bluuebunny/crossref_metadata_2025 huggingface dataset:
A distributed system security architecture
Authors: Mirhakkak Mohammad
Published: October 2004

A great deal of attention has been given to the development of Open Systems Interconnection (OSI) security protocols in recent years. However, limited work has been dedicated to using these protocols to develop security architectures for securing distributed systems consisting of trusted computer systems communicating via untrusted networks. This paper presents an overview of the Transport Layer Security Protocol (TLSP) and discusses its application to the development of a security architecture for a generic distributed system that uses the OSI transport layer protocol. In addition, the paper discusses the security services that can be achieved as a result of employing the TLSP in a distributed system. It also examines the security functions that are expected from the end-systems, and addresses the security management functions that are required for the operation of the TLSP.
Security protocol for Frame Relay
Authors: Katsavos Panagiotis , Varadharajan Vijay
Published: October 2004

This paper considers the protection of traffic using the Frame Relay service. First, we briefly describe the structure and functionality of the Frame Relay interface. Differences between the PTTs and the private vendor community with respect to Frame Relay interface are outlined. Then, we consider why the existing security protocols are inadequate in protecting the Frame Relay traffic effectively. This leads to the proposal of a new security sublayer (SFRC) which provides
Secure Frame Relay Connections.
Initially, we discuss the choice behind the placement of the SFRC sublayer within the Frame Relay interface. Then, we present the security services provided by the SFRC sublayer, the structure of the protocol data unit it employs for secure transfer of data and the types of MIB objects controlling its functionality. Finally, we suggest some supplementary security services not directly supported by the SFRC entities for future consideration.
Open shortest path first (OSPF) routing protocol simulation
Authors: Sidhu Deepinder , Fu Tayang , Abdallah Shukri , Nair Raj , Coltun Rob
Published: October 2004

Open Shortest Path First (OSPF) is a dynamic, hierarchical routing protocol designed to support routing in TCP/IP networks. A simulation of the OSPF Election Protocol shows three results: (1) The Designated Router (DR) can be elected in constant time. (2) If a router has a limited number of input buffers, a competition for buffers between the Election and the Flooding Protocols increases the election time and causes an oscillatory behavior.At each router, the Router-ID of the DR continuously changes causing instability. (3) In the worst case, when the DR and the BDR fail at the same time, the DR-agreement-time is bounded above by twice the HelloInterval. A simulation of the OSPF Flooding Protocol, using 20, 50 and 80 router point-to-point networks, shows three results: (1) For the 50 router network, as link speed exceeds 4000 Kbps, the probability of overflowing the input buffers increases causing retransmissions. The increase in bootup-convergence-time from retransmissions is bounded by two and three times the RxmtInterval for link speeds of 4000 to 6000 Kbps and above 50 Mbps respectively. The increase in the bootup-convergence-time is due to large number of unacknowledged flooding packets received within RxmtInterval. (2) For 20 and 50 router networks, the input buffer size has little impact on the bootup-convergence-time. For the 80 router network, a small change in the input buffer size drastically changes the bootup-convergence-time. (3) Reducing the value of the RxmtInterval lowers the bootup-convergence-time at high link speeds.
Causal ordering in reliable group communications
Authors: Aiello Rosario , Pagani Elena , Rossi Gian Paolo
Published: October 2004

In this paper we present a solution to the
causal reliable multicast
problem. User processes generate separate sequences of messages and specify the causal relation among them according to some application need; the algorithm ensures that the messages within the same sequence are delivered to all active, i.e. both correct and faulty, processes in the
group,
or to none of them, and are processed according to their causal order. Messages belonging to different sequences can be concurrently processed.This problem has few solutions presented in literature; in common with a part of them, the algorithm we describe has the centralized approach and the use of history buffers to recover from omission failures. The differences mainly concern the mechanism we devised to recover from crash failures, that avoids resorting to specialized protocols. As a consequence, under failure conditions, the algorithm performs better than other proposals in terms of both network load and throughput without affecting the performances under reliable conditions. Further, it allows to implement the most general interpretation of causality and it does not require any particular service to the underlying transport protocol.
Warp control
Authors: Park Kihong
Published: October 2004

