Showing papers in "Computer Networks and Isdn Systems in 1991"
TL;DR: A solution to the database access problem is presented which could be implemented with technology available in no more than 10 years and is argued that the incremental communications cost is small, as long as one assumes that there is already a network with sufficient bandwidth to the customer.
Abstract: This short paper examines the technological feasibility of a “video on demand” service that is provided from a centralized location over a digital network. The proposed, hypothetical video on demand service is considered to be a service similar to the currently popular video-tape rental services. The problem addressed is divided into two parts: communications and database access. It is argued that the incremental communications cost is small, as long as one assumes that there is already a network with sufficient bandwidth to the customer. A solution to the database access problem is presented which could be implemented with technology available in no more than 10 years.
274 citations
TL;DR: Four major formal techniques for conformance test generation reported in the literature are compared and the capability to generate abstract test suites that require a minimum number of steps to execute while maintaining complete coverage of the state transitions of the protocol is demonstrated.
Abstract: Recent evolution of communication networks has led toward increasingly complex communication protocols to interconnect heterogeneous systems. In order for such systems to function properly, communication protocols require formal methodologies for verification, implementation and testing. In this paper, the use of formal methods for protocol conformance testing is presented. Four major formal techniques for conformance test generation reported in the literature are compared: transition tours, distinguishing sequences, characterizing sequences and unique input/output sequences. The implementation of each approach as a test generation methodology is illustrated. The result is the capability to generate abstract test suites that require a minimum number of steps to execute while maintaining complete coverage of the state transitions (or test purposes) of the protocol. The impact of the formal methodologies on the practical aspects of conformance testing, including the test system implementation and automatic test script generation, is discussed. The experience based on testing various protocol implementations from multiple manufacturers at AT&T Bell Laboratories is described. The protocols tested include X.25 and ISDN Q.921 and Q.931 for basic and primary rate interfaces. In order to standardize various efforts on conformance testing, the ISO and the CCITT have developed principles to specify abstract and executable test suites, and methodologies to design testbed architectures. The relationship between such standards and the formal methods for test generation is explored.
90 citations
IBM1
TL;DR: This paper reviews applications of the analytical results for polling models to the following communication networks: the half-duplex transmission, polling data link control, MSAP (BRAM), Newhall loop, and explicit and implicit token passing protocols.
Abstract: In many computer-communication protocols, the transmission rights are circulated among the users in cyclic order for the sake of fairness. The performance of such protocols has been analyzed in terms, of multiple-queue cyclic-service models, or polling models. This paper reviews applications of the analytical results for polling models to the following communication networks: the half-duplex transmission, polling data link control, MSAP (BRAM), Newhall loop, and explicit and implicit token passing protocols. Substitution of the network parameters into the parameters of polling models is illustrated, and many numerical examples of network performance are provided. Protocol features that are difficult to incorporate into currently analyzable models are also discussed for potential future research.
87 citations
TL;DR: The business need for ODP is demonstrated, an overview of the technology is provided and the technical drivers and market forces co-existing with its development are discussed.
Abstract: Open Distributed Processing (ODP) relates to the development, use and management of applications distributed across networks of computer systems. It extends and incorporates work already performed independently in the fields of communications (OSI) and computing. ODP is intended to meet the following technical goals: • portability of applications in a distributed environment • interworking between conformant systems • distribution transparency in conformant systems As a result, ODP is being developed in the form of an architectural framework, or reference model, scheduled for initial release as a Draft International Standard (DIS) in 1993. This paper demonstrates the business need for ODP, provides an overview of the technology and discusses the technical drivers and market forces co-existing with its development.
55 citations
TL;DR: The ISO/OSI-reference model (ISO 7498) with its seven layers is a result of standardization efforts to standardize the protocols between the individual devices.
Abstract: As far as the communication between computer-based devices and the management of networks containing such devices is concerned, difficulties remain, especially arising from the manifold vendor specific solutions. In order to avoid these difficulties in communication, standards have been created which standardize the protocols between the individual devices. The ISO/OSI-reference model (ISO 7498) with its seven layers is a result of these standardization efforts. This division into seven layers was used as a basis for the definition of further standards.
48 citations
TL;DR: A small, didactically-oriented specification of a simple telephone service is provided, based on three types of constraints, i.e. global constraints, end-to-end constraints and local constraints.
Abstract: The LOTOS constraint-oriented style allows the design of well-structured, implementation-independent specifications of distributed systems. As an example, we provide a small, didactically-oriented specification of a simple telephone service. The design of the specification is based on three types of constraints, i.e. global constraints, end-to-end constraints and local constraints. The structure of the specification, as well as its design method, are described in some detail. We conclude with a discussion of the specification debugging method.
