Showing papers in "Computer Networks and Isdn Systems in 1997"

An introduction to ET-LOTOS for the description of time-sensitive systems

Abstract: Enhanced Timed-LOTOS, called ET-LOTOS, is an extension of LOTOS allowing the modelling of time-sensitive system (ie systems whose behaviour is influenced by the passing of time) It is the basis of the timed extension of LOTOS currently developed by ISO (1995) The purpose of this paper is to present ET-LOTOS in a tutorial style and show its applicability The detailed study of the formal semantics is addressed in another paper A collection of small, but realistic, examples illustrates a wide variety of time-sensitive protocol mechanisms These examples are used to introduce and justify the extensions of our language Finally, the basics of the formal semantics are given and a comparison is made with other timed formalisms

Applying military grade security to the Internet

Abstract: The explosive growth witnessed in the Internet over the last few years has encouraged companies to connect to it and to offer services to their customers over it. Concerns about security are holding them back from all but the most restrictive connectivity. This paper explores the use of a military development, the Compartmented Mode Workstation in a commercial setting, as a platform that is secure enough to implement services that are accessed over the Internet. Two applications have been investigated in detail, a firewalled Domain Name System and a World Wide Web service with enhanced authentication. Finally, there is discussion of how other Internet-based services might benefit from the application of CMW technology.

Providing scalable Web services using multicast communication

Abstract: The recent growth in use of the World-Wide Web in the Internet has caused a significant increase in the demand placed on Web servers. This increased load results in noticeably longer response times for users. We propose an approach to using multicast in the delivery of Web resources that reduces the load on servers as well as the networks that connect them. We analyze the issues involved in using multicast in the Web, especially those related to routing and addressing, and present an alternative approach to multicast routing that is appropriate for this application. We also describe the design and implementation of a system based on the existing WWW client and server architecture and the multicast support provided within IP. Experimental results from this implementation are presented.

Scalable video transmission for the Internet

Abstract: Information systems and distributed applications for the Internet show a growing demand for real-time audiovisual services. Support for those services within the Internet protocol layer will be widely available in the near future. Nevertheless, the heterogeneous structure of the Internet remains to be a great obstacle for establishing real-time video services. Scalable video codecs, generating bit-streams decodable at different rates, have been proposed to address the heterogeneity problem. In this article we present a scalable codec based on a spatio-temporal resolution pyramid combined with lattice vector quantization for efficient compression. With this approach additional lower bit-rate layers can be transmitted at the same overall bit-rate as needed by an H.263 single-layer transmission. The complexity of the codec is sufficiently low to allow software-only implementations of Internet video services. This is demonstrated on an Internet video server application.

On the role of basic design concepts in behaviour structuring

Abstract: This paper presents some basic design concepts for the design of open distributed systems. These concepts should form the basis for the development of effective design methodologies. The paper discusses how design concepts, such as interaction, action and causality relation, can be used for modelling and structuring behaviours of functional entities in a distributed environment. The paper also addresses some consequences of the application of these design concepts such as the choice of language elements and operations to represent behaviour structure, the structuring of the design process, and the definition of design operations for behaviour refinement.

Visualising and populating the Web: Collaborative virtual environments for browsing, searching and inhabiting Webspace

Abstract: This paper presents new services for accessing, exploring and collaborating via the World Wide Web. These are based on the use of Collaborative Virtual Environment (CVE) technology which is used to create navigable 3-D graphical, textual, audio and video representations of the structure of the Web and also of its users. The paper describes a number of different services which address the issues of: browsing the Web; searching the Web; directly representing the presence of other users on the Web and enabling communication with them; and finally new forms of interface to the Web, based on the notion of “mixed realities” which are used to create new forms of boundary between physical and virtual spaces.

