Magistriniame darbe išanalizuoti įvairios paskirties saugos modeliai. Pagal gautus rezultatus sudarytas apibendrintas informacijos saugos praradimo riziką įvertitnantis kompiuterių tinklų saugos modelis. Sukurta grėsmę keliančius įvykius aptinkanti sistema. / The master's work analysis different types of security models. It also proposes a new computer network security reference model, which includes risk management process. A suspicious network events detection system is designed to make network monitoring easier.

The Napster case has created a frenzy of controversy and confusion. The Peer to Peer technology developed by Napster creator Shawn Fanning, has forced the courts, the legislature, corporations, and individuals to reconsider the use of the Internet. Peer to peer networks create new challenges for the application of copyright law. However, these challenges are not that different from those which copyright law has evolved to accommodate in the past. Copyright law is intended to balance the interests of the creators and the public to promote the progress of science and useful arts. The premise behind copyright protection is to ensure that people continue creating, and that the public continues to enjoy those creations, through the mechanism of rewarding the creators with a temporary monopoly over their works. This balance of interests is fundamental to the interpretation of copyright law by the United States Congress and the Courts. This thesis focuses on the application and interpretation of copyright law through a case study of the law in the United States, in particular the Napster case. Although it now appears that the Internet can be subject to some form of regulation with the aid of technological innovation to enforce the regulation, the Courts in the Napster case have misinterpreted the previous judicial consideration attributed to copyright law. In essence, the fundamental principle of the balancing of interests has been lost. We are now left with an unequal balance in favor of large media conglomerates. It can be argued that the media conglomerates have used Napster as an example of their power to control the technology of peer to peer networking as a model of distribution. Napster demonstrates that peer to peer is an effective way of sharing information with an extremely large amount of people. This has the music industry scared, resulting in their legal battle to shut down the Napster technology. The claims of copyright misuse raise awareness of the need for regulation and a reassessment of copyright application in a digital age. There is a need for regulation. However, any attempts at further application of law and regulation to the Internet concerning copyright protection should consider the intent of the constitutional founders of the United States -- copyright law is intended to protect the interests of both the artists, and the public.

The Internet is becoming a more realistic means of accessing support, especially for those who are unable to or are uncomfortable with accessing supports in person. One population that experiences barriers to accessing face-to-face support is youth, and online counselling is an option available for youth to overcome these barriers (King, Bambling, Lloyd, et al., 2006). Online counselling can occur through e-mail and chat services; however, due to the text-based nature of these services, their effectiveness is criticized for having a lack of verbal and nonverbal communication (Cook & Doyle, 2002). Research, however, has suggested that it is possibly this lack of verbal and nonverbal cues that make online counselling effective. Research has also suggested that the effectiveness of counselling can be measured by the working alliance (Fletcher-Tomenius & Vossler, 2009; Hanley, 2009). This study explored if an effective working alliance can be established in online counselling mediums with youth who are in crisis. A quantitative research approach was taken, in which 91 youth completed an online survey that asked how they felt towards online support services. The results of this study suggest that youth respond positively to the lack of verbal and nonverbal cues; youth appear to enjoy an increase sense of anonymity that is created within online support services, which can contribute to open communication. In addition, the results suggest that an effective working alliance is established in online counselling services, as it was found that youth typical felt happy and satisfied with the services they received. / x, 135 leaves ; 29 cm

OMEN (On-demand Metadata Extraction Network) addresses a fundamental problem in Music Information Retrieval: the lack of universal access to a large dataset containing significant amounts of copyrighted music. This thesis proposes a solution to this problem that is accomplished by utilizing the large collections of digitized music available at many libraries. Using OMEN, libraries will be able to perform on-demand feature extraction on site, returning feature values to researchers instead of providing direct access to the recordings themselves. This avoids copyright difficulties, since the underlying music never leaves the library that owns it. The analysis is performed using grid-style computation on library machines that are otherwise under-used (e.g., devoted to patron web and catalogue use).

Thesis (M.Tech.: Library and Information Studies)-Durban Institute of Technology, 2004. viii, 71 leaves / The aim of the study was to investigate management and maintenance procedures that were used by other sites and how these could be used as a basis for formulating management and maintenance procedures for the SALO subject directory.

