Intrusive monitoring systems monitor the performance of data communication networks by transmitting and receiving test packets on the network being monitored. Even relatively small periods of monitoring can generate significantly large amounts of data. Primitive network performance data are details of test packets that are transmitted and received over the network under test. Network performance information is then derived by significantly processing the primitive performance data. This information may need to be correlated with information regarding the configuration and status of various network elements and the test stations. This thesis suggests that efficient processing of the collected data may be achieved by reusing and recycling the derived information in the data warehouses and information systems. This can be accomplished by pre-processing the primitive performance data to generate Intermediate Information. In addition to being able to efficiently fulfil multiple information requirements, different Intermediate Information elements at finer levels of granularity may be recycled to generate Intermediate Information elements at coarser levels of granularity. The application of these concepts in processing packet delay information from the primitive performance data has been studied. Different Intermediate Information structures possess different characteristics. Information systems can exploit these characteristics to efficiently re-cycle elements of these structures to derive the required information elements. Information systems can also dynamically select appropriate Intermediate Information structures on the basis of queries posted to the information system as well as the number of suitable Intermediate Information elements available to efficiently answer these queries. Packet loss and duplication summaries derived for different analysis windows also provide information regarding the network performance characteristics. Due to their additive nature, suitable finer granularity packet loss and duplication summaries can be added to provide coarser granularity packet loss and duplication summaries.

No description available.

In the past, techniques for specifying, verifying and implementing protocols have taken on a somewhat ad hoc (non -uniform) and informal nature. This lack of uniformity has resulted in an abundance of techniques and methodologies for analysing protocols, most of which are applicable to protocols having a small degree of complexity. Typically, different techniques are applied to various stages of a protocol development without an underlying formal basis for their integrated application. As a result, there may be no way to guarantee that subsequent stages of a development represent correct realisations of earlier ones. This thesis aims to address the problem of protocol development stated above by describing unified frameworks within which: 1) A formal theoretical foundation is laid for specifying, verifying and implementing protocols. 2) A knowledge based system is used for the formal development of a certain class of protocols. A number of limitations have been identified in the approach taken for developing the frameworks: a) The lack of 'compositional' expressiveness of the algebraic specification language. This makes it difficult to effectively analyse concurrently executing processes of protocols. b) The lack of support provided for addressing performance related issues. This makes it difficult to compare different protocols to assess their effect with respect to how long they take to achieve some data processing task. c) The protocol derivation algorithm can prove cumbersome in its application and may require a significant amount of domain knowledge (about types of 'primitives') in order to be machine automated. d) The knowledge based framework is currently limited to supporting the development of end-to-end protocols. This however is not a serious problem as the ideas and principles applied in developing these protocols form the basis for work in analysing other types. The above limitations form the basis for future work which will aim to address the problems stated. The thesis is in 5 main parts:- I) A description of various formalisms used in the past, to specify protocols. From this analysis, criteria are developed for assessing the relative merits of these formalisms, with a view towards choosing one such technique to be employed in specifying protocols. ii) A formal development of the protocol which includes a discussion of automatic theorem proving via a syntactic measure known as a trace. iii) A description of a notation with operational semantics developed for specifying and verifying protocols and services. In addition, a method utilising the notation is described whereby a service can be derived from a protocol. iv) A description of a framework within which a protocol may be verified in respect of the service it provides. v) A description of an interactive program (environment) allowing the formal development of a certain class of distributed protocols, such as the ECMA application layer protocol. The originality of this work lies in the: I) development of a methodology for automatically deriving and proving invariant properties of a specification. ii) development of a notation with operational semantics, capable of specifying and verifying distributed protocols and services. iii) identification of a means by which the correspondence between a specification and its implementation may be used as rewrite rules (not necessarily preserving all semantic information) in developing communication protocols. v) numerous algorithms described for addressing safety, liveness and conformity issues, as part of the interactive environment.

No description available.

This thesis concerns the optimization of the routing path in packet-switched computer-communication networks. Computer-communication networks over the past decade are outlined. A glossary of some of the terms used throughout this thesis are introduced. A brief description follows of the advantages of packet switching over the more conventional circuit-switched scheme for information transfer. The important design variables that a network planner is faced with in the design of these networks are discussed. A general design problem is stated and then decomposed into simpler subproblems one of which is the link-capacity assignment problem, which is briefly discussed. The route-assignment problem is identified as being of particular importance and is specified. A network model is introduced and relationships between performance measures, input parameters and constraints that appear in the general design problem are discussed. The routing problem is the formulated and a heuristic routing procedure is suggested as a sub-optimum solution to the problem. Basic routing methods are discussed. The principles of datagram and virtual circuit techniques are explained with reference to the routing of packets throughout the network. The directory routing technique with alternate routing is identified as being a specific requirement and the operation of this technique is explained in more detail. Two basic algorithms are introduced. The first which determines the shortest, second shortest, third shortest, etc., paths between all pairs of nodes in a network. The second which determines from all the paths in the first algorithm, the best alternative paths between all pairs of nodes in a network. A heuristic routing algorithm for establishing routing tables at each of the individual nodes in a packet switched data network is presented. Among the properties of a desirable routing algorithm is that the paths established between all node pairs are such that the average packet delay from source to destination node is minimal. The heuristic-routing algorithm proposed is to-be implemented on a newly proposed SAPONET packet-switching network, with special emphasis on the minimization of the average packet delay of the network. Results are presented and discussed for different combinations of the primary, secondary, tertiary and fourth alternative paths obtained. Finally, results are summarized and areas for further work identified.

