bluuebunny/crossref_metadata_2025 huggingface dataset:
Wide-area traffic
Authors: Paxson Vern , Floyd Sally
Published: October 2004

Network arrivals are often modeled as Poisson processes for analytic simplicity, even though a number of traffic studies have shown that packet interarrivals are not exponentially distributed. We evaluate 21 wide-area traces, investigating a number of wide-area TCP arrival processes (session and connection arrivals, FTPDATA connection arrivals within FTP sessions, and TELNET packet arrivals) to determine the error introduced by modeling them using Poisson processes. We find that user-initiated TCP session arrivals, such as remote-login and file-transfer, are well-modeled as Poisson processes with fixed hourly rates, but that other connection arrivals deviate considerably from Poisson; that modeling TELNET packet interarrivals as exponential grievously underestimates the burstiness of TELNET traffic, but using the empirical Tcplib[DJCME92] interarrivals preserves burstiness over many time scales; and that FTPDATA connection arrivals within FTP sessions come bunched into “connection burst”, the largest of which are so large that they completely dominate FTPDATA traffic. Finally, we offer some preliminary results regarding how our findings relate to the possibleself-similarityof wide-area traffic.
An object-based approach to protocol software implementation
Authors: Liu Chung-Shyan
Published: October 2004

In this paper, an object-based approach to protocol software implementation is presented. A protocol is specified by an FSM, then the FSM is implemented by a group of related objects. In our method, each state is implemented by an object. The member functions of an object are the interface vents that trigger state transitions, and actions associated with state transitions constitute the body of the member functions. An object
becomes
another object if a state transition is enabled. A real example is given for illustration. We also present a software tool that lets a designer edit a state machine graphically, and generates C++ class definitions automatically. We also discuss some implementation related issues and present an organization model for protocol layers.
Improved algorithms for synchronizing computer network clocks
Authors: Mills David L.
Published: October 2004

The Network Time Protocol (NTP) is widely deployed in the Internet to synchronize computer clocks to each other and to international standards via telephone modem, radio and satellite. The protocols and algorithms have evolved over more than a decade to produce the present NTP Version 3 specification and implementations. Most of the estimated deployment of 100,000 NTP servers and clients enjoy synchronization to within a few tens of milliseconds in the Internet of today.

This paper describes specific improvements developed for NTP Version 3 which have resulted in increased accuracy, stability and reliability in both local-area and wide-area networks. These include engineered refinements of several algorithms used to measure time differences between a local clock and a number of peer clocks in the network, as well as to select the best ensemble from among a set of peer clocks and combine their differences to produce a clock accuracy better than any in the ensemble.

This paper also describes engineered refinements of the algorithms used to adjust the time and frequency of the local clock, which functions as a disciplined oscillator. The refinements provide automatic adjustment of message-exchange intervals in order to minimize network traffic between clients and busy servers while maintaining the best accuracy. Finally, this paper describes certain enhancements to the Unix operating system software in order to realize submillisecond accuracies with fast workstations and networks.
The HetNOS network operating system
Authors: Barcellos Antônio Marinho Pilla , Filho Valdir Rossi Belmonte , Schramm João Frederico Lacava , Geyer Cláudio Fernando Resin
Published: October 2004

The HetNOS network operating system is a set of software layers laid over "native" operating systems to provide a distributed programming platform. The environment is composed of the HetNOS shell command language and the system calls interface (accessed through a procedure library). In both levels of interaction with users, the set of machines integrated by HetNOS are seen as a distributed virtual machine.The HetNOS command interpreter, namely
hsh
, implements most functions present in more traditional command interpreters. It is possible to spawn, monitor, and terminate processes in any host in the network like in the local case. The HetNOS distributed kernel uses a symbolic, global, location independent, process identification scheme. Distributed applications are split into sequential processes, which interact with each other by message exchange. There are neither connections nor ports, being the communication mechanism strongly influenced by the process identification scheme. This paper briefly describes the HetNOS software organization, presents the HetNOS environment for distributed programming, and then compares HetNOS with related work.
User interface system based on active objects
Authors: Choi Sungwoon , Minoura Toshimi
Published: October 2004

An
active-object user interface system
(AOUIS) is a user interface system implemented as an
active object system
(AOS). An AOS is a
transition-based
object-oriented system suitable for the design of various concurrent systems. In an AOUIS,
user interface objects
, which are sometimes called "widgets", are represented as
active user interface objects
(AUIOs). The behavior of an AUIO is defined by the transition rules, the equational assignment statements, and the event routines provided in its class definition. Furthermore, an AUIO can be constructed from its component AUIOs through structural composition as if it were a hardware object. Thus, AUIOs are better encapsulated and provide more flexible communication protocols than ordinary user interface objects. In addition,
declarative
descriptions of
multiple
views can be provided for each AUIO.
DIR/SEE
Authors: Barry Brian M. , McGugan James , Wilson Mike
Published: October 2004

