain applications, such as videoconferencing and information broadcast, require the ability to reserve network resources in advance. In a reservation system, users submit requests to a service center. Each request is characterized by a start time, a bandwidth requirement and a holding time. We consider a loss system where the service center rejects a request if it cannot accommodate the request at the preferred start time. Scheduling decisions may be made as soon as a request arrives or may be delayed until a later time. The latter allows the system to make more informed scheduling decisions, but the delay may be unacceptable to the users. In this paper, we investigate the benefits of delaying the scheduling decisions from the performance point of view. Our investigation is based on a reservation system that can accommodate a range of bandwidth requirements. Optimal scheduling decisions are first obtained for some static systems, that is, systems where all requests have arrived before the scheduling decisions are made. The results are then used to develop heuristic scheduling algorithms for systems with delayed decisions. Simulation results on the performance of these algorithms, as compared to a system where scheduling decisions are made immediately upon a request's arrival, are presented.
44084630
Distributed and Fail-Safe Routing Algorithms in Toroidal-Based Metropolitan Area Networks
Abstract A two-dimensional toroidal network is simply a rectangular mesh where opposite nodes on the left and right boundaries are connected to each other and opposite nodes on the upper and lower boundaries are also connected to each other. Examples of toroidal based metropolitan area networks are HR 4 -NET and Manhattan Street Network (MSN). The original routing algorithm for HR 4 -NET proposed by Borgonovo and Cadorin, however, does not direct packets through shortest paths. This paper presents shortest path routing algorithms for HR 4 -NET, which are distributed and fail-safe. These algorithms can also be applied to multiple traffic types. Simple routing rules that use of the regular structure of the network are compared to MSN.
7994830
Watermarking graph partitioning solutions
Trends in the semiconductor industry towards extensive design and code reuse motivate a need for adequate intellectual property protection (IPP) schemes. We offer a new general IPP scheme called constraint-based watermarking and analyze it in the context of the graph partitioning problem. Graph partitioning is a critical optimization problem that has many applications, particularly in the semiconductor design process. Our IPP technique for graph partitioning watermarks solutions to graph partitioning problems so that they carry an author's signature. Our technique is transparent to the actual CAD tool which does the partitioning. Our technique produces solutions that have very low quality degradation levels, yet carry signatures that are convincingly unambiguous, extremely unlikely to be present by coincidence, and difficult to detect or remove without completely resolving the partitioning problem.
1015013
Watermarking of SAT using combinatorial isolation lemmas
Watermarking of hardware and software designs is an effective mechanism for intellectual property protection (IPP). Two important criteria for watermarking schemes are credibility and fairness. In this paper, we present the unique solution-based watermarking technique which provides, in a sense, the ultimate answer to both credibility and fairness requirements. Leveraging on a combinatorial theorem of Valiant and Vazirani, we demonstrate how ultimate credibility and complete fairness can almost always be achieved with high probability during the watermarking of the solution of the satisfiability (SAT) problem. The effectiveness of the technique is demonstrated on both specially created examples where the number of solutions is known, as well as on common CAD and operation research SAT instances.
14591533
Leveraging broadband access for true on-demand delivery of Internet videos
We consider in this paper how the increasingly popular broadband access can be leveraged for scalable and cost-effective video service. Although much work has been done for such service, the existing techniques either are not designed for on-demand video delivery, or do not take into account the vastly improved client receiving capability. In this paper, we address this problem and develop three novel video delivery techniques with two ultimate goals: minimizing service latency and maximize data sharing. With the new techniques, a client can be served as soon as server resource becomes available and meanwhile, all its receiving bandwidth can be used for data receiving. In particular, in the proposed dynamic scheduling algorithm, the efficiency of data sharing is further improved by also exploring server bandwidth for early delivery of video segments. This innovation is contradicted to the intuition that each video segment should be delivered as late as possible in order to maximize data sharing. We evaluate the performance of our new techniques using simulation and our study convincingly shows that with the new schemes, zero service latency can indeed be achieved with very minimal system resource.
10964676
SpecAlign - processing and alignment of mass spectra datasets
SUMMARY
Pre-processing of chromatographic profile or mass spectral data is an important aspect of many types of proteomics and biomarker discovery experiments. Here we present a graphical computational tool, SpecAlign, that enables simultaneous visualization and manipulation of multiple datasets. SpecAlign not only provides all common processing functions, but also uniquely implements an algorithm that enables the complete alignment of each mass spectrum within a loaded dataset. We demonstrate its utility by aligning two datasets each containing six spectra; one set was acquired prior to instrument calibration and the other following calibration.


AVAILABILITY
The software is free of charge and available for download from http://ptcl.chem.ox.ac.uk/~jwong/specalign. Supports Windows operating systems including Windows 9X/NT/2000/XP.