Dissertations / Theses on the topic 'Broadband ISDN'

A structured organisation of tasks, possibly hierarchical, is necessary in a BISDN network due to the complexity of the system, its large dimension and its physical distribution in space. Feedback (possibly supplemented by feedforward) control has an essential role in the effective and efficient control of BISDN. Additionally, due to the nonstationarity of the network and its complexity, a number of different (dynamic) modelling techniques are required at each level of the hierarchy. Also, to increase the efficiency of the network and allow flexibility in the control actions (by extending the control horizon) the (dynamic) tradeoff between service-rate, buffer-space, cell-delay and cell-loss must be exploited. In this thesis we take account of the above and solve three essential control problems, required for the effective control of BISDN. These solutions are suitable for both stationary and nonstationary conditions. Also, they are suitable for implementation in a decentralised coordinated form, that can form a part of a hierarchical organisation of control tasks. Thus, the control schemes aim for global solutions, yet they are not limited by the propagation delay, which can be high in comparison to the dynamics of the controlled events. Specifically, novel control approaches to the problems of Connection Admission Control (CAC), flow control and service-rate control are developed. We make use of adaptive feedback and adaptive feedforward control methodologies to solve the combined CAC and flow control problem. Using a novel control concept, based on only two groups of traffic (the controllable and uncontrollable group) we formulate a problem aimed at high (unity) utilisation of resources while maintaining quality of service at prescribed levels. Using certain assumptions we have proven that in the long term the regulator is stable and that it converges to zero regulation error. Bounds on operating conditions are also derived, and using simulation we show that high utilisation can be achieved as suggested by the theory, together with robustness for unforeseen traffic connections and disconnections. Even with such a high efficiency and strong properties on the quality of service provided, the only traffic descriptor required from the user is that of the peak rate of the uncontrollable traffic. A novel scheme for the dynamic control of service-rate is formulated, using feedback from the network queues. We use a unified dynamic fluid flow equation to describe the virtual path (VP) and hence formulate two illustrative examples for the control of service-rate (at the VP level). One is a nonlinear optimal multilevel implementation, that features a coordinated decentralised solution. The other is a single level implementation that turns out to be computationally complex. Therefore, for the single level implementation the costate equilibrium solution is also derived. For the optimal policies derived, we discuss their implementation complexity and provide implementable solutions. Their performance is evaluated using simulation. Additionally, using an ad hoc approach we have extended previous published works on the decentralised coordinated control of large scale nonlinear systems to also deal with time-delayed systems.

In this thesis we analyze broadband switching architectures based on the Asynchronous Transfer Mode (ATM). Many architectures have been proposed in the literature for high-speed packet switches. We first review some of these switch architectures and their performance. The high-performance switch architectures, in general, require that the buffers be placed at the output ports. These output buffered switches tend to have large hardware complexity or require high speedup in their operation. Our focus is on high-performance switch architectures with low speedup output buffers or a shared buffer. An N $\times$ d ATM switch with finite output buffers is modeled as a discrete-time queue. The case d = 1 represents an ATM multiplexer with N input source and a finite capacity buffer. Loading at the input as well as at the output is considered to be imbalanced, which greatly affects the switch performance especially the hot spot traffic pattern. We also consider the switch with reduced speedup. In this case, the number of cells going to an output buffer in one time slot is limited to L N. This greatly simplifies the implementation of the switch. The arrivals to an input port of the switch, besides being bursty, are correlated in the sense that a burst arriving to an output port brings with it several cells belonging to the same virtual connection. As a worst case, we assume that consecutive cells in a burst are heading to the same output port. This greatly affects the dimensioning of the switch buffer. The input process to each input port is modeled by an Interrupted Bernoulli Process (IBP). We have developed an aggregation technique which allows the reduction of the state space that describes the arrival processes to the switch. This makes handling the output buffer driven by the induced process more manageable. Traffic priorities in ATM networks is an important issue because such networks will support applications with diverse traffic characteristics. In the light of this, we consider traffic priorities in an output buffered switch and in a completely shared-buffer switch. The transient analysis of the output buffer is also studied by considering the mean time until buffer overflow. The switch architecture that has the maximum mean-time-to-blocking is favorable. The busy period of the output buffer is also characterized. In routing the whole burst to an output buffer, the output process becomes more bursty than the input process.

