In ATM (asynchronous transfer mode) networks, rate-based regulation-scheduling (R&S) mechanisms guarantee certain quality of service (QoS) with controlling the rate of a tagged connection serviced by the switches. The R&S mechanisms, which consider only the issues of one tagged connection itself but the situation of the scheduling queue, can behave hand-over well. However, there may be many connections hand over in identical condition and compete for the position in the scheduler queue. It makes the transmission to be distorted greatly from the hand-over. There is already a scheme, dynamic R&S, to smooth rate jitter with counting the hand-over of other connections. Dynamic R&S doesn't count the idle slots, which also make the interval between two consecutive tagged cells, and results in unnecessary misses. The new scheme proposed considers the system time and scheduler queue's length. It has less difference between transmission intervals and the premised one of a tagged connection, so that is better in rate-jitter control. This mechanism has O(1) time-complexity, so conforms to the demand of high-speed ATM networks.

Los sistemas de tiempo real fueron, en un principio, concebi-dos para ser utilizados en aplicaciones críticas tales como sistemas espaciales, aviación, control de centrales, plantas industriales. En este tipo de aplicaciones, las decisiones que provienen de estos algoritmos de control deben ser aplicadas antes de un determinado instante de tiempo denominado vencimiento. Debido a que estas aplicaciones son conside-radas críticas, las primeras investigaciones definieron a estos sistemas como de tiempo real duro, en los cuales ningún ven-cimiento puede ser perdido. Generalmente, las condiciones para garantizar tiempo real duro son pesimistas y los sistemas resultan en consecuencia sobredimensionados. Esta capa-cidad de procesamiento ociosa fue utilizada para la ejecución de tareas denominadas blandas. Estas tareas son atendidas por el sistema una vez que las condiciones temporales duras están garantizadas. Una de las mayores áreas de utilización de sistemas de tiempo real son las aplicaciones de control. Sin embargo, y debido a las discrepancias existentes entre la teoría de control y la de tiempo real, existen perturbaciones que los sistemas de tiempo real producen en las aplicaciones de control. Estas perturbaciones son debido a que en un sistema de tiempo real, las estrategias de control pueden ser relegadas del uso del procesador produciendo retardos cuando existen tareas de mayor prioridad que requieren su utilización. Como estos retardos no son constantes de invocación a invocación de la tarea de control, se produce un jitter que no es tenido en cuenta por la teoría de control y que puede provocar efectos indeseables sobre la aplicación. Por consiguiente, el modelo de tareas considerado por la teoría clásica de tiempo real no es enteramente adecuado para su utilización en sistemas de control.Esto se debe a que en ellos, no resulta suficiente observar el cumplimiento de los vencimientos ya que aparecen nuevos requerimientos temporales no contemplados por dichos modelos como son las fluctuaciones en los tiempos de actualización de parámetros de control y de las señales de comando, que provocan per-turbaciones indeseadas en el sistema a controlar. En este contexto, esta tesis propone la utilización de técnicas que admiten una violación acotada de los requerimientos en pos de garantizar su aplicabilidad a sistemas de control intole-rantes a variaciones en los tiempos de activación y respues-ta de tareas críticas aprovechando tanto los tiempos ociosos del sistema como produciendo pérdidas controladas de venci-mientos que no comprometan la integridad del sistema. El objetivo principal de esta tesis consiste en el análisis y de-sarrollo de disciplinas de planificación en tiempo real de bajo jitter para aplicaciones de propósito dedicado en sistemas de control.

Movies, songs, conferences, video streams and other multimedia services are spreading in everybody’s life, needs and work. Different types of audio and video codecs of various qualities appear to be used for different purposes. However, each codec can be suitable for a special usage, as for example a codec that can be use for high quality film may not be suitable for streaming it into network. The main purpose of this thesis is to compare the performance of different codecs in one particular scenario and indicate which codec performance is the best. The thesis work includes the investigation of several codec aspects (audio and video) and problems related to choosing a multimedia codec (coder/decoder) suitable for large-scale multimedia distribution over the Internet. More specifically, the work focuses on various features of modern media codecs, compares them and finds the best application for each of them. Furthermore, the thesis provides an overview of available research results related to this work and codec comparison tables for codecs and their features. Additionally, as part of this work, a testbed was developed to measure the performance of codecs when used to stream media over a network. The testbed enabled the collection of various QoS parameters, such as bandwidth usage and burst, size for each codec considered in this thesis. / Address: Minervavägen 22A, Room 2, 371 41 Karlskrona, sweden. Cel: +46706456674

