Object Oriented Frameworks for Multimedia, Mobile Applications
AgentOS is a distributed systems framework based on mobile agents for next-generation applications such as groupware and mobile computing, running over the heterogeneous next-generation Internet. AgentOS is built on the philosophy that mobile agents can be viewed as the fundamental programming unit for distributed applications, and that such a system composed of mobile agents requires a middleware framework to support mobile agent execution, multi-agent management, and inter-agent communication. AgentOS is built using the Java programming language, is thus available on all Java-enabled platforms. Current areas of focus include flexible, secure inter-agent communication, mobile code security, reliable multicast for agent groups, and behavior modeling, analysis, and simulation of mobile agent systems.
ADAPTIVE Communication Environment (ACE) is an object-oriented framework that implements many core design patterns for concurrent communication software. ACE provide a rich set of reusable C++ wrappers and framework components that perform common communication sofware tasks across a range or operating system platforms. It simplifies the development of object-oriented network applications.
ACE has been widely accepted and is used by a number of univeirsities, research institutions and private companies. For instance, an ACE mailing currently holds over 1,200 members. ACE has been ported to a wide range of uniprocessor and multi-processor OS platforms including Win32, most versions of Unix, VxWorks, Chorus, LynxOS and MVS OpenEdition. There is also a Java version of ACE.
AudioActive used the ACE library to broadcast live audio from the 1997 Grammy awards.
The ACE was developed by Dr. Suda and Dr. Schmidt, while he was a graduate student at Univ. of Cal., Irvine. Dr. Schmidt is now an Associate Professor with the Washington University in St. Louis.
Real Time Video Multicast
Network architectures that can efficiently transport high quality, multicast video are rapidly becoming a basic requirement of emerging multimedia applications. The main problem complicating multicast video transport is variation in network bandwidth constraints. An attractive solution to this problem is to use an adaptive, multi-layered video encoding mechanism. In this paper, we consider two such mechanisms for the support of video multicast; one is a rate-based mechanism that relies on explicit rate congestion feedback from the network, and the other is a credit-based mechanism that relies on hop-by-hop congestion feedback. The responsiveness, bandwidth utilization, scalability and fairness of the two mechanisms are evaluated through simulations. Results suggest that while the two mechanisms exhibit performance trade-offs, both are capable of providing a high quality video service in the presence of varying bandwidth constraints.
Internet Research
End-to-end congestion control is an important reason why the Internet is robust, scalable and simple to use. Unfortunately, purely end-to-end congestion control algorithms are incapable of preventing the unfair bandwidth allocations and congestion collapse caused by unresponsive applications, which are becoming increasingly prevalent in the Internet. In this paper, we propose a new mechanism called Fair Queueing with Feedback-based Policing (FQFP) to address unfair bandwidth allocation and congestion collapse in the Internet. We demonstrate the promise of FQFP through simulations and suggest ways in which FQFP may leverage the mechanisms currently being developed in the context of differentiated services. The FQFP mechanism is compliant with the Internet philosophy of keeping router implementations simple and pushing complexity toward the edges of the network.
Network Applications
DICE (Distributed, Interactive Courseware Environment)
The Distributed and Interactive Courseware Environment is a system for large-scale delivery of multimedia video- and hypertext-based courseware to school sites without high-speed network connectivity using satellite technologies. DICE is being developed on a test bed consisting of (1) a network-resident architecture supported by a high-speed ATM WAN backbone, (2) a classroom-resident architecture consisting of PC LANs in participating school classrooms, and (3) a satellite communications infrastructure serving as a communications link between the network- and classroom-resident architectures. Based on real-time classroom performance evaluation, the network-resident architecture incrementally and adaptively delivers courseware segments to the receiving classroom-resident architecture via satellite.
Wireless and Ad Hoc Networks
Adaptive Bandwidth Reservation for Wireless Networks
This project addresses Quality-of-Service (QoS) guarantees for high-speed wireless environments and investigates an admission control scheme based on adaptive bandwidth reservation to provide QOS. The proposed scheme allocates bandwidth to a connection in the cell where the connection request originates and reserves bandwidth in all neighboring cells. When a user moves to a new cell and a hand-off occurs, reserved bandwidth is used to support a hand-off connection; bandwidth is reserved in the new neighboring cells; and bandwidth reserved in mcells which are no longer adjacent is released. The amount of bandwidth to reserve is dynamically adjusted, reflecting the current network conditions.
Multi-hop Ad-hoc Wireless Networks
Ad-hoc networks are self-organizing multi-hop wireless networks. Since no fixed infrastructure, such as base stations or routers, is required, ad-hoc networks are rapidly deployable networks. All mobile hosts are embedded with packet forwarding capabilities. Typical applications of ad-hoc networks are outdoor special events such as conferences, concerts and festivals; regions with no infra-structure; emergencies and natural disasters; and military maneuvers. We have been investigating issues such as medium access control, routing an location management, scheduling policies, security and privacy. A multicast multi-path routing protocol as well as an asymmetric routing protocol have been proposed.
ATM Networks
Data Service over ATM Networks
a. TCP over ATM
Data traffic will be the dominant traffic type on ATM networks in the near future. The performance of data traffic over ATM is dependent on several factors. Of particular concern are the TCP flow control protocol and its interaction with ATM's Available Bit Rate (ABR) protocols, such as ERICA, EPRCA and QFC. Current research investigates the performance of Internet type TCP traffic over ATM comparing various ABR schemes.
The transprt of data traffic over ATM msut provide for support of IP datagram routing either on the edges of the ATM network or within the ATM network. Within the ATM network, connectionless servers integrating IP routing and ATM switching equipment is one possible solution. Current research investigates the dimensioning of connectionless servers, selective cell discarding and cell forwarding techniques and connectionless server architectures.
Performance Modeling and Analysis of Computer Networks
Self-Similar Traffic: Modeling and Analysis
Recent measurements have revealed both data and video traffic over ATM exhibit self-similar property. The self-similar property is not adequately captured by the conventional Markov traffic models and often yield queueing behavior such as heavy-tailed or subexponential queue length distribution. This project models the fractal (or self-similar) nature of ATM traffic and investigates the causes, effects, and control of self-similarity in ATM traffic.
On-Line Sensitivity Queueing Analysis
In this project, a new on-line sensitivity queueing analysis which exploits a proportional relationship between the steady states probabilities of the nomial system and those of the perturbed systems is developed. Through the proportional relationship, various performance measures of the perburbed systems may be effectively and accurately estimated from the observation of a single path of the nomial systme. The on-line sensitivity queueing analysis is thus suitable for applications in real-time control sytems.