bluuebunny/crossref_metadata_2025 huggingface dataset:
Using real-time queueing theory to control lateness in real-time systems
Authors: Lehoczky John P.
Published: January 2007

This paper presents
real-time queueing theory,
a new theory which embeds the ability of real-time scheduling theory to determine whether task timing requirements are met into the context of queueing models. Specifically, this paper extends the analysis developed in Lehoczky [9] to the GI/M/1 case. The paper also applies these models to study queue control strategies which can control customer lateness. Arriving customers have deadlines drawn from a general deadline distribution. The state variable for the queueing system must include the number in the queue (with supplementary variables as needed to create a Markov model) and the
lead-time
(deadline minus current time) of each customer; thus the state space is infinite dimensional. One can represent the state of the system as a measure on the real line and can represent that measure by its Fourier transform. Thus, a real-time queueing system can be characterized as a Markov process evolving on the space of Fourier transforms, and this paper presents a characterization of the instantaneous simultaneous lead-time profile of all the customers in the queue. This profile is complicated; however, in the heavy traffic case, a simple description of the lead-time profile emerges, namely that the lead-time profile behaves like a Brownian motion evolving on a particular manifold of Fourier transforms; the manifold depending upon the queue discipline and the customer deadline distributions. This approximation is very accurate when compared with simulations. Real-time queueing theory focuses on how well a particular queue discipline meets customer timing requirements, and focuses on the dynamic rather than the equilibrium behavior of the system. As such, it offers the potential to study control strategies to ensure that customers meet their deadlines. This paper illustrates the analysis and performance evaluation for certain queue control strategies. Generalizations to more complicated models and to queueing networks are discussed.
Cache behavior of network protocols
Authors: Nahum Erich , Yates David , Kurose Jim , Towsley Don
Published: January 2007

In this paper we present a performance study of memory reference behavior in network protocol processing, using an Internet-based protocol stack implemented in the
x
-kernel running in user space on a MIPS R4400-based Silicon Graphics machine. We use the protocols to drive a validated execution-driven architectural simulator of our machine. We characterize the behavior of network protocol processing, deriving statistics such as cache miss rates and percentage of time spent waiting for memory. We also determine how sensitive protocol processing is to the architectural environment, varying factors such as cache size and associativity, and predict performance on future machines.We show that network protocol cache behavior varies widely, with miss rates ranging from 0 to 28 percent, depending on the scenario. We find instruction cache behavior has the greatest effect on protocol latency under most cases, and that cold cache behavior is very different from warm cache behavior. We demonstrate the upper bounds on performance that can be expected by improving memory behavior, and the impact of features such as associativity and larger cache sizes. In particular, we find that TCP is more sensitive to cache behavior than UDP, gaining larger benefits from improved associativity and bigger caches. We predict that network protocols will scale well with CPU speeds in the future.
File system aging—increasing the relevance of file system benchmarks
Authors: Smith Keith A. , Seltzer Margo I.
Published: January 2007

Benchmarks are important because they provide a means for users and researchers to characterize how their workloads will perform on different systems and different system architectures. The field of file system design is no different from other areas of research in this regard, and a variety of file system benchmarks are in use, representing a wide range of the different user workloads that may be run on a file system. A realistic benchmark, however, is only one of the tools that is required in order to understand how a file system design will perform in the real world. The benchmark must also be executed on a realistic file system. While the simplest approach may be to measure the performance of an empty file system, this represents a state that is seldom encountered by real users. In order to study file systems in more representative conditions, we present a methodology for aging a test file system by replaying a workload similar to that experienced by a real file system over a period of many months, or even years. Our aging tools allow the same aging workload to be applied to multiple versions of the same file system, allowing scientific evaluation of the relative merits of competing file system designs.In addition to describing our aging tools, we demonstrate their use by applying them to evaluate two enhancements to the file layout policies of the UNIX fast file system.
Operating system benchmarking in the wake of
lmbench
Authors: Brown Aaron B. , Seltzer Margo I.
Published: January 2007

The
lmbench
suite of operating system microbenchmarks provides a set of portable programs for use in cross-platform comparisons. We have augmented the
lmbench
suite to increase its flexibility and precision, and to improve its methodological and statistical operation. This enables the detailed study of interactions between the operating system and the hardware architecture. We describe modifications to
lmbench,
and then use our new benchmark suite,
hbench:OS,
to examine how the performance of operating system primitives under NetBSD has scaled with the processor evolution of the Intel x86 architecture. Our analysis shows that off-chip memory system design continues to influence operating system performance in a significant way and that key design decisions (such as suboptimal choices of DRAM and cache technology, and memory-bus and cache coherency protocols) can essentially nullify the performance benefits of the aggressive execution core and sophisticated on-chip memory system of a modern processor such as the Intel Pentium Pro.
A performance evaluation of cluster architectures
Authors: Qin Xiaohan , Baer Jean-Loup
Published: January 2007