Jitter is defined as timing uncertainties of digital signals at their intended ideal positions in time. While it undermines valuable clock budget and limits the maximum clock frequency in I/O circuitry, it is one of the most difficult parameters to measure accurately due to the small value and randomness. This thesis proposes a random jitter RMS measurement method using AND and OR operations, which targets BIST applications. This thesis is organized as follows. Chapter 1 introduces the motivation of the proposed work. It includes a comparison between two major approaches to jitter measurement. Chapter 2 explains the proposed random jitter estimation method in detail. Chapter 3 describes circuit implementations with design considerations. Chapter 4 demonstrates estimation results from circuit level simulation runs. Chapter 5 discusses the source of error in the jitter estimation and concludes. / text

Master of Engineering by Research / Service-level-agreement (SLA) monitoring measures network Quality-of-Service (QoS) parameters to evaluate whether the service performance complies with the SLAs. It is becoming increasingly important for both Internet service providers (ISPs) and their customers. However, the rapid expansion of the Internet makes SLA monitoring a challenging task. As an efficient method to reduce both complexity and overheads for QoS measurements, sampling techniques have been used in SLA monitoring systems. In this thesis, I conduct a comprehensive study of sampling methods for network QoS measurements. I develop an efficient sampling strategy, which makes the measurements less intrusive and more efficient, and I design a network performance monitoring software, which monitors such QoS parameters as packet delay, packet loss and jitter for SLA monitoring and verification. The thesis starts with a discussion on the characteristics of QoS metrics related to the design of the monitoring system and the challenges in monitoring these metrics. Major measurement methodologies for monitoring these metrics are introduced. Existing monitoring systems can be broadly classified into two categories: active and passive measurements. The advantages and disadvantages of both methodologies are discussed and an active measurement methodology is chosen to realise the monitoring system. Secondly, the thesis describes the most common sampling techniques, such as systematic sampling, Poisson sampling and stratified random sampling. Theoretical analysis is performed on the fundamental limits of sampling accuracy. Theoretical analysis is also conducted on the performance of the sampling techniques, which is validated using simulation with real traffic. Both theoretical analysis and simulation results show that the stratified random sampling with optimum allocation achieves the best performance, compared with the other sampling methods. However, stratified sampling with optimum allocation requires extra statistics from the parent traffic traces, which cannot be obtained in real applications. In order to overcome this shortcoming, a novel adaptive stratified sampling strategy is proposed, based on stratified sampling with optimum allocation. A least-mean-square (LMS) linear prediction algorithm is employed to predict the required statistics from the past observations. Simulation results show that the proposed adaptive stratified sampling method closely approaches the performance of the stratified sampling with optimum allocation. Finally, a detailed introduction to the SLA monitoring software design is presented. Measurement results are displayed which calibrate systematic error in the measurements. Measurements between various remote sites have demonstrated impressively good QoS provided by Australian ISPs for premium services.

<p>In todays GSM network more and more interfaces are run over IP instead of classic synchronized networks. This rises new issues to be solved, for example handling of jitter that use of IP networks introduces. The jitter can be handled by a jitter buffer which ensures that the packets are forwarded in evenly spaced intervals.</p><p>In GSM, data is requested a certain time in advance before delivery to a cellphone. This "time in advance" needs to be adjusted according to the delay of the channel. For an IP network this delay varies (jitter), which means that it would be beneficial to have an algorithm which continuously adjusts how long in advance the packets should be requested. The adjustment is made according to current channel delay and jitter size.</p><p>In this thesis work a model of a general IP network has been developed and isthen used for development of two algorithms for jitter buffer handling. Once the algorithms have been developed they are evaluated and compared to each other and previous solutions to the problem. One of the algorithms is new and the other is an already existing algorithm that has been extended.</p><p>The simplified conclusion is that the behaviors of both algorithms are very similar. They mainly have small packet loss but sometimes the packets are requested earlier than needed and therefore are kept in the buffer a bit longer than necessary. When comparing the two developed algorithms with previous solutions it is visible that they improve the buffer handling a great deal.</p>