This paper presents a distributed, end-to-end congestion control protocol for use in high-traffic packet switched networks. The network is represented as a stochastic single-server queue, with arrival rates being the control variables. A time-stamp based measure of network state called
warp
is defined, and it is shown to be an estimator of network utilization. Congestion is modeled explicitly using
unimodal load-service rate functions,
and its monotonicity property is exploited to yield characterizations of stability and optimality. A protocol based on "perfect" information is analyzed, whose prowess is then shown to be emulated by one which only uses locally computable, delayed information. The main effect of a unimodal load-service function is to induce a division of the phase space into stable and unstable regions, the optimal operating point being its "boundary." Protocols are devised for dealing with each regime separately,
rate adjustment protocol
being the control that guides the system to the optimal operating point.
Proactive rate protocol
and
reactive rate protocol
deal with the issue of the optimal operating point being near to the unstable zone. Protocols for handling fairness and structural perturbation augment the basic suite. The analysis is supported by simulations showing the global dynamical properties of the system.
Structural complexity and execution efficiency of distributed application protocols
Authors: Ravindran K. , Lin X. T.
Published: October 2004

The complexity and efficiency aspects of a distributed application protocol (e.g., replicated data access) are often intertwined with the application-specific communication requirements between protocol entities and the underlying primitives for message broadcasting. For instance, the choice between recovery by application from a mis-ordered message delivery versus providing message ordering property in the communication layer (CL) is based on tradeoffs between protocol complexity and efficiency. The paper systematically analyzes these tradeoffs with respect to message ordering and atomicity properties in broadcast communication. Enforcing these properties in the CL leads to uniform communication structure of applications; however, the CL incurs message and execution time overhead due to extensive communication state (e.g., message buffering). When these properties are not supported by CL but are required for an application, mechanisms to enforce it are built into the application protocol, thereby increasing complexity in the protocol structure. Detailed examples of applications are given to illustrate these tradeoffs. The analysis is useful in designing communication primitives and application protocols for distributed systems.
HAP
Authors: Lin Ying-Dar Jason , Tsai Tzu-Chieh , Huang San-Chiao , Gerla Mario
Published: October 2004

Applications to be supported on broadband networks exhibit a wide range of traffic statistics and many of them are sensitive to delay and loss violations. To accurately estimate admissible workload and bandwidth requirement, a detailed traffic model, HAP (Hierarchical Arrival Process) is proposed in this paper. Packets generated from HAP are modulated by processes at user, application, and message levels. This model is a generalization of on-off traffic models and is shown to be equivalent to a special class of MMPP (Markov Modulated Poisson Process). Three algorithmic methods along with simulations are applied to evaluate the queueing performance under HAP traffic. Delay under HAP traffic can be well over tens of times higher than Poisson traffic, depending on parameters and load. Congestion may persist for minutes. HAP's dramatic short-term behavior explains the occasional congestion in the real networks. Conventional traffic models, however, do not exhibit this behavior. With these results, we give implications for broadband network control.
Management of virtual private networks for integrated broadband communication
Authors: Schneider J. M. , Preuß T. , Nielsen P. S.
Published: October 2004

Management of Virtual Private Networks (VPNs) is becoming an increasingly important issue in the context of integrated broadband communication (IBC). In the near future corporate customers may want to subscribe to broadband VPN services offered by globally operating service providers to replace most of their leased line services that are used today to build their corporate networks. The concepts historically known as characterizing VPNs, such as the concept of closed user groups, will still be valid, but the importance of VPN service features and, in particular, the set of VPN management services offered to VPN customers will become dominant. In this paper we present a detailed technical approach to the management of broadband VPNs based on current technology and common standards. In particular, we discuss architectural solutions, management interfaces and management services provided at these interfaces, as well as managed objects.
Fault detection in an Ethernet network using anomaly signature matching
Authors: Feather Frank , Siewiorek Dan , Maxion Roy
Published: October 2004

In an Ethernet network, a common type of failure is the temporary of extended loss of bandwidth, or
soft
failure as it is referred to in the literature. Though the causes of soft failures vary, to the network user such failures are perceived as noticeably degraded or anomalous performance.This work uses anomaly detection as a means to signal performance degradations that are indicative of network soft failures. Detection is done via a signature matching mechanism, call a fault feature vector, which will detect the occurrence of a fault by looking for anomaly conditions particular to the fault. In a two-year study of the Carnegie Mellon University Computer Science Network the fault feature vector mechanism proved effective in detecting faults and discriminating between faults types. This mechanism was also effective at abstracting large amounts of network data to only those events which warranted operator attention; in this two-year study, over 32 million monitored data points were reduced to under a two hundred event matchings.
End-to-end packet delay and loss behavior in the internet
Authors: Bolot Jean-Chrysotome
Published: October 2004

