Analysis of the Reliability of a Nationwide Short Message Service
SMS has been arguably the most popular wireless data service for cellular networks. Due to its ubiquitous availability and universal support by mobile handsets and cellular carriers, it is also being considered for emergency notification and other mission-critical applications. Despite its increased popularity, the reliability of SMS service in real-world operational networks has received little study so far. In this work, we investigate the reliability of SMS by analyzing traces collected from a nationwide cellular network over a period of three weeks. Although the SMS service incorporates a number of reliability mechanisms such as delivery acknowledgement and multiple retries, our study shows that its reliability is not as good as we expected. For example the message delivery failure ratio is as high as 5.1% during normal operation conditions. We also analyze the performance of the service under stressful conditions, and in particular during a "flash-crowd" event that occurred in New Year's Eve of 2005. Two important factors that adversely affect reliability of SMS are also examined: bulk message delivery that may induce network-wide congestion, and the topological structure of the social network formed by SMS users, which may facilitate quick propagation of viruses or other malware.

title: Characterizing flows in large wireless data networks
abstract: Several studies have recently been performed on wireless university campus networks, corporate and public networks. Yet little is known about the flow-level characterization in such networks. In this paper, we statistically characterize both static flows and roaming flows in a large campus wireless network using a recently-collected trace. For static flows, we take a two-tier approach to characterizing the flow arrivals, which results a Weibull regression model. We further discover that the static flow arrivals in spatial proximity show strong similarity. As for roaming flows, they can also be well characterized statistically.We explain the results by user behaviors and application demands, and further cross-validate the modeling results by three other traces. Finally, we use two examples to illustrate how to apply our models for performance evaluation in the wireless context.

title: A study of the short message service of a nationwide cellular network
abstract: In recent years, cellular networks have experienced an astronomical increase in the use of Short Message Service (SMS), making it a popular communication means for inter-personal as well as content provider-to-person usage. Yet little is known about the traffic and message user behavior in real SMS systems. In this paper, we present a measurement study of SMS based on traces collected from a nationwide cellular carrier during a three-week period. We characterize message traffic at both the message level and the conversation thread level. We also examine the "store-and-forward" mechanism of SMS and present initial measurements on how messages are actually delivered.

title: An architectural infrastructure and topological optimization for end system multicast
abstract: Although IP-multicast has been proposed and investigated for the some time, there are major problems inherent in the IP-multicasting technique, for example, scalability problems, difficulty to allocate a globally unique multicast address, complexity to support higher level features such as reliable data transfer congestion/flow control and security, and more importantly, deployment problem due to architectural changes to core routers. Recently, end-system multicast (ESM) has been proposed as an alternative solution so that multicasting services can be quickly deployed. In this paper we consider the "architectural" and "optimization " issues on designing an ESM-tree. Specifically, we present a distributed algorithm on how to create and maintain an ESM-tree. We also propose a distributed algorithm to perform a tree optimization (TO) so that an ESM-tree can dynamically adapt to the changing network condition (e.g., drop in transfer bandwidth) so that nodes can receive the multicast data more efficiently. The propose distributed algorithm has the theoretical properties that at all times, a tree-topology can be maintained and that any node joining, leaving, as well as any tree optimization operation will not "partition" an ESM-tree. Therefore, our work can be used to provide an efficient architectural infrastructure for ESM services. We have implemented a prototype ESM system and carried out experiments to illustrate the effectiveness and performance of our ESM optimization protocol.

