A hybrid queueing model for fast broadband networking simulation

PhDThis research focuses on the investigation of a fast simulation method for broadband telecommunication networks, such as ATM networks and IP networks. As a result of this research, a hybrid simulation model is proposed, which combines the analytical modelling and event-driven simulation modelling to speeding up the overall simulation. The division between foreground and background traffic and the way of dealing with these different types of traffic to achieve improvement in simulation time is the major contribution reported in this thesis. Background traffic is present to ensure that proper buffering behaviour is included during the course of the simulation experiments, but only the foreground traffic of interest is simulated, unlike traditional simulation techniques. Foreground and background traffic are dealt with in a different way. To avoid the need for extra events on the event list, and the processing overhead, associated with the background traffic, the novel technique investigated in this research is to remove the background traffic completely, adjusting the service time of the queues for the background traffic to compensate (in most cases, the service time for the foreground traffic will increase). By removing the background traffic from the event-driven simulator the number of cell processing events dealt with is reduced drastically. Validation of this approach shows that, overall, the method works well, but the simulation using this method does have some differences compared with experimental results on a testbed. The reason for this is mainly because of the assumptions behind the analytical model that make the modelling tractable. Hence, the analytical model needs to be adjusted. This is done by having a neural network trained to learn the relationship between the input traffic parameters and the output difference between the proposed model and the testbed. Following this training, simulations can be run using the output of the neural network to adjust the analytical model for those particular traffic conditions. The approach is applied to cell scale and burst scale queueing to simulate an ATM switch, and it is also used to simulate an IP router. In all the applications, the method ensures a fast simulation as well as an accurate result

Novel techniques in large scaleable ATM switches

Bibliography: p. 172-178.This dissertation explores the research area of large scale ATM switches. The requirements for an ATM switch are determined by overviewing the ATM network architecture. These requirements lead to the discussion of an abstract ATM switch which illustrates the components of an ATM switch that automatically scale with increasing switch size (the Input Modules and Output Modules) and those that do not (the Connection Admission Control and Switch Management systems as well as the Cell Switch Fabric). An architecture is suggested which may result in a scalable Switch Management and Connection Admission Control function. However, the main thrust of the dissertation is confined to the cell switch fabric. The fundamental mathematical limits of ATM switches and buffer placement is presented next emphasising the desirability of output buffering. This is followed by an overview of the possible routing strategies in a multi-stage interconnection network. A variety of space division switches are then considered which leads to a discussion of the hypercube fabric, (a novel switching technique). The hypercube fabric achieves good performance with an O(N.log₂N)²) scaling. The output module, resequencing, cell scheduling and output buffering technique is presented leading to a complete description of the proposed ATM switch. Various traffic models are used to quantify the switch's performance. These include a simple exponential inter-arrival time model, a locality of reference model and a self-similar, bursty, multiplexed Variable Bit Rate (VBR) model. FIFO queueing is simple to implement in an ATNI switch, however, more responsive queueing strategies can result in an improved performance. An associative memory is presented which allows the separate queues in the ATM switch to be effectively logically combined into a single FIFO queue. The associative memory is described in detail and its feasibility is shown by laying out the Integrated Circuit masks and performing an analogue simulation of the IC's performance is SPICE3. Although optimisations were required to the original design, the feasibility of the approach is shown with a 15Ƞs write time and a 160Ƞs read time for a 32 row, 8 priority bit, 10 routing bit version of the memory. This is achieved with 2µm technology, more advanced technologies may result in even better performance. The various traffic models and switch models are simulated in a number of runs. This shows the performance of the hypercube which outperforms a Clos network of equivalent technology and approaches the performance of an ideal reference fabric. The associative memory leverages a significant performance advantage in the hypercube network and a modest advantage in the Clos network. The performance of the switches is shown to degrade with increasing traffic density, increasing locality of reference, increasing variance in the cell rate and increasing burst length. Interestingly, the fabrics show no real degradation in response to increasing self similarity in the fabric. Lastly, the appendices present suggestions on how redundancy, reliability and multicasting can be achieved in the hypercube fabric. An overview of integrated circuits is provided. A brief description of commercial ATM switching products is given. Lastly, a road map to the simulation code is provided in the form of descriptions of the functionality found in all of the files within the source tree. This is intended to provide the starting ground for anyone wishing to modify or extend the simulation system developed for this thesis

Performance analysis and improvement of InfiniBand networks. Modelling and effective Quality-of-Service mechanisms for interconnection networks in cluster computing systems.