We use the measured round trip delays of small UDP probe packets sent at regular time intervals to analyze the end-to-end packet delay and loss behavior in the Internet. By varying the interval between probe packets, it is possible to study the structure of the Internet load over different time scales. In this paper, the time scales of interest range from a few milliseconds to a few minutes. Our observations agree with results obtained by others using simulation and experimental approaches. For example, our estimates of Internet workload are consistent with the hypothesis of a mix of bulk traffic with larger packet size, and interactive traffic with smaller packet size. We observe compression (or clustering) of the probe packets, rapid fluctuations of queueing delays over small intervals, etc. Our results also show interesting and less expected behavior. For example, we find that the losses of probe packets are essentially random unless the probe traffic uses a large fraction of the available bandwidth. We discuss the implications of these results on the design of control mechanisms for the Internet.
The logical disk
Authors: de Jonge Wiebren , Kaashoek M. Frans , Hsieh Wilson C.
Published: October 2004

The Logical Disk (LD) defines a new interface to disk storage that separates file management and disk management by using logical block numbers and block lists. The LD interface is designed to support multiple file systems and to allow multiple implementations, both of which are important given the increasing use of kernels that support multiple operating system personalities.A log-structured implementation of LD (LLD) demonstrates that LD can be implemented efficiently. LLD adds about 5% to 10% to the purchase cost of a disk for the main memory it requires. Combining LLD with an existing file system results in a log-structured file system that exhibits the same performance characteristics as the Sprite log-structured file system.
Concurrent compacting garbage collection of a persistent heap
Authors: O'Toole James , Nettles Scott , Gifford David
Published: October 2004

We describe a replicating garbage collector for a persistent heap. The garbage collector cooperates with a transaction manager to provide safe and efficient transactional storage management. Clients read and write the heap in primary memory and can commit or abort their write operations. When write operations are committed they are preserved in stable storage and survive system failures. Clients can freely access the heap during garbage collection because the collector concurrently builds a compact replica of the heap. A log captures client write operations and is used to support both the transaction manager and the replicating garbage collector.Our implementation is the first to provide concurrent and compacting garbage collection of a persistent heap. Measurements show that concurrent replicating collection produces significantly shorter pause times than stop-and-copy collection. For small transactions, throughput is limited by the logging bandwidth of the underlying log manager. The results suggest that replicating garbage collection offers a flexible and efficient way to provide automatic storage management in transaction systems, object-oriented databases and persistent programming environments.
Improving IPC by kernel design
Authors: Liedtke Jochen
Published: October 2004

Inter-process communication (ipc) has to be fast and effective, otherwise programmers will not use remote procedure calls (RPC), multithreading and multitasking adequately. Thus ipc performance is vital for modern operating systems, especially μ-kernel based ones. Surprisingly, most μ-kernels exhibit poor ipc performance, typically requiring 100 μs for a short message transfer on a modern processor, running with 50 MHz clock rate.In contrast, we achieve 5 μs; a twentyfold improvement.This paper describes the methods and principles used, starting from the architectural design and going down to the coding level. There is no single trick to obtaining this high performance; rather, a synergetic approach in design and implementation on all levels is needed. The methods and their synergy are illustrated by applying them to a concrete example, the L3 μ-kernel (an industrial-quality operating system in daily use at several hundred sites). The main ideas are to guide the complete kernel design by the ipc requirements, and to make heavy use of the concept of virtual address space inside the μ-kernel itself.As the L3 experiment shows, significant performance gains are possible: compared with Mach, they range from a factor of 22 (8-byte messages) to 3 (4-Kbyte messages). Although hardware specific details influence both the design and implementation, these techniques are applicable to the whole class of conventional general purpose von Neumann processors supporting virtual addresses. Furthermore, the effort required is reasonably small, for example the dedicated parts of the μ-kernel can be concentrated in a single medium sized module.
Fbufs: a high-bandwidth cross-domain transfer facility
Authors: Druschel Peter , Peterson Larry L.
Published: October 2004

We have designed and implemented a new operating system facility for I/O buffer management and data transferacross protection domain boundaries on shared memory machines. This facility, called
fast buffers
(fbufs), combines virtual page remapping with shared virtual memory, and exploits locality in I/O traffic to achieve high throughput without compromising protection, security, or modularity. goal is to help deliver the high bandwidth afforded by emerging high-speed networks to user-level processes, both in monolithic and microkernel-based operating systems.This paper outlines the requirements for a cross-domain transfer facility, describes the design of the fbuf mechanism that meets these requirements, and experimentally quantifies the impact of fbufs on network performance.
Efficient software-based fault isolation
Authors: Wahbe Robert , Lucco Steven , Anderson Thomas E. , Graham Susan L.
Published: October 2004

