Showing papers on "Communications protocol published in 1982"

The newcastle connection or UNIXes of the world unite

Abstract: In this paper we describe a software subsystem that can be added to each of a set of physically interconnected UNIX or UNIX look-alike systems, so as to construct a distributed system which is functionally indistinguishable at both the user and the program level from a conventional single-processor UNIX system. The techniques used are applicable to a variety and multiplicity of both local and wide area networks, and enable all issues of inter-processor communication, network protocols, etc., to be hidden. A brief account is given of experience with such a distributed system, which is currently operational on a set of PDPlls connected by a Cambridge Ring. The final sections compare our scheme to various precursor schemes and discuss its potential relevance to other operating systems.

Protocols for Deadlock Detection in Distributed Database Systems

Abstract: In distributed databases, deadlocks may occur due to conflicts in data file lockings A system is in a deadlock if and only if there is a directed cycle in its demand graph. However, due to the inherent communication delay in a distributed system, it is not easy to construct a consistent demand graph for a distributed system. In this paper, three deadlock detection protocols are discussed. The first protocol uses two communication phases. The second protocol uses a single communication phase. Based on the second protocol, a one-phase hierarchical deadlock detection protocol is developed.

Specification and Verification of Communication Protocols in AFFIRM Using State Transition Models

Abstract: It is becoming increasingly important that communication protocols be formally specified and verified. This paper describes a particular approach–the state transition model–using a collection of mechanically supported specification and verification tools incorporated in a running system called AFFIRM. Although developed for the specification of abstract data types and the verification of their properties, the formalism embodied in AFFIRM can also express the concepts underlying state transition machines. Such models easily express most of the events occurring in protocol systems, including those of the users, their agent processes, and the communication channels. The paper reviews the basic concepts of state transition models and the AFFIRM formalism and methodology and describes their union. A detailed example, the alternating bit protocol, illustrates varous properties of interest for specification and verification. Other examples explored using this formalism are briefly described and the accumulated experience is discussed.

A Survey of Formal Methods

Abstract: As evidenced by the earlier chapters in this book, increasingly numerous and complex communication protocols are being employed in distributed systems and computer networks of various types The informal techniques used to design these protocols have been largely successful, but have also yielded a disturbing number of errors or unexpected and undesirable behavior in most protocols This chapter describes some of the more formal techniques which are being developed to facilitate design of correct protocols

A Theory for Protocol Validation

Abstract: This paper introduces a simple algebra for the validation of communication protocols in message passing systems. The behavior of each process participating in a communication is first modeled in a finite state machine. The symbol sequences that can be accepted by these machines are then expressed in "protocol expressions," which are defined as regular expressions extended with two new operators: division and multiplication. The interactions of the machines can be analyzed by combining protocol expressions via multiplication and algebraically manipulating the terms.

Bounds on the size and transmission rate of communications protocols

Abstract: Using a pair of finite-state automata to model the transmitter-receiver protocol in a data communications system, we derive lower bounds on the size of automata needed to achieve reliable communication across an error-prone channel. We also show that, at the cost of increasing the size of the automata, a transmission rate close to the theoretical maximum can be achieved.

From state machines to temporal logic - Specification methods for protocol standards

Abstract: This paper attempts to lend perspective to several different methods that have been employed for specifying computer communication protocols by comparing a spectrum of specification techniques. The paper characterizes specification languages such as state transition diagrams, variants of temporal logic approaches, and sequence expressions by the extent to Which information is encoded as properties of a single state versus properties of a history of the entire computation state sequence. Taking the prototypical alternating bit protocol as an example, each method is used to specify the requirements for the send process of the distributed system.

Verification of communications protocols and abstract process models

Abstract: Communications protocols are crucial for the reliable exchange of information in distributed systems. In this dissertation, we consider the problem of formally specifying and verifying properties of protocol systems. Such systems are modeled by hierarchies of concurrent processes, where interprocess communication is achieved by message passing rather than through arbitrary shared variables. Based on this model, a methodology is developed for mechanically assisted protocol analysis. The Gypsy methodology for concurrent program verification is the point of departure for much of this work. Specialized methods applicable to protocols are derived from the Gypsy methods. Behavior of protocol modules is specified in a fairly abstract manner using a state transition paradigm, thus avoiding a highly procedural form of specification. Protocol services are specified by means of assertions over message histories. Proof techniques are introduced for verifying safety properties of the process models. In addition, a specification and assertion language is developed. This language emphasizes features and operations useful for expressing protocol oriented concepts and constructing proofs about them. An important aspect of this work is use of machine assisted analysis, most notably the use of mechanical theorem proving. A strategy for applying a particular automatic theorem prover, the Boyer-Moore prover, to protocol verification problems is put forth. A consequence of this strategy is the accumulation of a large body of proved lemmas, constituting a rudimentary deductive theory for protocols. With this theory, the methodology has successfully been applied to a pair of sample transport protocols. These include the Stenning protocol and an abstraction of the data transfer function of TCP.