Building a practical, cost-effective multilingual software engineering environment requires a well factored architecture which allows substantial code reuse during implementation. Object-oriented technology provides the facilities required to achieve this. DIR/SEE is a prototype for a Smalltalk based environment designed to support new applications written in Smalltalk and Ada, as well as existing software ("legacies") written in other languages such as C, CMS II and assembler. It provides team programming support, full version and configuration management, and a network-based software repository. The key components of the DIR/SEE, including those which represent tools and program units for other languages, are all Smalltalk objects. Consequently they have well-defined interfaces and realize a high level of software reuse through inheritance, without sacrificing the flexibility and tight integration which Smalltalk users expect.
“Environment integration” working group summary SETA2
Authors: Brown Alan W. , Penedo Maria H.
Published: October 2004

The Second International Symposium on Environments and Tools for Ada (SETA2) was held in Washington DC, in January 1992. This document summarizes the discussions of the SETA2 Software Engineering Environment (SEE) Integration working group.
Semaphores in Ada-94
Authors: Yue Kwok-bun
Published: October 2004

The new protected type and requeue features in Ada-94 make possible the efficient implementations of many concurrent solutions, previously not possible in Ada-83. In this paper, the implementations of various semaphore systems in Ada-94 are presented. These systems are more general and powerful than the familiar binary and counting semaphores. As examples, the uses of the most general one, PV
general
, in resource management and the synchronization of general mutual exclusion problems are discussed.
Advancing Ada 9X solutions in real time avionics computers
Authors: Blázquez V. , Correa A. , Freniche J. L.
Published: October 2004

A real case of priority inversion in Avionics Computers is described, as well as the experiences in the decisions, implementation and testing of the Basic Priority Inheritance Protocol in an Ada 83 Run Time System. The increased overhead of this protocol is less than 1%, which makes it tolerable for Real Time Avionics Computers using Ada tasking. Ada 9X offerings in this field are also analysed and the conclusion is reached that the case described here should be revised in the new Ada.
Static worst-case timing analysis of Ada
Authors: Chapman Roderick , Burns Alan , Wellings Andy
Published: October 2004

This paper describes recent work on static timing analysis of Ada. Previous work on static timing analysis has not considered Ada, so one goal of this paper is to raise awareness of the topic within the Ada community. We believe the technology is now sufficiently well-understood that commercial tools for a small subset are within reach. We first consider timing analysis in general, and then look at the particular features of Ada in this light. The technical detail of one recently developed tool is then covered. Finally, we consider the impact of Ada9X and some open issues raised by our research.
Vectorized presentation-level services for scientific distributed applications
Authors: Stanberry L. C. , Branstetter M. L. , Nessett D. M.
Published: October 2004

The use of heterogeneous distributed systems is a promising approach to significantly increase computational performance of scientific applications. However, one key to this strategy is to minimize the percentage of time spent by an application moving data between machines. This percentage is composed of two parts: 1) the time to translate data between the formats used on different machines, and 2) the time to move data over the network that interconnects the machines. Previous work suggests that data format conversion activity, generally known as presentation-level services, is by far the more costly of the two.In this paper we describe how vectorization can be used to improve presentation-level performance in scientific applications by one or two orders of magnitude over the conventional approach. While others have recognized the advantages of vectorized data format conversion, we describe how to automate this process so that an application programmer need not explicitly call vectorization routines. We explore the impact of presentation-level vectorization on software portability, programming efficiency and protocol standards. We compare our performance results with those of two other popular distributed scientific application programming tools and then summarize the lessons we have learned during the course of our research.
Providing the X.500 directory user with QOS information
Authors: Barker Paul
Published: October 2004

This paper describes some work which helps users of the X.500 directory to understand the unevenness of quality of service (QOS) concomitant with a widely distributed directory. In particular a user may see highly variant response times and availability of information for different parts of the directory.The paper discusses, and dismisses, two possible sources of QOS information. I use a third approach whereby a directory user interface maintains a record of response times and information availability and uses this database to provide a user with feedback about those aspects of the service. The DE user interface has been modified to incorporate this facility. The technique used also provides directory managers with a view of directory performance from a user's perspective.The work described has been partly funded by the PARADISE projects, through the European COSINE project and VALUE programme.
Network management viewpoints
Authors: Znaty Simon , Sclavos Jean
Published: October 2004