One way to provide fault isolation among cooperating software modules is to place each in its own address space. However, for tightly-coupled modules, this solution incurs prohibitive context switch overhead. In this paper, we present a software approach to implementing fault isolation within a single address space.Our approach has two parts. First, we load the code and data for a distrusted module into its own
fault do main
, a logically separate portion of the application's address space. Second, we modify the object code of a distrusted module to prevent it from writing or jumping to an address outside its fault domain. Both these software operations are portable and programming language independent.Our approach poses a tradeoff relative to hardware fault isolation: substantially faster communication between fault domains, at a cost of slightly increased execution time for distrusted modules. We demonstrate that for frequently communicating modules, implementing fault isolation in software rather than hardware can substantially improve end-to-end application performance.
Handling audio and video streams in a distributed environment
Authors: Jones Alan , Hopper Andrew
Published: October 2004

Handling audio and video in a digital environment requires timely delivery of data. This paper describes the principles adopted in the design of the Pandora networked multi-media system. They attempt to give the user the best possible service while dealing with error and overload conditions.Pandora uses a sub-system to handle the multi-media peripherals. It uses transputers and associated Occam code to implement the time critical functions. Stream implementation is based on self-contained segments of data containing information for delivery, synchronisation and error recovery. Decoupling buffers are used to allow concurrent operation of multiple processing elements. Clawback buffers are used to resynchronise streams at their destinations with minimum latency.The system has proved robust in normal use, under overload, and in the presence of errors. It has been in use for a number of years.The principles involved in this design are now being used in the development of two complementary systems. One approach explodes Pandora by having the camera, microphone, speaker and display as independent units linked only by the LAN. The other approach integrates these devices as peripheral cards in a powerful workstation.
Applying multiple views to information systems
Authors: Baldwin Dirk
Published: October 2004

Multiple views are essential to decision making. In science there are multiple views of light, and in economics there are Keynesian and Monetarist views of the economy. Decision makers exposed to multiple views might find that one view is more useful or they might synthesize various views to gain a better understanding of the situation. This paper adds to the understanding of multiple views by defining key terms and by presenting a scheme that highlights view differences. The definitions and concepts present in the scheme are illustrated through examples in systems analysis. The view difference scheme and the examples help indicate potential characteristics of multiple view system architectures and highlight areas of research concerning the nature of multiple views in decision making.
An experience with CASE tool support for financial product design
Authors: Stickel Eberhard U.
Published: October 2004

The development of enterprise-wide information systems is a key success factor for the banking industry. This paper addresses the problems and benefits resulting from the use of a well-known CASE tool for the design of an information system to support product design in financial institutions. One goal of the project was to build an information system to allow the design of products not limited to existing lines of business. The design process is based on an enterprise-wide data model, which is stored in the tool's encyclopedia and which provides a binding framework for the design process. During the design phase, we discovered that the semantic power of the relational model was not sufficient for our purposes. Object-oriented or deductive database systems would have been helpful. The CASE tool did not sufficiently support nonstandard database models on the conceptual level.
The development of IS faculty
Authors: Stolen Justin
Published: October 2004

This article considers the place of doctoral dissertations as they pertain to research methodology in the MIS area. The paper compares research methodologies utilized in doctoral dissertations with previous findings related to dissertations, published articles and researcher views. It further subdivides the dissertations by research area and by the size of the doctoral program. The study finds that MIS dissertations cover a wide variety of areas, and that empirical research, particularly experimental research and field studies are the most common form of dissertation research methodology.
A simple encoder for fieldbus applications
Authors: Prasad Raja , Gonzalo Ulloa
Published: October 2004

In this paper we present a Simple Encoder for Fieldbus applications. The Simple Encoder is tailored to support the special kind of data transfer in a Fieldbus. The encoding rules have been simplified to such an extent that only required information between peers are exchanged, so that the coding/decoding process does not cause any significant delay during real time operation of the network. The PDUs obtained are upto 55% shorter than PDUs of Basic Encoding Rules,
BER
, and the Simple Encoder is upto four times faster than BER encoder.
Forwarding database overhead for inter-domain routing
Authors: Rekhter Yakov
Published: October 2004

The network layer of the current Internet is built around the packet switched architecture. As the Internet grows both in size and diversity of services, providing mechanisms to contain the growth of information that is necessary to correctly perform packet switching becomes one of the crucial issues in the overall Internet architecture. The dominate factor of this issue is the routing data stored in Forwarding Information Bases. This paper analyzes storage overhead associated with the inter-domain component of Forwarding Information Bases and evaluates possible techniques for containing the growth of this overhead.
The architecture of a Gb/s multimedia protocol adapter
Authors: Rütsche Erich
Published: October 2004