In this thesis, we present an analysis of three novel switch architectures for Broadband-ISDN using the Asynchronous Transfer Mode (ATM). Our focus is on high-performance switch architectures, which have low to medium hardware complexity. The first switch architecture presented is a speed-up switch with input and output buffers, where a back-pressure mechanism is applied to avoid packet loss at the output buffers. We examine the maximum throughput, mean delay and packet loss rate at the input buffers of this speed-up switch. The switch with a speed-up of 3, and 20 buffers at each output port can achieve a maximum throughput of 90% or more. These results are of a great practical value since a switch with high speed-up is difficult to realize. A simple implementation of the switch is also presented. The second switch architecture, called Limited Intermediate Buffer (LIB) switch, is based on a crossbar switch fabric. A buffer to store a single packet is provided at each crosspoint of this switch. In addition to this, buffers are provided at the input ports to reduce the packet loss. We propose a new scheduling policy called head-of-line priority selection, which reduces the head-of-line blocking and thus improves the performance of the LIB switch substantially. A 16 x 16 switch under uniform random traffic can achieve a throughput of 87.5%. A three-stage interconnection network consisting of symmetric and asymmetric LIB switch modules is also presented. The simulation results of the interconnection network prove the efficacy of the LIB switch architecture and the proposed head-of-line priority selection scheme. Finally, the handling of delay and loss sensitive traffic in ATM networks is discussed. To keep the protocols simple at the ATM layer, we suggest that the handling of these priorities should be de-linked. The performance of two classes of delay-sensitive traffic in an input buffered nonblocking switch architecture is analyzed. The result of the analysis under two different non-preemptive priority schemes suggests that, to reduce the hardware complexity, the packets should not be distinguished based on their priority within the switch fabric. To overcome the throughput limitation of the input buffered switch, a dual plane switch architecture is presented, where each plane is a nonblocking switch with input buffers.

This thesis analyzes the different Quality of Service (QoS) parameters that are important in setting up multimedia calls in Broadband ISDN (B-ISDN). Unlike in traditional telecommunication networks, service providers of Broadband ISDN provide guaranteed Quality of Service. This requires a comprehensive QoS management framework. The users of B-ISDN are able to adapt the Quality of Service of multimedia to their requirements. The main adaptable QoS parameters include video parameters, audio parameters and synchronization parameters. Intra-media synchronization and inter-media synchronization are important aspects of overall QoS provision. The audio and video streams of a particular source can be transmitted in different paths as these streams may have varying QoS requirements. Thus the audio and video streams will incur different transfer delays. The encoder and decoder processing delays of audio and video are also different. When presenting audio and video, the video stream should not be allowed to lag or lead the audio stream beyond acceptable skew tolerances. In specialized applications, multiple audio and video streams have to be played out in synchrony at the receiver. Also the layers of a layered coding system may be transmitted in different paths and the layers should be perfectly synchronized at the receiver. Management of special resources such as layered encoders and decoders, media combiners code converters etc., ensures that intra-media and inter-media synchronization is maintained in isochronous communications. The different special resources and their relevance to QoS parameters such as intra-media and inter-media synchronization is discussed in detail. In this thesis, a comprehensive synchronization mechanism called Static Delay Compensation (SDC) is proposed to guarantee synchronization QoS. When synchronizing two or more media streams static delays are added to streams with lower end-to-end delays. It will be shown that SDC will satisfy almost all of the synchronization QoS requirements.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada
As technology progresses we are faced with ever increasing volumes and rates of raw and processed telemetry data along with digitized high resolution video and the less demanding areas of video conferencing, voice communications and general LAN-based data communications. The distribution of all this data has traditionally been accomplished by solutions designed to each particular data type. With the advent of Asynchronous Transfer Modes or ATM, a single technology now exists for providing an integrated solution to distributing these diverse data types. This allows an integrated set of switches, transmission equipment and fiber optics to provide multi-session connection speeds of 622 Megabits per second. ATM allows for the integration of many of the most widely used and emerging low, medium and high speed communications standards. These include SONET, FDDI, Broadband ISDN, Cell Relay, DS-3, Token Ring and Ethernet LANs. However, ATM is also very well suited to handle unique data formats and speeds, as is often the case with telemetry data. Additionally, ATM is the only data communications technology in recent times to be embraced by both the computer and telecommunications industries. Thus, ATM is a single solution for connectivity within a test center, across a test range, or between ranges. ATM can be implemented in an evolutionary manner as the needs develop. This means the rate of capital investment can be gradual and older technologies can be replaced slowly as they become the communications bottlenecks. However, success of this evolution requires some planning now. This paper provides an overview of ATM, its application to test ranges and telemetry distribution. A road map is laid out which can guide the evolutionary changeover from today's technologies to a full ATM communications infrastructure. Special applications such as the support of high performance multimedia workstations are presented.

