Showing papers on "Communications protocol published in 1991"

The x-Kernel: an architecture for implementing network protocols

Abstract: A description is given of an operating system kernel, called the x-Kernel, that provides an explicit architecture for constructing and composing network protocols. The authors' experience implementing and evaluation several protocols in the x-Kernel shows that this architecture is general enough to accommodate a wide range of protocols, yet efficient enough to perform competitively with less-structured operating systems. Experimental results demonstrating the architecture's generality and efficiency are provided. The explicit structure provided by the x-Kernel has the following advantages. First, the architecture simplifies the process of implementing protocols in the kernel, making it easier to build and test novel protocols. Second, the uniformity of the interface between protocols avoids the significant cost of changing abstractions and makes protocol performance predictable. Third, it is possible to write efficient protocols by tuning the underlying architecture rather than heavily optimizing protocols themselves. >

Apparatus and method for providing decoupling of data exchange details for providing high performance communication between software processes

Abstract: A communication interface for decoupling one software application from another software application such communications between applications are facilitated and applications may be developed in modularized fashion. The communication interface is comprised of two libraries of programs. One library manages self-describing forms which contain actual data to be exchanged as well as type information regarding data format and class definition that contain semantic information. Another library manages communications and includes a subject mapper to receive subscription requests regarding a particular subject and map them to particular communication disciplines and to particular services supplying this information. A number of communication disciplines also cooperate with the subject mapper or directly with client applications to manage communications with various other applications using the communication protocols used by those other applications.

Method and apparatus for managing and facilitating communicationsin a distributed heterogeneous network

Abstract: A data communication method and apparatus is presented that allows communication in a distributed heterogeneous network. Communications managers reside in local processing environments and are responsible for interfacing local end users with the remainder of the heterogeneous network. Each communications manager receives distribution units from end users, the distribution units being assigned various priority levels and levels of assurance. Within each communications manager, an adjacent communications manager is determined in accordance with a communications path to a destination for the distribution unit. The distribution unit is then configured according to a network protocol stack existing between the communications manager and the adjacent communications manager, and the distribution units are transmitted according to priority. Each communications manager can have any number of adjacent communications managers each communicating through different network protocol stacks. Also described is load distribution among a complex of processors that share common functions, as well as control of information flow between adjacent communications managers.

Stabilizing communication protocols

Abstract: A communication protocol is stabilizing if and only if starting from any unsafe state (i.e. one that violates the intended invariant of the protocol), the protocol is guaranteed to converge to a safe state within a finite number of state transitions. Stabilization allows the processes in a protocol to reestablish coordination between one another whenever coordination is lost due to some failure. The authors identify some important characteristics of stabilizing protocols; they show in particular that a stabilizing protocol is nonterminating, has an infinite number of safe states, and has timeout actions. They also propose a formal method for proving protocol stabilization: in order to prove that a given protocol is stabilizing, it is sufficient (and necessary) to exhibit and verify what is called a 'convergence stair' for the protocol. Finally, they discuss how to redesign a number of well-known protocols to make them stabilizing; these include the sliding-window protocol and the two-way handshake. >

Method and apparatus for collaborative use of application program

Abstract: Method and apparatus permitting the collaborative use of a computer application program simultaneously by multiple users at different stations. The method is useful with communication protocols having client/server control structures. The method of the invention requires only a sole executing copy of the application program and a sole executing copy of software comprising the invention. Users may collaboratively use a set of application programs by invoking for each desired application program one copy of software comprising the invention.

Method and apparatus for adding data compression and other services in a computer network

Abstract: A connection specific compression system is selectively implemented in connections having the greatest data redundancy and utilizes modularity in implementing data compression in a layered network communication system. A data compression facility is interfaced in the layered system and intercepts data at a protocol layer prior to the data being packetized for transmission. A system acting as a compression host comprises a data packet switch driver which intercepts application data packets passing over layered network interfaces and routes selected client application data packets to an associated local compression process which has an integral network protocol and which compresses the data stream in accordance with a selected compression algorithm. The compressed data passes through the system network protocol and the packet switch driver subsequently sends the compressed data back into the communications stream through a network driver. The compressed data passes across the network communication channel and is received by a decompression host having peer compression/decompression capabilities. The peer compression process decompresses the received data and sends it, via a second/decompression host resident packet switch driver, as though received from the network, into the decompression host system network protocol for connection with an application running on the second host.