In this paper a new multiprocessor--based communication adapter is presented. The adapter architecture supports isochronous multimedia traffic and asynchronous data traffic by handling them separately. The adapter architecture and its components are explained and the protocol processing performance for TCP/IP and for ST-II is evaluated. The architecture supports the processing of ST-II at the network speed of 622 Mb/s. The calculated performance for TCP/IP is more than 30000 segments/sec. The architecture can be extended to protocol processing at one Gb/s.
Analysis of polling protocols for fieldbus networks
Authors: Raja Prasad , Noubir Guevara , Ruiz Luis , Hernandez Jean , Decotignie Jean-Dominique
Published: October 2004

Roll-call polling mechanisms are considered for fieldbus networks. Based on a producer/consumer communication model, two different protocols are presented, namely the standardized FIP (Factory Instrumentation Protocol) and a modified FIP protocol that we propose here. The modified protocol uses redundancy to eliminate local timers used by the FIP protocol. The two protocols are analyzed for efficiency, jitter and robustness. We compare the two protocols based on implementation and analytical results. Practical aspects concerning: clock precision; computing time; and hard real-time constraints are also discussed. The results show that: (1) the original FIP protocol is fractionally more efficient with respect to its execution time than the modified one; (2) the modifications proposed, however, reduce the jitter and improve the robustness considerably; (3) the slot time of the original FIP protocol has theoretical upper bound but the modified protocol has no such limitations.
Inspecting continuations
Authors: da Rocha Costa Antônio Carlos , Rodrigues Vanderlei Moraes
Published: October 2004

This note discusses some implications of allowing programs to inspect their continuations.
BATCES solution #2
Authors: Hirasuna Michael
Published: October 2004

An approach to derive an Object-Oriented Design (OOD) from a simplified Structure Analysis (SA) is presented. The approach is demonstrated with the BATCES problem statement defined by the Object Oriented Work Group (OOWG) [CRA92]. Unlike other methodologies, the simplified SA/OOD is targeted specifically for Ada. Assuming that Ada is self-documenting, the approach defines the diagrams and tables that complement the code, and not just repeat the information already there. As demanded by typical Ada customers, special emphasis is placed on requirements tracing.The lack of CASE tools has been the primary argument against an Ada specific methodology. Hence, the approach only uses general productivity tools that can run on today's personal computers. Such an approach is practical because the required diagrams and tables have been greatly simplified.
An Ada 9X subset for inheritance-based reuse and its translation to Ada 83 (Part 1)
Authors: Hirasuna Michael
Published: October 2004

An object oriented reuse strategy based on the Ada 9X inheritance syntax is presented. This paper defines a minimal Ada 9X subset that implements inheritance-based reuse, and outlines its translation to Ada 83. Inheritance allows software modules to be reused without modification to the original source. It is preferred to the "copy and tailor" approach, which has limited software life-cycle benefit since tailored copies need to be tested and maintained.Reuse may be applied at the low level, for components, or at higher levels, for subsystems. Inheritance may be used at any level of reuse, but it is more important for the higher levels. Ada 83 does not support inheritance, but low-level reuse can still be implemented in the form of generic components [BOO87]. The cost advantage from low-level reuse is already assumed when planning today's software systems. Further cost savings must come from high-level reuse, which needs inheritance to be implemented properly. Inheritance will be fully supported in Ada 9X.The approach presented here may be used in a reuse plan for a system that will start development before Ada 9X becomes viable. The Ada 9X subset allows the system software to be structured for reuse, to be implemented in Ada 83, and to be ready for migration to Ada 9X.This is the first part of a two-part paper. This part will discuss the reuse strategy and define an Ada 9X subset that will implement it. In the second part, a translation from the Ada 9X subset to Ada 83 will be outlined.
A high resolution event timer Ada package for DOS environments
Authors: Paul Michael J. , Gochenouer John E.
Published: October 2004

DOS provides real time clock functions with a resolution of 55 milliseconds. Unfortunately, this is not sufficient for many applications. By directly accessing the IBM PC hardware, however, one can theoretically develop a timing function with the same resolution of the system clock. Direct hardware access, however, is not without side effects. The following paper discusses the difficulties in achieving high resolution timings and provides a practical Ada solution.
Computational geometry
Authors: O'Rourke Joseph
Published: October 2004

The class of
n
2
-hard geometric problems is described, with special concentration on detecting collinearities among a set of points in the plane.
A short note on implementing thread exclusiveness and address space locking
Authors: Liedtke Jochen
Published: October 2004

A thread can make itself
exclusive
by disabling execution of all other threads running in the same address space. This brute force synchronization mechanism is useful in cases otherwise requiring numerous semaphore or mutex operations or when synchronizytion has to be added to existing software. Based on the L3 experiences, the paper describes how to implement exclusiveness by locking the relevant region of a task's address space. This optimistic method scales better than suspending and later reactivating all threads explicitly.
A comparative study of information system curriculum in U.S. and foreign universities
Authors: Goslar Martin D. , Deans P. Candace
Published: October 2004