This paper investigates the performance of shared-memory cluster-based architectures where each cluster is a shared-bus multiprocessor augmented with a protocol processor maintaining cache coherence across clusters. For a given number of processors, sixteen in this study, we evaluate the performance of various cluster configurations. We also consider the impact of adding a remote shared cache in each cluster. We use Mean Value Analysis to estimate the cache miss latencies of various types and the overall execution time. The service demands of shared resources are characterized in detail by examining the sub-requests issued in resolving cache misses. In addition to the architectural system parameters and the service demands on resources, the analytical model needs parameters pertinent to applications. The latter, in particular cache miss profiles, are obtained by trace-driven simulation of three benchmarks.Our results show that without remote caches the performance of cluster-based architectures is mixed. In some configurations, the negative effects of the longer latency of inter-cluster misses and of the contention on the protocol processor are too large to counter-balance the lower contention on the data buses. For two out of the three applications best results are obtained when the system has clusters of size 2 or 4. The cluster-based architectures with remote caches consistently outperform the single bus system for all 3 applications. We also exercise the model with parameters reflecting the current trend in technology making the processor relatively faster than the bus and memory. Under these new conditions, our results show a clear performance advantage for the cluster-based architectures, with or without remote caches, over single bus systems.
File server scaling with network-attached secure disks
Authors: Gibson Garth A. , Nagle David F. , Amiri Khalil , Chang Fay W. , Feinberg Eugene M. , Gobioff Howard , Lee Chen , Ozceri Berend , Riedel Erik , Rochberg David , Zelenka Jim
Published: January 2007

By providing direct data transfer between storage and client, network-attached storage devices have the potential to improve scalability for existing distributed file systems (by removing the server as a bottleneck) and bandwidth for new parallel and distributed file systems (through network striping and more efficient data paths). Together, these advantages influence a large enough fraction of the storage market to make commodity network-attached storage feasible. Realizing the technology's full potential requires careful consideration across a wide range of file system, networking and security issues. This paper contrasts two network-attached storage architectures---(1) Networked SCSI disks (NetSCSI) are network-attached storage devices with minimal changes from the familiar SCSI interface, while (2) Network-Attached Secure Disks (NASD) are drives that support independent client access to drive object services. To estimate the potential performance benefits of these architectures, we develop an analytic model and perform trace-driven replay experiments based on AFS and NFS traces. Our results suggest that NetSCSI can reduce file server load during a burst of NFS or AFS activity by about 30%. With the NASD architecture, server load (during burst activity) can be reduced by a factor of up to five for AFS and up to ten for NFS.
Support to the management of clinical activities in the context of protocol-based care
Authors: Pisanelli Domenico M. , Consorti Fabrizio
Published: January 2007

In this paper we describe the system SMART (
S
upporting
M
edical
A
ctivities in
R
eal-
T
ime). The goal of the system is real-time assistance to physicians who execute diagnostic or therapeutic protocols in a clinical context. SMART is able to retrieve a protocol from its knowledge base and to monitor its execution step by step for a single patient. Different protocols for different patients can be followed at the same time in a health care structure.The prototype realized supports the execution of protocols for evaluating surgical risks. It has been implemented according to the specifications given by the 4th Surgical Clinic of "Policlinico Umberto I" and reflects the activities actually performed in that hospital. However, the protocol model defined is general-purpose and we envisage an easy application to other contexts and therefore to the informatization of other protocols.
On issues and tradeoffs in design of fault tolerant VOD servers
Authors: Golubchik Leana
Published: January 2007

Recent technological advances in digital signal processing, data compression techniques, and high speed communication networks have made Video-on-Demand (VOD) servers feasible. A challenging task in such systems is servicing multiple clients simultaneously while satisfying real-time requirements of continuous delivery of objects at specified rates. To accomplish these tasks and realize economies of scale associated with servicing a large user population, a VOD server requires a large disk subsystem. Although a single disk is fairly reliable, a large disk farm can have an unacceptably high probability of disk failure. Furthermore, due to real-time constraints, the reliability and availability requirements of VOD systems are even more stringent than those of traditional information systems. In this paper we discuss some of the main issues and tradeoffs associated with providing fault tolerance in multidisk VOD systems.
Adaptive TTL schemes for load balancing of distributed Web servers
Authors: Colajanni Michele , Yu Philip S.
Published: January 2007