A neural network controller for congestion control in ATM multiplexers

Abstract: This paper presents and adaptive approach to the problem of congestion control arising at the User-to Network Interface (UNI) of an ATM multiplexer. We view the ATM multiplexer as a non-linear stochastic system whose dynamics are ill-defined. Real-time measurements of the arrival rate process and the queueing process, are used to identify, and minimize congestion episodes. The performance of the system is evaluated using a performance-index function which is a quantative measure of “how well” the system is performing. A three-layers backpropagation neural network controller generates a signal that attempts to minimize congestion without degrading the quality of the traffic. During periods of buffer over-load the control signal, adaptively, modulates the arrival process such that its peak-rate is throttled-down. As soon as congestion is terminated, the control signal is adjusted such that the coding rates are restored back to their original values. Adaptability is achieved by continuously adjusting the weights of the neural network controller such that the performance of the system, measured by its performance index function, is maximized over a certain optimization period. The performance index function is defined in terms of two main objectives: (1) to minimize the cell loss rate (CLR), i.e., minimize congestion episodes, and (2) to maintain the quality of the video/audio traffic by maintaining its original source coding rate. The neural network learning process can be viewed as a specialized form of reinforcement learning in the sense that the control signal is reinforced if it tends to maximize the performance index function. Performance evaluation results prove that this approach is effective in controlling congestion while maintaining the quality of the traffic.

Network management by delegation—from research prototypes towards standards

Abstract: This paper gives an overview of recent activities to integrate the Management by Delegation (MbD) model into the major network management standards. The paper gives a short introduction to the MbD model and reviews some research prototypes in order to identify a set of design issues. The proposals developed within the ISO and the IETF standardization process are presented and related to the design issues.

Relating architecture and specification

Abstract: The problems of multiple specification languages for multiple architectures are discussed. It is concluded that an architectural semantics is of practical value in ensuring consistent and effective development of specifications. The approach is discussed in general and by examples, concentrating mainly on an architectural semantics for Open Systems Interconnection in relation to Estelle, Lotos and SDL. It is shown how an architectural semantics can be realised using a library of specification templates, allowing the specifier to work at a higher, more architectural level. Some Lotos templates are discussed, mainly for Open Systems Interconnection.

Structural models for specifying telephone systems

Abstract: Two approaches, resource-oriented and constraint-oriented, for structuring telephone systems specifications, are presented. Both approaches express behaviour by collections of communicating processes, using the language LOTOS. However, requirements are distributed differently among processes. Examples are taken from specifications of telephone systems, first basic, and then with features. The features used as examples are call forwarding, originating call screening, and three-way calling. The two structuring methods are compared.

JCAT: collaborative active textbooks using Java

Abstract: This paper describes JCAT, a Java-based system for building Web-based collaborative active textbooks on algorithms. JCAT augments the expressive power of Web pages for publishing passive multimedia information with a full-fledged interactive algorithm animation system. The system is built in such a way that views of a running program may reside on different machines, thereby making JCAT particularly well-suited for electronic classrooms. In such a setting, an instructor controls the animation, while students view the animation by pointing their Web browsers at the appropriate page.

An analytical paradigm to calculate multiplexer performance in an ATM multimedia environment

Abstract: In this paper a finite-buffer discrete-time approach is presented in order to analyze the performance of a multiplexer loaded by N multimedia sources. For this purpose the emission process of each multimedia source is defined as the superposition of heterogeneous correlated emission processes, each of which models one monomedia source as a Switched Batch Bernoulli Process (SBBP). In order to model the intermedia relationships, the Markov chain underlying each SBBP consists of a 2-state process, where the transition probabilities are functions of the states of the other monomedia sources. Correlation functions are derived for each monomedia source as well as for the multimedia source as a whole. The proposed analytical model is used to calculate the loss probability and the delay jitter pdf for each media in an ATM multimedia multiplexer structure. The effectiveness of the proposed paradigm is shown by means of various examples in a case study.

Emerging home digital networking needs

Abstract: In this paper, the situation of an emerging home network environment is examined. There are four driving needs for a home network. They are home automation, home computer, digital audio and video distribution, and digital access network. In the past, the home network is driven by home automation and analog audio and video distribution systems. Most recently, the effort on the development of a digital home network has been driven by emerging digital access and digital consumer electronics technologies. The system requirements are analyzed for different home network applications. The possibility of using IEEE 1394 protocol for a digital home network is explored.