Synthesis of communication protocols: survey and assessment

Abstract: Eleven methods for the synthesis of communication protocols are described. Based on particular features of the synthesis process, these methods are classified and compared. In particular, it is noted that interactive methods allow flexibility in the design process; as a result, communication patterns are not prespecified but may be constructed interactively. Methods that only consider the synchronous mode of behavior of communicating entities exclude a wide range of real-life protocols. Methods that make no reference to service requirements do not guarantee the semantic correctness of the synthesized protocol and therefore require the application of a semantic verification procedure. Most methods concentrate on the synthesis of the control part of the protocol entities, which mainly consists of the exchange of synchronization messages. The data part is not adequately treated by any of the synthesis methods. Other than the exchange of synchronization messages, some methods have been extended to deal with unreliable media by synthesizing error-recovery patterns. Some new research directions for enhancing the applicability of the synthesis approach to the design of real-life protocols are obtained. >

TCP/IP and Related Protocols

Abstract: Written for those either using or managing data communications systems and networks, this book explains all facets of not only the Transmission Control Protcol/Internet Protocol (TCP/IP), but also the many protocols that operate within these two standards. Coverage in this book includes gateway protocols GGP, EGP, Hello, RIP and OSPF, naming and addressing conventions and the Domain Name System, migration issues, TCP/IP and operating environments, networks, bridges, gateways, and routers.

Finite state machine based formal methods in protocol conformance testing: from theory to implementation

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.

Frequency agile tdma communications system

Abstract: An intelligent communications node (20) is capable of dynamically selecting frequency and time slot assignments for com-munications with remote communication devices (22, 24, 26) having different communication protocols including different avail-able frequencies and time slots in a TDMA system. A frequency agile transmitter (62) and receiver (32) combined with an adapt-able time slot selector (38, 60) enables communications with remote devices utilizing different protocols. The time and frequency management capabilities of the node (20) makes greater spectral efficiencies possible.

Performance Petri net analysis of communications protocol software by delay-equivalent aggregation

Abstract: Performance analysis of Petri net models is limited by state explosion in the underlying Markovian model. To overcome this problem, an iterative approximate technique is obtained, using a number of auxiliary models, each of much lower state complexity. It is demonstrated on a substantial model which represents a parallel implementation of two layers of protocols for data communications. The model represents ten separate software tasks and their interactions via rendezvous, and is based on a testbed implementation in the laboratory. Submodels can be constructed in various ways, and this is illustrated with four different decompositions. Their state space complexity, solution time and solution accuracy are evaluated. >

A protocol structure for high-speed communication over broadband ISDN

Abstract: Various possibilities for improving the performance of communications protocols and interfaces so that the slow-software-fast-transmission bottleneck can be alleviated are investigated. An architecture that is an alternative to the existing layered architectures is proposed. The novel feature of the proposed architecture is the reduction in the vertical layering; services that correspond to the definitions of layers four to six in the Open Systems Interconnection Reference Model are combined into a single, horizontally structured layer. This approach lends itself more naturally to parallel implementation. Moreover, the delay of a set of processes implemented in parallel is determined by the delay of the longest process, not by the sum of all the process delays, as is the case in a sequential implementation. In the same way, the total throughput need not be limited by the lowest-capacity process, but can be increased by concurrently performing the function on several devices. >

A model for interface groups

Abstract: How a model for interface groups can be integrated with the ANSA computational model is discussed. The result is a uniform model for one-to-one, one-to-many, many-to-one, and many-to-many communication. Whether a service is provided by a single server or distributed over a collection of servers cannot be inferred from the interface to the service. The proposed model thus provides full transparency of groups, and-if groups are used to support replication-full replication transparency. The interface group model is more general than those of ISIS and CIRCUS. In the prototype implementation of interface groups, the multi-endpoint communication protocol is implemented on top of a communication package with synchronous RPCs. The protocol ensures total order if a client uses RPC or no order if a client uses asynchronous calls. >

Smart enabling system for home automation

Abstract: The author describes an enabling system called SMART HOUSE that provides the common resources needed for home automation in a multiproduct, multivendor environment. The system includes the following: a system controller, housewide wiring network, communications protocols, standard interfaces (outlet designs) for connecting other products, and basic user controls such as programmable wall switches and DTMF telephone. Providing complete home automation functionality depends on the addition of other products such as more complex user controls, appliances that include consumer electronics, and application-specific controllers for energy management, security, climate control, etc. These compatible appliances and controllers are equipped with proprietary communications circuits that permit them to communicate with the system controller and with each other. The author provides a concise technical description of the system, concentrating upon the control communications aspects, including system architecture, protocols, messaging, and logic structure. >

Generating minimal length test sequences for conformance testing of communication protocols

Abstract: A new technique of generating a test sequence for conformance testing of communication protocols is presented. This approach shows that it is possible to generate optimal length test sequences which include multiple unique input output sequences that overlap under certain conditions. In the absence of these conditions, a heuristic technique is used to obtain sub-optimal solutions, which show significant improvement over optimal solutions without overlapping. A comparison is also made of the computational complexity of the author's algorithm with that of existing techniques. A brief discussion of bounds on test sequence length is presented and results are compared against these bounds. >

