Showing papers on "Communications protocol published in 1989"

An analysis of TCP processing overhead

Abstract: The transport layer of the protocol suite, especially in connectionless protocols, has considerable functionality and is typically executed in software by the host processor at the end points of the network. It is thus considered a likely source of processing overhead. However, a preliminary examination has suggested to the authors that other aspects of networking may be a more serious source of overhead. To test this proposition, a detailed study was made of the Transmission Control Protocol (TCP), the transport protocol from the Internet protocol suite. In this set of protocols, the functions of detecting and recovering lost or corrupted packets, flow control, and multiplexing are performed at the transport level. The results of that study are presented. It is concluded that TCP is in fact not the source of the overhead often observed in packet processing, and that it could support very high speeds if properly implemented. >

Formal methods for protocol testing: a detailed study

Abstract: The authors present a detailed study of four formal methods (T-, U-, D-, and W-methods) for generating test sequences for protocols. Applications of these methods to the NBS Class 4 Transport Protocol are discussed. An estimation of fault coverage of four protocol-test-sequence generation techniques using Monte Carlo simulation is also presented. The ability of a test sequence to decide whether a protocol implementation conforms to its specification heavily relies on the range of faults that it can capture. Conformance is defined at two levels, namely, weak and strong conformance. This study shows that a test sequence produced by T-method has a poor fault detection capability, whereas test sequences produced by U-, D-, and W-methods have comparable (superior to that for T-method) fault coverage on several classes of randomly generated machines used in this study. Also, some problems with a straightforward application of the four protocol-test-sequence generation methods to real-world communication protocols are pointed out. >

Guaranteed reliable broadcast network

Abstract: This system guarantees reliable data transmission for one-to-one, one-to-many and/or many-to-many communications among data processing stations over a communications network. A general solution is presented, and a new concept (the arbitrator node) is discussed in detail. Special logical nodes and a new communications protocol are used so that a message is guaranteed to be received if a receiver(s) wants to receive the message even though a receiver(s) may be busy, slow or temporarily powered off. An optional management station controls orderly start and stop of group communications or conferences, and may also handle secure, confidential communications. This guaranteed, reliable, one-to-one, one-to-many or many-to-many system can be applied to overcome previously unsolved problems.

With microscope and tweezers: an analysis of the Internet virus of November 1988

Abstract: In early November 1988 the Internet, a collection of networks consisting of 60,000 host computers implementing the TCP/IP protocol suite, was attacked by a virus, a program which broke into computers on the network and which spread from one machine to another. The authors present a detailed analysis of the virus program. The describe the lessons that this incident has taught the Internet community and topics for future consideration and resolution. A detailed routine-by-routine description of the virus program, including the contents of its built-in dictionary is provided. >

Lan with dynamically selectable multiple operational capabilities

Abstract: Multiple different operational capabilities, such as data transfer rates or communication protocols, are selectable for use on a single LAN comprising a plurality of nodes (40). Enhanced nodes (21, 29, 30) of the LAN have the capability of utilizing either an enhanced capability or a common capability in communicating with other nodes. Those basic nodes (81, 153, 247) which are not of the enhanced variety have the capability of communicating utilizing the common capability. The enhanced nodes dynamically select the operational capability for the most efficient communication with other nodes.

Link utilization control mechanism for demand assignment satellite communications network

Abstract: A link utilization control mechanism for a demand assignment satellite communication network employs a modified point-to-point communications protocol (X.25) in order to simulate point-to-point communication ports and thereby interface what is effectively a multidrop network with point-to-point landlink communication resources. Through an acknowledgement reservation mechanism the return link channel is subdivided into interleaved data and (preassigned) acknowledgement time slots, in order to substantially obviate overhead and throughput penalties encountered in the use of large data packets to transmit reduced size acknowledgement messages. In addition, the normal contention mode of operation of the return link is augmented with a data time slot reservation mechanism through which, during periods of increased message input density at a remote station (30), transmission throughput is facilitated, so that congestion at the remote station (30) is reduced.

Wireless communication system

Abstract: This invention relates to a wireless communication system, which comprises plural wireless communication units having different communication protocols, and in which a proper wireless communication unit is automatically selected from the plural wireless communication units in accordance with the operation states of the plural wireless communication units to make communication possible. Thereby, troublesome operation is not required, an optimum wireless communication method can be automatically selected, and communication cost can be reduced. In the wireless communication system of the present invention, when mobile stations are registered in a fixed station, preferential orders of the mobile stations are stored, and calling/call-reception and communication processings are controlled according to the preferential orders.

