Showing papers on "Communications protocol published in 1983"

Distributed network protocols

Abstract: A unified approach to the formal description and validation of several distributed protocols is presented. After introducing two basic protocols, a series of known and new protocols for connectivity test, shortest path, and path updating are described and validated. All protocols are extended to networks with changing topology.

Implementing Remote procedure calls

Abstract: Remote procedure calls (RPC) are a useful paradigm for providing communication across a network between programs written in a high level language. This paper describes a package, written as part of the Cedar project, providing a remote procedure call facility. The paper describes the options that face a designer of such a package, and the decisions we made. We describe the overall structure of our RPC mechanism, our facilities for binding RPC clients, the transport level communication protocol, and some performance measurements. We include descriptions of some optimisations we used to achieve high performance and to minimize the load on server machines that have many clients.Our primary aim in building an RPC package was to make the building of distributed systems easier. Previous protocols were sufficiently hard to use that only members of a select group of communication experts were willing to undertake the construction of distributed systems. We hoped to overcome this by providing a communication paradigm as close as possible to the familiar facilities of our high level languages. To achieve this aim, we concentrated on making remote calls efficient, and on making the semantics of remote calls as close as possible to those of local calls.

On the Construction of Submodule Specifications and Communication Protocols

Abstract: The problem of elaborating the specification for the submodules of a system is considered. A new method for the construction of submodule specifications is described. If the system is to consist of n submodules and the system as well as (n 1) submodules are specified, then the method described determines the specification of the additional n t h submodule. A formula is given which defines the specification of the additional submodule in the general case where module specifications are given in terms of sets of possible execution sequences, and interaction occurs when several modules participate in the execution of an atomic interaction. For the restricted context of finite-state machines, a constructive algorithm for the evaluation of the formula is given. The use of this design method is demonstrated by examples, including a simple communication protocol involving error detection and retransmission. Possible applications in other areas, as well as remaining problems, are indicated.

Modular Verification of Computer Communication Protocols

Abstract: Programs that implement computer communications protocols can exhibit extremely complicated behavior, and neither informal reasoning nor testing is reliable enough to establish their correctness. In this paper we discuss the application of modular program verification techniques to protocols. This approach is more reliable than informal reasoning, but has an advantage over formal reasoning based on finite-state models, the complexity of the proof need not grow unmanageably as the size of the program increases. Certain tools of concurrent program verification that are especially useful for protocols are presented, history variables that record sequences of input and output values, temporal logic for expressing properties that must hold in a future system state such as eventual receipt of a message), and module specification and composition rules. The use of these techniques is illustrated by verifying two data transfer protocols from the literature: the alternating bit protocol and a protocol proposed by Stenning.

A Layered Network Protocol for Packet Voice and Data Integration

Abstract: This paper discusses considerations in the design of packet protocols suitable for interactive voice and interactive data communication, and then outlines a potential layered protocol architecture for the internal communication of a long haul network that might support packet voice and packet data transport. Following the protocol description, the paper compares potential delays for two voice/data packet network architectures: one using only link retransmission, the other using only edge retransmission for data (as included by the voice/data protocol). The underlying data traffic loads offered to the network are the same for the two methods, although they give rise to different traffic patterns. This preliminary analysis shows that the average delay using an edge-to-edge recovery discipline can be made comparable to the delays introduced with a link-by-link recovery discipline, if the network uses high speed transmission facilities (e.g., over 1 Mbits/s) having good error characteristics (e.g., one or less packets corrupted in each 1000), and sends up to 128 bytes of customer data as a single packet.

An HDLC protocol specification and its verification using image protocols

Abstract: We use an event-driven process model to specify a version of the High-Level Data Link Control (HDLC) protocol between two communicating protocol entities. The protocol is verified using the method of projections. The verification serves as a rigorous exercise to demonstrate the applicability of this method to the analysis of real-life communication protocols. The HDLC protocol has two characteristics found in most real-life communication protocols. First, the HDLC protocol operates under real-time constraints that are important not only for its performance but also for its correct logical behavior. We specify this real-time behavior using time variables and time events. Second, the HDLC protocol has three distinguishable functions: connection management, and one-way data transfers between the protocol entities. For each of these functions, we construct an image protocol using the method of projections. With each image protocol we obtain inductively complete invariant assertions that state various desirable logical safety properties. From the properties of image protocols it follows that these safety properties as proved for the image protocols are also satisfied by the HDLC protocol presented herein. We also suggest a minor modification to HDLC that will make it well-structured.