Cooperative negotiation in concurrent engineering design

Abstract: Design can be modeled as a cooperative multi-agent problem solving task where different agents possess different knowledge and evaluation criteria. These differences may result in inconsistent design decisions and conflicts that have to be resolved during design. The process by which resolution of inconsistencies is achieved in order to arrive at a coherent set of design decisions is negotiation. In this paper, we discuss some of the characteristics of design which make it a very challenging domain for investigating negotiation techniques. We propose a negotiation model that incorporates accessing information in existing designs, communication of design rationale and criticisms of design decisions, as well as design modifications based on constraint relaxation and comparison of utilities. The model captures the dynamic interactions of the cooperating agents during negotiations. We also present representational structures of the expertise of the various agents and a communication protocol that supports multi-agent negotiation.

Survey of switching techniques in high-speed networks and their performance

Abstract: One of the most promising approaches for high speed networks for integrated service applications is fast packet switching, or ATM (asynchronous transfer mode). ATM can be characterized by very high speed transmission links and simple, hard-wired protocols within a network. To match the transmission speed of the network links, and to minimize the overhead due to the processing of network protocols, the switching of cells is done in hardware switching fabrics in ATM networks. A number of designs have been proposed for implementing ATM switches. Although many differences exist among the proposals, the vast majority of them are based on self-routeing multistage interconnection networks. This is because of the desirable features of multi-stage interconnection networks such as self-routeing capability and suitability for VLSI implementation. Existing ATM switch architectures can be classified into two major classes: blocking switches, where blockings of cells may occur within a switch when more than one cell contends for the same internal link, and non-blocking switches, where no internal blocking occurs. A large number of techniques have also been proposed to improve the performance of blocking and non-blocking switches. In this paper, we present an extensive survey of the existing proposals for ATM switch architectures, focusing on their performance issues.

Hierarchical performance evaluation based on formally specified communication protocols

Abstract: Combining formal description techniques (FDTs) with performance evaluation (PE) is a requirement known from the 'single-specification/multiple-techniques' approach associated with the protocol engineering vision. The approach presented here assumes that a formally defined open systems interconnection (OSI) communication protocol can be syntactically transformed to a form suitable to a performance evaluation tool, and afterwards enhanced by implementation-dependence information on the protocol's resource requirements. Such a module, describing functional and performance behavior of the protocol, can then be embedded in a framework which allows its performance evaluation. This framework comprises an OSI-service provider as a transportation medium, processors providing computing services, and means for communication with the adjacent upper layer by use of associated input and output buffers. The present approach uses concepts from the performance evaluation tool HIT. Its applicability to OSI-communication architectures is sketched by means of the PE-modeling language HI-SLANG and the FD-language SDL. >

Geometric arguments yield better bounds for threshold circuits and distributed computing

Abstract: The computational power of two-party probabilistic communication protocols is investigated. This model generalizes the concepts of nondeterministic and conondeterministic communication protocols in a natural way. Applications of the technique are presented, and some open problems are stated. >

Dynamics of congestion control and avoidance of two-way traffic in an OSI testbed

Abstract: An extensive set of measurements were made in an OSI testbed to study the behavior of congestion control and avoidance. Testbed systems used the Connectionless Network Protocol (CLNP) and Transport Protocol Class 4 (TP4), which had been modified to perform the CE-bit [10] congestion avoidance and the "CUTE" [6] congestion recovery algorithms.We found that two-way traffic has dynamics which can significantly decrease fairness among competing connections using congestion avoidance. We present experiments that demonstrate this problem and our analysis of how two-way traffic results in reduced fairness. This analysis led us to develop an effective modification to the congestion avoidance algorithms to maintain fairness with two-way traffic.Our analysis of experimental results also points to undesirable interactions between two-way traffic dynamics and a sending strategy that times data transmissions, by the receipt of acknowledgements. These interactions reinforce burstiness of transmissions. therefore increasing buffering requirements and delay in routers. They may also decrease throughput.

Multimedia synchronization

Abstract: Multimedia synchronization has been recognized by many researchers as a signif- icant requirement for applications using time-dependent media. The orchestration of static data elements such as images and text, and the "lip-sync" of audio and video are examples of such synchronization. In this paper, many aspects of multimedia synchronization are re- viewed at the physical, service, and human interface levels of integration. Applicable areas include temporal modeling with intervals and abstractions, conceptual and physical models for databases, and systems support for synchronization including real-time scheduling and communications protocols.