With ever increasing web traffic, a distributed Web system can provide scalability and flexibility to cope with growing client demands. Load balancing algorithms to spread the load across multiple Web servers are crucial to achieve the scalability. Various
domain name server
(DNS) based schedulers have been proposed in the literature, mainly for multiple homogeneous servers. DNS provides (logical) host name to IP-address mapping (i.e., the server assignment), but the mapping is not done for each server access. This is because the address mapping is cached for a time-to-live (TTL) period to reduce network traffic. The presence of heterogeneous Web servers not only increases the complexity of the DNS scheduling problem, but also makes previously proposed algorithms for homogeneous distributed systems such as round robin not directly applicable. This leads us to propose new policies, called
adaptive TTL
algorithms, that take both the uneven distribution of client request rates and heterogeneity of Web servers into account to adaptively set the TTL value for each address mapping request. Extensive simulation results show that these strategies are effective in balancing load among geographically distributed heterogeneous Web servers.
Book review: Prime Time Freeware for AI by Mark Kantrowitz (Editor) (Prime Time Freeware, 1994)
Authors: Monfroglio Angelo
Published: January 2007

As described by the editor Mark Kantrowitz, this book is "an unusual object." It contains two standard ISO-9660 CD-ROMs with 5,000 megabytes (after decompression) of AI-related freeware, evaluation versions of shareware, and commercial AI software. The software comes from the Carnegie Mellon University Artificial Intelligence (CMU AI) Repository, and enormous FTP archive established by Mark Kantrowitz in 1993. The book, 224 pages, includes descriptions of all of the tools and information that one needs to use this software: operating system notes (a brief tutorial on Unix and shorter notes on other systems); descriptions of how to decompress the software; a brief, but complete, fundamental bibliography on all of the AI fields covered by the collection; a well-annotated and ordered package list; and two keyword indexes.
Performance modeling of the IDES framework
Authors: Nicol David M. , Johnson Michael M. , Yoshimura Ann S. , Goldsby Michael E.
Published: January 2007

The IDES project at Sandia National Laboratories is developing a large scale portable parallel simulator for use in stockpile stewardship. IDES will use the Breathing-Time-Buckets synchronization protocol; to support IDES development, this paper studies a performance model and describes performance experiments on expected work load and architectural parameters. A new parallel algorithm for terminating the window quickly is also described and analyzed.
Timestamp representations for virtual sequences
Authors: Cleary John G. , McWha J. A. David , Pearson Murray
Published: January 2007

The problem of executing sequential programs in parallel using the optimistic algorithm Time Warp is considered. This is done by first mapping the sequential execution to a control tree and then assigning timestamps to each node in the tree.For such timestamps to be effective in either hardware or software they must be finite, this implies that they must be periodically rescaled to allow old timestamps to be reused. A number of timestamp representations are described and compared on the basis of: their complexity; the frequency and cost of rescaling; and the cost of performing basic operations, including comparison and creation of new timestamps.
Breadth-first rollback in spatially explicit simulations
Authors: Beelman Ewa , Szymanski Boleslaw K.
Published: January 2007

The efficiency of parallel discrete event simulations that use the optimistic protocol is strongly dependent on the overhead incurred by rollbacks. The paper introduces a novel approach to rollback processing which limits the number of events rolled back as a result of a straggler or antimessage. The method, called breadth-first rollback (BFR), is suitable for spatially explicit problems where the space is discretized and distributed among processes and simulation objects move freely in the space. BFR uses incremental state saving, allowing the recovery of causal relationships between events during rollback. These relationships are then used to determine which events need to be rolled back. The results demonstrate an almost linear speedup-a dramatic improvement over the traditional approach to rollback processing.
The practical management of information ethics problems
Authors: Smith John W.
Published: January 2007

At the 1994 Computing Services Management Symposium Susan Stager (Ferencz) and I presented a workshop on
The Practical Management of Computer Ethics Problems.
My written materials for that workshop were presented in a series of articles in recent SIGUCCS Newsletters. This column offers a continuing exploration of the ideas presented in those articles.
Users lost
Authors: Saracevic Tefko
Published: January 2007

The paper is the acceptance address for the 1997 ACM SIGIR Gerard Salton Award for Excellence in Research. In the preamble, the approach of dealing with the broader context of information science when considering information retrieval (IR) is justified. The first part contains personal reflections of the author related to the major events and issues that formed his professional life and research agenda. The second, and major part, considers the broad aspects of information science as a field: origin, problems addressed, areas of study, structure, specialties, paradigm splits, and education problems. The third part discusses the limits of information science in terms of internal limits imposed by the activities in the field and external limits imposed by the very human nature of information processing and use. Throughout, issues related to users and use are transposed, as being of primary concern.
Notes for a seminar
Authors: Creak G. Alan
Published: January 2007

