Research : Robust Audio Tool

Orta — an Overlay for Real Time Applications

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We present Orta, a new peer-to-peer network overlay protocol intended for use with interactive real-time conferencing applications. The implementation is presented as a reusable software library, that is not tied to any existing application. One application, the UCL Robust-Audio Tool, is modified to use this library rather than IP multicast as a proof-of-concept implementation. We present the protocol design, along with evaluation results describing the performance of the overlay, with focus on its usefulness for real-time applications.

Stephen Strowes — Peer-to-Peer Audio Conferencing

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Congratulations to Stephen Strowes on submitting his MSci dissertation on Peer-to-Peer Audio Conferencing. This dissertation proposes a new overlay multicast service, Orta, that can be used for real-time group conferencing. As a proof-of-concept, the Robust-Audio Tool has been modified to use Orta in place of IP multicast. Stephen presents implementation details and evaluation results detailing the characteristics of the overlay, with some focus on its usefulness for real-time applications.

Robust Audio Tool

Posted on in category rat

This page is retained for historical interest only. The main Robust Audio Tool page is maintained at University College London.

RAT screenshot

The Robust Audio Tool (RAT) was one of the earliest voice-over-IP applications. It pioneered the use of forward error correction in VoIP systems, and furthered development of receiver-based loss concealment algorithms, adaptive playout scheduling, and RTCP-based diagnostics for multicast conferencing [more...]. RAT was widely used for distance education, and for e-Science as part of the AccessGrid toolkit.

RAT required no special features for point-to-point communication, just a network connection and a soundcard. For multiparty conferencing RAT used IP multicast and therefore all participants had to reside on a multicast capable network. RAT was based on, and influenced the development of, IETF standards, using RTP running over UDP/IP as its transport protocol, and conforming to the RTP profile for audio and video conferences with minimal control.

RAT featured a range of different rate and quality codecs, receiver based loss concealment to mask packet losses, and sender based channel coding in the form of redundant audio transmission. It offered better sound quality relative to the network conditions than most audio tools available at the time. It also featured encryption to keep conversations private. [more...]

Various versions of RAT ran on a range of platforms including FreeBSD, Linux, Solaris and Windows 95 or later. The source code is available for download under a BSD-style license.

Acknowledgments

Project Management:
Vicky Hardman, Peter Kirstein, Angela Sasse
RAT 4 Development Team:
Orion Hodson, Colin Perkins
RAT 3 Development Team:
Vicky Hardman. Orion Hodson, Isidor Kouvelas, Colin Perkins
RAT 1 & 2 Hackers:
Vicky Hardman, Isidor Kouvelas
Additional Contributions:
Julian Cable, Jon Crowcroft, Mark Handley, Eric Fox, Geir Harald Hansen, Darren Harris, Tristan Henderson, Marcus Iken, Jerry Isdale, Roman Kurmanowyts, Bob Lindell, Jim Lowe, Dimitrios Miras, Bob Olson, Piers O'Hanlon, Dimitris Terzis, Socrates Varakliotis, Terje Vernly, Michael Wallbaum, Anna Watson

The RAT project was funded by the EPSRC under the Multimedia and Networked Applications Programme, Bristish Telecommunications plc, and the European Commision (Telematics Applications Programme, Research Sector, Project 1007; Telematics for Research Programme, Project 4007).  It benefited from hardware donations by Hewlett-Packard and Sun Microsystems, and software donations by Microsoft.

Portions of the application were developed under other projects at UCL. The 3D rendering and lip synchronization support was contributed by the MEDAL project, and layered audio support was contributed by the JAVIC project.