This paper defines viewpoints in order to deal with the network management complexity. A network management viewpoint leads to the representation of a network management system with emphasis on a specific concern. Five viewpoints are identified, namely information, functional, communication, architectural and organizational. The network management standards provisions and lacks for every viewpoint are enhanced and some elements of solutions are presented. Then, these viewpoints are integrated and applied to every management layer of an FDDI subnetwork considered as a componet of a high speed multi-network.
Computational geometry column 23
Authors: O'Rourke Joseph
Published: October 2004

Three open problems on tetrahedralizations are described: Does bisection refinement keep solid angle bound away from zero? Can a tetrahedralization be frozen with respect to flips? Do points in convex position have a Hamiltonian tetrahedralization?
A simple LAN performance measure
Authors: Vis Jan
Published: October 2004

A simple formula is presented for the assessment of the performance of LAN's. It is based on the most essential performance parameters only and is found to be a quite accurate, conservative estimate when compared to the classical closed queuing model of a time sharing system.
Mechanisms of MPEG stream synchronization
Authors: Lu G. J. , Pung H. K. , Chua T. S.
Published: October 2004

Media synchronization is an important issue in developing multimedia applications. MPEG is an international standard for coding moving pictures and associated audio for multimedia applications. Coded audio, video and other data streams are multiplexed into an MPEG stream. We introduce the syntax of the multiplexed MPEG stream and explain the mechanisms used to maintain media synchronization in a hypothetical model, system target decoder, in which it is assumed that data transfer and decoding are carried out instantaneously. Then we propose extensions to these mechnisms to achieve MPEG stream synchronization in a practical decoder.
Summary of the 4th international workshop on Network and Operating System Support for Digital Audio and Video (NOSSDAV'93)
Authors: Blair G. S. , Campbell A. , Coulson G. , Davies N. , Garcia F. , Shepherd D.
Published: October 2004

This paper presents a summary of the fourth International Workshop on Network and Operating System Support for Digital Audio and Video held at Lancaster. The contents of each session (including panel and work in progress sessions) are described and major areas of controversy are highlighted. A complete bibliography of all papers presented is included.
Local states in distributed computations
Authors: Fromentin Eddy , Raynal Michel
Published: October 2004

If events produced by processes of a distributed computation are generally supposed to be instantaneous, it is not the case for local states generated by these events. Due to message exchanges and synchronization local states have some duration. This paper defines notions about local states such as
weak precedence, strong precedence, weak concurrency
and
strong concurrency
. Moreover a few formulas based on vector clocks, and consequently usable in an operational context, are introduced to decide about relations between local states. These relations and formulas can be used either to debug, test or analyze distributed programs (especially for global properties detection) or to define consistent checkpoints.
Accessibility rules OK!
Authors: Barnes John
Published: October 2004

This paper shows that the intuitive notion of accessibility is correctly met by the rules of Ada 9X. In particular, it shows that despite the notion of accessibility being intrinsically dynamic, nevertheless the rules can in the majority of situations be checked statically without any loss of capability. It also explores the impact of access parameters and shows that the mechanism suggested in the Annotated Reference Manual [AARM] does indeed exactly map onto the requirements of the rules.
Output from generic packages
Authors: Slater Paul
Published: October 2004

Ada83 suffers from being a non-polymorphic statically bound language in that, the types of data need to be known before run-time. The generic mechanism helps to overcome this limitation in that a non-type specific package can be written and instantiated for several actual data types, depending on the generic formal parameter chosen. One problem that is not solved by the generic mechanism is that of input and output of data values. Since actual data types are represented in different ways, there is no single routine which can be called upon to get or put items of a generic formal type. This paper outlines a possible solution to this problem.
Transparent remote execution in LAHNOS by means of a neural network device
Authors: Cena M. , Crespo M. L. , Gallard R.
Published: October 2004

LAHNOS is a Local Area Heterogeneous Operating System [1] being currently developed at the Universidad Nacional de San Luis over which distributed services are to be built. This paper shows some enhancements to be introduced into the original design in order to achieve automatic allocation of remote execution requests to the best fitted node under some chosen performance criteria.Following current trends in Distributed Systems we propose the insertion of a neural network device into the kernel of LAHNOS to reflect a selected allocation policy to provide improved system performance as long as to release the user of some cumbersome decisions.
An introduction to intelligent operating system KZ2
Authors: Xie Li , Du Xing , Chen Jun , Zheng Yuhua , Sun Zhongxiu
Published: October 2004

