Mon-Song Chen

A media-access protocol for packet-switched wavelength division multiaccess metropolitan area networks

A dynamic time-wavelength division multiaccess protocol (DT-WDMA) is proposed for metropolitan-sized multichannel optical networks employing fixed wavelength transmitters and tunable optical receivers. Control information is sent over a dedicated signaling channel and data are sent over channels owned by the transmitters. Time is divided into slots on each channel and slots on the control channel are further split into mini-slots. Fixed time-division multiaccess (TDM) is used within each slot on the control channel. Transmitters indicate their intention to transmit a packet by transmitting the destination address during their appropriate mini-slot in the control channel and then transmit their packet in the next slot on their data channel. Receivers listen to the control channel and tune to the appropriate channel to receive packets addressed to them. A common but distributed arbitration algorithm is used to resolve conflicts when packets from many transmitters contend for the same receiver. Each receiver executes the same deterministic algorithm to choose one of the contending packets. Each transmitter uses the same algorithm to determine the success or failure of its packet. >

A multimedia desktop collaboration system

Desktop multimedia conferencing, which can enhance the quality of collaboration between remote participants, is considered. The architectural and implementation issues involved in the design of such an application are discussed. A prototype desktop conferencing system is presented. It provides a multiparty collaborative environment which integrates high-quality video and audio with a shared workspace manager. Some of the distinguishing features of this system are the flexibility to support various types of collaboration, full-motion (30-frames/s) video, support for multiple video windows, and unconstrained audio. The shared workspace manager allows existing X-windows applications to be used concurrently by the participants in the conference.<<ETX>>

POPSMAC: A Medium Access Protocol for Packet- Switched Passive Optical Networks using WDMA

Abstmct-A simple medium access protocol, POPSMAC, based on using both tunable transmitter and tunable receiver is proposed and analyzed in this paper. The feasibility and architectures of using this protocol to establish a passive optical packetswitched metropolitadwide area network (MAN/WAN) are also investigated. In POPSMAC, each transmission consists of a small header packet over the signaling wavelength of the destination receiver, and a data packet over the distinct wavelength of the transmitter. The receiver is tuned to the transmitter wavelength after successfully received the header packet and knowing there is an incoming data packet. Both connection-oriented and datagram traffic can be supported by this protocol. Performance study shows that the maximum average throughput of each transmitter or receiver approaches 50% with small header packet size (as compared to the data packet). This performance is achieved without requiring network synchronization and is thus suitable to MANNAN applications in which network synchronization is difficult.

Gain equalization in metropolitan and wide area optical networks using optical amplifiers

Optical metropolitan/wide area networks with arbitrary topology usually require optical amplifiers to compensate for the fiber attenuation and splitting loss introduced by the star couplers. An amplifier placement algorithm using spanning tree traversal is proposed. Using this algorithm, the authors show that it is possible to equalize the arriving optical signals at each receiver of the network. This technique enhances other static or dynamic gain equalization schemes and presents a more effective and robust solution to the power equalization problem for WDMA networks with arbitrary topology.<<ETX>>

Video bandwidth allocation for multimedia teleconferences

To ensure the quality of a multimedia teleconference, it is essential that sufficient bandwidth be allocated for its use. In this paper a conference traffic model is formulated and link level and conference level congestion measures are derived. Motivated by the advantages of sharing transmission resources in TASI related voice communication systems, an analogous transmission policy for conference videos is proposed. The quantification of conference traffic also enables us to set an admission policy so that the network can accommodate as many conferences as possible without violating conference quality constraints. >

Mixing and playback of JPEG compressed packet videos

Video mixing, which is the simultaneous display of multiple motion videos received from multiple independent sources across a packet switched network, is addressed. A straightforward approach, which performs mixing at the pixel level, is analyzed and found undesirable because of the requirements of large amount of expensive memory and decompression capacity. A technique that performs direct mixing of JPEG compressed data is introduced. An efficient structure based on this technique, which needs only a frame worth of buffering and decompression regardless of the number of video windows and their sizes, is presented. Packet video playback is discussed, and two simple heuristics are proposed.<<ETX>>

System support for computer mediated multimedia collaborations

Future advances in networking and storage will enable a wide spectrum of computer mediated structured collaborations among individuals. In this paper, we present a model that can capture diverse types of structured collaborations. The model combines both efficiency and power via a hierarchy of three abstractions, at the lowest level of which are streams for media communication modulated by access rights of participants within collaborations. The higher two levels of abstractions are sessions, which represent collections of semantically related media streams, and conferences, which represent temporally related sequences of sessions. Using these abstractions, the model supports unification of both synchronous and asynchronous collaborations, sophisticated access control, and intra-group and inter-group collaborations, yielding a powerful set of building blocks for constructing multimedia applications and a rich environment for carrying out structured multimedia collaborations.

An integrated algorithm for probabilistic protocol verification and evaluation

An integrated approach is presented to probabilistic verification and performance evaluation of a communication protocol. The approach, following best-first rules, generates, verifies, and evaluates states and transitions in a global reachability graph. A new recursion is found to reduce the computational complexity of the procedure from O(n/sup 4/) to O(n/sup 2/m) in generating n states and exploring m transitions. This procedure (1) is computationally very efficient; (2) provides interesting performance and reliability measures such as mean-time-to-unknown, which is the average operation time before any unchecked scenario occurs, and protocol throughput, and (3) takes important reliability measures as its stopping criteria.<<ETX>>

Software architecture of DiCE: a distributed collaboration environment

Recent advances in network technology has significantly increased the network bandwidth as well as enriched the set of network functions, enabling a rich set of computer assisted collaborations. DiCE (Distributed Collaborative Environment) is a multimedia collaboration environment that is being developed at the IBM T. J. Watson Research Center. The challenge of DiCE is to explore the advanced functionalities enabled by high speed networking and multimedia computing technologies to develop effective computer assisted systems that will significantly increase the productivity of collaborations. The main objectives of DiCE are, first, to design an efficient multimedia collaboration environment, and then to prototype the design as the base for the development of a workstation based, hub-free (fully distributed) multimedia conferencing system.

Designing a distributed collaborative environment

The features of DiCE (distributed collaborative environment) are described in terms of its flexibility in supporting various types of collaborations, and an overview of the collaboration management in DiCE is given. A collaboration is defined as an aggregation of conferences, and the functionality of connection management necessary for instantiating conferences is discussed. The networking environment, and design principles are described. The software architecture of the conferencing system is outlined, the hardware environment is described, and results are given.<<ETX>>