Algebraic specification of communication protocols

Abstract: Modern computer networks now circle the world, but the transmission of information among them depends on the many different protocols that define the behavior of the sender and receiver. It is clear therefore, that the accurate description of these protocols is important if harmonious communication is to be maintained. In this book the authors use the formal specification language PSF to provide an unambiguous description of several communication protocols of varying levels of complexity, ranging from the alternating bit protocol to the token ring protocol. Beginners, as well as professionals in the field of communication protocols, will benefit from both the methods of specification described, and the protocols discussed in this book.

Services and protocols of the data link layer

Abstract: Data Link control protocols are among the oldest recognized communication protocols. The protocol provides a well-defined set of rules which govern the interchange of supervisory information and user data over the interconnecting communication link. Such rules are essential to successful and efficient operation. Data Link protocols have evolved continuously from the early free-wheeling protocols, through the widely implemented character-oriented protocols, to the increasingly popular bit-oriented protocols. Data Link protocols play a vital role in the drive toward Open Systems Interconnection (OSI). Constituting Layer 2 of the International Standards Organization (ISO) Reference Model, these procedure and the services that they offer, are directed at assuring successful and reliable transfer of information over point-to-point or multipoint data links. This paper reviews the role of link protocols in the open systems environment. It discusses the objectives and functions of these protocols and delineates the services provided to the higher layers. A review, with examples, of the protocols suitable for use within the framework of OSI is included. The paper concludes with a look at some of the current Data Link issues.

An argument for soft layering of protocols

Abstract: This thesis is about the efficiency of protocol layering It examines the technique of protocol layering in an abstract way and finds two major sources of inefficiency in protocol implementations which are caused by the imposition on them of a layered structure The conventional approach to making layered protocol implementations run efficiently -- for avoiding the sources of inefficiency discussed herein -- are all independent of the protocol specification, and thus all decrease the value of the protocol specification as a guide for implementing protocols We introduce a new means of avoiding the problems of layered protocol implementations which operates within the domain of the protocol specification We allow an increase in the flow of state information between the layers of a layered protocol implementation in a very controlled manner, so as to decrease the modularity of the protocol architecture as little as possible The increased flow of information is specified in the protocol specification as a model of all the layered protocols that use the protocol being specified, called the "usage mode" Since our approach decreases the rigidity of the layered structure without entirely eliminating it, we coin the term "Soft Layering" for the approach

CSNET protocol software: the IP-to-X.25 interface

Abstract: CSNET is built on the Department of Defense network (ARPANET), public packet-switched physical networks (Telenet), and a telephone-based relay network (Phonenet). Some CSNET sites have direct connections to ARPANET, some have direct connections to Telenet, and some have connections only to telephone-based relay machines. The chief objective of CSNET is to provide a network interconnection for all groups engaged in Computer Science Research.CSNET has adopted TCP/IP as its standard transport level protocols. The Transmission Control Protocol (TCP) [POST81] is an end-to-end protocol. It establishes communications between two processes that are running on different machines, detects and corrects errors, controls data flow, and provides reliable communications. Application programs call TCP to transfer data across the network. TCP, in turn, uses the Internet Protocol (IP) [POST81] to send data to the appropriate network. CSNET communications such as file transfer, remote login, and process-to-process communication over the network assume that a TCP interface is available at CSNET sites.Since ARPANET sites are required to support the TCP/IP protocols, CSNET sites connected directly to the ARPANET automatically have access to TCP/IP. Phonenet relays connect directly to the ARPANET; they too have access to TCP to relay mail onto the ARPANET. Telenet does not use the TCP/IP protocols. Consequently, CSNET sites that are connected only to Telenet need additional software before they can communicate on CSNET. That software is described in this paper -- it provides an interface between the public packet - switched protocol X.25 [CCITT78] and TCP/IP. Although the design outlined here is applicable to any vendor's system, our implemention is for a Digital Equipment Corporation VAX running the Western Electric UNIX [UNIX78] operating system as modified by the University of California at Berkeley.This report focuses on the technical issues involved in building software to interface TCP/IP and X.25. The tariff structure for public networks is discussed only to the extent that it influences our design. Other issues such as access control, and protocol selection are beyond the scope of this report.