This paper proposes an intelligent operating system, KZ2, which is a new generation OS to manage the resources of massively parallel computing systems, to provide a friendly human-computer interface, and control the execution of programs based on knowledge processing and parallel processing. A knowledge based demonstrative example is also described in the paper to show how KZ2 improves the functions and performance of existing operating systems.
Application-aware adaptation for mobile computing
Authors: Satyanarayanan M. , Noble Brian , Kumar Puneet , Price Morgan
Published: October 2004

This paper identifies
application-aware adaptation
as an essential capability of mobile clients, and provides an overview of
Odyssey,
an architecture that supports this capability. Functionality that has hitherto been implemented monolithically must now be split between the operating system and individual applications. The role of the operating system is to sense external events, and to monitor and allocate scarce resources. In contrast, the role of individual applications is to adapt to changing conditions by using the information and resources provided by the operating system.
The operating system kernel as a secure programmable machine
Authors: Engler Dawson R. , Kaashoek M. Frans , O'Toole James W.
Published: October 2004

To provide modularity and performance, operating system kernels should have only minimal embedded functionality. Today's operating systems are large, inefficient and, most importantly, inflexible. In our view, most operating system performance and flexibility problems can be eliminated simply by pushing the operating system interface lower. Our goal is to put abstractions traditionally implemented by the kernel out into user-space, where user-level libraries and servers abstract the exposed hardware resources. To achieve this goal, we have defined a new operating system structure,
exokernel,
that safely exports the resources defined by the underlying hardware. To enable applications to benefit from full hardware functionality and performance, they are allowed to download additions to the supervisor-mode execution environment. To guarantee that these extensions are safe, techniques such as code inspection, inlined cross-domain procedure calls, and secure languages are used. To test and evaluate exokernels and their customization techniques a prototype exokernel,
Aegis,
is being developed.
What is a “pointer machine”?
Authors: Ben-Amram Amir M.
Published: October 2004

A "Pointer Machine" is many things. Authors who consider referring to this term are invited to read the following note first.
An overview of the new routing algorithm for the ARPANET
Authors: McQuillan John M. , Richer Ira , Rosen Eric C.
Published: October 2004

The original routing algorithm of the ARPANET, in service for over a decade, has recently been removed from the ARPANET and replaced with a new and different algorithm. Although the new algorithm, like the old, is a distributed, adaptive routing algorithm, it is not similar to the old in any other important respect. In the new algorithm, each node maintains a data base describing the delay on each network line. A shortest-path computation is run in each node which explicitly computes the minimum-delay paths (based on the delay entries in the data base) from that node to all other nodes in the network. The average delay on each network line is measured periodically by the nodes attached to the lines. These measured delays are broadcast to all network nodes, so that all nodes use the same data base for performing their shortest-path computations. The new routing algorithm was extensively tested on the ARPANET before being released. This paper describes the algorithm and summarizes the results of these tests.
Measured capacity of an Ethernet
Authors: Boggs D. R. , Mogul J. C. , Kent C. A.
Published: October 2004

Ethernet, a 10 Mbit/sec CSMA/CD network, is one of the most successful LAN technologies. Considerable confusion exists as to the actual capacity of an Ethernet, especially since some theoretical studies have examined operating regimes that are not characteristic of actual networks. Based on measurements of an actual implementation, we show that for a wide class of applications, Ethernet is capable of carrying its nominal bandwidth of useful traffic, and allocates the bandwidth fairly. We discuss how implementations can achieve this performance, describe some problems that have arisen in existing implementations, and suggest ways to avoid future problems.
On the self-similar nature of Ethernet traffic
Authors: Leland Will E. , Willinger Walter , Taqqu Murad S. , Wilson Daniel V.
Published: October 2004

We demonstrate that Ethernet local area network (LAN) traffic is statistically
self-similar
, that none of the commonly used traffic models is able to capture this fractal behavior, and that such behavior has serious implications for the design, control, and analysis of high-speed, cell-based networks. Intuitively, the critical characteristic of this self-similar traffic is that there is no natural length of a "burst": at every time scale ranging from a few milliseconds to minutes and hours, similar-looking traffic bursts are evident; we find that aggregating streams of such traffic typically intensifies the self-similarity ("burstiness") instead of smoothing it.Our conclusions are supported by a rigorous statistical analysis of hundreds of millions of high quality Ethernet traffic measurements collected between 1989 and 1992, coupled with a discussion of the underlying mathematical and statistical properties of self-similarity and their relationship with actual network behavior. We also consider some implications for congestion control in high-bandwidth networks and present traffic models based on self-similar stochastic processes that are simple, accurate, and realistic for aggregate traffic.
TCP and explicit congestion notification
Authors: Floyd Sally
Published: October 2004