The continued shift toward a more integrated world economy and the need to be more informed regarding business events outside the domestic (U.S.) marketplace have contributed to a need for better collaboration among IS academicians in both U.S. and foreign schools of business. IS educators are developing new curriculum initiatives, broadening the scope to incorporate international business environment forces.This research provides the IS academic community with insights into IS curriculumin business schools worldwide in order to better understand differences and similarities across programs. These insights will prove valuable as efforts are made to broaden the scope of IS curriculum content to an international dimension. Theoretical foundations for this study are derived primarily from the international business discipline. The methodology incorporates a questionnaire targeted for a representative sample of U.S. and foreign schools of business. The results of this study provide IS academicians with a reference point from which to proceed in developing a more refined international IS component. Insights derived from IS curriculum approaches currently in place in foreign schools of business will contribute to an understanding of international IS issues and encourage collaboration with academicians outside the United States.
Teaching Computational Complexity
Authors: Hemaspaandra Lane A .
Published: October 2004

This article describes and discusses textbooks, monographs, and collections that are excellent resources from which to teach courses on computational complexity theory.
A comparative analysis of MIS project selection mechanisms
Authors: McKeen James D. , Guimaraes Tor , Wetherbe James C.
Published: October 2004

MIS projects are selected by any of four different groups within organizations: top management, steering committees, user departments, and MIS departments. Because of their inherent differences, each of these groups is likely to favor different types of MIS projects. That is, they exhibit different selection biasing. An investigation of the nature and extent of this biasing is examined in this research.Data were collected from 176 MIS projects selected from 60 organizations. Projects were categorized as being selected by top management, steering committees, user departments, or MIS departments, and specific characteristics (e.g., size, risk, and organizational commitment) were measured for each project.As hypothesized, the research showed that projects selected by different groups did indeed differ significantly with respect to these characteristics.• Projects selected by top management do not tend to be more strategic, profitable, resource consuming, larger risk, or related to organizational well-being than other project selection groups. These projects, however, did tend to experience the longest start delay and elapsed development time.• Projects selected by steering committees tended to be larger and riskier, and required more organizational change. Formal cost-benefit analysis is more predominant, but surprisingly, projects selected are not more cross-functional in scope. AB• User department-selected projects, comparatively, are smaller, more quickly developed, and involve the fewest users, layers of management, and business functions.• MIS-selected projects have more of an integration focus and follow more logical sequences in development. Their projects experience fewer delays in deliberation and duration, and less concern is given to cost-benefit analysis.The individual biasing attributable to each of the four selection mechanisms is described. The paper concludes by presenting the implications of having each of these groups select MIS projects. Using this information, organizations can establish or assess the effect of using different mechanisms for selecting MIS projects.
Establishing viable programs of research
Authors: Watson Hugh J. , Satzinger John W. , Singh Sanjay K.
Published: October 2004

Programs of research can help develop in-depth knowledge in a field through a series of interrelated studies and have been used successfully by several universities. This article describes one of the MIS research programs: the executive information system (EIS) program of research at the University of Georgia. We discuss its motivation and history, the resources involved, the outputs to date, and the benefits. The general approach used is portable, and we discuss how the approach used by Georgia can be adopted by others.
Reusable software components
Authors: Levine Trudy
Published: October 2004

Once a year, we publish a "theme" column that includes the viewpoints of leading practitioners on a specific reuse theme, and suggest references for those who wish to study the topic in more depth. Unfortunately, a page was omitted in the publication of our column on Reuse Education. We repeat that column, with an update on the Third Annual Workshop on Reuse Education and Training.
Prospective on the next twenty five years…
Authors: Cule Paul E. , Grover Varun
Published: October 2004

In this, the 25th anniversary issue of DATA BASE, other authors have looked back from whence we came. As in most retrospectives, we find we have come much farther than we originally thought in some things, yet nowhere near as far in others. It has been said that we never move as far in five years as we forecast. However, we move far beyond the wildest forecasts over the span of a generation. This is particularly so in the rapidly changing information systems (IS) field. In this article, we will gaze into the crystal ball and consider where IS might be heading in the next 25 years. The intent is to engage the reader through postulating future possibilities. To do this, we are going to consider where the consumers of information technology are going and the role IT will play in getting them there. We will consider the technology itself, and where that might be going. We will discuss some impacts on the information technology industry, or what might be a better future name, the information industry. Finally, we will consider the future role of academe and its journals, as they are impacted and impact the field of IS.
The effect of definitional variations on users' evaluations of information systems
Authors: Mathieson Kieran , Ryan Terence
Published: October 2004

