Showing papers by "Jon Crowcroft published in 1991"

A new congestion control scheme: slow start and search (Tri-S)

Abstract: Recently there have been many measures proposed to tackle the problem of congestion in computer networks. In this paper, we first analyze some of the measures and then present a new scheme in which the optimal operating point is obtained by evaluation of throughput gradient and resource sharing is adjusted only at the beginning and the end of a connection. Simulation results show that the scheme converges to an optimal operating point quickly and fairly.

Specification, design, and implementation of an interactive conferencing system

Abstract: The specification, design and implementation of a text-based multiway interactive conferencing program are presented. The system is described in three parts: the user interface, the distribution mechanism for users' contributions, and the floor control scheme. One specific system of floor control using the formal specification language Z is specified. The separation of the distributed operation of the exchange of speech in the conference from the floor control mechanism has led to the possibility of implementing an open floor conferencing system, and then adding floor control. The only operations necessary to add floor control are those required to allow or prevent use of a channel from each user to any other. The extra state incurred in the conference server processes is the 2-D matrix of user by user channels, with each entry showing allowed/disallowed. >

Multimedia teleconferencing over international packet switched networks

Abstract: A description is presented of the current configuration and projected future work on the world's first multimedia teleconferencing system. The communications architecture (by which the authors refer to the protocols and supporting network management system) is based around the DARPA Internet Protocol suite, but with certain enhancements to support real time traffic. The CODEC runs a standard bitstream encoding of video, and this is packetized by the PC. However, this is not sufficiently flexible a protocol to traverse the Internet. The stream protocol (ST) gateway then runs two further protocols to carry the video and voice: (1) packet video protocol (PVP) and (2) voice traffic protocol (VT). Each of these is tuned to the special requirements of video and voice. To carry these in a reasonably consistent fashion, the gateways then run the ST. The performance of the system is limited mainly by the bandwidth of the first few hops of the path. >

International links for research collaboration

Abstract: The European and US Research Communities have been linked for fifteen years by various communication channels. Recently, it has been decided to upgrade some of the connections to higher speed links. These links can support not only the conventional services like terminal access, file transfer, electronic mail and directory services, but also video conferencing using compressed video. Moreover the channels are being provided by different agencies with different missions and support different protocols and services. Some of the technical aspects of the links, and the policy and administrative questions which have had to be resolved, are discussed in this paper; there is particular emphasis on the UK-US link, but the discussion includes extension to other European countries. We then discuss at length the provision of video conferencing facilities over the UK-US channel, and consider how such facilities could be provided on a broader European basis.