In todays GSM network more and more interfaces are run over IP instead of classic synchronized networks. This rises new issues to be solved, for example handling of jitter that use of IP networks introduces. The jitter can be handled by a jitter buffer which ensures that the packets are forwarded in evenly spaced intervals. In GSM, data is requested a certain time in advance before delivery to a cellphone. This "time in advance" needs to be adjusted according to the delay of the channel. For an IP network this delay varies (jitter), which means that it would be beneficial to have an algorithm which continuously adjusts how long in advance the packets should be requested. The adjustment is made according to current channel delay and jitter size. In this thesis work a model of a general IP network has been developed and isthen used for development of two algorithms for jitter buffer handling. Once the algorithms have been developed they are evaluated and compared to each other and previous solutions to the problem. One of the algorithms is new and the other is an already existing algorithm that has been extended. The simplified conclusion is that the behaviors of both algorithms are very similar. They mainly have small packet loss but sometimes the packets are requested earlier than needed and therefore are kept in the buffer a bit longer than necessary. When comparing the two developed algorithms with previous solutions it is visible that they improve the buffer handling a great deal.

Phase locked loops (PLL) are used in many applications. Application examples include clock and data recovery, clock synthesis, frequency synthesis, modulator, and de-modulator. In many circuits, PLL must provide an output clock to follow the input clock closely. For high speed environments, the noises also rise up. Noises mainly come from the power supply and substrate. They produce jitter. A low jitter design is important in PLL circuit. In this thesis, we discuss the Voltage Controlled Oscillator (VCO) which has the largest jitter in PLL system. We propose a low jitter voltage controlled oscillator designed in TSMC 0.35£gm 2P4M Mixed-Signal process technology. We include a regulator to reduce jitter by increasing the VCO PSRR. This structure also provides a high linearity gain (Kvco) which decreases the VCO jitter in the PLL circuit and improve the system stability.

Master of Engineering by Research / Service-level-agreement (SLA) monitoring measures network Quality-of-Service (QoS) parameters to evaluate whether the service performance complies with the SLAs. It is becoming increasingly important for both Internet service providers (ISPs) and their customers. However, the rapid expansion of the Internet makes SLA monitoring a challenging task. As an efficient method to reduce both complexity and overheads for QoS measurements, sampling techniques have been used in SLA monitoring systems. In this thesis, I conduct a comprehensive study of sampling methods for network QoS measurements. I develop an efficient sampling strategy, which makes the measurements less intrusive and more efficient, and I design a network performance monitoring software, which monitors such QoS parameters as packet delay, packet loss and jitter for SLA monitoring and verification. The thesis starts with a discussion on the characteristics of QoS metrics related to the design of the monitoring system and the challenges in monitoring these metrics. Major measurement methodologies for monitoring these metrics are introduced. Existing monitoring systems can be broadly classified into two categories: active and passive measurements. The advantages and disadvantages of both methodologies are discussed and an active measurement methodology is chosen to realise the monitoring system. Secondly, the thesis describes the most common sampling techniques, such as systematic sampling, Poisson sampling and stratified random sampling. Theoretical analysis is performed on the fundamental limits of sampling accuracy. Theoretical analysis is also conducted on the performance of the sampling techniques, which is validated using simulation with real traffic. Both theoretical analysis and simulation results show that the stratified random sampling with optimum allocation achieves the best performance, compared with the other sampling methods. However, stratified sampling with optimum allocation requires extra statistics from the parent traffic traces, which cannot be obtained in real applications. In order to overcome this shortcoming, a novel adaptive stratified sampling strategy is proposed, based on stratified sampling with optimum allocation. A least-mean-square (LMS) linear prediction algorithm is employed to predict the required statistics from the past observations. Simulation results show that the proposed adaptive stratified sampling method closely approaches the performance of the stratified sampling with optimum allocation. Finally, a detailed introduction to the SLA monitoring software design is presented. Measurement results are displayed which calibrate systematic error in the measurements. Measurements between various remote sites have demonstrated impressively good QoS provided by Australian ISPs for premium services.

Techn. University, Diss., 2003--Berlin.