The number and heterogeneity of traffic sensors are steadily increasing. A large part of the emerging sensors are measuring point speeds or travel times and in order to make efficient use of this data, it is important to develop methods and frameworks for fusion of point speed and travel time measurements in real-time. The proposed method combines a macroscopic traffic model and a non-linear filter with a new measurement model for fusion of travel time observations in a system that uses the velocity of cells in the network as state vector. The method aims to improve the fusion efficiency, especially when travel time observations are relatively long compared to the spatial resolution of the estimation framework. The method is implemented using the Cell Transmission Model for velocity (CTM-v) and the Ensemble Kalman Filter (EnKF) and evaluated with promising results in a test site in Stockholm, Sweden, using point speed observations from radar and travel time observations from taxis.

The LTE standard has been developed for high-bandwidth mobile access for today’s data-heavy applications. With broadband cellular available already from the UMTS system, users are expecting the LTE network to provide high quality communication. To ensure the quality and correctness of complex systems of LTE, it is important to evaluate the behavior of traffic on a LTE network in relation to UMTS. In this paper, LTE and UMTS measurements on video traffic were performed in a real environment, allowing for greater development, and understanding of network traffic performance.

The first study that investigates the characteristics of received probe packets and the reliability of bandwidth estimates when actively measuring the available bandwidth over radio interfaces in mobile communication networks is presented. Knowledge of available bandwidth is very useful in various contexts, e. g. in network management and adaptive streaming applications. Bandwidth measuring tools have so far primarily been designed for and evaluated in wired networks. However, such tools should also be examined in wireless networks since the use of, e. g., mobile broadband is rapidly increasing. The properties of wired and wireless links differ substantially, which affect the performance of the tools. We have made active-probing experiments over a high-speed downlink shared channel, which is used for High-Speed Downlink Packet Access (HSDPA) in the mobile communication technology UMTS, and over a forward traffic channel in CDMA2000 1xEV-DO. Both experiments were performed over commercial networks. They show that one cannot always expect uniform per-packet processing over the radio channel in mobile networks, which is expected by many probing tools. This reduces the reliability of the available-bandwidth estimates, however we suggest how this can be handled. Finally, the mobile-network measurements are compared to experiments performed in an IEEE 802.11 wireless LAN, where the radio channel does not create the same packet-processing behaviour. We also discuss the possibility of using the probe traffic for the purpose of identifying the communication technology at the bottleneck of the network path, assumed this is a wireless broadband link, by mapping specifications of standardised communication technologies to observed probe-traffic characteristics.

This thesis presents novel methods that are able to perform real-time estimation of the available bandwidth of a network path. In networks such as the Internet, knowledge of bandwidth characteristics is of great significance in, e.g., network monitoring, admission control, and audio/video streaming.

The term bandwidth describes the amount of information a network can deliver per unit of time. For network end users, it is only feasible to obtain bandwidth properties of a path by actively probing the network with probe packets, and to perform estimation based on received measurements. In this thesis, two active-probing based methods for real-time available-bandwidth estimation are presented and evaluated.

The first method, BART (Bandwidth Available in Real-Time), uses Kalman filtering for the analysis of received probe packets. BART is examined analytically and through experiments which are carried out in wired and wireless laboratory networks as well as over the Internet and commercial mobile broadband networks. The opportunity of tuning the Kalman filter and enhancing the performance by introducing change detection are investigated in more detail. Generally, the results show accurate estimation with only modest computational efforts and minor injections of probe packets.

However, it is possible to identify weaknesses of BART, and a summary of these as well as general problems and challenges in the field of available-bandwidth estimation are laid out in the thesis. The second method, E-MAP (Expectation-Maximization Active Probing), is designed to overcome some of these issues. E-MAP modifies the active-probing scheme of BART and utilizes the expectation-maximization algorithm before filtering is used to generate a bandwidth estimate.

Overall, this thesis shows that in many cases it is achievable to obtain efficient and reliable real-time estimation of available bandwidth by using light-weight analysis techniques and negligible probe-traffic overhead. Hence, this opens up exciting new possibilities for a range of applications and services in communication networks.

The knowledge of the present available bandwidth on a network path is essential in numerous contexts, such as network management and streaming applications. A network path nowadays often contains at least one wireless link. This is obviously true for mobile users having a wireless connection to the Internet through a laptop or mobile terminal. The existing tools for measuring end-to-end available bandwidth are developed and optimized for paths with only guided media links. Since the characteristics for wired links and radio links differ in many aspects, such as fluctuations in capacity and stability, the network tools need to be evaluated also for network paths containing wireless links. In this investigation we have performed experiments over a high-speed downlink UMTS channel. This makes the present paper unique in the sense that it evaluates and analyzes the applicability of available-bandwidth measurement tools over a radio interface in a wide-area mobile communication network. For the experiments, a commercial mobile network has been used. The measurements show that it is feasible to achieve reliable estimates under certain circumstances. However, some cases pose challenges which motivate further studies.

This paper presents a filter-based method BART (Bandwidth Available in Real-Time) for real-time estimation of end-to-end available bandwidth in packet-switched communication networks. BART relies on self-induced congestion, and repeatedly samples the available bandwidth of the network path with sequences of probe-packet pairs. The method is light-weight with respect to computation and memory requirements, and performs well when only a small amount of probe traffic is injected. BART uses Kalman filtering, which enables real-time estimation. It maintains a current estimate, which is incrementally improved with each new measurement of the inter-packet time separation in a sequence of probe-packet pairs. It is possible to tune BART according to specific needs. The estimation performance can be significantly enhanced by employing a change-detection technique. An implementation of BART has been evaluated in a physical test network with carefully controlled cross traffic. In addition, experiments have been performed over the Internet as well as over a mobile broadband connection. © 2009 Elsevier B.V. All rights reserved.

   This paper presents a method for improving filter-based network-state estimation by adding detection and estimation of sudden changes in the system state. This can be of benefit in various contexts, e.g. in network management and adaptive streaming applications. In particular, it is shown that the performance of available-bandwidth estimation can be significantly enhanced by employing change detection in conjunction with a filter-based estimator. The use of filtering makes it feasible to track the communication network state and to estimate selected properties in real-time. In addition, filter-based methods may be combined with change detection in order to overcome the trade-off regarding stable estimation versus speed of adaptation to change. We discuss filtering and change detection in general, and present the novel approach of combining the filter-based available-bandwidth estimator BART with the Generalized Likelihood Ratio (GLR) change-detection test, which estimates both the time and magnitude of changes.

This paper presents the concept of change detection for filter-based network-state estimation. This could be useful in various contexts; two examples are network management and adaptive applications. In particular, it is shown that the performance of available-bandwidth estimation can be significantly enhanced by employing a change-detection technique in conjunction with a filter-based estimator. By using filter-based approaches, it is possible to track the state of communication systems, and to estimate network properties in real-time. A virtue of filter-based methods is the ability to enhance the estimation performance by combining them with change detection. This makes it feasible to overcome the tradeoffs regarding speed of adaptation to changes versus stable estimation. We discuss filtering and change detection in general, and illustrate the power of this combination with the filter-based available-bandwidth estimator BART enhanced by the light-weight change-detection test CUSUM