An algorithmic procedure for checking safety properties of protocols

Abstract: A procedure for checking safety properties of communication protocols is presented. A protocol is specified as a collection of communicating finite-state machines (FSMs). Two novel algorithms used in this procedure are described. The first algorithm does incremental composition and reduction of FSMs. It uses three heuristic rules which reduce the number of states in the global FSM by one to two orders of magnitude while maintaining its observational equivalence. The second algorithm checks whether the behavior of one FSM is a subset of another FSM's behavior. This procedure has been applied to the ISDN Q.931 and alternating bit protocols. >

Sirpent: a high-performance internetworking approach

Abstract: A clear target for computer communication technology is to support a high-performance global internetwork. Current internetworking approaches use either concatenated virtual circuits, as in X.75, or a “universal” internetwork datagram, as in the DoD Internet IP protocol and the ISO connectionless network protocol (CLNP). Both approaches have significant disadvantages.This paper describes Sirpent™ (Source Internetwork Routing Protocol with Extended Network Transfer)1, a new approach to an internetwork architecture that makes source routing the basis for interconnection, rather than an option as in IP. Its benefits include simple switching with low per-packet processing and delay, support for accounting and congestion control, and scalability to a global internetwork. It also supports flexible, user-controlled routing such as required for security, policy-based routing and realtime applications. We also propose a specific internetwork protocol, called VIPER™2, as a realization of the Sirpent approach.

Trace analysis for conformance and arbitration testing

Abstract: The authors explore a testing approach where the concern for selecting the appropriate test input provided to the implementation under test (IUT) is separated as much as possible from the analysis of the observed output. Particular emphasis is placed on the analysis of the observed interactions of the IUT in order to determine whether the observed input/output trace conforms to the IUT's specification. The authors consider this aspect of testing with particular attention to testing of communication protocol implementations. Various distributed test architectures are used for this purpose, where partial input/output traces are observable by local observers at different interfaces. The error-detection power of different test configurations is determined on the basis of the partial trace visible to each local observer and their global knowledge about the applied test case. The automated construction of trace analysis modules from the formal specification of the protocol is also discussed. Different transformations of the protocol specification may be necessary to obtain the reference specification, which can be used by a local or global observer for checking the observed trace. Experience with the construction of an arbiter for the OSI (open systems interconnection) transport protocol is described. >

Analysis of transport measurements over a local area network

Abstract: Measurements of the end-of-end delay and maximum throughput are reported for a typical implementation of the bottom four layers of the Open Systems Interconnection (OSI) protocols. These comprise the transport, network, data link, and physical protocols. An overview of the four protocols is given, and the experimental environment is described. The measurement results are discussed, and some of the implementation factors that affect the performance of OSI protocols are identified. >

Conformance testing: architectures and test sequences

Abstract: With wide-spread acceptance of the ISO-OSI reference model and its standardized protocols in the areas of computer communication and information exchange, protocol testing has become an area of active research and development. This paper surveys recent developments in conformance testing. The discussion includes four important aspects of protocol testing: test architectures, test sequence selection techniques, conformance test suites for various protocols, and protocol test theory.

Measured performance of transport service in LANs

Abstract: This paper attempts to organize, explain, and compare performance results reported for various implementations of a transport service realized by different protocols: OSI TP4/CLNS, TCP/IP, NETBLT, and VMTP. The study concentrates on the throughput and delays achieved in local-area networks.

VLSI implementations of communication protocols-a survey

Abstract: Several protocol controllers for the IEEE 802 local area networks are surveyed and some characteristics for classifying them are given. Some case studies from these controllers are given as illustrations. Two new developments-the protocol engine and the programmable protocol engine-are also described. The protocol engine, currently under development, implements a new protocol called XTP which performs the functions of both the network and transport layers. The programmable protocol engine can implement several connection-oriented protocols by changing contents of a programmable random access memory. >

Tools for implementing network protocols

Abstract: This paper describes two software tools—a message manager and a map manager—used to implement network protocols. The tools are provided as part of the x-kernel, an operating system kernel designed to support the construction and composition of protocols. For each tool, we briefly motivate the network task that needs to be done, give a high-level specification of the tool, outline the algorithms and data structures used to implement the tool and give concrete examples of how the tool is used to implement real protocols. We also demonstrate how the tools, even though they are designed for general use, perform efficiently.