Prior research has shown that different users can define a given information system (IS) in different ways. That is, two users evaluating the same IS may not agree on what the system actually is. This study tests whether variations in users' definitions of a system cause variations in their evaluations of the system. It is argued that users who define an IS differently will use different information in evaluating it. Under some circumstances, this will lead them to form different attitudes towards the IS. An experiment confirmed that definitional variations affect evaluations. It is suggested that systematic variations in IS definitions complicate both the interpretation of user attitude data and interactions between users and analysts. Some directions for further research are suggested.
User-space protocols deliver high performance to applications on a low-cost Gb/s LAN
Authors: Edwards Aled , Watson Greg , Lumley John , Banks David , Calamvokis Costas , Dalton C.
Published: October 2004

Two important questions in high-speed networking are firstly, how to provide Gbit/s networking at low cost and secondly, how to provide a flexible low-level network interface so that applications can control their data from the instant it arrives.

We describe some work that addresses both of these questions. The Jetstream Gbit/s LAN is an experimental, low-cost network interface that provides the services required by delay-sensitive traffic as well as meeting the performance needs of current applications. Jetstream is a combination of traditional shared-medium LAN technology and more recent ATM cell- and switch-based technology.

Jetstream frames contain a channel identifier so that the network driver can immediately associate an incoming frame with its application. We have developed such a driver that enables applications to control how their data should be managed without the need to first move the data into the application's address space. Consequently, applications can elect to read just a part of a frame and then instruct the driver to move the remainder directly to its destination. Individual channels can elect to receive frames that have failed their CRC, while applications can specify frame-drop policies on a per-channel basis.

Measured results show that both kernel- and user-space protocols can achieve very good throughput: applications using both TCP and our own reliable byte-stream protocol have demonstrated throughputs in excess of 200 Mbit/s. The benefits of running protocols in user-space are well known- the drawback has often been a severe penalty in the performance achieved. In this paper we show that it is possible to have the best of both worlds.
TCP Vegas
Authors: Brakmo Lawrence S. , O'Malley Sean W. , Peterson Larry L.
Published: October 2004

Vegas is a new implementation of TCP that achieves between 40 and 70% better throughput, with one-fifth to one-half the losses, as compared to the implementation of TCP in the Reno distribution of BSD Unix. This paper motivates and describes the three key techniques employed by Vegas, and presents the results of a comprehensive experimental performance study—using both simulations and measurements on the Internet—of the Vegas and Reno implementations of TCP.
A structured TCP in standard ML.
Authors: Biagioni Edoardo
Published: October 2004

This paper describes the design of an implementation of the Transmission Control Protocol using an extension of the Standard ML (SML) language. SML supports higher-order functions, modularity, and type-safe module composition. We find that by using SML we can achieve good structure and good performance simultaneously. Good structure includes a modular decomposition of the protocol stack and of the TCP implementation, a control structure that imposes a total ordering on all events and processes them synchronously, and a test structure that allows component testing to catch problems before system integration. Strategies that help achieve good performance include using fast algorithms, using language constructs that make it easy to stage function evaluation, and language implementation features such as compacting garbage collection.
Scalable feedback control for multicast video distribution in the Internet
Authors: Bolot Jean-Chrysostome , Turletti Thierry , Wakeman Ian
Published: October 2004

We describe a mechanism for scalable control of multicast continuous media streams. The mechanism uses a novel probing mechanism to solicit feedback information in a scalable manner and to estimate the number of receivers. In addition, it separates the congestion signal from the congestion control algorithm, so as to cope with heterogeneous networks.

This mechanism has been implemented in the IVS video conference system using options within RTP to elicit information about the quality of the video delivered to the receivers. The H.261 coder of IVS then uses this information to adjust its output rate, the goal being to maximize the perceptual quality of the image received at the destinations while minimizing the bandwidth used by the video transmission. We find that our prototype control mechanism is well suited to the Internet environment. Furthermore, it prevents video sources from creating congestion in the Internet. Experiments are underway to investigate how the scalable proving mechanism can be used to facilitate multicast video distribution to large number of participants.
Statistical analysis of generalized processor sharing scheduling discipline
Authors: Zhang Zhi-Li , Towsley Don , Kurose Jim
Published: October 2004