There is a growing interest in the development of broadband services and networks for commercial use in both local area and wide area networks. The primary reasons for this is a pressing need to meet the demand for increased bandwidth for remote sites interconnection, and in high speed data transfer of bulk data such as images etc. There has also been a significant change in the characteristics of network traffic. It is increasingly taking the form of bursty traffic characterized by an unpredictable demand for bandwidth of several megabytes. A new generation of networking technologies have emerged to meet the demand of growing and uncertain bandwidth requirements. One such technology is called Asynchronous Transfer Mode (ATM) for use on broadband networks under the banner of broadband ISDN. ATM enables interconnection at high speeds in the range of Mbit/s or Gbit/s over wide areas, which effectively moves the bottleneck from networks to end systems. Furthermore, the user is able to access bandwidth on demand and the user is only charged for the bandwidth actually used. As more and more information (audio, image and data) is transferred over ATM networks, security issues are becoming increasingly critical. The rapidly growing use of the Internet to transfer confidential and sensitive information only enhances the importance of security services. One may even argue that the success of ATM will be determined not by its cost effectiveness but also to the level of trust that can be placed on its performance, security and availability. The objective of this dissertation is to address the issues involved in the design of security services for ATM networks.
Master of Science (Hons)

The research presented in this thesis aims to demonstrate that fuzzy logic is a useful tool for developing mechanisms for controlling traffc flow in ATM based multimedia networks to maintain quality of service (QoS) requirements and maximize resource utilization. The study first proposes a hierarchical, multilevel control structure for ATM networks to exploit the reported strengths of fuzzy logic at various control levels. Then, an extensive development and evaluation is presented for a subset of the proposed control architecture at the congestion control level. An ATM based multimedia network must have quite sophisticated traffc control capabilities to effectively handle the requirements of a dynamically varying mixture of voice, video and data services while meeting the required levels of performance. Feedback control techniques have an essential role for the effective and efficient management of the resources of ATM networks. However, development of conventional feedback control techniques relies on the availability of analytical system models. The characteristics of ATM networks and the complexity of service requirements cause the analytical modeling to be very difficult, if not impossible. The lack of realistic dynamic explicit models leads to substantial problems in developing control solutions for B-ISDN networks. This limits the ability of conventional techniques to directly address the control objectives for ATM networks. In the literature, several connection admission and congestion control methods for B-ISDN networks have been reported, and these have achieved mixed success. Usually they either assume heavily simplified models, or they are too complicated to implement, mainly derived using probabilistic (steady-state) models. Fuzzy logic controllers, on the other hand, have been applied successfully to the task of controlling systems for which analytical models are not easily obtainable. Fuzzy logic control is a knowledge-based control strategy that can be utilized when an explicit model of a system is not available or, the model itself, if available, is highly complex and nonlinear. In this case, the problem of control system design is based on qualitative and/or empirically acquired knowledge regarding the operation of the system. Representation of qualitative or empirically acquired knowledge in a fuzzy logic controller is achieved by linguistic expressions in the form of fuzzy relational equations. By using fuzzy relational equations, classifications related to system parameters can be derived without explicit description. The thesis presents a new predictive congestion control scheme, Fuzzy Explicit Rate Marking (FERM), which aims to avoid congestion, and by doing so minimize the cell losses, attain high server utilization, and maintain the fair use of links. The performance of the FERM scheme is extremely competitive with that of control schemes developed using traditional methods over a considerable period of time. The results of the study demonstrate that fuzzy logic control is a highly effective design tool for this type of problems, relative to the traditional methods. When controlled systems are highly nonlinear and complex, it keeps the human insight alive and accessible at the lower levels of the control hierarchy, and so higher levels can be built on this understanding. Additionally, the FERM scheme has been extended to adaptively tune (A-FERM) so that continuous automatic tuning of the parameters can be achieved, and thus be more adaptive to system changes leading to better utilization of network bandwidth. This achieves a level of robustness that is not exhibited by other congestion control schemes reported in the literature. In this work, the focus is on ATM networks rather than IP based networks. For historical reasons, and due to fundamental philosophical differences in the (earlier) approach to congestion control, the research for control of TCP/IP and ATM based networks proceeded separately. However, some convergence between them has recently become evident. In the TCP/IP literature proposals have appeared on active queue management in routers, and Explicit Congestion Notication (ECN) for IP. It is reasonably expected that, the algorithms developed in this study will be applicable to IP based multimedia networks as well.

