<p>Internet has gained much popularity among the public since the mid 1990's and is now an integrated part of our society. A large range of high-speedbroadband providers and the development of new and more efficient Internet applications increase the possibilities to watch movies and live TV, use IP-telephony and share files over the Internet. Such applications demand high data transmission rates, which in turn consume network bandwidth. Since several users must share the common bandwidth capacity on the Internet, there will be locations in the network where the demand is higher than the capacity. This causes network congestion, which has negative impact on both the data transmission rate and transmission quality.</p><p>This thesis is about methods for measuring the available bandwidth of a network path between two computers. The available bandwidth can be interpreted as the maximum transfer rate possible without causing congestion. By deploying the methods studied in this thesis the available bandwidth can be measured without previous knowledge of the network topology. When an estimate of the available bandwidth is obtained, the transfer rate when sending messages between computers can be set to the measured value in order to avoid congestion.</p><p>In the thesis an active end-to-end available bandwidth measurement method called "Bandwidth Available in Real Time" (BART for short) is evaluated. BART measures the available bandwidth by injecting probe packets into the network at a given rate and then analysing how this rate has changed on the receiving side. A Kalman filter is used to update the current estimate of the available bandwidth using the new measurement sample.</p><p>The focus of the thesis is on how methods, such as BART, function in wireless 802.11 networks, which are very popular in work as well as in home environments. Wireless networks have a different construction compared to many other types of networks and this can affect the accuracy of the measurement methods discussed in this thesis. The effects must be analyzed and understood in order to obtain accurate available bandwidth estimates. Since wireless links are often parts of the network path between a sender and a receiver on the Internet, it is important to study how these links affect the estimates of the available bandwidth.</p>

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The problem of ensuring Quality of Service (QoS) on a TCP/IP based fixed-infrastructure network has been well studied and several working proposals exist. An allied problem is that of ensuring QoS on an ad-hoc wireless network, where the requirements are similar, but the operating conditions are different enough to warrant this problem to be dealt with separately and extensively. The QoS reservation and management schemes which work on a fixed infrastructure network perform poorly in ad-hoc wireless networks, mainly because of the difficulty in reserving bandwidth on a contention-based medium, and problems which arise from the possible motion of the hosts and the variability of the quality of the connection. This thesis is a proposal to use the concept of active nodes to set up and maintain QoS. Active nodes are nodes which can execute code on behalf on other remote applications. An algorithm for using active nodes to set up and maintain QoS parameters is proposed, and the use of buffer reservation schemes in reserving bandwidth is explained. The proposal is implemented on the network simulator NS-2, and we study the uses and limitations of this proposal, with specific reference to the performance under different operating conditions. / Graduation date: 2003

Efficient routing of messages is critical to the performance of multicomputers. Many adaptive routing algorithms have been proposed to improve the network efficiency; however, they can make only short-sighted decisions to choose a channel for message routing because of limited information about network condition. The short-sighted decisions may cause unnecessary waits at the next clock cycle if the adaptive routing algorithm chooses a channel which has high probability of message block at the next clock cycle. In this thesis, look-ahead routing scheme is introduced to provide better performance for conventional adaptive routing algorithms. The look-ahead scheme as an adaptive routing algorithm makes longer-sighted decision to avoid possible blocks at the next clock cycle. This thesis also simulates the XY, the West-First, and the Double-Y channel routing algorithms, which are deterministic, partially-adaptive and fully-adaptive, respectively, in a 16 x 16 mesh network. Their performances are compared and analyzed. The simulation includes the examination of look-ahead effect for the West-First and the Double-Y channel routing algorithms. / Graduation date: 1996

Graduation date: 1993

TASKMASTER is an experimental microcontroller node of a real-time control oriented network which was proposed by James H. Herzog and Tinggui Zhang to demonstrate the feasibility of a task oriented control structure in performing distributed control actions. This study is a continuation of research involving the TASKMASTER network. A high performance microcontroller the 32-bit Motorola MC68332 has been used in this study to implement a node of the TASKMASTER network. Use of the MC68332 with its powerful peripheral subsystems offers significant scope for improvement of the overall performance of the network in addition to strengthening its control processing capabilities. An 8-bit microcontroller the Intel 8052 has also been used to implement a node of the network. A high-level language C has been used for coding of the operating system of the network which previously has been coded in assembly. In addition to being more readable, use of a high-level language offers other significant advantages such as portability, smaller code development time and code debugging time and the ability to compare different microcontrollers on a common basis. A performance analysis and comparison between the two microcontrollers used and the language used in coding them was also performed using performance measures designed as part of this study. / Graduation date: 1994

Packet switched networks offer a particularly challenging research subject to the control community: the dynamics of a network buffer, their simplest component, are nonlinear and exhibit a saturation effect that cannot be neglected. In many practical cases, networks are made up of the interconnection of a large number of such basic elements. This gives rise to high dimensional nonlinear systems for which few general results exist today in the literature. Furthermore, these physical interconnections that may sometimes span a very long distance induce a transmission delay and the queues in intermediary nodes induce a buffering delay. Finding a model able to both take into account as much of this complexity as possible while being simple enough to be analysed mathematically and used for control purposes is the first objective of this thesis. To accomplish this goal, a so-called "fluid-flow model" based on fluid exchange between buffers is presented. Neglecting the transmission and propagation delays, this model concentrates on the dynamics of the buffer loads and is particularly well suited for a mathematical analysis. Throughout the work, a systematic system point of view is adopted in an effort to perform a rigorous analysis using tools from automatic control and dynamical systems theory. This model is then used to study a feedback control law where each node receives state information from its directly connected neighbours, hence referred to as hop-by-hop control. The properties of the closed-loop system are analysed and a global stability analysis is performed using existing results from the compartmental and cooperative system literature. The global mass conservation typically ensured by end-to-end control protocols is studied in the last chapter using, once again, a compartmental framework. Finally, a numerical study of a strategy combining the end-to-end and the hop-by-hop approaches is presented. It is shown that problems encountered with hop-by-hop control may then be successfully alleviated.

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Thesis (Ph. D.)--University of Florida, 2001. / Title from first page of PDF file. Document formatted into pages; contains xi, 86 p.; also contains graphics. Vita. Includes bibliographical references (p. 82-85).

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 255-261).