This thesis addresses a novel type of network known as a mobile ad hoc network. A mobile ad hoc network is a collection of entirely mobile nodes that can establish communication in the absence of any fixed infrastructure. Envisioned applications of these networks include virtual classrooms, emergency relief operations, military tactical communications, sensor networks and community networking. Mobile ad hoc networking poses several new challenges in the design of network protocols. This thesis focuses on the routing problem. The main challenges in the design of a routing protocol for mobile ad hoc networks result from them having limited resources and there being frequent topological changes that occur unpredictably. Moreover, there is no fixed infrastructure that supports routing. The conventional routing protocols are not generally suitable for mobile ad hoc networks, as they cannot react quickly to the changing network topology, cause excessive communication and computation, or converge very slowly creating routing loops. In this thesis we propose two classes of routing schemes for mobile ad hoc networks. The first class is known as Limited Flooding Protocol. The protocol is fully reactive and does not require the computation of routing tables. It uses some basic principles of flooding, but reduces the communication overhead by restricting packet propagation through the network. Several variations of limited flooding are considered including deterministic, randomised and priority-based mechanisms. The main advantage of this protocol is that it can be used in networks with unpredictable topological changes and highly mobile nodes, since maintaining routing table at the intermediate nodes is not required. The second class of routing protocols is based on hierarchical clustering architecture and is intended for use in a relatively low mobility environment. The basic idea of this protocol is to partition the entire network into smaller units known as clusters and define routing mechanisms both within and between clusters using a hierarchical architecture. The main advantage of this architecture is reduction of storage requirements of routing information, communication overhead and computational overhead at each node. Discrete-event simulation is used for modelling and performance evaluation. Various options and variations of the protocols are examined in the…[Page 2 of abstract is missing.] / Thesis (Ph.D.)-University of Natal, Durban, 2000.

Wireless cellular communications is witnessing a rapid growth in, and demand for, improved technology and range of information types and services. Future third generation cellular networks are expected to provide mobile users with ubiquitous wireless access to a global backbone architecture that carries a wide variety of electronic services. This thesis examines the topic of multiple access protocols and models suitable for modem third-generation wireless networks. The major part of this thesis is based on a proposed Medium Access Control (MAC) protocol for a Code Division Multiple Access (CDMA) data packet radio network, as CDMA technology is proving to be a promising and attractive approach for spectrally efficient, economical and high quality digital communications wireless networks. The proposed MAC policy considers a novel dual CDMA threshold model based on the Multiple Access Interference (MAl) capacity of the system. This protocol is then extended to accommodate a mixed voice/data traffic network in which variable length data messages share a common CDMA channel with voice users, and where the voice activity factor of human speech is exploited to improve the data network performance. For the protocol evaluation, the expected voice call blocking probability, expected data throughput and expected data message delay are considered, for both a perfect channel and a correlated Rayleigh fading channel. In particular, it is shown that a significant performance enhancement can be made over existing admission policies through the implementation of a novel, dynamic, load-dependent blocking threshold in conjunction with a fixed CDMA multiple access threshold that is based on the maximum acceptable level of MAl. / Thesis (Ph.D.)-University of Natal, Durban, 1999.

Modern telecommunications companies are moving away from conventional circuit-switched architectures to more versatile packet-switched infrastructures. Traditional First-In-FirstOut (FIFO) queues that are currently multiplexing IP traffic are not able to meet the strict Quality-of-Service (QoS) requirements of delay sensitive real-time traffic. Two main solution families exist that separate heterogeneous traffic into appropriate classes. The first is known as Generalized Processor Sharing (GPS), which divides the available bandwidth among the contending classes, proportionally to the throughput guarantee negotiated with each class. GPS and its myriad of packetised variants are relatively easy to analyse, as the service rate of individual classes is directly related to its throughput guarantee. As GPS splits the arriving traffic into separate queues, it is useful for best-effort traffic, supplying each class of traffic with either a maximum or minimum amount of bandwidth that it deserves. The second solution is the Earliest Deadline First (EDF) scheduler, also known as Earliest Due Date (EDD). Each traffic class has a delay deadline, by which the individual packets need to be served in order to meet their heterogeneous QoS requirements. EDF selects packets that are closest to their deadline. It is therefore primarily useful for delay sensitive real-time traffic. Although this is a simple algorithm, it turns out to be surprisingly difficult to analyse. Several papers attempted to analyse EDF. Most of them found either discrete bounds, which lie far away from the mean, or stochastic bounds which tend to capture the delay behaviour of the traffic more accurately. After the introductory first chapter, this thesis simulates a realistic cellular environment, where packets of various classes of service are transmitted across an HSDPA air interface. The aim is to understand the behaviour of EDF and its channel aware Opportunistic EDF scheduler compared to other scheduling families commonly used in HSDPA environments. In particular, Round Robin is simulated as the most simplistic scheduler. Max ell chooses packets solely based on the best channel conditions. Finally, PF -T is a scheme that tries to maximise the overall transmission rate that packets experience, but this metric gets divided by the throughput that each class already achieved. This introduces a form of long-term fairness that prevents the starvation of individual classes. The third chapter contains the main analysis, which uses Large Deviation principles and the Effective Bandwidth theory to approximate the deadline violation probability and the delay density function of EDF in a wired network. A definition for the fairness of EDF is proposed. The analysis is extended to approximate the stochastic fairness distribution. In the fourth chapter of the thesis an opportunistic EDF scheduler is proposed for mobile legs of a network that takes advantage of temporary improvements in the channel conditions. An analytical model is developed that predicts the delay density function of the opportunistic EDF scheduler. The channel propagation gain is assumed to be log-normally distributed, which requires graphical curve fitting, as no closed-form solution exists / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.

