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.>

In this paper we present an address coding mechanism for multicast source routing packets in packet-switched networks. A simple algorithm for processing these address codes at intermediate output link adaptors is presented. It involves only the recognition of a particular link label at the front part of the address code and the stripping off of a front segment of the address code and so can easily be implemented in hardware. Recognizing that the recipients of a multicast packet very often need to respond to the source node, we designed the reverse path address code that allows an individual destination node to retrieve the reverse path address without searching the topology database and invoking any route computation program.>

Grouped Sweeping Scheduling was proposed in [1] as a general formulation of a class of disk arm scheduling schemes.This class includes, for example, the fixed-order and SCAN scheduling schemes.An optimum design was presented for the homogeneous case, i.e., when all multimedia streams have the same characteristics.In this paper we examine the more general situation in which a mixture of different format multimedia streams, with different characteristics, coexist on the disk.The emphasis is to present and prove a simple procedure for optimizing GSS in this heterogeneous situation.Finally, we discuss how GSS can be used in dynamic settings to support heterogeneous request streams.

Effectiveness of managing collaborations directly impacts the productivity of a group, and can be significantly improved through computer supported tools made available by the advent of high speed networks and multimedia computer systems. In this paper, we propose a framework for characterizing the requirements of person-to-person (e.g. telephony), person-to-person (e.g., collaboration with software agents), and service-to-service collaborations (e.g., business workflow applications). The framework defines a hierarchy of three abstractions, at the lowest level of which are conferences which characterize the access rights of participants involved in a collaborative endeavor. The higher two levels are activities, which represent a collection of semantically related conferences, and collaborations, which represent temporally ordered sequences of activities. We describe the mechanisms for establishing and controlling the progress of a wide variety of multimedia collaborations. The framework for modelling collaborations and the mechanisms for their instantiation described in this paper form the basis of DiCE—a DistributedCollaborative Environment being developed at the IBM T.J. Watson Research Center.

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. KEYWORDS ...

A new dynamic state exploration algorithm which is applied to probabilistic protocol verification and performance evaluation for synchronous as well as asynchronous models of a protocol is introduced. Properties of the technique are analyzed and proposed to further enhance the verification and evaluation procedure. The procedure based on this technique evaluates the importance of states in the dynamic course of a global reachability graph generation, explores only the most probable subset of states based on their dynamically computed importance, and quantifies and bounds important reliability and performance measures such as mean time to failure and turnaround time. Properties of the algorithm are demonstrated via the call establishment phase of the X.75 protocol.>

A method of flow control that requires very few buffers to be allocated at each node to virtual circuits (or sessions) that have to transverse many links is described. Transmissions are scheduled using the golden ratio policy of A. Itai and Z. Rosberg (1984). It is shown that the buffer requirements of a session grow at most logarithmically with the number of slots allotted to it. As an immediate consequence, intra-network delays are bounded.>

An address coding mechanism is presented for multicast source routing packets in packet-switched networks. A simple algorithm for processing these address codes at intermediate output link adaptors is presented. It involves only the recognition of a particular link label at the front part of the address code and the stripping off of a front segment of the address code and so can easily be implemented in hardware. Recognizing that the recipients of a multicast packet very often need to respond to the source node, a reverse-path address code is designed that allows individual destination nodes to retrieve the reverse path address without searching the topology database and invoking any route computation program.>

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.>

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.>

The problem of analyzing the thoughput of packet radio networks with realistic topologies is considered. We present an algorithm for the solution of this problem and show that both the memory requirements and running time of this algorithm in practice grow polynomially with the size of the problem. Although in theory both can grow exponentially in the worst case, we offer computational experience with the procedure and show that for realistic topologies where connectivity is related to distance, the rate of growth is quadratic in the number of links. Even for regular grids, which are pathological in their symmetry, the rate of growth is only cubic in the number of links. We thus conclude that the procedure is effective for realistic topologies with up to several hundred nodes.