43 citations
IBM1
TL;DR: A selection of the most popular state-of-the-art mechanisms designed to protect information, objects and other resources found in networks and distributed systems are discussed, starting with basic cryptographic tools and explaining how these can be exploited to achieve various forms of authentication services.
Abstract: With the ever increasing pervasiveness of computer networks, security of information stored in or transported through networks, as well as security of network components and resources themselves are becoming the focus of intense concern on the part of network users and operators. This paper discusses a selection of the most popular state-of-the-art mechanisms designed to protect information, objects and other resources found in networks and distributed systems. The various techniques discussed are introduced in a bottom-up order, starting with basic cryptographic tools, then explaining how these can be exploited to achieve various forms of authentication services, and finally sketching very briefly more recent, mostly experimental developments in the area of access controls for networks and network resources. The paper is addressed to readers with a background in networks and distributed systems but little or no understanding of security issues in general, system security in networking and distributed environments in particular.
35 citations
Journal Article•
30 citations
TL;DR: A comprehensive tutorial on the distributed operation of the Directory, which shows the rationale behind the design and provides further insights into various aspects, revealing potential traps and optimisations for implementors.
Abstract: The CCITT/ISO standard “The Directory” defines a major new OSI application and represents a major milestone in the development of large-scale distributed systems. The Standard provides a specification for a distributed global on-line directory. Distributed operation of the Directory is achieved through a complex combination of protocols and the knowledge each component system has of the others. This paper examines the distributed operation of the Directory. It has a threefold purpose: firstly, it gives a comprehensive tutorial on the distributed operation of the Directory; secondly, it shows the rationale behind the design; and thirdly, it provides further insights into various aspects, revealing potential traps and optimisations for implementors. Together the material caters for a range of reader, from those wanting to understand the subject for the first time through to X.500 implementors.
21 citations
TL;DR: In this paper, various multicast design issues are addressed and solutions are proposed to provide an effective multicast extension for a wide range of existing unicast protocols.
Abstract: This paper describes a multicast model which can be integrated into existing unicast communication systems to provide better support for group communications. Multicast services are becoming more important, as more and more of today's network workstation environments are used to provide group communications for the exchange of multimedia information [29]. These environments allow users to exchange information in the form of ‘documents’ containing text, graphics and voice; some systems support both store-and-forward (e.g., mail) and real-time (e.g., conferencing) material. In this paper, various multicast design issues are addressed and solutions are proposed to provide an effective multicast extension for a wide range of existing unicast protocols.
20 citations
TL;DR: A unifying framework is presented to conclude explicit product form expressions for the steady state distribution of busy sources (transmitters, lines) for random access communication protocols with insensitivity means that the underlying random distributions play a role through only their means while a product form stands for factorization in individual transmitters or links.
Abstract: A unifying framework is presented to conclude explicit product form expressions for the steady state distribution of busy sources (transmitters, lines) for random access communication protocols. Transmission times and packet lengths are generally distributed. The main results are: 1. (1) An insensitive product form expression. 2. (2) A concrete condition in terms of system protocols. 3. (3) A generalization of product form random access protocols. Here, insensitivity means that the underlying random distributions (transmission times and packet lengths) play a role through only their means while a product form stands for factorization in individual transmitters or links. These results unify and extend known results. Particularly its includes CSMA-protocols with 1. (i) Non-exponential transmissions and packets. 2. (ii) State dependent transmission speeds. 3. (iii) Link selective characteristics. A variety of “novel” examples is given such as with hierarchical circuit switching, synchronous serving, randomized grading, message priorities, error probabilities, link selective transmissions and an extension of rude-CSMA.
TL;DR: The helminthiasis (infestation with, or disease caused by parasitic worms) of the Internet was the result of a self-replicating program that infected VAX computers and SUN-3 workstations running the 4.2 and 4.3 Berkeley UNIX code.
Abstract: The helminthiasis (infestation with, or disease caused by parasitic worms) of the Internet was the result of a self-replicating program that infected VAX computers and SUN-3 workstations running the 4.2 and 4.3 Berkeley UNIX code. The worm disrupted the operations of computers by accessing known security loopholes in applications closely associated with the operating system. Despite system administrators' efforts to eliminate the program, the infection continued to attack and spread to other sites across the United States.
TL;DR: The role of networks in providing an efficient supercomputing environment has become more critical and continues to grow and at a faster rate than the increase in the processing capabilities of supercomputers.