Reliability and availability issues in distributed component object model (DCOM)

Abstract: Distributed Component Object Model (DCOM) is one of the emerging standards for distributed objects. Before DCOM can be used to build mission-critical applications, the reliability and availability issues must be addressed. In this position paper, we outline the current research directions of the InterCOM project, which exploits the dynamic behavior, the extensible architecture, and the component software model of DCOM to provide fault tolerance capabilities to distributed applications.

Physically-based modeling of brush painting

Abstract: This paper introduces physically-based modeling of brush painting. To provide the user with 3D brushes that can be manipulated and interact with the surface of the paper like real brushes, elastic bristles are designed and fixed at the bottom of the brush holder. A linear equation system is derived to calculate the physical deflection of bristles according to the force exerted on them from the surface of the paper. Our brushes provide naturalness in computer painting, and drastically decrease the designing complexity inherent in the conventional 2D outline-based painting.

Algorithm for efficient generation of link-state updates in ATM networks

Abstract: In the routing framework defined by the ATM Forum Private Network Node Interface (P-NNI) working group, each node broadcasts link-state update (LSU) messages (which include information such as available bandwidth, maximum delay, etc.) about the outgoing links attached to it to other nodes in the network. For each connection request, the source node selects an end-to-end route that meets the quality of service (QoS) requirements of the connection based on the most recent information that it has about network links. Up-to-date information about network links is, therefore, key to making “good” routing decisions. The triggering of LSU broadcasts after adding or removing a single connection on any link would certainly enable optimal paths to be calculated but at a potentially significant cost in processing and bandwidth. A periodic update scheme, on the other hand, might be more preferable since it can be used to bound the frequency of updates at the expense of delaying important updates (such as those reporting large changes in link load). The goal of an efficient LSU generating algorithm is, therefore, to provide “accurate” information on link loads while keeping the number of LSUs under control. In this paper, we investigate the issue of when to broadcast LSUs and its effects to the network performance. A simulation model is built to model the basic routing framework developed at the ATM Forum P-NNI working group. Based on the intuition gained by running the simulation model with different schemes and parameters, a hybrid LSU generating algorithm, combining event-driven and periodic update strategies, is proposed to substantially reduce the number of LSUs generated in the network without a significant negative impact on the network performance. The proposed algorithm is not limited to the P-NNI framework and it can be used in networking technologies that are based on the link-state principles.

Continuous free form deformation

Abstract: In this paper, we present a new free-form deformation model which uses 3D lattices as deformation tool. With this technique called CFFD, the deformation tool made of Bezier tetrahedral volumes can describe any 3D space subdivision. Furthermore, this model maintains the continuity of the surface of objects throughout the deformation. We show that the C1 continuity constraint between tetrahedral lattices is useless to control the continuity of the deformation. Thus, in order to maintain it, we introduce a new type of constraint which applies only on the lattice deformation. We first define this constraint on a set of two tetrahedral lattices. Then, using this outcome, we study the case of m tetrahedral lattices around a central edge.

A specification architecture for multimedia systems in open distributed processing

Abstract: The field of distributed systems is now entering a stage of maturity with work focusing on standards for Open Distributed Processing (ODP). However, it is still important that standardisation remains responsive to new technological demands such as the emergence of distributed multimedia computing. This paper focuses on the likely impact of multimedia computing on formal description within ODP. In particular, a specification architecture is proposed for the formal specification and verification of quality of service and more general real-time concerns in distributed multimedia systems. This specification architecture exhibits a separation of concerns between the specification of behaviour and requirements and also between the specification of abstract behaviour and real-time concerns. The architecture also supports refinement to the computational language defined by the ODP standard. It is important to stress that the architecture does not prescribe the use of specific formal notations or languages; particular specification disciplines can however be developed by populating the architecture with appropriate languages. The usefulness of this architecture is demonstrated by the development of such an approach based on LOTOS together with a real-time temporal logic, QTL. This is applied to a simple multimedia example.