This paper discusses the use of Explicit Congestion Notification (ECN) mechanisms in the TCP/IP protocol. The first part proposes new guidelines for TCP's response to ECN mechanisms (e.g., Source Quench packets, ECN fields in packet headers). Next, using simulations, we explore the benefits and drawbacks of ECN in TCP/IP networks. Our simulations use RED gateways modified to set an ECN bit in the IP packet header as an indication of congestion, with Reno-style TCP modified to respond to ECN as well as to packet drops as indications of congestion. The simulations show that one advantage of ECN mechanisms is in avoiding unnecessary packet drops, and therefore avoiding unnecessary delay for packets from low-bandwidth delay-sensitive TCP connections. A second advantage of ECN mechanisms is in networks (generally LANs) where the effectiveness of TCP retransmit timers is limited by the coarse granularity of the TCP clock. The paper also discusses some implementation issues concerning specific ECN mechanisms in TCP/IP networks.
High performance TCP in ANSNET
Authors: Villamizar Curtis , Song Cheng
Published: October 2004

This report concentrates on specific requirements and goals of the research networks supported by ANSNET, but applies to any TCP dominated high speed WAN and in particular those striving to support high speed end-to-end flows. Measurements have been made under conditions intended to better understand performance barriers imposed by network equipment queueing capacities and queue drop strategies.The IBM RS/6000 based routers currently supporting ANSNET performed very well in these tests. Measurements have been made with the current software and performance enhanced software. Single TCP flows are able to achieve 40 Mb/s and competing multiple TCP flows achieve over 41 Mb/s link utilization on 44.7 Mb/s DS3 links with delays comparable to US cross continent ANSNET delays. Congestion collapse is demonstrated with intentionally reduced queueing capacity and using window sizes much larger than optimal.A variation of Floyd and Jacobson's Random Early Detection (RED) algorithm [1] is tested. Performance improved with the use of RED for tests involving multiple flows. With RED and queueing capacity at or above the delay bandwidth product, congestion collapse is avoided, allowing the maximum window size to safely be set arbitrarily high.Queueing capacity greater than or equal to the delay bandwidth product and RED are recommended. RED provides performance improvement in all but the single flow case, but cannot substitute for adequate queueing capacity, particularly if high speed flows are to be supported.
Protected types with entry barriers depending on parameters of the entries
Authors: Ledru Pascal
Published: October 2004

Entry barriers of a protected type have one subtle restriction: they are not allowed to depend on parameters of the entry. This paper reviews how to implement protected types with entry barriers depending on parameters of the entries.
Assessing computer security vulnerability
Authors: Alves-Foss Jim , Barbosa Salvador
Published: October 2004

The lack of a standard gauge for quantifying computer system vulnerability is a hindrance to communicating information about vulnerabilities, and is thus a hindrance to reducing those vulnerabilities. The inability to address this issue through uniform semantics often leads to uncoordinated efforts at combating exposure to common avenues of exploitation. The de-facto standard for evaluating computer security is the government's Trusted Computer Evaluation Criteria, also known as the
Orange Book.
However, it is a generally accepted fact that the majority of non-government multi-user computer systems are classified into one of its two lower classes. The link between the higher classes and government classified data, makes the measure unsuitable for commercial use.This project presents a feasible approach for resolving this problem by introducing a standardized assessment. It introduces a method, termed the System Vulnerability Index (SVI), that analyzes a number of factors that affect security. These factors are evaluated and combined, through the use of special rules, to provide a measure of vulnerability. The strength of this method is in its abstraction of the problem, which makes it applicable to various operating systems and hardware implementations. User and superuser actions, as well as clues to a potentially breached state of security, serve as the basis for the security relevant factors. Facts for assessment are presented in a form suitable for implementation in a rule-based expert system.
Implementing real-time services in MINIX
Authors: Wainer Gabriel A.
Published: October 2004

In this work we present the results of a project devoted to provide programming facilities to develop hard real-time software. We have used MINIX operating system as a tool for our experience. We allow the programmer to define timing constraints for the tasks, letting to the Operating System the work of running these tasks in a timely fashion. In this way, we can improve productivity, security and costs in the system development cycle.
Operating system kernel automatic construction
Authors: Jia Xiaohua , Maekawa Mamoru
Published: October 2004

Each year a large amount of resources have been devoted into porting operating system kernels from one machine to another. This paper proposes a new system which is able to construct operating system kernel automatically based on kernel functions specification and hardware interface specification. The system can increase the efficiency and productivity of porting operating systems or building new systems. It can also generate more reliable kernels than human programmers.
Business implications of knowledge-based systems. part II
Authors: Sviokla John J
Published: October 2004

