Research Overview [Talks] [Publications] [Students]

Throughout my academic career, I have been actively engaged in two main research thrusts: Scalable Internet Protocols and Systems and Real-Time Embedded Systems and Networks. In the past, I have also dabbled in other areas, ranging from parallel computing to robotics!

• Scalable Internet Protocols and Systems: My interest in this subject stems from the eminent need for scalable services to match the explosive growth in availability and use of the Internet. My work in this area is conducted within the WING research group, which has as its goal the improvement of Web and Internet protocols and systems based on measurement, analysis, and careful redesign. In that regard, with collaborators, I undertook one of the first studies on the effectiveness of caching in the Web -- a study that led to a number of projects under the Oceans research initiative, including eager content dissemination (my 1995 papers on this topic advanced the CDN "push" content distribution model adopted years later by the likes of Akamai, SightPath, Sandpiper, Digital Island, and Speedera), speculative prefetching, and the characterization of Web traffic self similarity (my 1996 paper on this with Mark Crovella is among the most cited on that subject) and reference locality properties in the Web. Another one of WING's early projects was Commonwealth, a full-scale implementation of a number of our techniques in the context of an experimental high-performance, low-cost distributed scalable Web server. Ideas from that project catalyzed in a patent on Distributed Routing, which led to a successful startup, now part of Network Appliance Inc. As a follow-up to that project, and in light of the unique perspective that a large number of servers may possess about network conditions (e.g., available paths, traffic conditions, etc.), in the Mass Servers Project, we investigated the use of end-to-end inference techniques to build caricatures of the underlying network cloud--caricatures that could be used to optimize the performance of content delivery protocols through better utilization of network resources. Alternatively, in the ITM Project, we investigated the use of traffic managers--special network elements strategically placed in the Internet--to complement end-to-end approaches through the use of novel in-network and overlay control strategies to reducing traffic burstiness and improving network utilization. Our investigation of traffic control approaches led us to the identification of a major, previously unrecognized vulnerability of complex systems such as the Internet, namely the ability of an adversary to exploit the dynamics of adaptation mechanisms that are invariably incorporated in systems and networks (e.g., admission control, congestion control, adaptive routing, load balancing, power management, etc.) We coined exploits of this nature Reduction of Quality (RoQ) attacks, which we investigated in a number of settings. The adversarial behaviors exemplified in RoQ could be considered extreme, in the sense that the goal is to maximize the damage to a system. More practically, non-altruistic behaviors are likely to be "selfish" as opposed to "adversarial". This has led us to investigate the implication of selfish behavior in a number of networking and distributed systems settings, and to design protocols that leverage (as oppose to combat) such selfish behaviors.  

• Real-Time Embedded Systems and Device (Sensor and Actuator) Networks: My interest in this line of research stems from the fact that for most of the applications of computing and networking  that matter (medical devices, power grids, automotive control, financial trading systems, air-traffic control systems, robotics, and process control, just to name a few), worst-case performance, as opposed to average performance, is key. For such applications, building a system that minimizes the average response time or maximizes the average throughput is useless, if such a system ends up missing critical deadlines, for example. As it turns out, if one focuses on worst-case (as opposed to average) performance, most of the practices that are common in system and network design must be revisited. To that end, the BU Real-Time Computation and Communication Research Group that I founded and led since 1991 focused its early work on three main areas: Real-time communication protocols (e.g. TCP protocols over ATM networks), real-time databases (e.g. real-time concurrency control and admission control), and real-time programming languages and OS support (e.g. the TRA model, and the Cleopatra programming environment, statistical scheduling, and on load profiling in distributed real-time systems). Two of my currently active projects in this general area are the iBench Initiative, and the Sensorium Project. In the iBench Initiative, we have as our central goal the development of a rigorous discipline for the specification, programming, and maintenance of distributed networked applications, with a particular focus on Internet and video sensor network applications. In the Sensorium project, we aim to catalyze fundamental advances in image and video computing, network protocols, and resource management to deal with unique spatio-temporal constraints of sensor networks in general and of video sensor networks in particular. snBench is an example project pursued within the Sensorium infrastructure, in which we aim to design and implement  the means via which applications may (1) locate, monitor, and query Sensor Elements (SEs) and Computing Elelments (CEs) for services they support, and (2) initiate, control, or otherwise use such SE and CE services. In addition to supporting these functionalities, snBench aims to provide basic resource virtualization and management services for QoS support, including resource mapping and allocation to satisfy expressive QoS constraints in a distributed setting.