Abstract: In several cases, new visualization techniques have vastly increased the researcher's ability to analyze and comprehend data. Similarly, the role of networks in providing an efficient supercomputing environment have become more critical and continue to grow at a faster rate than the increase in the processing capabilities of supercomputers. A close relationship between scientific visualization and high-speed networks in providing an important link to support efficient supercomputing is identified. The two technologies are driven by the increasing complexities and volume of supercomputer data. The interaction of scientific visualization and high-speed networks in a Computational Fluid Dynamics simulation/visualization environment are given. Current capabilities supported by high speed networks, supercomputers, and high-performance graphics workstations at the Numerical Aerodynamic Simulation Facility (NAS) at NASA Ames Research Center are described. Applied research in providing a supercomputer visualization environment to support future computational requirements are summarized.
TL;DR: This paper presents a formal technique to synthesize a converter by inserting the PUT and GET operations into two given protocols to manipulate the buffer for indirect conversion, and an algorithm for indirect Conversion is presented and applied to a practical example for conversion between ISO OSI and IBM SNA protocols.
Abstract: With the proliferation of different computer networks, protocol conversion is needed to achieve interoperability between computer networks that implement different protocols, so that users on different networks can communicate with one another. In its most efficient form, protocol conversion is performed on the fly, i.e. the messages produced in one protocol are converted and passed immediately to the other protocol; this is called direct conversion, and no buffer is needed to store the messages. For many practical protocols, however, it is possible that the messages produced in one protocol need to be re-ordered and converted before they are passed to the other protocol; this is called indirect conversion, and the messages produced in one protocol must be first stored in a non-FIFO buffer and then converted in proper order for the other protocol. This paper presents a formal technique to synthesize a converter by inserting the PUT and GET operations into two given protocols to manipulate the buffer for indirect conversion. The PUT operation inserts messages in one protocol into a non-FIFO buffer, and then the GET operation retrieves the messages in proper order from the buffer and converts them for the other protocol. Since the PUT and GET operations are asynchronous, they may create some problems for the buffer: (1) buffer overflow, i.e., the number of messages stored in the buffer exceeds its capacity; and (2) improper termination, i.e., the protocol terminates with some messages leftover in the buffer. Therefore, the synthesized converter needs to be validated. Several techniques are proposed to reduce the computing time and space spent in validating the converter. Finally, an algorithm for indirect conversion is presented and applied to a practical example for conversion between ISO OSI and IBM SNA protocols.
TL;DR: This work demonstrates that starvation is a serious problem and presents a protocol to prevent it, and it is shown that the new protocol is correct, stable and does not substantially degrade the otherwise efficient operation of the ring.
Abstract: Of several existing designs for local area networks, the buffer insertion ring has been shown to provide higher throughputs, lower mean delays and greater spatial reuse than competing designs such as the token ring and slotted ring networks. However, one disadvantage is that the normally unregulated access scheme of the insertion ring allows for the phenomenon of “starvation” — when a network node has to wait too long before it can access the ring. In our work, we demonstrate that starvation is a serious problem and present a protocol to prevent it. It is shown that the new protocol is correct, stable and does not substantially degrade the otherwise efficient operation of the ring.
TL;DR: The design of transit control mechanisms for sensitive environments is explored and the performance overhead of the proposed mechanisms are investigated and a secure policy routing protocol is described and evaluated.
Abstract: When independent administrative domains (ADs) interconnect their networks, usage control mechanisms are needed to preserve the autonomy of each AD. Neither traditional network access control methods nor current internetwork routing protocols are well-suited to the enforcement of network usage policies. Consequently, new policy sensitive inter-domain routing protocols are under development. While these protocols are designed to enforce network policies, they raise new security-related concerns. This paper explores the design of transit control mechanisms for sensitive environments and investigates the performance overhead of the proposed mechanisms. After evaluating the application of stub-network access control and policy routing techniques, we describe and evaluate a secure policy routing protocol for transit ADs.
TL;DR: Esterel is a new parallel programming language based on a model of perfectly synchronous parallelism and communication that provides an excellent framework for the modular decomposition of programs that engage in complex patterns of deterministic interaction, such as protocol entities.
Abstract: Esterel is a new parallel programming language based on a model of perfectly synchronous parallelism and communication. Because this model is naturally deterministic, it provides an excellent framework for the modular decomposition of programs that engage in complex patterns of deterministic interaction, such as protocol entities. Furthermore, because the Esterel compiler performs all the scheduling and synchronization at compile-time, modular with lots of subprocesses and internal communication can be just as efficient as monolithic sequential state machines. A restricted model of an HDLC entity is used to illustrate the new programming style that is made possible by these features. An Esterel program is developed in several steps, starting from a simple restricted case, and then adding features and complexity. The emphasis is first on design as we develop a program architecture that captures the basic procedures of the protocol in independent modules; then it shifts to maintenance as we add new features into the initial architecture by plugging new modules into the base program.
