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.

Ad hoc networks are commonly known to implement IEEE 802.11 standard as their medium access control (MAC) protocol. It is well known that token passing MAC schemes outperform carrier-sense-multiple-access (CSMA) schemes, therefore, token passing MAC protocols have gained popularity in recent years. In recent years, the research extends the concept of token passing ' scheme to wireless settings since they have the potential of achieving higher channel utilization than CSMA type schemes. In this thesis, a hybrid Token-CDMA MAC protocol that is based on a token passing scheme with the incorporation of code division multiple access (CDMA) is introduced. Using a dynamic code distribution algorithm and a modified leaky-bucket policing system, the hybrid protocol is able to provide both Quality of Service (QoS) and high network resource utilization, while ensuring the stability of a network. This thesis begins with the introduction of a new MAC protocol based on a token-passing strategy. The input traffic model used in the simulation is a two-state Markov Modulated Poisson Process (MMPP). The data rate QoS is enforced by implementing a modified leaky bucket mechanism in the proposed MAC scheme. The simulation also takes into account channel link errors caused by the wireless link by implementing a multi-layered Gilbert-Elliot model. The performance of the proposed MAC scheme is examined by simulation, and compared to the performance of other MAC protocols published in the literature. Simulation results demonstrate that the proposed hybrid MAC scheme is effective in decreasing packet delay and significantly shortens the length of the queue. The thesis continues with the discussion of the analytical model for the hybrid Token CDMA protocol. The proposed MAC scheme is analytically modelled as a multiserver multiqueue (MSMQ) system with a gated service discipline. The analytical model is categorized into three sections viz. the vacation model, the input model and the buffer model. The throughput and delay performance are then computed and shown to closely match the simulation results. Lastly, cross-layer optimization between the physical (PHY) and MAC layers for the hybrid token-CDMA scheme is discussed. The proposed joint PHY -MAC approach is based on the interaction between the two layers in order to enable the stations to dynamically adjust the transmission parameters resulting in reduced mutual interference and optimum system performance. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.

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.

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.

No description available.

Communication and networking are vast areas which are developing rapidly. It is very important to know in detail how the system works, how it can be enhanced to meet today's requirement, how to implement the appropriate techniques to obtain desired results etc. To explain all of the above, simulation techniques were adopted. Simulation plays an important role in developming new designs and modifying existing systems to make them more feasible and efficient.Protocols are the back bones of the communication systems and play a major role in data transfer. The review of literature provides an explanation of ISO/OSI models, layered approach and concepts of simulation. The simulation was carried out to explain the concepts of error detection, error correction and flow control in Data Link layer. Ada was used to develop the software, because of its concurrent processing tools called tasks. Also state-of-the-art utilities like Vax/Vms Screen Management System, File Definition Language, and Debugger were us ed in the program development. / Department of Computer Science

As Multi-Protocol Label Switched (MPLS) networks increase in usage and size, the number of traffic engineered tunnels or Label Switched Paths (LSPs) which must be established has an impact on network state maintenance, administration and scalability. The ability to signal and meet Quality-of-Service (QoS) requirements in such networks has been addressed through the addition of Differentiated Services (Diff-Serv) mappings and other traffic engineering mechanisms. However, for the purpose of path computation, route advertisements, signaling and admission control, multiple traffic classes carried together are still treated as a single class. This work explores extensions to MPLS which allow for the accommodation of up to eight distinct traffic classes per label switched path. Through an examination of simulation results. a comparison between existing methods and the proposed additions is made that shows scenarios in which such traffic class aggregation or "bundling" provides a significant reduction in the number of paths which must be maintained in the network.

Location-based service (LBS) is a geographical location-related service that provides highly personalized services for users. It is a platform for network operators to provide new and innovative ways of increasing profits from new services. With the rapidly growing trend toward LBS, there is a need for standard LBS protocols. This thesis started with introducing the Internet Engineering Task Force GEOPRIV working group, which endeavors to provide standard LBS protocols capable of transferring geographic location information for diverse location-aware applications. Through careful observation, it was found that Session Initiation Protocol (SIP) is well suited to the GEOPRIV requirements. The aim of this research was therefore to explore the possibility of the integration of LBS and the SIP protocol and, to some extent fulfill the GEOPRIV requirements.

<p>SIP is receiving much attention these days and it seems to be the most promising candidate as a signaling protocol for the current and future IP telephony services. Realizing this, there is the obvious need to provide a certain level of quality comparable to the traditional telephone service signalling system. Thus, we identified the major costs of SIP, which were found to be delay and security. This thesis discusses the costs of SIP, the solutions for the major costs, and the development of a low cost SIP application. The literature review of the components used to develop such a service is discussed, the networks in which the SIP is used are outlined, and some SIP applications and services previously designed are discussed. A simulation environment is then designed and implemented for the instant messaging service for wireless devices. This environment simulates the average delay in LAN and WLAN in different scenarios, to analyze in which scenario the system has the lowest costs and delay constraints.</p>

Thesis (PhDTelecommunications)--University of South Australia, 2002.