Implementation mechanisms for packet switched voice conferencing

Abstract: A distributed control mechanism for managing a packet-switched voice conference connection is presented. The principal concept introduced is the idea of viewing a conference connection as a logical ring of participants. Alternative methods for implementing voice conferencing on both broadcast and point-to-point networks are introduced, analyzed, and compared. Tradeoffs between the two methods with respect to station workload and maximum number of conference participants are discussed. Experimental implementations on both a carrier-sense multi-access with collision detection (CSMA/CD) Ethernet and a token-ring ProNet are described. The mechanisms presented can be used as part of a packet-switched voice communications protocol that includes conferencing capabilities. >

An architecture for a mobile OSI mail access system

Abstract: An architecture and implementation which support an interface to the X.400 mail environment using the full open-systems communications protocols for a portable computer are described. The implementation is designed to be used over a cellular radio telephone network. The portable computer is used to implement the user agent interface of the CCITT X.413 (1988) message store. A full set of security facilities, designed for use with interpersonal messaging (IPM), is included in the architecture. A number of important issues are discussed regarding the placement and management of keys for the IPM security, as well as authentication between the user and the portable computer and between the user agent and the message store. To support the use of the CCITT message-store model, it was necessary to implement a full protocol stack for open systems interconnection on the portable computer. The design and the author's experiences are described. >

Individual communication function of RACS: Road Automobile Communication System

Abstract: An explanation is given of the radio transmission system for realizing a road-automobile communication function within a minimum radio zone (about 50-100 m in diameter). The beacon station having the radio zone is connected to a wire transmission line, thus constituting a wide-area network designed as a packet-switching network. The communication protocol has hierarchical layers with reference to the technological tendency and OSI model of the ISO standard. When the system configuration is established, a nationwide total data communication system can be supported using a pair of frequencies. >

PROTOB - A Hierarchical Object-Oriented CASE Tool for Distributed Systems

Abstract: This paper presents PROTOB, an object-oriented CASE system based on high level Petri nets called PROT nets. It consists of several tools supporting specification, modelling and prototyping activities within the framework of the operational software life cycle paradigm. As its major application area it addresses distributed systems, such as real-time embedded systems, communication protocols and manufacturing control systems. The paper illustrates a case study involving the design of a distributed file system.

On ferry clip approaches in protocol testing

Abstract: The context of this paper is protocol testing, i.e. testing communications protocol implementations against the relevant protocol standards or recommendations. This paper presents a framework for the realization of the ferry clip — a generalized application of the ferry principle in protocol testing. The framework has been developed through experience gained in the design and implementation of prototype ferry clip test systems. Different ferry clip test approaches are explored and analyzed. A refined ferry control protocol is proposed and pertinent issues in defining such protocols are discussed.

Low cost RF identification and locating system

Abstract: A security system which enables the user to locate immediately any personnel in a building is described. This system uses a network of receiver units to pick up identification (ID) codes transmitted from portable transmitters worn by all personnel in the building. The ID codes are collected from the receiver units by a central processor via a communication line. The central processor then updates a database and presents the information to the user. A special communication protocol which enhances the communication between the receivers and the central processor through selected networks has also been designed. This protocol increases the bit efficiency of the information transfers. >

Guaranteed, reliable, secure broadcast networks

Abstract: A patent-pending invention for handling reliable and secure broadcasts is presented. This invention guarantees all computers in the network the reception of all broadcast messages in the proper sequence, even though there may be line noise, hardware malfunction, or busy receivers. This makes possible correct distributed database updates, parallel information retrieval, and many other applications. The invention adds four specialized components to existing networks and uses a special communication protocol. It can be applied to both local area and wide area networks. >

A formal specification technique for communication protocol

Abstract: A formal method for communication protocol specification is presented in which the best features of approaches using finite-state machines, communication sequential processes, and abstracting data types are combined. First, the formal techniques of the communication protocol are briefly described. Then, the hybrid method of protocol specification is presented. Finally, an example, i.e IEEE 802.3 MAC protocol for a LAN described by the proposed formal method is given. >