TL;DR: The basic services required from a communication subsystem to support a distributed, reliable, reconfigurable, and replicated database environment are identified and a new communication facility is designed that features an unobtrusive IPC paradigm and a transaction-oriented multicasting mechanism.
Abstract: This paper identified the basic services required from a communication subsystem to support a distributed, reliable, reconfigurable, and replicated database environment. These services include multicasting, remote procedure calls (RPC), inexpensive data-gram services, and efficient local interprocess communication (IPC). Data are included from experiments that measure communication performance in four areas: (i) layered implementations of communication protocols, (ii) local interprocess communication methods, (iii) multicasting, and (iv) commitment processing. We have used the results of those experimental studies to design and implement a new communication facility. It features an unobtrusive IPC paradigm and a transaction-oriented multicasting mechanism.
TL;DR: This paper provides a novel representation of memory reference data which can used to calculate interarrival distributions directly, and shows how integrating communication with computation can be used to control both traffic and performance.
Abstract: We believe that many distributed computing systems of the future will use distributed shared memory as a technique for interprocess communication. Thus, traffic generated by memory requests will be a major component of the traffic for any networks which connect nodes in such a system. In this paper, we study memory reference strings gathered with a tracing program we devised. We study several models. First, we look at raw reference data, as would be seen if the network were a backplane. Second, we examine references in units of “blocks”, first using a one-block cache model and then with an infinite cache. Finally, we study the effect of predictive prepaging of these “blocks” on the traffic. We provide a novel representation of memory reference data which can used to calculate interarrival distributions directly. Integrating communication with computation can be used to control both traffic and performance.
TL;DR: This paper presents a scheme that combines two new adaptive algorithms for flow control and routing that has a lower delay, at about the same throughput than some schemes given in the literature, thus resulting in a higher power.
Abstract: In this paper we present a scheme that combines two new adaptive algorithms for flow control and routing. The flow control algorithm increments or decrements the window size based on the value of the sessions' delay and the routing algorithm uses a new fast and accurate Learning Automaton presented in [23] to choose the minimum delay routes in the network. We compare the performance of this new scheme with similar ones discussed in the literature. The new scheme, being a delay-oriented one, has a lower delay, at about the same throughput than some schemes given in the literature, thus resulting in a higher power ( = throughput/delay).
TL;DR: The development and definition of ODA document application profiles is described, which have now been developed as functional standards by regional standards bodies, and are being progressed as International Standards, thus enabling global document interchange.
Abstract: This paper describes the development and definition of ODA document application profiles Initial implementations of ODA have not, in the main, covered every aspect of the standard: rather, particular applications, such as interworking between existing equipment, have demanded the definition of particular subsets of the base standard, tailored to specific uses The ODA standard provides for the definition of such subsets as document application profiles A key concept in the definition of document application profiles is the “metaclass” or “constituent constraint” by which generalised ODA mechanisms are grouped for the purpose of representing conventional document features such as footnotes A specialised notation is required for the precise definition of constituent constraints, which is provided by a proposed Addendum to the base standard Particular document application profiles have been developed to support different levels of functionality and combinations of content types These have now been developed as functional standards by regional standards bodies, and are being progressed as International Standards, thus enabling global document interchange Practical experience, such as the document interworking demonstrations mounted by the ESPRIT PODA project, has been formative in arriving at suitable profile definitions, and in their validation
Journal Article•
TL;DR: SGML (ISO 8879) and ODA (ISO 8613) are the two predominant international standards in the realm of open document processing, gaining more and more importance for the interchange of documents in both the publishing environment and the office environment.
Abstract: SGML (ISO 8879) and ODA (ISO 8613) are the two predominant international standards in the realm of open document processing, gaining more and more importance for the interchange of documents in both the publishing environment and the office environment. To ensure early availability the functionality currently provided by these standards has been restricted with respect to some future requirements. The pertinent international standardization committees are currently working on the required future extensions to these standards.
TL;DR: The paper summarises the salient features of document transfer over X.400, and of an ODA server implemented over an Autonomous Active Mail box, based on these implementations.