In this paper, we consider the problem of providing statistical guarantees (for example, on the tail distribution of delay) under the Generalized Processor Sharing (GPS) scheduling discipline. This work is motivated by, and is an extension of, Parekh and Gallager's deterministic study of GPS scheduling discipline with leaky-bucket token controlled sessions [PG93a,b, Parekh92]. Using the exponentially bounded burstiness (E.B.B.) process model introduced in [YaSi93a] as a source traffic characterization, we establish results that extend the deterministic study of GPS: for a single GPS server in isolation, we present statistical bounds on the tail distributions of backlog and delay for each session. In the network setting, we show that networks belonging to a broad class of GPS assignments, the so-called Consistent Relative Session Treatment (CRST) GPS assignments, are stable in a stochastic sense. In particular, we establish simple bounds on the tail distribution of backlog and delay for each session in a Rate Proportional Processor Sharing (RPPS) GPS network with arbitrary topology.
Dynamics of TCP traffic over ATM networks
Authors: Romanow Allyn , Floyd Sally
Published: October 2004

We investigate the performance of TCP connections over ATM networks without ATM-level congestion control, and compare it to the performance of TCP over packet-based networks. For simulations of congested networks, the effective throughput of TCP over ATM can be quite low when cells are dropped at the congested ATM switch. The low throughput is due to wasted bandwidth as the congested link transmits cells from “corrupted” packets, i.e., packets in which at least one cell is dropped by the switch. This fragmentation effect can be corrected and high throughput can be achieved if the switch drops whole packets prior to buffer overflow; we call this strategy Early Packet Discard. We also discuss general issues of congestion avoidance for best-effort traffic in ATM networks.
Credit-based flow control for ATM networks
Authors: Kung H. T. , Blackwell Trevor , Chapman Alan
Published: October 2004

This paper presents three new results concerning credit-based flow control for ATM networks: (1) a simple and robust credit update protocol (CUP) suited for relatively inexpensive hardware/software implementation; (2) automatic adaptation of credit buffer allocation for virtual circuits (VCs) sharing the same buffer pool; (3) use of credit-based flow control to improve the effectiveness of statistical multiplexing in minimizing switch memory. These results have been substantiated by analysis, simulation and implementation.
Flexible routing and addressing for a next generation IP
Authors: Francis Paul , Govindan Ramesh
Published: October 2004

Due to a limited address space and poor scaling of backbone routing information, the Internet Protocol (IP) is rapidly reaching the end of its useful lifetime. The Simple Internet Protocol Plus (SIPP), a proposed next generation Internet Protocol, solves these problems with larger internet layer addresses. In addition, SIPP provides a number of advanced routing and addressing capabilities including mobility, extended (variable-length) addressing, provider selection, and certain forms of multicast. These capabilities are all achieved through a single mechanism, a generalization of the IP loose source route. We argue that, for reasons of simplicity and evolvability, a single powerful mechanism to achieve a wide range of routing and addressing functions is preferable to having multiple specific mechanisms, one for each function.
Distributed, scalable routing based on link-state vectors
Authors: Behrens Jochen , Garcia-Luna-Aceves J. J.
Published: October 2004

A new family of routing algorithms for the distributed maintenance of routing information in large networks and internets is introduced. This family is called link vector algorithms (LVA), and is based on the selective diffusion of link-state information based on the distributed computation of preferred paths, rather than on the flooding of complete link-state information based on the distributed computation of preferred paths, rather than on the flooding of complete link-state information to all routers. According to LVA, each router maintains a subset of the topology that corresponds to the links used by its neighbor routers in their preferred paths to known destinations. Based on that subset of topology information, the router derives its own preferred paths and communicates the corresponding link-state information to its neighbors. An update message contains a vector of updates; each such update specifies a link and its parameters. LVAs can be used for different types of routing. The correctness of LVA is verified for arbitrary types of routing when correct and deterministic algorithms are used to select preferred paths at each router. LVA is shown to have smaller complexity than link-state and distance-vector algorithms, and to have better average performance than the ideal topology-broadcast algorithm and the distributed Bellman-Ford algorithm.
Controlling alternate routing in general-mesh packet flow networks
Authors: Sibal Sandeep , DeSimone Antonio
Published: October 2004

High-speed packet networks will begin to support services that need Quality-of-Service (QoS) guarantees. Guaranteeing QoS typically translates to reserving resources for the duration of a call. We propose a state-dependent routing scheme that builds on any base state-independent routing scheme, by routing flows which are blocked on their primary paths (as selected by the state-independent scheme) onto alternate paths in a manner that is guaranteed—under certain Poisson assumptions— to improve on the performance of the base state-independent scheme. Our scheme only requires each node to have state information of those links that are incident on it. Such a scheme is of value when either the base state-independent scheme is already in place and a complete overhaul of the routing algorithm is undesirable, or when the state (reserved flows) of a link changes fast enough that the timely update of state information is infeasible to all possible call-originators. The performance improvements due to our controlled alternate routing scheme are borne out from simulations conducted on a fully-connected 4-node network, as well as on a sparsely-connected 12-node network modeled on the NSFNet T3 Backbone.