This research examines the place of ferries in the national communication network of Scotland between the Union of the Crowns and the advent of steam. A total of 431 ferries were identified and are listed in the Gazetteer. The effect upon the ferries is assessed in both the era of pre-modernisation and during that of modernisation with certain trends and patterns being defined. The search for data revealed that papers in some private collections as well as those in some of the public archives are as yet uncategorised. In both the uncategorised papers as well as in the classified documents, evidence regarding ferries is sporadic and fragmentary. Moreover, it is unusual to find the topic "Ferries" appearing in any table of contents or index, even in published works. Information derived from primary historical and geographical sources, together with legal and civil administration records, augmented by social comments recorded at the time, in addition to secondary sources form the basis for the work. While changes occurred at ferries throughout the period studied these accelerated in the early nineteenth century by reason of the growing demands resulting from economic modernisation in Scotland. The need for speedier and more convenient travel gave rise to a proliferation of bridge building which in turn had an adverse affect on ferry services in the locality of the new bridges. Surviving ferry services were faced with three options in response to the pressures of economic modernisation. Firstly, they could remain unchanged, secondly, facilities could be adapted and the boats re-designed or thirdly, the man-propelled or sail-powered boats could be replaced by steam-driven boats. Although the building of the railway extended the system of communication in Scotland it had little affect on ferry services in general apart from the expansion of those ferry services situated near railway termini. In other parts of the country little attention was paid to existing ferries which continued to operate before. Therefore, the national communication network in Scotland in the early nineteenth century remained irregular and incomplete.

We attempt to analyze why the adoption of the mobile number portability policy incurs no (or very little) effect in encouraging competition in the telecommunication market. The cause is related to network externality. The level of network externality can be characterized by the proportion of any individual’s friends who are also adopting in the same carrier as the individual does. We find that such network externality may prohibit competition in the telecommunication market when termination-based pricing is prevailing. When termination-based pricing is prohibited, carriers cannot take advantage of network externality. We characterize the conditions such that without termination-based pricing, carriers become more competitive and consumers benefit more than with termination-based prices. Our study provides insightful implication on how to effectively impose the mobile number portability policy to improve competition in the telecommunication market.

The increase in the interconnection of computers has led to a corresponding increase in the complexity of effective network design. This increase is partly to the size and diversity of computer networks, but also is due to the proliferation of available network hardware and software. As with any system, computer networks are made up of various interrelated components, all of which are essential to the network design process. Some of these components are physical in nature, that is, they specify a piece of hardware or software with certain perfomance properties. Other components are considered to be logical elements of network design. The problem of designing, implementing and controlling present and planned data communication networks is rapidly exceeding manual planning and design capabilities. Network managers and designers are looking more and more to computer resources to manage the volume of traffic information, to develop and evaluate network configurations, and to assist in allocating and placing control functions among network processors. The number of network alternatives is increasing so fast that the demand for network optimization--both in private network design and in the interface to, and use of, public network facilities--can be satisfied only through computer aids. These aids range from simple scratch-pad systems that store and compile network statistics to complete traffic emulators, design configurators, and software for data-distribution modelling. Network design generates a set of performance/cost tradeoffs for an existing or proposed network. The network design process generates and regenerates these performance curves in response to changes in critical design parameter such as protocols, line capacity, concentration points, host processor capability and message routing techniques. This dissertation considers the development of a generalized model of the network design process. This model proposes that the physical and logical network components can be described using a set of objects, properties and relationships. Objects are used to describe network physical and logical components. These components are given properties, thus associating with each object a set of network descriptions. Linkages between objects or classes of objects are provided by object-object relationships. The prototype system provides a generalized network design tool which allows a concise and explicit statement of network requirements providing a network planning and design model which is independent of any particular network or application.

This thesis has mainly focused on investigating the effect of communication network on the power system operation. The main objective of this research has been to develop a set of communication network simulation tools and verify their suitability for realistic cosimulation of a power system and an associated data-communication network within a power system simulation environment. Based on a background study, a set of communication components have been developed for the PSCAD/EMTDC power system simulation software, which can simulate communication delay and packet losses. Furthermore, an analytical method based on queuing theory has also been developed to evaluate the communication delay and packet loss probability of a typical PMU-PDC communication network. Finally, the communication components developed in this thesis have been integrated into the simulation of a wide area power system application to investigate the effect of communication network parameters on the power system operation.

This thesis has mainly focused on investigating the effect of communication network on the power system operation. The main objective of this research has been to develop a set of communication network simulation tools and verify their suitability for realistic cosimulation of a power system and an associated data-communication network within a power system simulation environment. Based on a background study, a set of communication components have been developed for the PSCAD/EMTDC power system simulation software, which can simulate communication delay and packet losses. Furthermore, an analytical method based on queuing theory has also been developed to evaluate the communication delay and packet loss probability of a typical PMU-PDC communication network. Finally, the communication components developed in this thesis have been integrated into the simulation of a wide area power system application to investigate the effect of communication network parameters on the power system operation.