title: End system multicast: an architectural infrastructure and topological optimization
abstract: Although IP multicast has been proposed and investigated for years, there are major problems inherent in the IP multicasting technique, e.g. difficulty to scale up the system, difficulty in allocating a globally unique multicast address, complexity in supporting higher level features such as reliable data transfer and congestion/flow control, more importantly, difficulty to deploy on the current Internet infrastructure due to necessity to change many core routers. Recently, end-system multicast (ESM) has been proposed as an alternative solution so that multicasting services can be quickly deployed. In this paper, we consider the'architectural' and 'optimization' issues on designing an ESM-tree. Specifically, we present a distributed algorithm on how to create and maintain an ESM-tree. We propose a distributed algorithm to perform tree optimization (TO) so that an ESM-tree can dynamically adapt to the changing network condition (e.g. drop in transfer bandwidth) so that the nodes within an ESM-tree can receive data more efficiently. The distributed algorithm has the important theoretical properties that at all times, a tree topology can be maintained and any node joining, leaving, as well as any TO operation will not 'partition' the underlying ESM-tree. Therefore, our work can be used to provide an efficient architectural infrastructure for ESM services. We have implemented a prototype ESM system and carried out experiments to illustrate the effectiveness and the performance gains of our ESM optimization protocol.

title: A Distributed Approach to Musical Composition
abstract: Current techniques for automated composition use a single algorithm, focusing on one aspect of musical generation. In our system we make use of several algorithms, distributed using an agent oriented middleware, with each specialising on a separate aspect of composition. This paper describes the architecture and algorithms behind this system, with a focus on the agent framework used for implementation. We show early results which encourage a future application of this framework in automated music composition and analysis.

title: 76-Space analysis of grey matter diffusivity: Methods and applications
abstract: Diffusion Weighted Imaging (DWI) and Diffusion Tensor Imaging (DTI) are widely used in the study and diagnosis of neurological diseases involving the White Matter (WM). However, many neurological and neurodegenerative diseases (e.g., Alzheimer's disease and Creutzfeldt-Jakob disease) are generally considered to involve the Grey Matter (GM). Investigation of GM diffusivity of normal aging and pathological brains has both scientific significance and clinical applications. Most of previous research reports on quantification of GM diffusivity were based on the manually labeled Region of Interests (ROI) analysis of specific neuroanatomic regions. The well-known drawbacks of ROI analysis include inter-rater variations, irreproducible results, tediousness, and requirement of a priori definition of interested regions. In this paper, we present a new framework of automated 76-space analysis of GM diffusivity using DWI/DTI. The framework will be evaluated using clinical data, and applied for study of normal brain, Creutzfeldt-Jakob disease and Schizophrenia.

title: Design patterns for games
abstract: Designing a two-person game involves identifying the game model to compute the best moves, the user interface (the "view") to play the game, and the controller to coordinate the model and the view. A crucial task is to represent the algorithms used in their highest abstract forms. This can prove to be a difficult and subtle endeavor. It is made easier however by the use of good object-oriented (OO) design principles to help maintain a high level abstract viewpoint during the design process. The state pattern is used to represent the game board and is coupled with the visitor pattern to provide state-dependent, variant behaviors. The min-max algorithm and its variants are implemented as the strategy pattern, which allows flexible and extensible computational capability. Careful analysis is performed to properly abstract the interactions between the model and the view. The command design pattern is used to provide callback services between the model and the view. Leading students through this design process enables them to learn algorithms and architectures that easily scale to full-sized applications.

title: Stability Analysis of RED Gateway with Multiple TCP Reno Connections
abstract: It has been observed that a bottleneck random early detection (RED) gateway becomes oscillatory when regulating a flow in multiple TCP connections. The stability boundary of the TCP-RED system depends on various network parameters, making the adjustment of the RED gateway a difficult task. Based on a fluid-flow model, analytical conditions were formulated that describe the stable boundary of the RED gateway depending on the number of TCP Reno connections. The proposed model accurately generates a stability boundary surface in a four dimensional space, which facilitates the adjustment of parameters for stable operation of the RED gateway. The accuracy of the analytical results has been verified using the ns-2 network simulations.

title: Fast analytical approach to finding steady-state waveforms for power electronics circuits using orthogonal polynomial basis functions
abstract: This paper describes a general analytical procedure for steady-state waveform analysis of power electronics circuits using orthogonal polynomials. The proposed method exploits the time-domain piecewise property of power electronics circuits as well as the orthogonality of certain polynomials in order to maximize the accuracy and computational efficiency. This new analytical approach can provide a fast means to obtain improved and more robust solutions of steady-state waveforms of power electronics circuits