The first section of this article showed how expert systems (ESs) evolved from a branch of the artificial intelligence (AI) field which focused on solving difficult, real world problems. A number of frameworks were put forth to show how ESs compare to other information systems (IS), and to help the practitioner identify valuable and feasible ES applications. Further, it was argued that a well-targeted ES may provide the user with a defensible competitive advantage, and because ESs are currently moving from universities into commerce it is now time to investigate their potential.This section moves on from the discussion of identification of ES opportunity into the issues of development and implementation. In comparison to other IS projects, ESs should prove more demanding. And even though the opportunity for strategic advantage may be available, the execution of a successful ES presents many managerial challenges. The discussion draws on previous literature to help identify issues which are likely to be encountered in practical application of ESs in business. Throughout the discussion, research opportunities are raised and the summary presents a research agenda.
Business graphics: A taxonomy for information systems managers
Authors: Lehman John A
Published: October 2004

The impact of computer graphics on organizational effectiveness can be considerable. The cost of these benefits can also be substantial, both in system cost and in personnel investment. Most discussions of computer graphics technology are driven by technology rather than by applications. Most managers do not understand the technology, and most of the graphics literature is directed either at engineers or at persuading customers in general to purchase systems. This paper provides information for managers and system designers on the major application areas in computer graphics, and the technological alternatives appropriate to different applications.
SIGACT News Complexity Theory Column 10
Authors: Hemaspaandra Lane A.
Published: October 2004

We survey techniques and results obtained over the past thirty years for space-bounded probabilistic computation. We use a common framework for the study of both finite-state automata and logarithmic-space-bounded Turing machines. In particular, we present recent advances on space-efficient deterministic simulation of probabilistic automata.
A dual bus approach for LAN interworking with ATM networks
Authors: Wu Chiung-Shien , Huang Nen-Fu , Ma Gin-Kou
Published: October 2004

The interworking between conventional legacy LANs and the ATM network plays an important role in the initial step of the ATM roadmap. This paper presents a dual bus approach for connecting LAN interworking units (IWU) to ATM networks. Several IWUs connecting heterogeneous LANs are configured into a dual bus structure and the end of the buses are directly connected to the ATM ports. Each IWU transforms the connectionless frame from the legacy LAN to fixed-length time-slots on the dual bus. To provide reliable connectionless services, a cell-based flow control scheme is proposed for dynamically adjusting the cell input rate so as to match with the current resources in the ATM switch. The scheme is further verified to be able to provide an optimal, best-effort and reliable interconnection scenario through simulations. The results show that the total throughput obtained by each local subnetwork dynamically matches with the cell processing throughput of the ATM switch. Besides, each IWU on the dual bus shares a fair bandwidth.
Lovelace
Authors: Wheeler David A.
Published: October 2004

Lovelace is a free interactive tutorial for Ada 95 [RM 95] and is available through the World Wide Web (WWW). This paper describes Lovelace, including basic facts about it, its organization, implementation, user comments, and lessons learned. This paper should be of use to educators considering the use of Lovelace in courses using Ada, users of Lovelace, and educators considering the development of computer-aided instruction programs for the World Wide Web (WWW).
Problems with DCE security services
Authors: White Gregory , Pooch Udo
Published: October 2004

Distributed computing is receiving an ever increasing amount of interest and with it come many challenges, not the least of which is how to maintain system and network security. Issues relating to user authentication, access authorization, and communication security must be addressed when multiple, heterogeneous systems are connected. While these issues have been addressed in OSFs DCE, several problems remain. This paper describes some of these problems.
An architectural approach for integrated network and systems management
Authors: Boutaba Raouf , Znaty Simon
Published: October 2004

Today's enterprises are accepting networked systems as a fundamental part of their information technology strategy. The constant growth in quantity and quality of networked systems and the thereby arising problems concerning complexity, heterogeneity and diversity of components in a multi-vendor environment require a sophisticated management of resources. Increasingly the automation of such management is being demanded.In this paper we introduce an architecture for the integrated management of all resources in a networked system, i.e. application, system and network resources. The architecture uses domains as flexible and pragmatic means of grouping resources and of specifying management responsibility and authority boundaries. It maintains a clear distinction between management objectives and the resources being managed in order to provide an integrated view of the various tasks of management as well as an integrated and uniform view of the distributed and heterogeneous managed environment. The uniform management model on which the architecture is based is expressive enough to capture the full richness of management structures and policies both within enterprises and between them. It allows for recursive and generic structuring, we consider as the basis for management activity automation.As an example, we apply our architectural concepts to structure the management of a high speed multi-network (ATM, DQDB, FDDI). Emphasis lies on an automated Quality of Service management in the FDDI management domain.
Measuring user involvement
Authors: Kappelman Leon A.
Published: October 2004