The InfiniBand Architecture (IBA) network has been proposed as a new industrial standard with high-bandwidth and low-latency suitable for constructing high-performance interconnected cluster computing systems. This architecture replaces the traditional bus-based interconnection with a switch-based network for the server Input-Output (I/O) and inter-processor communications. The efficient Quality-of-Service (QoS) mechanism is fundamental to ensure the import at QoS metrics, such as maximum throughput and minimum latency, leaving aside other aspects like guarantee to reduce the delay, blocking probability, and mean queue length, etc. Performance modelling and analysis has been and continues to be of great theoretical and practical importance in the design and development of communication networks. This thesis aims to investigate efficient and cost-effective QoS mechanisms for performance analysis and improvement of InfiniBand networks in cluster-based computing systems. Firstly, a rate-based source-response link-by-link admission and congestion control function with improved Explicit Congestion Notification (ECN) packet marking scheme is developed. This function adopts the rate control to reduce congestion of multiple-class traffic. Secondly, a credit-based flow control scheme is presented to reduce the mean queue length, throughput and response time of the system. In order to evaluate the performance of this scheme, a new queueing network model is developed. Theoretical analysis and simulation experiments show that these two schemes are quite effective and suitable for InfiniBand networks. Finally, to obtain a thorough and deep understanding of the performance attributes of InfiniBand Architecture network, two efficient threshold function flow control mechanisms are proposed to enhance the QoS of InfiniBand networks; one is Entry Threshold that sets the threshold for each entry in the arbitration table, and other is Arrival Job Threshold that sets the threshold based on the number of jobs in each Virtual Lane. Furthermore, the principle of Maximum Entropy is adopted to analyse these two new mechanisms with the Generalized Exponential (GE)-Type distribution for modelling the inter-arrival times and service times of the input traffic. Extensive simulation experiments are conducted to validate the accuracy of the analytical models

Quality of service modeling and analysis for carrier ethernet

Today, Ethernet is moving into the mainstream evolving into a carrier grade technology. Termed as Carrier Ethernet it is expected to overcome most of the\ud shortcomings of native Ethernet. It is envisioned to carry services end-to-end serving corporate data networking and broadband access demands as well as backhauling wireless traffic. As the penetration of Ethernet increases, the offered Quality of Service (QoS) will become increasingly important and a distinguishing factor between different service providers. The challenge is to meet the QoS requirements of end applications such as response times, throughput, delay and jitter by managing the network resources at hand. Since Ethernet was not designed to operate in large public networks it does not possess functionalities to address this issue. In this thesis we propose and analyze mechanisms which improve the QoS performance of Ethernet enabling it to meet the demands of the current and next generation services and applications.\u

Operational support systems for satellite communications

The role of satellite communications is changing from providing bandwidth linking network operators interconnections towards providing IP enabled communications to end users. This migration from few high-value routes towards many low-value routes means that integration and automation of processes with terrestrial networks becomes critical in driving down unit costs. Integration and automation is necessary on all planes: user, control and management. In satellite communications, management aspects, underpinned by Operational Support Systems (OSS) have received the least research attention, making this a valuable topic for study. In most areas, OSS for satellite systems are similar to other domains. However there are some notable areas of difference which have been the focus of this research. The eTOM business framework, developed by the TMF, has been used to highlight aspects of OSS unique to satellite. Since satellite capacity represents the highest operational cost of a satellite route, effective management while minimising the overhead traffic is critical. The transmission of IP packets is assumed and the real-time measurement of QoS parameters such as packet delay and loss emerged as the most important differences. A number of approaches to QoS measurement are feasible, however the use of trace packets is most promising especially for high network loads. An experiment compares the results from simulations, mathematical models and from a test network, using Poisson and self-similar traffic flows. The relationship between measurement accuracy and trace packet intensity is explored and the measurement response time to steps in traffic load is estimated. It is discovered that measurement accuracy improves as the queue load increases, in contrast to alternative approaches such as sampling of user packets. The response time to steps depends upon the degree of self-similarity and is generally longer than the times recommended by standards. A pragmatic approach to management of different modes is proposed where the measurement method is changed depending on the load