An object-oriented approach to the management of distributed application systems

Abstract: General purpose distributed object-oriented environments exist to allow for the efficient construction of client/server software systems. Standard network and distributed systems management environments exist for the efficient operation of heterogeneous networked hardware and software systems. As distributed software systems get larger, the economies of systems development and the economies of software operation demand that we find an efficient way of integrating these two technologies. While the use of standardized distributed systems management for the management of distributed software applications seems reasonable, very little research has been done to confirm this. In this paper, we propose the integration of standardized distributed resource management technologies and distributed application software. In our work we have facilitated this integration using techniques based on mainstream object-oriented dynamic modeling. We will describe our techniques of integration as well as discuss the need for methodical engineered approaches when working in this area.

Two formal methods for the synthesis of discrete event systems

Abstract: The design of discrete event systems (DES) is based mainly on either analysis or synthesis approaches. In the synthesis approach, the design process starts from high level requirements which are then automatically refined to obtain lower abstraction levels. In this paper, we begin by introducing the two design approaches and defining the synthesis problem in DESs, and in protocols in particular. Then, we survey and assess some existing protocol synthesis methods. Then, we present two novel formal and systematic methods we have developed for the synthesis of DESs. The first method is used for the design of distributed systems which must satisfy some temporal constraints. The second method takes into account concepts such as controllability and observability, which are used in the control theory of DESs. Finally, we conclude and propose some future works.

Models for network design, servicing and monitoring of ATM networks based on the virtual path concept

Abstract: Virtual Path (VP) concept has gained attention in terms of effective deployment of ATM networks for wide-area environment. In this paper, we present models and algorithms for network design and management of ATM networks based on virtual path concept from a network planning perspective. Our approach is based on statistical multiplexing of traffic within a traffic class by using a virtual path for the class and deterministic multiplexing of different virtual paths, and on providing dynamic bandwidth and reconfigurability through virtual path concept depending on traffic load during the course of the day. For some realistic example networks, we observe that considering network dynamism through variation of traffic during the course of a day by doing dynamic bandwidth and virtual path reconfiguration can save between 10 to 14% in network design costs compared to a static network based on maximum busy hour traffic.

Challenges to the network: Telecoms and the internet

Abstract: Readers are likely to be interested in “Challenges to the Network”, published recently (September, 1997) by the ITU. As you know, the International Telecommunications Union is a United Nations agency specialized in telecommunications and successor to the C.C.I.T.T. We know it best as the publisher of telecommunications standards. The book is based on the notion, that although the Internet of today rides on top of the telephone network, it is conceivable that this relationship will reverse in the future. This would have a strong impact on common carriers. The book is a compendium of commentary and useful information including a wealth of statistical data. An executive summary of the report's contents can be found on the World Wide Web; the URL is http://www.itu. int/indicators.

Properties of secure transaction protocols

Abstract: Communication protocols are the computational basis for distributed electronic commerce systems, and thus the properties of these protocols define the forms of commerce possible in electronic systems. Existing protocols used for electronic commerce focus primarily on security properties, including message integrity, privacy and non-repudiation, and on basic transaction properties, usually just atomicity; their structural properties are limited to supporting two-party transactions with fixed semantics. We believe that the properties provided by these protocols limit their use to simple forms of commerce. In this paper we define the properties we believe are necessary for electronic commerce protocols. These include the security properties of existing protocols, and extend the transactional properties to include isolation and causality. Causality is a new property for transactions. It allows the order of the messages in a completed transaction to be independently verified, and thus inferences can be made about causal relationship between messages. We also extend the structural properties to support scalability, layering and separation of roles. Scalable protocols allow several parties to join each transaction. Protocol layering enables arbitrary transaction semantics and greater system modularity. Separation of roles provides independent adjudication of disputes between transaction participants and allows the use of varied exchange media. We term a protocol with the above properties a secure transaction protocol. Lastly, we present a protocol that provides these properties. We believe that this protocol can be used to support more complex and extended forms of electronic commerce than existing protocols.