Abstract: Following the emergence of a number of international standards, ISO-8613 ODA standardises a number of facilities that allow interchange of multimedia documents structured in terms of logical and layout components. This paper discusses characteristic of a proprietary multimedia editor, how far its facilities could be represented in ODA, and how conversion between the proprietary and the ODA format has been implemented. The paper summarises the salient features of document transfer over X.400, and of an ODA server implemented over an Autonomous Active Mail box. It finally discusses some of the salient features of the document interchange, based on these implementations.
TL;DR: A bounding algorithm has been developed that provides upper and lower bounds for the source-to-terminal reliability of an arbitrary network that possesses linear time-complexity when the maximum indegree of all network nodes is limited.
Abstract: The best known solution methods for network reliability problems are of exponential time-complexity. This exponential behavior can render even moderately sized problems computationally intractable due to the enormous amount of time required to generate a solution. To render such problems manageable, a bounding algorithm has been developed that provides upper and lower bounds for the source-to-terminal reliability of an arbitrary network. A unique feature of this bounding algorithm is that it possesses linear time-complexity when the maximum indegree of all network nodes is limited.
TL;DR: A distributed version of VIS-5D running on a workstation and a supercomputer will make it possible to interactively explore data sets containing up to 1010 points to help scientists develop numerical models of atmospheric phenomena.
Abstract: The VIS-5D system running on large workstations lets scientists interactively explore atmospheric simulation data sets containing up to 5 x 10(exp 7) points. A distributed version of VIS-5D running on a workstation and a supercomputer will make it possible to interactively explore data sets containing up to 10(exp 10) points. Wide area gigabit networks will bring this capability to scientists at most academic and research institutions. This software will help scientists to interactively develop numerical models of atmospheric phenomena.
TL;DR: Experience with the specifications is presented: in particular, how readable and precise the teams found their specifications and how they mapped the specifications into Ada constructs, and the number and classification of implementation faults.
Abstract: A controlled experiment was conducted in which six protocol implementations were developed. They were derived by integrating two protocols specified with the ISO and CCITT Formal Description Techniques (FDTs) Estelle, LOTOS, and SDL. The implementations were written in the Ada programming language by six independent programming teams (two teams worked from each FDT). Experience with the specifications is presented: in particular, how readable and precise the teams found their specifications and how they mapped the specifications into Ada constructs. Results are also presented concerning the number and classification of implementation faults. Experience using Ada, particularly its concurrency features and the efficiency of the implementation, is also included.
TL;DR: An exact algorithm is presented for the calculation of such quantities as the (time-dependent) probability of an empty buffer and the mean buffer occupancy of discrete-time buffer systems with random output interruptions and general independent arrivals.
Abstract: A simple model for discrete-time buffer systems with random output interruptions and general independent arrivals is considered. A method is developed for the derivation of transient statistics of this kind of queueing system. In particular, an exact algorithm is presented for the calculation of such quantities as the (time-dependent) probability of an empty buffer and the mean buffer occupancy. A few examples illustrate the analysis.
TL;DR: To satisfy the fairness of equal delays among stations in the bus network, the unslotted pi-persistent CSMA-CD protocol with the combined retransmision strategy is presented, and the persistent probability pi and its delay performance are determined.
Abstract: We present an unslotted 1-persistent carrier sense multiple access with collision detection (CSMA-CD) protocol with the combined preemptive-resume/-repeat-identical retransmission strategy for fiber optic bus and ring networks. Under this protocol, if the information field of a packet is preempted by upstream packets, its remaining portion is retransmitted with the identical header. However, when the header field of a packet is preempted, the packet is retransmitted from its beginning. Treating the bus and ring networks with M stations as an M-class priority queueing system and a two-class priority queueing system with the combined retransmision strategy, respectively, we show numerically that this protocol provides better delay-throughout performance than the unslotted CSMA-CD protocol in both networks, and it solves the instability problem of the unslotted CSMA-CD protocol in the ring network. To satisfy the fairness of equal delays among stations in the bus network, we next present the unslotted pi-persistent CSMA-CD protocol with the combined retransmision strategy, and determine the persistent probability pi and its delay performance. Simulation results are present to verify the analytical results.
TL;DR: This paper models and analyzes the stability of a slotted-ALOHA network hosting heterogeneous users by carrying out Liapunov's indirect method in association with the properties of M-matrix to obtain the sufficient condition for the structural stability of the networks.
Abstract: This paper models and analyzes the stability of a slotted-ALOHA network hosting heterogeneous users. The scheme is modeled by dividing the total user-population into groups of homogeneous users. The behavior of the system is represented by state equations. The stability analysis is carried out by Liapunov's indirect method, in association with the properties of M-matrix, to obtain the sufficient condition for the structural stability of the networks. The analysis also points out the method of hierarchical grouping of the heterogeneous users.