I describe an approach to specifying computing systems which shows promise as an aid in the design of systems for rehabilitation purposes. This approach has been developed as part of a continuing programme of investigation into the use of multiple communication channels in rehabilitation computing systems. When the work began ( 1988 ) there was little material on the design of computer systems for rehabilitation, and much evidence from the indifferent quality of some of the available software that design aids would be of value. It seemed clear that aids for design and specification could lead to better rehabilitation computing systems; here I advocate what appears to be a new approach to specification. Some earlier work is described in two reports, while the context of the study is set out in a previous note.The approach is directed primarily at computists as they develop designs for the computer component of a rehabilitation system. Clinical questions are not explicitly treated, and are assumed to have been settled before the technical design begins. ( That is
not
a requirement of the approach, and one would hope for interaction between clinical and technical design in practice, but the assumption gives a useful demarcation line for the discussion. )Why might we need special design techniques for rehabilitation systems ? At the level of detail, we don't, as there are already many tested methods for developing software from specifications --- although it would be encouraging to have rather more evidence that they are widely used. Composing the specifications is another matter, and here rehabilitation systems have two special features. First, the proper aim is communication, not merely character transmission; I shall discuss this point further. Second, we are commonly working with unconventional input or output equipment, where the computists' usual assumptions might not be appropriate. It is in these areas that the specification aid is effective.The approach is not ( yet ? ) a formal design technique. At present it is in the nature of a checklist, focusing attention on certain attributes of information handled in the system under consideration.
Fraction-free algorithms for linear and polynomial equations
Authors: Nakos George C. , Turner Peter R. , Williams Robert M.
Published: January 2007

This paper extends the ideas behind Bareiss's fraction-free Gauss elimination algorithm in a number of directions. First, in the realm of linear algebra, algorithms are presented for fraction-free LU "factorization" of a matrix and for fraction-free algorithms for both forward and back substitution. These algorithms are valid not just for integer computation but also for any matrix system where the entries are taken from a unique factorization domain such as a polynomial ring. The second part of the paper introduces the application of the fraction-free formulation to resultant algorithms for solving systems of polynomial equations. In particular, the use of fraction-free polynomial arithmetic and triangularization algorithms in computing the Dixon resultant of a polynomial system is discussed.
Factors of iterated resultants and discriminants
Authors: McCallum Scott
Published: January 2007

The motivation for this poster comes from observations made by Collins [2] about factors of iterated resultants and discriminants of polynomials in three variables. This poster presents theorems which explain some of Collins' observations. A starting point for our work was a letter from van der Waerden [7] to Collins which provides intuitive and informal explanations for some of Collins' observations. We are hopeful that the results contained herein could provide the basis for improvements to some algorithms involving resultant and discriminant calculation, such as the cylindrical algebraic decomposition algorithm.
Parallelism in MuPAD
Authors: Heckler Christian , Kluge Oliver , Metzner Torsten , Sorgatz Andreas , Zimmermann Paul
Published: January 2007

S
INGULAR
is a computer algebra system designed to be a power-house for polynomial computations with special features for algebraic geometry and singularity theory.The development of S
INGULAR
started in 1986, motivated by the question of the existence of complete intersection singularities which are not quasi-homogeneous, but whose Poincare-complex is exact. The existence of such singularities could be shown in 1987 with an implementation of Mora's algorithm on an Atari in Modula-2 [11]. In 1990, S
INGULAR
was ported to Unix, and a first public-domain distribution followed. The code of S
INGULAR
was rewritten in C/C++. An interpreted user-level programming language and user-written libraries were added in 1993. With the release of version 1.0 in May 1997, many important features were added, including:• Polynomial factorization• Factorizing Buchberger algorithm• FGLM algorithm• Primary decomposition of ideals• MP links for general and efficient storage and inter-process communicationsThe goal of the poster is to discuss and demonstrate these new features of S
INGULAR
where, in combination with the posters on MP and MuPAD, special emphasize will be paid to S
INGULAR
's MP interface and its resulting possibilities and problems.
LiDIA—a library for computational number theory
Authors: Maurer Markus , Pfahler Thomas , Wetzel Susanne
Published: January 2007

We will sketch the basic concepts and main features of the object-oriented C++ library LiDIA, that is developed by LiDIA group at Universität des Saarlandes and the Technische Hochschule in Darmstadt. We will present in more detail the classes for factoring polynomials over finite fields together with some running times.
Parallel simulations of wireless networks with TED
Authors: Panchal Jignesh , Kelly Owen , Lai Jie , Mandayam Narayan , Ogielski Andarew T. , Yates Roy
Published: January 2007