Rate-based control schemes for ABR traffic—design principles and performance comparison

Abstract: A new ATM service category, the Available Bit Rate service, has been introduced in the ATM Forum. It dynamically allocates available bandwidth to users by controlling the flow of user traffic with feedback. The Forum has ratified the rate-based flow control framework for the support of this new service. In this paper, we provide a recipe for designing rate-based feedback schemes demonstrating the rich variety of available switch mechanisms. Each aspect of the feedback control loop mechanism is explored in detail and several available choices are investigated. Two example switch mechanisms are provided that illustrate the rate-based control design principles. The ability of these mechanims to support the desired objectives of an ABR service is compared using a reference network configuration. Simulation results show that the rate-based framework allows a great degree of architectural flexibility in the design of switch mechanisms. However, the explicit rate based approach is more capable than single bit feedback approaches in providing immediate access to available bandwidth in the presence of VBR sources. The rate-based framework provides switch vendors sufficient flexibility to choose a mechanism among several available options, based on their performance requirements and cost budges.

Providing global broadband Internet access using low-earth-orbit satellites

Abstract: Using a constellation of several hundred low-Earth-orbit satellites — a global, broadband “Internet-in-the-sky” — Teledesic will enable affordable access to fiber-like telecommunications capability anywhere in the world. The Teledesic Network will allow local Service Providers to extend their networks in terms of both scope of services and geographic reach. It will be a local service provided through a global network.

A fast algorithm for selective refinement of terrain meshes

Abstract: An efficient way to render terrain data is to display an approximating surface whose resolution has been enhanced in areas of interest. We present a new reduced expansion algorithm which extracts such a selectively-refined mesh faster than our previous minimal surface algorithm. A mesh can be generated from the output of any surface approximation process which can be viewed as a set of refinement operations acting on a base triangulation. We prove that our new algorithm generates a complete, although not necessarily minimal, surface which will satisfy any given resolution criteria and which may, in addition, satisfy the Delaunay triangulation criterion.

An analytic study of partially ordered transport services

Abstract: This paper presents an analytic model for investigating the throughput, delay and buffer utilization characteristics of partially ordered transport services. We analyze the effects of packet and ack losses as well as applications' order requirements on overall system performance. The analytic model is verified by comparing its results against those of an OPNET simulation model. Analytic results show that for applications that can tolerate some reordering in the delivery of objects, use of partially ordered service instead of ordered service provides important buffer utilization and delay improvements, particularly as the loss rate increases and the order requirements of applications decrease. In terms of throughput, it makes no difference which service (i.e., ordered, partially ordered, unordered) an application uses. Analytic study also shows that by judicious choice of sender's transmission order, overall system performance can further be improved in a partially ordered service.

Use of instructional material in universal teleteaching environments

Abstract: This article classifies teaching media, which are used in teleteaching and traditional forms of instruction. A definition for flexible teleteaching solutions is given and a list of requirements for universal teleteaching environments is named. Criteria such as variability, quality, scalability and cost effectiveness are considered in the light of a flexible teleteaching solution. In addition an environment constructed with these criteria in mind is presented, as it is currently being realised under the auspices of the ‘Multimedia Teleteaching—MMTT’ project of the DFN-Verein (Association for Promoting a German Research Network) at the department of information systems at the University of Erlangen-Nuremberg. While developing the concept particular consideration has been attached to the high quality which is to be expected of the various teaching media. Experiences from this and the preceding project ‘Multimedia based decentralisation of interdisciplinary teaching’, which was also sponsored by the DFN-Verein, are to prove that the integration of conventional and electronic teaching media can, under certain circumstances, fulfil all the outlined criteria. The article closes with an overview of a possible future teleteaching environment in cyberspace and the ensuing renaissance of conventional teaching materials.

Access architecture for a multiprotocol broadband backbone

Abstract: We present a comprehensive architectural model of a modular communication infrastructure for providing interconnection between a wide variety of networks with like protocols across a common backbone network. Our concepts are demonstrated to be an appropriate framework for the provision of (a-)synchronous virtual channels, LAN interconnection, and standard internetworking, thus covering the most typical current connectivity requirements. The base architecture has been implemented, and first products are being offered with interfaces for Frame Relay, Fiber Channel Standard, ATM, voice and clear channel services.