Oblivious memory computer networking

Abstract: Independent heterogeneous computers are interconnected for oblivious, high speed, long distance communications. A printed circuit board with onboard RAM repeats all write commands through a data transmission media to a remote system. Each read and write cycle of the communicating computer is completed locally (using only local RAM). Apart from repeating write commands to a remote system, the invention is oblivious to the remote system. Data is transmitted from one machine to another without expensive communication protocols or transmission line latency induced wait states. A remote computer accesses network data only after it has been transmitted and stored in local memory. Multiple data transfers can be pipelined, that is, multiple datum may simultaneously reside in a high latency network/long transmission line. Although the time required to transmit any single datum remains proportional to the signal propagation delay, the time required to transmit multiple data is significantly reduced. Geographic separation, high speed transmission lines, low speed transmission lines, alternative means for data transmission, fault tolerance, one-way communications, multi-way communications, and high security can be supported by a single computer network of heterogeneous machines.

Network security: the parts of the sum

Abstract: Attention is given to the three basic elements of network security, i.e. encryption, network protocols, and trusted computer system protocols. It is noted that each of these measures is needed to achieve overall network security and yet frequently the advocates of individual measures ignore the others for a variety of technical and/or doctrinal reasons. The author attempts to convey the importance of applying these measures in proper perspective to achieve true network security. Examples of problems in network security are discussed, including personal-computer encryption services, secure data network issues, and COMSEC procurements. >

Packet communication protocol for image services on a high-speed multimedia LAN

Abstract: The authors describe the requirements for high-speed multimedia communication and propose a high-speed communication protocol to provide congestion-free access and efficient retransmission/flow control. Its usefulness is proved in a 400 Mb/s multiaccess loop local area network (LAN) with a 100 Mb/s user interface. The main characteristics of the protocol are separation of image communication handling, guarantee of no buffer overflow in a network, and end-to-end block-based transfer. Buffer reservation control in the user-network interface and a retransmission scheme based on a long-size block are used to realize high-speed congestion control and error recovery. A multimedia terminal architecture suitable for real-time image communication is also discussed. In the prototype system, a few frames of high-resolution image information can be transferred in a second. Around 26 Mb/s effective throughput between application entities has been obtained. >

Characterizations of delay-insensitive communication protocols

Abstract: This paper studies protocols for asynchronous communication over an interface consisting of unidirectional channels. In asynchronous communication, the sender can initiate a transmission without cooperation of the receiver. Contrasting with traditional data-flow networks, the channels that we consider do not synchronize at the receiving end: messages, once on their way, are delivered regardless of the readiness of the receiver to accept them. The situation where a message is delivered to an unready receiver is called computation interference. A protocol is said to be deiay-insensitive when it can be guaranteed-without making assumptions about propagation delays-that computation interference cannot occur. We give several characterizations of delay-insensitive protocols and a new prooHor the Fundamental Characterization Theorem. The emphasis is on the mathematical treatment of the concepts involved. o Introduction and Overview We begin by giving a physical motivation for our investigation. Consider a digital circuit connected to its environment by an interface consisting of conducting wires. In the digital mode of operation, circuit and environment communicate by exchanging discrete voltage transitions. A voltage transition, once initiated, propagates along a wire to the receiver. The receiving end, however, need not always be ready to process an incoming transition.

Construction of network protocols by stepwise refinement

Abstract: We present a heuristic to derive specifications of distributed systems by stepwise refinement. The heuristic is based upon a conditional refinement relation between specifications. It is applied to construct four sliding window protocols that provide reliable data transfer over unreliable communication channels. The protocols use modulo-N sequence numbers. They are less restrictive and easier to implement than sliding window protocols previously studied in the protocol verification literature.

Connection caching of traffic adaptive dynamic virtual circuits

Abstract: Local Area Networks may be interconnected using X.25 networks. If only the OSI connectionless network protocol (CLNP) is supported on the LANs, then this same protocol must operate above X.25, using the X.25 service as a virtual data link layer. The intermediate systems in this case must support CLNP packet delivery over X.25 virtual circuits, implementing the ISO 8473/DAD1 subnetwork dependent convergence function to resolve the differences which exist between the OSI connectionless network service and the connection-oriented service offered by the X.25 subnetwork. This means that the main functionality of this subnetwork dependent convergence function is to open virtual circuits on packet demand and to close them when no traffic has occurred for a period of time. This paper describes an algorithm, which calculates such a time period by taking into account the current traffic load, the connection cost and the maintenance cost.