User involvement is a need-based motivational attitude toward information systems and their development. As such, it has important implications for the successful creation and deployment of information systems in organizations. This paper reports on the development and validation of an instrument to determine if the distinction between a user's involvement in the process of information system diffusion can be measured independently of that user's involvement with the information system innovation itself. Utilizing previously-validated instruments from consumer behavior research, these two object-based categories of user involvement were operationalized.A longitudinal field study was conducted of users in a large financial institution during the implementation phase, in particular the later activities of the adaptation stage, of the information system diffusion process. During adaptation, the information system product becomes available for use in the organization. Late adaptation stage activities include hardware installation, system conversion, and training. The instruments were pre-tested and assessed as to their content validity, internal consistency, convergent validity, unidimensionality, temporal stability, discriminant validity, predictive validity, and factorial validity. The evidence indicates that the measurement scales are reliable and valid. The primary question of scale independence was examined by discriminant validity. The empirical evidence supports the theoretical distinction between user process involvement and user system involvement. The implications of these findings to research and practice are discussed.
Performance of checksums and CRCs over real data
Authors: Partridge Craig , Hughes Jim , Stone Jonathan
Published: October 2004

Checksum and CRC algorithms have historically been studied under the assumption that the data fed to the algorithms was entirely random. This paper examines the behavior of checksums and CRCs over real data from various UNIX® file systems. We show that, when given real data in small to modest pieces (e.g., 48 bytes), all the checksum algorithms have skewed distributions. In one dramatic case, 0.01% of the check values appeared nearly 19% of the time. These results have implications for CRCs and checksums when applied to real data. They also cause a spectacular failure rate for the both TCP and Fletcher's checksums when trying to detect certain types of packet splices.
Performance bounds in communication networks with variable-rate links
Authors: Lee Kam
Published: October 2004

In most network models for quality of service support, the communication links interconnecting the switches and gateways are assumed to have fixed bandwidth and zero error rate. This assumption of steadiness, especially in a heterogeneous internet-working environment, might be invalid owing to subnetwork multiple-access mechanism, link-level flow/error control, and user mobility. Techniques are presented in this paper to characterize and analyze work-conserving communication nodes with varying output rate. In the deterministic approach, the notion of "fluctuation constraint," analogous to the "burstiness constraint" for traffic characterization, is introduced to characterize the node. In the statistical approach, the variable-rate output is modelled as an "exponentially bounded fluctuation" process in a way similar to the "exponentially bounded burstiness" method for traffic modelling. Based on these concepts, deterministic and statistical bounds on queue size and packet delay in isolated variable-rate communication server-nodes are derived, including cases of single-input and multiple-input under first-come-first-serve queueing. Queue size bounds are shown to be useful for buffer requirement and packet loss probability estimation at individual nodes. Our formulations also facilitate the computation of end-to-end performance bounds across a feedforward network of variable-rate server-nodes. Several numerical examples of interest are given in the discussion.
A system for constructing configurable high-level protocols
Authors: Bhatti Nina T. , Schlichting Richard D.
Published: October 2004

New distributed computing applications are driving the development of more specialized protocols, as well as demanding greater control over the communication substrate. Here, a network subsystem that supports modular, fine-grained construction of high-level protocols such as atomic multicast and group RPC is described. The approach is based on extending the standard hierarchical model of the
x
-kernel with composite protocols in which micro-protocol objects are composed within a standard runtime framework. Each micro-protocol realizes a separate semantic property, leading to a highly modular and configurable implementation. In contrast with similar systems, this approach provides finer granularity and more flexible inter-object communication. The design and prototype implementation runing on Mach are described. Performance results are also given for a micro-protocol suite implementing variants of group RPC.
Evaluation of TCP Vegas
Authors: Ahn Jong Suk , Danzig Peter B. , Liu Zhen , Yan Limin
Published: October 2004

This paper explores the claims that TCP Vegas [2] both uses network bandwidth more efficiently and achieves higher network throughput than TCP Reno [6]. It explores how link bandwidth, network buffer capacity, TCP receiver acknowledgment algorithm, and degree of network congestion affect the relative performance of Vegas and Reno.
Leave-in-Time
Authors: Figueira Norival R. , Pasquale Joseph
Published: October 2004