We describe the
TeD
/C++ implementation of

WiPPET

, a parallel simulation testbed for mobile wireless networks. In this article we emphasize the techniques for modeling of radio propagation (long- and short-scale fading and interference) and protocols for integrated radio resource management in mobile wireless voice networks. The testbed includes the standards-based AMPS, NA-TDMA and GSM protocols, and several research-oriented protocol families.
IS downsizing survivor's career management attitudes
Authors: Jiang James J. , Margulis Stephen T. , Klein Gary
Published: January 2007

IS downsizing is a significant tool of management in the 1990's. A key element in downsizing success is how it is perceived by employees. Still, no widely published study has examined the attitudes of IS survivors to downsizing. Moreover, in the age of a new psychological contract between organizations and employees, employees have assumed responsibility for managing their careers. However, no studies of the career management strategies of IS survivors in the downsized workplace are found. In addition, studies of downsizing in the general workforce have shown that demographic differences may affect employees' responses to downsizing. Again, no study appears to have focused on Information System personnel. For all of these reasons, this study examines the attitude of IS employees toward downsizing, the career management approach of survivors, and whether demographic characteristics of IS survivors of organizational downsizing are related to their attitudes and strategies. The results of a survey indicate that IS survivors, regardless of their demographic characteristics tend to be neutral toward downsizing as a means of improving the organization. Demographic characteristics were also unrelated to internally-oriented career management strategies but were related to externally-oriented strategies.
Information systems managers' perceptions of the advantages and disadvantages of telecommuting
Authors: Ellis T. Selwyn , Webster Robert L.
Published: January 2007

Prior research on telecommuting has not addressed the attitudes of Information Systems managers concerning the advantages and disadvantages of telecommuting. Additionally, telecommuting research has not investigated if differences in attitudes concerning telecommuting exist based on geographical location or if attitudes are affected if a telecommuting program is currently in place. This research extends the body of knowledge by concentrating on these heretofore unstudied areas.Seven hundred and eighty-nine Information Systems (IS) managers from two diverse geographic regions of the United States, the West Coast and the Southeast, were surveyed in this study. The IS managers were asked to respond to a series of twelve advantages and eleven disadvantages associated with telecommuting. These advantages and disadvantages were derived from previously published studies. Each item's importance was recorded on a seven point Likert scale, where a one indicated very unimportant and a seven indicated very important. In addition to geographic region of the respondent, information was collected to identify if the respondent's organization had a telecommuting program in place. Survey variables were reduced using factor analysis and results are reported.As expected, several of the variables were perceived differently by survey respondents. Explanations are offered for the reported differences and areas for future research are discussed.
Information and resource referral center project
Authors: Miller Nancy E. , Lamb Ann Marie , Chi Fei-Jiuan Joan
Published: January 2007

The Rehabilitation Research and Training Center (RRTC) on Blindness and Low Vision at Mississippi State University (MSU) has developed software for a rehabilitation database system. The database includes the most current national resources on blindness and visual impairments to assist persons in locating resources to further their own rehabilitative efforts, or on behalf of someone else who may need information. In addition, users can also obtain information about professional development training programs, current Washington, DC legislative liaisons, and national resources and research data related to blindness and visual impairments. Materials requested are disseminated by mail or fax in regular print, large print, on audio tape, or in braille.
Requisite IS management knowledge and skills construct
Authors: Shi Nansi , Bennett David
Published: January 2007

A review of the literature suggests that various IS knowledge and skills should be grouped into a construct because many IS tasks require a combination of diverse disciplines. Many studies argue that today's IS executives should be multidisciplinary, while the organizational skills are becoming increasingly important. However, the outstanding issue is what is the appropriate balance of disciplines between the organizational domain and technical domain. For understanding such a balance, it is easier to refer to quantitative proportions than to qualitative descriptions. Therefore, this study suggests a way to quantitatively identify an IS management knowledge and skills construct - a combination that comprises six related knowledge and skills categories suggested by the literature. By analyzing the data obtained in a 1996's survey, two such constructs for current proficiency and expected level have been quantitatively identified. To people aiming at a senior IS executive career, the deficiencies between current and expected constructs suggest not only the direction but also the extent should be enhanced, and the constructs indicate the balance among various disciplines should be maintained.
Cello
Authors: Shenoy Prashant J. , Vin Harrick M.
Published: January 2007