Rules for synthesizing correct communication protocols

Abstract: An approach to communication protocols synthesis is proposed which permits the development of general (FIFO and non-FIFO channels), N-party (N>=2) protocols with the following properties: completeness, deadlock freeness, livelock or tempo-blocking freeness, termination or cyclic behavior, liveness, boundedness and absence of non-executable interactions.

A prototype generalized network technology for hospitals: initial implementation.

Abstract: A demonstration implementation of a distributed data-processing hospital information system using an intelligent local area communications network (LACN) technology is described. This system is operational at the UCSF Medical Center and integrates four heterogeneous, stand-alone minicomputers. The applications systems are PID/Registration, Outpatient Pharmacy, Clinical Laboratory, and Radiology/Medical Records. Functional autonomy of these systems has been maintained, and no operating system changes have been required. The LACN uses a fiber-optic communications medium and provides extensive communications protocol support within the network, based on the ISO/OSI Model. The archtecture is reconfigurable and expandable. This paper decribes system architectural issues, the applications environment, and the local area network.

Specifying and Verifying Protocols Represented as Abstract Programs

Abstract: Network protocols form the cornerstone upon which distributed systems are built. Because of their fundamental importance, protocols must be designed with care so that they work correctly. In this chapter we discuss the techniques that have evolved for specifying and verifying protocols. In particular, we concentrate on those techniques that model protocols as abstract parallel programs.

A Hierarchical Architecture for Computer-Based Message Systems

Abstract: In this paper we present an overview of an architectural model for large, distributed computer-based message systems. This model specifies 1) the organization of message systems in terms of functional entities; 2) the operation of the system; 3) the protocols and interfaces needed for interprocess communication; 4) the organization of the directory system used to support identification services. General architectural considerations related to the communications protocols for computer-based message systems are presented; these follow the general framework of the ISO model for open system interconnection. The organization and operation of the directory system are discussed in detail. Special emphasis is given to the importance of identification services in international and interconnected message systems.

A Hybrid Model and the Representation of Communication Services

Abstract: Different approaches have been used for the formal specification and verification of communication protocols. As explained in Chapter 20, most of these approaches use finite state transition diagrams or programs written is some high-level programming language or both. The purpose of this chapter is threefold.

A new design language for communication protocols and a systematic design method of communication systems

Abstract: A systematic design method of a communication system is given, by which the design, validation, implementation and maintenance of the system can be developed under the consistent philosophy. Next, the DAI-expression method for describing communication protocols is proposed to support the above design method. Here, the DAI-expression consists of three types of expressions, namely, the D-expression, A-expression and I-expression depending upon the purposes such as design, validation and implementation. And the new design language COPDEL is given as the D-expression which is a logical design-oriented expression. Finally, the validation algorithm EXPA is given, which is a generalization of the perturbation analysis given by C.H.West. Furthermore, the EXPA can validate communication protocols described by the COPDEL.

Communication environments for local networks

Abstract: This dissertation studies the problem of providing high performance communication services to computers on a local network, or other high speed network, without sacrificing compatibility with existing communication protocols. The focus of the investigation is the network interface, the I/O controller which interfaces computers to the network medium. The network interface proposed in this dissertation contains a novel processing element called the filter, in addition to a fairly common microprocessor based architecture. The filter is a high speed custom processor and a memory which holds programmable descriptions of packet formats and connection records for the protocols supported by the interface. The filter could be implemented using VLSI or a small amount of readily available bit slice components. The filter enables the interface to process most transmissions as they arrive on the communications medium. Filter processing adds negligible delay to the overall communication path and, in most cases, replaces processing which is conventionally performed in the software of the interface microprocessor or the host. Thus, communications systems built with the new interface are limited by the speed of the medium and not by processing delays. The filter interface is shown to be practical for a 10 Mbps medium and several protocols, including the Internet Protocol (IP) and the Transmission Control Protocol (TCP). The dissertation also considers additional methods for improving communications which are only applicable to the local network environment. Reliable multicast and special acknowledge mechanisms are considered. These appear to be of significant value, especially when combined with the high performance of the filter interface.

FSTV: The Software Test Vehicle for the Functional Hierarchy of the INFOPLEX Database Computer.

Abstract: : This report describes in detail the current implementation of the Software Test Vehicle (STV) for the Functional Hierarchy of the INFOPLEX database computer. The purpose of STV is to provide a better understanding of the architecture and functionalities of the INFOPLEX design by emulating its architecture and simulating its functionalities in software. It aims at validating the communication protocols among its various components, tightening functional algorithms for database management and data movements, providing behavioral and preliminary performance information concerning the architecture, and serving as a test bed before realizing the design in the hardware prototype. Implementation of FSTV is based on a preliminary design of the Functional Hierarchy presented in Hsu80. In that design, data base management functions are decomposed into hierarchical levels, each level to be implemented as a level of the Functional Hierarchy. The current version of FSTV is implemented with special attention paid to a richer set of data base capabilities and architectural compatibility. (Author)