The Specification of Computer Graphics Systems

Abstract: Specification techniques for computer graphics systems should emulate those employed in the specification of computer communication protocols and software systems, not the specification of programming languages.

Early Experience With Fiber Optic Picture Archival Communication System (PACS) For Medical Images

Abstract: At the First International Conference on PACS for medical applications, the fiber optic communication network in our department was introduced. Since that time, the network has expanded substantially, the communication protocols have been significantly modified, new fiber optic interfaces have been designed, built, and installed and even further hardware changes are planned. As we gained experience during this evolutionary period, we have acquired even more confidence in the use of fiber optics, the star network configuration, standard television for review and comparison, and the hierarchical communication protocols described in this paper.

An integrated microcomputer network for experiments in distributed programming

Abstract: A network computer is a computer network designed to function not as a collection of autonomous hosts but as one machine. Systems intended to support experiments with asynchronous distributed programs, including both distributed systems programs and distributed applications, form a major sub-class of network computers. The goal of the Stony Brook Network (SBN) project is to construct such a general-purpose network computer. Unlike most other systems in its class, SBN is a language-centered design. SBN's starting point is the distributed programming language Linda. To run on SBN, a distributed program must either be written in or be pre-processed into Linda; the language is intended to be a maximally powerful, flexible and expressive vehicle for distributed programming. The role of SBN's hardware and communication software is to support Linda with greatest possible efficiency, or in other words to implement a maximally-efficient Linda machine. Part I discusses the Linda design, which encompasses unusual inter-process communication primitives and program-structuring devices. Inter-process communication takes place via a shared data structured called "structured memory". Though logically shared, structured memory may be implemented over many memory-disjoint nodes. Processes in Linda communicate by means of the three operations that structured memory defines. Linda's four basic structuring tools allow the construction of a large variety of program components--sequential, concurrent and mutual-exculsion statements, tasks, remote-procedure-like blocks and monitor-like blocks, conditional and timed receives among others. Part II discusses algorithms to be incorporated in a communication system that supports Linda and structured memory. Runtime rendez-vous between outputting and inputting processes is a requirement of Linda and an implementation technique that is optimal given well-defined assumptions is described. Store-and-forward deadlock is a potential problem in any packet-swtiching communication system, and SBN is a packet-switching design; a new algorithm for packet deadlock prevention is described and its correctness is proven. Finally, a new communication protocol and associated architecture that, we argue, are well-suited to network computers of SBN's class is discussed.

Filing and printing services on a local-area network

Abstract: This paper describes the design and implementation of filing and printing services in a distributed system based on a token-ring local-area network. The main emphasis is put on the communication aspects of the client/server scenario: roles of a client and a server in a communication protocol, and the integration of communication protocols with applications.

An approach to testing specifications

Abstract: An approach to testing the consistency of specifications is explored, which is applicable to the design validation of communication protocols and other cases of step-wise refinement. In this approach, a testing module compares a trace of interactions obtained from an execution of the refined specification (e. g. the protocol specification) with the reference specification (e. g. the communication service specification).Non-determinism in reference specifications presents certain problems. Using an extended finite state transition model for the specifications, a strategy for limiting the amount of non-determinacy is presented.An automated method for constructing a testing module for a given reference specification is discussed. Experience with the application of this testing approach to the design of a Transport protocol and a distributed mutual exclusion algorithm is described.

A System to Evaluate Communication Protocols for Automotive Multiplex

Abstract: An electronic system has been developed to evaluate serial multiplexing protocols which utilize synchronously clocked data bits on a bidirectional line. The architecture of the system is assumed to be implemented in a master controller-slave controller(s) form. The controllers are microprocessor-based and utilize EPROM storage for easy modification of the control programs.

