Research Interests


Photonic switching, optical interconnection networks, reconfigurable systems and parallel algorithms.

All-optical networks, WDM/TDM communications, network architectures, control and management.

Advanced networking and internetworking issues such as IP over WDM and next generation wireless system.




Optical Burst Switching

There are two basic drivers for optical internetworks. One is the explosion of the multimedia (mainly data) traffic over the Internet, especially the World-Wide-Web, which as many discovered recently, can be bursty at all time scales and various multiplexing levels. The other is the continuing advances of WDM optical networking technologies, which offer many opportunities to streamline both software (protocols) and hardware (electronic equipments) for reduced latency and cost.

The objective of this research is to explore a novel switching paradigm for WDM (Wavelength Division Multiplexed) optical networks, called optical burst switching (OBS). OBS uses an offset time between a control (or set-up) packet and its corresponding data burst when making one-way delayed reservation, which facilitates all-optical data transfers and distinguishes it from other one-way reservation schemes and label/tag switching schemes. By combining the best of the coarse-grained optical circuit switching (via wavelength routed lightpaths) and the fine-grained optical packet/cell switching, while avoiding their shortcomings, OBS can efficiently support applications requiring many short-lived (or bursty) sessions during which a substantial amount of data needs to be transferred at a high bit rate and with a low end-to-end latency. More importantly, it will help realize the vision of building a flexible, efficient and bandwidth-abundant fiber-optic internetworking infrastructure capable of providing ubiquitous services through TCP/IP (as well as ATM and other existing and future protocols).

In this project, we will focus on the design and performance evaluation of efficient OBS protocols that can reduce burst dropping probability, and support flow and congestion control as well as multicasting, priority and fault-tolerant routing. We will also study how upper layer protocols (e.g. IP) interact with OBS, investigate related optical-layer control and management issues such as resource provisioning, protection and restoration, and in addition, compare OBS with other burst switching and lable/tag switching techniques. Finally, we will examine the synchronization problem and the cost-effective designs of the interface between the upper layers and the optical layer as well as the designs of the WDM switches.

Acknowledgment and Disclaimer: This material is based upon work supported by the National Science Foundation under Grant No. ANI-9801778. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

For more information on this project, please follow the link to OBS home page.

iCAR: An Integrated Cellular and Ad-hoc Relaying System

Ever increasing data traffic and limited capacity are major causes for congestion in current cellular systems. Adding to the problem of limited capacity in existing wireless systems is the presence of unbalanced traffic. Specifically, some cells may be heavily congested (called hot spots), while the other cells still have available DCH's. In other words, even though the traffic load doesn't reach the maximum capacity of the entire system, call blocking and dropping may occur due to localized congestion. Since the locations of hot spots vary from time to time (e.g. downtown areas in Monday morning, or amusement parks in Sunday afternoon), it's difficult, if not impossible, to provide the guarantee of a sufficient amount of resources in each cell in an cost-effective way. Other problems in cellular systems include the presence of shadows where MH's cannot receive strong enough signals, and the need for MH's to transmit at high power when they are farther away from base stations thus limiting their battery life.

In this work, we study the important problem of how to evolve from the existing, heavily-invested cellular infrastructure to wireless systems that scale well with the number of mobile hosts. We propose to integrate the cellular infrastructure with modern Ad-hoc relaying technologies to achieve dynamic load balancing among different cells in a cost-effective way. The basic idea of the proposed iCAR (integrated Cellular and Ad-hoc Relay) system is to place a number of Ad-hoc Relay Stations} (or ARS) at strategic locations, which can be used to relay signals between MH's and base stations. By using ARS's, it's possible to divert traffic in one (possibly congested) cell to another (non-congested) cell. This helps circumvent congestion, and make it possible to maintain (or hand-off) calls involving MH's (especially a high-priority call) that are moving into a congested cell, or to accept new call requests involving MH's that are in a congested cell. Other benefits include enhanced coverage and reliability (or fault-tolerance) of the system, and potential improvement in MHs' battery life and transmission rate.

Acknowledgment and Disclaimer: This material is based upon work supported by the National Science Foundation under Grant No. NSF/ITR ANI-0082916. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

For more information on this project, please follow the link to iCAR home page.

Mobile Ad Hoc and Sensor Networks

Although this is a relatively new area for us, we have published over two dozen papers in journals and conferences on ad hoc and sensor networks. More detailed desription to come.
Dynamic Proximity Networking





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