Leave-in-Time is a new rate-based service discipline for packet-switching nodes in a connection-oriented data network. Leave-in-Time provides sessions with upper bounds on end-to-end delay, delay jitter, buffer space requirements, and an upper bound on the probability distribution of end-to-end delays. A Leave-in-Time session's guarantees are completely determined by the dynamic traffic behavior of that session, without influence from other sessions. This results in the desirable property that these guarantees are expressed as functions derivable simply from a single fixed-rate server (with rate equal to the session's reserved rate) serving only that session. Leave-in-Time has a non-work-conserving mode of operation for sessions desiring low end-to-end delay jitter. Finally, Leave-in-Time supports the notion of
delay shifting
, whereby the delay bounds of some sessions may be decreased at the expense of increasing those of other sessions. We present a set of admission control algorithms which support the ability to do delay shifting in a systematic way.
RCBR
Authors: Grossglauser M. , Keshav S. , Tse D.
Published: October 2004

Compressed video traffic is expected to be a significant component of the traffic mix in integrated services networks. This traffic is hard to manage, since it has strict delay and loss requirements, but at the same time, exhibits burstiness at multiple time-scales. In this paper, we observe that slow time-scale variations can cause sustained peaks in the source rate, substantially degrading performance. We use large deviation theory to study this problem and to motivate the design of Renegotiated Constant Bit Rate Service (RCBR), that adds renegotiation and buffer monitoring to traditional CBR service. We argue the the load placed on signalling by RCBR can be handled by current technology. We present a) an algorithm to compute the optimal renegotiation schedule for stored (off-line) traffic, and b) a heuristic to approximate the optimal schedule for online traffic. Simulation experiments show that RCBR is able to extract almost all of the statistical multiplexing gain available by exploiting slow time-scale variations in traffic. In more general terms, we believe that a clean system design must match control time-scales to the time scales over which the workload varies. RCBR works well because it makes intelligent use of this time-scale separation.
The case for persistent-connection HTTP
Authors: Mogul Jeffrey C.
Published: October 2004

The success of the World-Wide Web is largely due to the simplicity, hence ease of implementation, of the Hypertext Transfer Protocol (HTTP). HTTP, however, makes inefficient use of network and server resources, and adds unnecessary latencies, by creating a new TCP connection for each request. Modifications to HTTP have been proposed that would transport multiple requests over each TCP connection. These modifications have led to debate over their actual impact on users, on servers, and on the network. This paper reports the results of log-driven simulations of several variants of the proposed modifications, which demonstrate the value of persistent connections.
Experiences implementing a high performance TCP in user-space
Authors: Edwards Aled , Muir Steve
Published: October 2004

The advantages of user-space protocols are well-known, but implementations often exhibit poor performance. This paper describes a user-space TCP implementation that outperforms a 'normal' kernel TCP and that achieves 80% of the performance of a 'single-copy' TCP. Throughput of 160 Mbit/s has been measured. We describe some of the techniques we used and some of the problems we encountered.
Ada type interchange—moving data between platforms
Authors: Kruchten Philippe , Ehrenfried Dan , Thompson Kim , Thompson Chris
Published: October 2004

This article presents a strategy to convert any Ada type to and from a byte stream, for the purpose of communication or storage of values in a heterogeneous environment:• different Ada compilers,• different hardware platforms with different "endian-ness,"• different versions of the same compiler,• or even different programming languages.These operations are sometimes called 'marshalling' and 'unmarshalling' (RM95 E.4(9)
1
).The strategy is systematically supported by a tool built on top of the Ada Semantic Interface Specification (ASIS)
2
, which builds or updates the conversion routines based on the type definitions.The strategy presented is similar to the Ada 95 mechanism of stream and stream-oriented attributes, however the tool applies to both Ada 83 and Ada 95 with only slight differences in the aspect of the source code generated.
Using Ada and C++ in computer science education
Authors: Toal Raymond J.
Published: October 2004

Undergraduate students of Computer Science or Software Engineering must become familiar with imperative programming languages, due to the extensive use of these languages in industry. Perhaps the two most interesting imperative languages, from a technical standpoint, are Ada and C++, as these two languages include a number of modern features and enjoy widespread popularity. We argue that a four-year undergraduate curriculum in Computer Science which emphasizes imperative programming languages benefits from a thorough coverage of Ada in the first two years, while deferring the direct use of C++ until the junior year. The argument is supported by an overview of the technical features of Ada and C++ which both aid and hinder the learning of software development skills.
A comparison of system monitoring methods, passive network monitoring and kernel instrumentation
Authors: Moore A. W. , McGregor A. J. , Breen J. W.
Published: October 2004

This paper presents the comparison of two methods of system monitoring, passive network monitoring and kernel instrumentation. The comparison is made on the basis of passive network monitoring being used as a replacement for kernel instrumentation in some situations. Despite the fact that the passive network monitoring technique is shown to perform poorly as a direct replacement for kernel instrumentation, this paper indicates the areas where passive network monitoring could be used to the greatest advantage and presents methods by which the discrepancies between results of the two techniques could be minimised.