Quality-of-service management in IP networks

Quality of Service (QoS) in Internet Protocol (IF) Networks has been the subject of active research over the past two decades. Integrated Services (IntServ) and Differentiated Services (DiffServ) QoS architectures have emerged as proposed standards for resource allocation in IF Networks. These two QoS architectures support the need for multiple traffic queuing systems to allow for resource partitioning for heterogeneous applications making use of the networks. There have been a number of specifications or proposals for the number of traffic queuing classes (Class of Service (CoS)) that will support integrated services in IF Networks, but none has provided verification in the form of analytical or empirical investigation to prove that its specification or proposal will be optimum. Despite the existence of the two standard QoS architectures and the large volume of research work that has been carried out on IF QoS, its deployment still remains elusive in the Internet. This is not unconnected with the complexities associated with some aspects of the standard QoS architectures. [Continues.

Performance of a ATM Lan switching fabric

This thesis provides a focus on the architecture of a high-speed packet switching fabric and its performance. The switching fabric is suited for existing transparent protocols, based on Asynchronous Transfer Mode (ATM) technology and standards in an environment of Local Area Network (LAN). A high-speed switching fabric architecture which adopts Time Division mode and bases on a shared medium approach is proposed. This is an architecture for nonblocking performance, no congestion and high reliability. Its principle for performance is a method of sequentially scheduling the inputs and the transferring of bits in parallel. To study the performance of the switching fabric architecture one uses OPNET communication simulation software. Some parameters including the throughputs, the transfer (the switching fabric) delay, the switching overflow and the packet size in the buffer (the input buffer and the output buffer) are implemented through the simulation. And finally, an analysis for the results of the simulation for local ATM IDS fabric architecture is discussed. The results display an architecture that provides a rational design with some expected characteristics

Some topics in web performance analysis

This thesis consists of four papers on web performance analysis. In the first paper we investigate the performance of overload control through queue length for two different web server architectures. The simulation result suggests that the benefit of request prioritization is noticeable only when the capacities of the sub-systems match each other. In the second paper we present an M/G/1/K*PS queueing model of a web server. We obtain closed form expressions for web server performance metrics such as average response time, throughput and blocking probability. The model is validated through real measurements. The third paper studies a queueing system with a load balancer and a pool of identical FCFS queues in parallel. By taking the number of servers to infinite, we show that the average waiting time for the system is not always minimized by routing each customer to the expected shortest queue when the information used for decision is stale. In the last paper we consider the problem of admission control to an M/M/1 queue under periodic observations with average cost criterion. The problem is formulated as a discrete time Markov decision process whose states are fully observable. A proof of the existence of the average optimal policy by the vanishing discounted approach is provided. We also show that the optimal policy is nonincreasing with respect to the observed number of customers in the system

Performance measurement methodology for integrated services networks

With the emergence of advanced integrated services networks, the need for effective performance analysis techniques has become extremely important. Further advancements in these networks can only be possible if the practical performance issues of the existing networks are clearly understood. This thesis is concerned with the design and development of a measurement system which has been implemented on a large experimental network. The measurement system is based on dedicated traffic generators which have been designed and implemented on the Project Unison network. The Unison project is a multisite networking experiment for conducting research into the interconnection and interworking of local area network based multi-media application systems. The traffic generators were first developed for the Cambridge Ring based Unison network. Once their usefulness and effectiveness was proven, high performance traffic generators using transputer technology were built for the Cambridge Fast Ring based Unison network. The measurement system is capable of measuring the conventional performance parameters such as throughput and packet delay, and is able to characterise the operational performance of network bridging components under various loading conditions. In particular, the measurement system has been used in a 'measure and tune' fashion in order to improve the performance of a complex bridging device. Accurate measurement of packet delay in wide area networks is a recognised problem. The problem is associated with the synchronisation of the clocks between the distant machines. A chronological timestamping technique has been introduced in which the clocks are synchronised using a broadcast synchronisation technique. Rugby time clock receivers have been interfaced to each generator for the purpose of synchronisation. In order to design network applications, an accurate knowledge of the expected network performance under different loading conditions is essential. Using the measurement system, this has been achieved by examining the network characteristics at the network/user interface. Also, the generators are capable of emulating a variety of application traffic which can be injected into the network along with the traffic from real applications, thus enabling user oriented performance parameters to be evaluated in a mixed traffic environment. A number of performance measurement experiments have been conducted using the measurement system. Experimental results obtained from the Unison network serve to emphasise the power and effectiveness of the measurement methodology