Multi Process Structuring of X.25 Software

Abstract: Modern communication protocols present the software designer with problems of asynchrony, real-time response, high throughput, robust exception handling, and multi-level interfacing. An operating system which provides lightweight processes and inexpensive inter-process communication offers solutions to all of these problems. This thesis examines the use of the multi-process structuring facilities of one such operating system, Verex, to implement the protocols defined by CCITT Recommendation X.25. The success of the multi-process design is confirmed by a working implementation that has linked a Verex system to the Datapac public network for over a year. .br The processes which make up the Verex X.25 software are organized into layers according to the layered definition of X.25. Within the layers, some processes take the form of finite-state machines which execute the state transitions specified in the protocol definition. Matching the structure of the software to the structure of the specification results in software which is easy to program, easy to understand, and likely to be correct. .br .br Multi-process structuring can be applied with similar benefits to protocols other than X.25 and systems other than Verex.

Reliability issues in distributed systems

Abstract: Depending upon the philosophy used to implement fault-tolerant systems, one can distinguish two classes of algorithms: reconfiguration algorithms and fault masking algorithms. The precise statement and analysis of the problems and the underlying assumptions associated with these classes of algorithms is the subject of this dissertation. The first part of the thesis investigates strategies for dynamically reconfiguring shared memory multiprocessor systems that are subject to common memory faults and unpredictable processor deaths. These strategies aim at determining a communication page, i.e., a page of common memory that can be used by a group of processors for storing crucial common resources such as global locks for synchronization and global data structures for voting algorithms. To insure system reliability, the reconfiguration strategies must be distributed so that each processor independently arrives at exactly the same choice. This type of reconfiguration strategy is currently used in the STAGE operating system on the PLURIBUS multiprocessor {24}. We analyze the weak points of the PLURIBUS algorithm and examine alternative strategies satisfying optimization criteria such as maximization of the number of processors and the number of common memory pages in the reconfigured system. We also present a general distributed algorithm which enables the processors in such a system to exchange the local information that is needed to reach a consensus on system reconfiguration. In the second part of the thesis, we deal with fault-masking algorithms as applied to the development of network protocols with an underlying communication medium that may reorder, duplicate or lose messages. In chapter (3) we present a simple network, whose communication medium is assumed to be reliable, and develop a strategy for the remote submission and processing of requests. We also show how to formally specify and verify the network behavior. In the final chapter we describe a more complex network model where the communication medium is no longer assumed to be reliable. We then show that despite the reordering, duplication or loss of messages, all requests are eventually processed exactly once at the remote site and that responses are received in the right order at their submission site.

Satellite Link Communication Protocols

Abstract: This paper deals with a class of satellite link communication protocols which are based on hierarchical sublayering of the link layer. The new protocols (called ‘virtual subchannel schemes’) may be used in order to overcome the deficiencies of ‘classical’ HDLC when applied to high bandwidth satellite links. The performance of a special protocol version (static virtual subchannel concept) is evaluated by analytical methods.

Semantics of a communication mechanism in a distributed system

Abstract: In existing distributed systems a large gap between the application and the low level communication protocols does exist. Usually, this gap results in a rather ad hoc implementation of the application.To reduce this gap, an intermediate level called abstract network has been introduced and a notation based on Petri net, for describing the semantics of the internode communication of the abstract network is presented.

A Secure Computer Network.

Abstract: : In this thesis, the initial design for a secure computer network is developed. The requirement for a secure computer network is based on the need to protect sensitive and personal information currently processed by computer networks. The concepts of physical security, reference monitors, encryption, and network protocols are presented. Then, the top-level design of the secure computer network is developed. This design consists of secure data bases controlled by Kernelized secure operating systems which are connected by a secure communications subnetwork. The phases of secure communications: location, identification, request, and request response are discussed. A model for the secure communications subnetwork is then presented. This model relies on two major components: Secure Network Interface Computers (SNICs) and a Network Directory and Security Center (NDSC). A finite state analysis of the communication channels demonstrates the security of the model. Recommendations are presented to continue the development of this secure network. (Author)

Supply Point Logistics Integrated Communications Environment (SPLICE) Local Area Computer Network Design Issues for Communications.

Abstract: : This thesis examines the topology and transmission mediums for a local computer network to support interconnection of heterogeneous computing devices within the Supply Point Logistics Communications Environment (SPLICE). A topology and appropriate network protocols for management of the intranetwork communications are recommended. Additionally, a protocol to ensure proper delivery of messages which must pass outside the local network to reach another SPLICE configuration via an interconnecting network is discussed. (Author)

UNIXes of the World Unite

Abstract: SUMMARY In this paper we describe a software subsystem that can be added to each of a set of physically interconnected UNIX or UNIX look-alike systems, so as to construct a distributed system which is functionally indistinguishable at both the user and the program level from a conventional singleprocessor UNIX system. The techniques used are applicable to a variety and multiplicity of both local and wide area networks, and enable all issues of inter-processor communication, network protocols, etc., to be hidden. A brief account is given of experience with such a distributed system, which is currently operational on a set of PDP11s connected by a Cambridge Ring. The final sections compare our scheme to various precursor schemes and discuss its potential relevance to other operating systems.