Multiaccess protocols for integrated voice and data transmissions over satellite channels are studied, based on the SENET(slotted envelope network) structure. The satellite system is characterized as a wide band system with a large number of geographically distributed small voice and data users. Performance evaluations of commonly used protocols, i.e., ALOHA and reservation protocols, are first conducted, both analytically and by simulations. The effect of different voice backgrounds on data access protocols are shown explicitly. Based on these results, a control algorithm is proposed. Analyses and simulations show that ALOHA protocol incorporated with such a control mechanism is globally stable under the integrated environment; moreover, the performance deterioration due to voice backgrounds is dramatically reduced. The actual implementation aspects of the control algorithm are considered. An extension of the above results leads to a combined random/reservation protocol. Simulation and analysis results show that the combined protocol exhibits desired low delay and high throughput performance characteristics, with satisfactory voice blocking probability, under the worst user population assumption, i.e., all the voice sources and data sources are independent of each other — reflecting the nature of small earth station environment. The absence of the need for mini-slot structure lends ease and simplicity to the implementation of the combined protocol. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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This dissertation studied cognitive packet networks (CPN) which build networked learning systems that support adaptive, quality of service-driven routing of packets in wired networks and in wireless, mobile ad hoc networks. The first part of this study completed the design of the CPN algorithm for wired systems by revisiting the decision making procedure employed by smart packets in the former initiative. To conduct evaluation studies, this work proposed two implementation architectures, both of which were integrated into the Linus 2.4 kernel. The second part of this dissertation extended CPN to ad hoc networks by introducing mechanisms to handle node mobility with a new quality-of-service metric that makes better use of the limited resources typically present in such networks. in ad hoc CPN (AHCPN), path availability quantifies a path via the probability to find nodes and links available for routing; it is defined as a function of battery lifetime at nodes and signal-to-noise ratio of communication channels. As a result, nodes which have low power are able to extend their working lifetime and routes are selected based on power considerations, leading to the establishment of more robust communication paths over time. This research included the deployment of three network testbeds and extensive experimentation to verify the performance of both CPN and AHCPN. In addition, a simulation model of ACHPN was developed using Network Simulator 2 (NS-2). Measurements on real systems and simulations revealed great capacity for adaptability and successful performance of both CPN and AHCPN under different network conditions.

This thesis develops a stochastic model for satellite packet switching networks, using results from queueing theory that have been previously explored in modeling communication networks. This thesis also analyzes message queueing delay when users of the network are generating data at moderate to high rates. Average packet delay and average number of packets in the system are formulated. The model developed herein is applied to two cases. In the first case packet transmission and back off times are deterministic. In the second case packet transmission and back off times are exponentially distributed. The input parameters to this model are packet arrival rate, average packet transmission time, average back off time and probability of packet collision. The model yields average packet delay and average number of packets in the system. Methods to compute the probability of collision are presented. / Master of Science

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / The Automatic Position Reporting System (APRS) is a well-established packet communication protocol that offers users a graphical position display system and a peer-to-peer textual message service. APRS is used in temporary and mobile networks where rapid deployment of infrastructure is required and limited a priori knowledge of the network topology is available. The APRS protocol can be used for emergencies and public service applications. ARPS, functioning as an access network, was originally designed to require low complexity and support high flexibility of a network. These design directives have limited APRS’s performance by resulting in low throughput and poor reliability. In order for APRS to be used in time-critical applications, these limitations would need to be improved. The thesis considers the limitations of ARPS by proposing an improved protocol stack with a substitution of the media access control (MAC) layer. The new protocol is modelled in order to develop a largely platform-independent implementation, which could be efficiently retargeted for different platforms. Lastly, a protocol performance evaluation is done in order to determine the resulting improvements on APRS and the overall viability of the proposal.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

In order to provide improved service quality to applications, networks need to address the need for reliability of data delivery. Reliability can be improved by incorporating fault tolerance into network routing, wherein a set of multiple routes are used for routing between a given source and destination. This thesis proposes a new fault-tolerant protocol, called the Multipath Fault Tolerant Protocol for Routing (MFTPR), to improve the reliability of network routing services. The protocol is based on a multipath discovery algorithm, the Quasi-Shortest Multipath (QSMP), and is designed to work in conjunction with the routing protocol employed by the network. MFTPR improves upon the QSMP algorithm by finding more routes than QSMP, and also provides for maintenance of these routes in the event of failure of network components. In order to evaluate the resilience of a pair of paths to failure, this thesis proposes metrics that evaluate the non-disjointness of a pair of paths and measure the probability of simultaneous failure of these paths. The performance of MFTPR to find alternate routes based on these metrics is analyzed through simulation.

In our work, we have proposed a new framework for the classification and comparative study of ATM congestion control schemes. The different aspects on which we have classified the algorithms are control theoretic approach, action and congestion notification. These three aspects present of the classification present a coherent framework on which congestion control algorithms are to be classified. Such a classification will also help in developing new algorithms.

by Lau Chu Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 76-83). / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Basic Notions --- p.13 / Chapter 3 --- Fast Knockout --- p.19 / Chapter 3.1 --- The Algorithm of Fast Knockout --- p.20 / Chapter 3.2 --- Complexity of the Fast Knockout Algorithm --- p.29 / Chapter 3.3 --- Summary --- p.35 / Chapter 4 --- k-Sortout --- p.36 / Chapter 4.1 --- A Brief Review of k-Sorting --- p.37 / Chapter 4.2 --- The Algorithm of k-Sortout --- p.47 / Chapter 4.3 --- Complexity of the k- Sortout Algorithm --- p.53 / Chapter 4.4 --- Summary --- p.58 / Chapter 5 --- General Sortout --- p.59 / Chapter 5.1 --- The General Algorithm of Sortout --- p.59 / Chapter 5.2 --- Complexity of Concentrators by the General Algorithm --- p.64 / Chapter 5.3 --- Summary --- p.69 / Chapter 6 --- Concluding Remarks --- p.70 / Chapter 6.1 --- Summary of Results --- p.70 / Chapter 6.2 --- Directions for Further Research --- p.73 / Bibliography --- p.76