Within the fields of network operation and performance measurement, it is a common requirement that the technologies involved must provide the basis for an effective, reliable, measurable and controllable service. In order to comply with the service performance criteria, the constrains often lead to very complex techniques and methodologies for the simulation, control, test, and measurement processes. This thesis addresses some of the factors that contribute to the overall spectrum of statistical performance measurements in telecommunication services. Specifically, it is concerned with the development of three low complexity and effective techniques for real-time traffic generation, control and measurement. These techniques have proved to be accurate and near optimum. In the three cases the work starts with a literature survey of known methodologies, and later new techniques are proposed and investigated by simulating the processes involved. The work is based on the use of high-speed Asynchronous Transfer Mode (ATM) networks. The problem of developing a fast traffic generation technique for the simulation of Variable Bit Rate traffic sources is considered in the first part of this thesis. For this purpose, statistical measures are obtained from the analysis of different traffic profiles or from the literature. With the aid of these measures, a model for the fast generation of Variable Bit Rate traffic at different time resolutions is developed. The simulated traffic is then analysed in order to obtain the equivalent set of statistical measures and these are compared against those observed in real traffic traces. The subject of traffic control comprises a very wide area in communication networks. It refers to the generalised classification of actions such as Connection Admission and Flow Control, Traffic Policing and Shaping. In the second part of this thesis, a method to modify the instantaneous traffic profile of a variable rate source is developed. It is particularly useful for services which have a hard bound on the cell loss probability, but a soft bound on the admissible delay, matching the characteristics of some of the services provided by ATM networks. Finally, this thesis is also concerned with a particular aspect of the operation and management of high speed networks, or OAM functions plane, namely with the monitoring of network resources. A monitoring technique based on numerical approximation and statistical sampling methods is developed and later used to characterise a particular traffic stream, or a particular connection, within a high speed network. The resulting algorithms are simple and computationally inexpensive, but effective and accurate at the same time, and are suitable for real-time processing.

碩士
國立臺灣科技大學
工程技術研究所
81
There is a growing interest nowadays in MAN as providers of high speed transmissions and the integration of various services, such as data, voice, and images, in limited geographical areas and as backbones for LAN interconnection. The DQDB protocol has been accepted as a new IEEE 802.6 standard MAC protocol for MAN. The ATM has been proposed by CCITT as the transfer mode for B-ISDN. ATM networks support multimedia information transport in an efficient and flexible manner. It is anticipated that MANs will become widespread both in public and private environments. In parallel with the MAN proliferation, B-ISDN are being developed by the public carriers to provide geographical, integrated services. After the establishment of B-ISDN, the need will arise for the interconnection of MANs to the B-ISDN, in order to extend the MAN services geographically. This paper examines the interworking of the DQDB MAN with B- ISDN. For the similarity of DQDB and B-ISDN, we proposed a simple and fast strategy for the interconnection bridge. For the DQDB network is of a two-unidirectional-bus topology, we also discuss the impact of the position of the bridge on the DQDB network.

Asynchronous Transfer Mode (ATM) is an emerging networking technique which supports quality of service (QoS) guarantees for different traffic types. The Available Bit Rate (ABR) service is proposed to provide the efficient use of limited network resources for data traffic. For ABR service, ATM Forum has suggested the rate-based congestion control schemes: Explicit Forward Congestion Indication (EFCI, a binary feedback scheme) scheme, Explicit Rate (ER) scheme, and Enhanced Proportional Rate Control Algorithm (EPRCA). In addition, the segmented closed-loop scheme was also recommended to reduce the size of the control loop. In this thesis, the effects of satellite link (long delay) on the EFCI and ER schemes are analyzed by using calculation results. Based on the analytical results, the simulations of endto- end congestion control schemes are performed. For the EFCI scheme, both the calculation and simulation results show that the long delay will worsen the network performance in terms of buffer occupancy, link utilization and cell loss ratio (CLR). Our study also finds that the buffer threshold, buffer size in ATM switch, as well as the rate increase and decrease factors, will affect the buffer occupancy, link utilization and cell loss ratio in the various ways. Procedures are suggested to minimize the buffer requirement and maximize the link utilization with the required CLR and maximum link delay. Moreover, a delay-based method (DBCI scheme) is proposed to dynamically adjust the traffic rate in order to minimize the buffer requirement. For the ER scheme, since-the product of data rate and link delay in each ABR connection plays a key role on the buffer occupancy of the ATM switch, the delaybased adaptation method (DBER scheme) to reallocate the left-over bandwidth is proposed. Simulation results show that the suggested approaches can improve the buffer occupancy efficiently when congestion happens. The generic and delay-based EPRCA schemes are investigated with different parameters in different links. Simulation results are compared and the delay-based EPRCA scheme is found to be a more efficient scheme. Furthermore, the segmented (double-loop) congestion control schemes are evaluated by simulations methods and analyzed with different combinations of EFCI and ER schemes. The results are compared with those of end-to-end (single-loop) schemes. From the comparisons, the segmented congestion control scheme is considered to be a better scheme in the long delay environment because it can respond to congestion more quickly and be able to distribute the queued cells (e.g. the long queue length occurred in the single loop scheme) into more ATM switches involved in the congestion.