A comparative study of three token ring protocols for real-time communications

Abstract: When developing distributed scheduling algorithms such as communication protocols, issues in achieving optimal policy and minimizing overhead must be addressed. This problem is examined in the context of a specific distributed system-the token ring communication network. Three token ring protocols are considered which are representative of many existing ones in the sense that they incorporate message time constraints at different levels and implement the earliest deadline first transmission (scheduling) policy at different degrees with different overheads. Through a worst-case analysis, the performance of these three token ring protocols is compared. It is concluded that to evaluate a distributed scheduling algorithm such as a communication protocol, it is necessary to not only consider the scheduling policy employed but also to take into account the overhead incurred due to the implementation of the scheduling policy. >

SQL Access: an implementation of the ISO Remote Database Access Standard

Abstract: As an enterprise begins tying heterogeneous systems into a single information system, it encounters the difficult task of interfacing different platforms running different operating systems, network protocols, and data management systems. Bringing all these elements together into a coherent information resource can require substantial effort and might result in a system that needs the interfaces reworked every time a new platform or product is introduced into the system. To address these issues, the International Organization for Standardization has drafted the Remote Database Access Standard to provide a protocol that can be universally accepted, implemented, and validated, and thereby provide users with a single, well-defined interface for heterogeneous environments. Based on a client-server architecture, RDA uses well-defined Open Systems Interconnect services as the basis for the RDA services. >

Information processing equipment having communication capabilities and which calculates load factor

Abstract: The present invention relates to information processing equipment having communication capabilities capable of executing a communication protocol processing at high speed and comprising a main processor and a communication processor If a load factor of the main processor is higher than a predetermined threshold value, the main processor executes the communication protocol processing and if the load factor of the main processor is lower than the predetermined threshold value, the communication processor executes the communication protocol processing

ACCESSING REPLICATED DATA IN A LARGE-SCALE DISTRIBUTED SYSTEM (M.S. Thesis)

Abstract: Many distributed applications use replicated data to improve the availability of the data, and to improve access latency by locating copies of the data near to their use This thesis presents a new family of communication protocols, called *quorum multicasts*, that provide efficient communication services for replicated data Quorum multicasts are similar to ordinary multicasts, which deliver a message to a set of destinations The new protocols extend this model by allowing delivery to a subset of the destinations, selected according to distance or expected data currency These protocols provide well-defined failure semantics, and can distinguish between communication failure and replica failure with high probability The thesis includes a performance evaluation of three quorum multicast protocols This required taking several measurements of the Internet to determine distributions for communication latency and failure The results indicate that the behavior of recent messages is a useful predictor for the performance of the next A simulation study of quorum multicasts, based on the Internet measurements, shows that these protocols provide low latency and require few messages A second study that measured a test application running at several sites confirmed these results

An incremental specification of the sliding-window protocol

Abstract: The sliding-window protocol is specified using the notation of Communicating Sequential Processes and its partial correctness is proved using the trace semantics. First the stop-and-wait protocol is defined; its correctness, that it forms a 1-place buffer, is almost evident. Next the alternating-bit protocol is defined and described in terms of the stop-and-wait protocol, and its correctness deduced from that of the stop-and-wait protocol. Finally the sliding-window protocol is described in terms of the alternating-bit protocol and its correctness deduced accordingly. The paper has two thrusts: that modularity of a specification helps to structure proofs about it (in this case, proofs that the protocols implement buffers); and that refinement in CSP leads to structured, correct implementations in occam. In support of the latter point the appendix contains a refinement and implementation of the protocols in oc-cam 2.

Constructing protocols with alternative functions

Abstract: The author describes a method for designing communication protocols which can perform several distinct functions, but are limited to the execution of one function at a time. The construction of such a protocol consists of two steps: (1) developing a component protocol for each function to be included, and (2) integrating the components into the target protocol. The integration involves the resolution of potential component competition and process synchronization problems. A sufficient condition for the safety of the integrated protocol is also discussed. This design method is simple to use and promotes reuse of existing protocols. The construction of two protocols-the call setup phase of a data link control protocol and a portion of the CCITT's X.21 Recommendation-is demonstrated. >

Communication facilities for distributed transaction-processing systems

Abstract: The study of communication designs in the context of the Raid system, a robust and adaptable distributed database system for transaction processing, is discussed. Related research work on local interprocess communication, remote interprocess communication, and communication protocols for both local area and wide area networks is briefly summarized. A series of experiments on the performance of the facilities available for building the Raid communication software is described. Raid's communication software, called Raidcomm, has evolved as a result of the knowledge gained both from other systems and from the authors' experiments. Several communication services and mechanisms that can be used to make Raid efficient are identified. >

Experience with formal methods in protocol development

Abstract: Communication protocols are complex software systems and key components of computer networks. They must be specified completely and implemented correctly. The development of a protocol typically involves several tedious steps. Experience has shown that the use of informal techniques in these steps of protocol development generally produces systems with errors and undesirable behaviors. Formal methods permit the development of highly reliable and easily maintainable communication protocols. This paper presents our experience with using formal methods in the specification, verification, implementation, and conformance testing of OSI protocols.