Wireless Sensor Networks (WSN), a new class of devices, has the potential to revolutionize the capturing, processing, and communication of critical data at low cost. Sensor networks consist of small, low-power, and low-cost devices with limited computational and wireless communication capabilities. These sensor nodes can only transmit a finite number of messages before they run out of energy. Thus, reducing the energy consumption per node for end-to-end data transmission is an important design consideration for WSNs. The Medium Access Control (MAC) protocols aim at providing collision-free access to the wireless medium. MAC protocols also provide the most direct control over the utilization of the transceiver, which consumes most of the energy of the sensor nodes. The major part of this thesis is based on a proposed MAC protocol called Distributed Receiver-oriented MAC (DRMACSN) protocol for code division multiple access (CDMA) based WSNs. The proposed MAC protocol employs the channel load blocking scheme to reduce energy consumption in the network. The performance of the proposed MAC protocol is verified through simulations for average packet throughput, average delay and energy consumption. The performance of the proposed MAC protocol is also compared to the IEEE 802.15.4 MAC and the MAC without the channel load sensing scheme via simulations. An analytical model is derived to analyse the average packet throughput and average energy consumption performance for the DRMACSN MAC protocol. The packet success probability, the message success and blocking probabilities are derived for the DRMACSN MAC protocol. The discrete-time multiple vacation queuing models are used to model the delay behaviour of the DRMACSN MAC protocol. The Probability Generating Functions (PGF) of the arrivals of new messages in sleep, back-off and transmit states are derived. The PGF of arrivals of retransmitted packets of a new message are also derived. The queue length and delay expressions for both the Bernoulli and Poisson message arrival models are derived. Comparison between the analytical and simulation results shows that the analytical model is accurate. The proposed MAC protocol is aimed at having an improved average packet throughput, a reduced packet delay, reduced energy consumption performance for WSN. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

This project was undertaken for a commercial electronics company, CONTROL LOGIC (CONLOG) which is involved in the research, design, development and manufacture of data acquisition, control, energy management and automotive equipment. Currently CONLOG uses an inhouse token passing local area network CONET for industrial data communications.The need had arisen to provide a means of data communication amongst widely geographically distributed remote terminal units (RTUs) generating demands at a very low duty cycle. A need for communications between RTUs and a centralised controller was also required. In addition to this, multihop communications between the RTUs was required. Packet switching using a broadcast radio network provides an efficient means of achieving this. An investigation into to the various media access control protocols and contention techniques using packet radio was carried out. The various media access techniques were compared with respect to throughput and normalised delay. This led to the selection of a media access scheme for the packet radio network using RTUs. A protocol specification control is centralised or Interconnect Organisation.The switching protocol (OSI) for the packet radio network, in which distributed, was done. The architechure of specified adheres to the Open Systems model of the International Standards.An experimental packet switching radio network was implemented using the protocol specification defined above. The packet radio network (PACNET) uses existing off the shelf radios and purpose built hardware for the remote terminal units. The thesis describes methods of data communications suitable for widely dispersed industrial data communications, the selection of the packet switching media access methods and control protocols, and the design and implementation of the prototype system. / Thesis (M.Sc.Eng.)-University of Natal, 1992.