In this paper, we present the Cello disk scheduling framework for meeting the diverse service requirements of applications. Cello employs a two-level disk scheduling architecture, consisting of a class-independent scheduler and a set of class-specific schedulers. The two levels of the framework allocate disk bandwidth at two time-scales: the class-independent scheduler governs the coarse-grain allocation of bandwidth to application classes, while the class-specific schedulers control the fine-grain interleaving of requests. The two levels of the architecture separate application-independent mechanisms from application-specific scheduling policies, and thereby facilitate the co-existence of multiple class-specific schedulers. We demonstrate that Cello is suitable for next generation operating systems since: (i) it aligns the service provided with the application requirements, (ii) it protects application classes from one another, (iii) it is work-conserving and can adapt to changes in work-load, (iv) it minimizes the seek time and rotational latency overhead incurred during access, and (v) it is computationally efficient.
Is service priority useful in networks?
Authors: Bajaj Sandeep , Breslau Lee , Shenker Scott
Published: January 2007

A key question in the definition of new services for the Internet is whether to provide a single class of relaxed real-time service or multiple levels differentiated by their delay characteristics. In that context we pose the question: is service priority useful in networks? We argue that, contrary to some of our earlier work, to properly address this question one cannot just consider raw network-centric performance numbers, such as the delay distribution. Rather, one must incorporate two new elements into the analysis: the utility functions of the applications (how application performance depends on network service), and the adaptive nature of applications (how applications react to changing network service). This last point is especially crucial; modern Internet applications are designed to tolerate a wide range of network service quality, and they do so by adapting to the current network conditions. Most previous investigations of network performance have neglected to include this adaptive behavior.In this paper we present an analysis of service priority in the context of audio applications embodying these two elements: utility functions and adaptation. Our investigation is far from conclusive. The definitive answer to the question depends on many factors that are outside the scope of this paper and are, at present, unknowable, such as the burstiness of future Internet traffic and the relative offered loads of best-effort and real-time applications. Despite these shortcomings, our analysis illustrates this new approach to evaluating network design decisions, and sheds some light on the properties of adaptive applications.
Application and evaluation of large deviation techniques for traffic engineering in broadband networks
Authors: Courcoubetis Costas , Siris Vasilios A. , Stamoulis George D.
Published: January 2007

Accurate yet simple methods for traffic engineering are important for efficient dimensioning of broadband networks. The goal of this paper is to apply and evaluate large deviation techniques for traffic engineering. In particular, we employ the recently developed theory ofeffective bandwidths, where the effective bandwidth depends not only on the statistical characteristics of the traffic stream, but also on a link's operating point through two parameters, thespaceandtimeparameters, which are computed using themany sources asymptotic. We show that this effective bandwidth definition can accurately quantify resource usage. Furthermore, we estimate and interpret values of the space and time parameters for various mixes of real traffic demonstrating how these values can be used to clarify the effects on the link performance of the time scales of burstiness of the traffic input, of the link parameters (capacity and buffer), and of traffic control mechanisms, such as traffic shaping. Our approach relies on off-line analysis of traffic traces, the granularity of which is determined by the time parameter of the link, and our experiments involve a large set of MPEG-1 compressed video and Internet Wide Area Network (WAN) traces, as well as modeled voice traffic.
LoGPC
Authors: Moritz Csaba Andras , Frank Matthew I.
Published: January 2007

In many real applications, for example those with frequent and irregular communication patterns or those using large messages, network contention and contention for message processing resources can be a significant part of the total execution time. This paper presents a new cost model, called LoGPC, that extends the LogP [9] and LogGP [4] models to account for the impact of network contention and network interface DMA behavior on the performance of message-passing programs.We validate LoGPC by analyzing three applications implemented with Active Messages [11, 18] on the MIT Alewife multiprocessor. Our analysis shows that network contention accounts for up to 50% of the total execution time. In addition, we show that the impact of communication locality on the communication costs is at most a factor of two on Alewife. Finally, we use the model to identify tradeoffs between synchronous and asynchronous message passing styles.
Total acknowledgements (extended abstract)
Authors: Waldby J. , Madhow U. , Lakshman T. V.
Published: January 2007

End-to-end data transport protocols have two main functions: error recovery and congestion control. The information required by the sender to perform these functions is provided by acknowledgements (ACKs) from the receiver. The Internet transport protocol, TCP/IP, uses cumulative acknowledgements (CACKs), which provide a robust but minimal mechanism for error recovery which is inadequate for heterogeneous networks with random loss. Furthermore, TCP's congestion control mechanism is based on counting ACKs, and is therefore vulnerable to loss of ACKs on the reverse path, particularly when the latter may be slower than the forward path, as in asymmetric networks. The contributions of this paper are as follows:(a) We show that a simple enhancement of CACK provides sufficient information for end-to-end
congestion control
. We term this ACK format total ACKs (TACKs).(b) We devise a novel ACK format that uses TACKs for congestion control, and negative ACKs (NACKs) for efficient error recovery. Typically, the main concern with NACKs is that of robustness to ACK loss, and we address this using an implementation that provides enough redundancy to provide such robustness.(c) We use the TACK+NACK acknowledgement format as the basis for a new transport protocol that provides efficient error recovery and dynamic congestion control. The protocol provides large performance gains over TCP in an environment with random loss, and is robust against loss of ACKs in the reverse path. In particular, the protocol gives high throughput upto a designed level of random loss, independent of the bandwidth-delay product. This is in contrast to TCP, whose throughput deteriorates drastically if the random loss probability is higher than the inverse square of the bandwidth-delay product.
Auditory Icons
Authors: Gaver William W.
Published: January 2007