A perspective on communications and computing

Abstract: Presented is an essay on the dynamics of the relationships between communications and computing. Movement of computer applications from the back office to the front office, from batch to on-line data processing, is illustrated and conclusions are drawn regarding communications protocols, network management, application and data base design, and system generality. The influence and requirements of several new technologies are presented, inlcuding those of microprocessors and teleconferencing.

A methodology for verifying request processing protocols

Abstract: In this paper, we view computer networks as distributed systems that provide their users with a set of services, in a way which hides the distinction between those services which are local and those which are remote. We conceive of a given target network configuration as a network of communicating virtual machines and its behavior is modelled by a system of communicating sequential processes. Network protocols are described by a high level concurrent language (CSP) and a methodology is developed which permits the verification of partial and total correctness assertions about the system in a simple and natural way. Global invariants are used to establish invariant properties of the whole system and histories to record the sequence of communication exchanges between every matching pair of processes. Eventuality properties are expressed using linear temporal logic.

The new mexico state university ring‐star system: A distributed unix environment

Abstract: A distributed version of the UNIX operations system is currently under development through a joint effort of New Mexico State University and the Hebrew University of Jerusalem. A microprocessor version of the UNIX kernel has been developed which will run on any PDP-11 or LSI-11 based processing element and allows processes to run in a UNIX ‘look-alike’ environment. Each process is fully transportable among all processors in the system. Although the preliminary version of the system was built in a star configuration, the system is currently being upgraded by the addition of a communication ring with 8-bit microprocessors as ring interface units. The current paper describes the software structure, the hardware structure and the communication protocol of the system.

Architecture of the Communication Subsystem for Local Area Networks Operating under a New CSMA-Protocol with Dynamic Priorities

Abstract: A local area network with a completely distributed control is considered, where the connected peripherals (terminals, host computers) communicate with each other through addressed messages via a common high speed carrier. The network consists of three main layers: peripherals, network access controllers (NAC), and the communication subsystem. The higher levels of the network protocols are implemented within the NAC or the connected peripherals. The communication subsystem consists of the common high speed carrier and the channel access modules (CAM). The communication subsystem operates under a new carrier-sense-multiple-access (CSMA) protocol with collision detection and conflict resolution by dynamically controlled send priorities. This protocol combines both advantages of pure contention protocols for low traffic and fixed/demand assignment protocols for heavy traffic and reveals specific advantages with respect to overload control.

Performance potential of communications interface processors

Abstract: Interface processors are being developed in hardware and firmware for communications protocols at higher and higher levels (HDLC, X.25, Ethernet ...), for smaller and smaller host systems. How far this process will go depends on the driving factors of increased performance and simpler implementation of the systems which use the protocols. A simplified performance model with parameters, which encompasses a large part of all systems using communications, is used to find those parameter combinations offering various degrees of performance improvement. The results can be used to approximately distinguish those cases which will provide the market for performance improvement via higher-level interface processors.

Automated techniques for specification and validation of communications protocols

Abstract: This dissertation research is concerned with the extension and application of some formal language based techniques for modeling and validation of communication protocols. The transmission grammar provides a way of representing the states, actions, and responses of protocol machines. The transmission grammars of individual protocol machines can also be combined to provide a global model of a communication system. Combining several complex protocol machines can result in an unmanageable explosion of the number of states in the global model since, in the worst case, the number of global states is the product of the number of states in the individual machines. Communication protocols which permit the addressing and delivery of a single message to more than one destination (multi-destination protocols) are a distinctly difficult challenge to model via state machine related techniques because of the "state explosion" problem. Such multi-destination protocols are the target for application of the transmission grammar. Some single destination protocols more complex than those successfully modeled in the past are modeled and validated as a first step to prepare the way for the advance to multi-destination protocols. Validation of protocols by state space exploration is reasonable only for the simplest protocols without the procedure being automated. A Pascal program, called Multi-Valid is described and listed which automatically constructs the global state graph for an n-party protocol given Transmission Grammar specifications for the n entities. The program design is intended to allow easy modification to incorporate new developments in protocol design and validation. The use of Multi-Valid will greatly expand the usefulness of the Transmission Grammar/Validation Automaton technique for validating protocols. The program can be used to test existing protocols, and as a tool to design new protocols through successive validation and refinement steps to achieve a protocol which is completely deadlock free and completely specified.