Carroll and Campbell have exercised themselves over a straw man not subscribed to by us. In doing so, they have misrepresented our position and even the statements in our paper. In reply, we restate as clearly as we can the position for which we actually did and do argue and give examples of their misrepresentations. The underlying issue seems to concern the advantages of using technical psychological theories to identify underlying mechanisms in human-computer interaction. We argue that such theories are an important part of a science of human-computer interaction. We argue further that technical theories must be considered in the context of the uses to which they are put. Such considerations help the theorist to determine what is a good approximation, the degree of formalization that is justified, the appropriate commingling of qualitative and quantitative techniques, and encourages cumulative progress through the heuristic of divide and conquer.
A comparison of textual information retention from CRT terminals and paper
Authors: Wyle Mitchell F.
Published: January 2007

An experiment measuring the difference in reading comprehension and retention between paper and CRT displays is described. Results, conclusions, and implications are presented. The results indicate that textual information is retained significantly better when it is presented on paper.
Dynamic patterns as an alternative to conventional text for the partially sighted
Authors: Veal David
Published: January 2007

When the partially sighted can no longer read even enlarged conventional text then possible aids include Touch Braille and speech synthesis. Touch Braille has proved to be very useful for those with no vision and also for the partially sighted who can only read with difficulty and hence liable to suffer from early fatigue. However, both of these aids lack any visual feedback useful for those with some residual sight. Visual Braille may also be of use but is limited to a given set of standard patterns. It should be noted that many partially sighted people may still be able to see a few areas of different color which maybe sufficient to allow different combinations of colored elements to represent a useful character set.The authors propose a possible alternative reading aid called Dynamic Pattern System (DPS) where each pattern or series of patterns can represent an ASCII character. Each pattern consists of a number of distinct areas, each of which can assume one of a set number of colors. A particular set of patterns representing a character set is known as a patternset. There are many conditions that can lead to partial sight and hence these patternsets may be individualised to each user thereby making full use of their limited vision. This can be regarded as an interface matching solution.The input or output of a DPS can be read as standard text by conventional text-based word processors, web browsers and other standard IT equipment. Using a DPS it may be possible for some partially sighted users to communicate with each other each using their own individualised patternset. Furthermore a fully sighted person may be able to both send and receive conventional text when communicating with a person using a DPS. An extensive literature search has failed to find any comparable work.Hence the advantages of such a system include:-• Standard PCs (minimum 386, Windows 3.x, 4M RAM) with no special equipment may be used to encourage the full integration of some partially sighted individuals, who are unable to read even enlarged text, into a standard office environment.• A standard PC running DPS may be used by the fully sighted.• DPS is a very small (one floppy disk) and easy to use software driven user interface requiring no special hardware and hence offers a low cost solution.• Individualized patternsets may allow the most effective use of a user's limited vision.
Co-array Fortran for parallel programming
Authors: Numrich Robert W. , Reid John
Published: January 2007

Co-Array Fortran, formerly known as F
--
, is a small extension of Fortran 95 for parallel processing. A Co-Array Fortran program is interpreted as if it were replicated a number of times and all copies were executed asynchronously. Each copy has its own set of data objects and is termed an image. The array syntax of Fortran 95 is extended with additional trailing subscripts in square brackets to give a clear and straightforward representation of any access to data that is spread across images.References without square brackets are to local data, so code that can run independently is uncluttered. Only where there are square brackets, or where there is a procedure call and the procedure contains square brackets, is communication between images involved.There are intrinsic procedures to synchronize images, return the number of images, and return the index of the current image.We introduce the extension; give examples to illustrate how clear, powerful, and flexible it can be; and provide a technical definition.
CASE tools
Authors: Chervany Norman L. , Lending Diane
Published: January 2007

Computer-Aided Software Engineering (CASE) technologies are tools that provide automated assistance for software development [3]. The goal of introducing CASE tools is the reduction of the time and cost of software development and the enhancement of the quality of the systems developed [3], [20]. This paper explores the use of CASE tools. We ask several questions. Are CASE tools being used? If yes, what features within the tool are being used? Next, we explore two potential reasons for the expected low use. Do CASE tools change the job of the systems developer in an unattractive way? And are the people who are expected to use CASE tools motivated to use them?233 systems developers were surveyed to answer these questions. We found that CASE tools are being used but not in many companies. Within the companies that have adopted CASE tools, few people are actually using the tools. The systems developers who use CASE tools are using formal methodologies more often than systems developers who do not use CASE tools. Systems developers allocate their time differently depending on whether they are using a CASE tool or not. Those who use the tools are using few of the functions within the tools. Finally we found that people were basically neutral on whether they enjoyed using the tool and whether the tool was useful.
Book review: Artificial Minds By Stan Franklin (MIT Press)
Authors: Causey Robert L.
Published: January 2007

This book is primarily an exposition of theories of mind and of recent attempts to invent artificial minds. It reviews a large body of work in the fields of artificial intelligence (AI), artificial life, cognitive science, and neuroscience. It is also informed by work in philosophy and in biology, especially neuroscience and the study of animal behavior. The author's own view of the nature of mind emerges largely through his assessments of the various theories he presents. He believes that recent research is leading toward a "new paradigm of mind" (p. 421), a viewpoint which will be appraised later in this review. Franklin writes with a clear and pleasant style, and his expository descriptions are aimed at a broad audience. The reader should have some general mathematical and scientific knowledge, including the basic ideas of how computers and programming languages work, but otherwise no special technical background is required. The level of difficulty of the book is a little higher than that of aScientific Americanarticle.
A literature survey on distributed discrete event simulation
Authors: Kaudel Fred J.
Published: January 2007

Much literature over the past decade has examined using multiprocessors to increase the speed and lower the cost of discrete event simulation. Three orthogonal approaches have been suggested, using simulation parallelism in support functions, in model functions and on the application level. This overview brings together these past approaches into a new framework wherein all three can be used simultaneously and suggests several promising research areas.
Symbolic computation of potential energy functions
Authors: Popov Atanas
Published: January 2007

We derive potential energy functions for a shallow cylindrical panel. The starting point is a system of two coupled partial differential equations based on Donnell's shallow shell theory. The total potential energy is approximated using a finite number of degrees of freedom. All calculations are performed by computer algebra routines. Two applications of potential energy functions are discussed: the analysis of shell buckling and the derivation of systems of ordinary differential equations that govern dynamic behaviour.
Coordinating distributed applets with Shade
Authors: Ciancarini P. , Rossi D.
Published: January 2007

As coordinated activities like electronic commerce and workflow systems are emerging as an important applications field of the Internet, it is necessary to invent and test new programming languages suitable to design these applications. Shade is a language for coordinating active pages including Java applets. Shade is based on a concept called the object space, that is used both as repository for objects and as coordination medium. The object space offers several services which can be exploited by Java objects. We describe the basic ideas in the language, its current implementation and programming environment, and two applications in the fields of electronic commerce and workflow applications.
Community viewer
Authors: Nishimura Toshikazu , Yamaki Hirofumi , Komura Takaaki , Ishida Toru
Published: January 2007

Mobile computing has been mainly utilized for point-to-point communication services, such as E-mail or FAX among people. To advance this field, the challenge is to encourage group communication by providing information that encourages community formation. As the first step towards this goal, we experimentally implemented the
community viewer,
which dynamically visualizes the communication interaction among people in the community. To design the community viewer, we introduced (1) the
party room metaphor,
which provides a virtual place for representing various community activities, and (2) the
reflector icon,
which reflects the activity of the corresponding individual while protecting his/her privacy. The static relationship among people and their dynamic activities are displayed in the spatial arrangement of reflector icons in the party room. We report our experiments on implementing and testing the community viewer in an international conference using 100 personal digital assistants.
A prolog program for decomposing clothing orders into lays
Authors: Rosenblueth David A.
Published: January 2007

We describe a Prolog program for solving a problem occurring in the clothing industry. The input of the problem is a clothing "order," consisting of a number of requested garments for each size. The output is a decomposition of the given order into "lays," producing exactly the requested number of garments per size. We wish to minimize both the fabric and the labor costs. For each lay we are only interested in knowing how many copies of the set of pieces of each size are to be placed (we do not deal with the geometrical problem of placing such pieces). Computing an optimal decomposition can be viewed as a generalization of the bin-packing problem.Our system uses an enumerative, branch-and-bound method to traverse a search space. This approach resulted practical only for orders with up to seven sizes. However, since most of the orders in the firm where we found this problem have exactly this number of sizes, our system is useful in spite of having this limitation.