Research : Robust Audio Tool
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 play-out scheduling, and RTCP-based diagnostics for multicast conferencing. 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 sound card. 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...]
This technical report presents 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.
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.
The Real-time Transport Protocol, RTP, provides quality of service feedback through reception reports sent alongside an audio/video stream. If the media stream is sent via IP multicast, it is possible for a third party to monitor these reception reports and display reception quality for all members of a multicast group. The RQM application performs such monitoring.
RAT v3.2.6 was released on 9 October 1998. (changelog). This is the last release in the RAT v3.2 series, which added support for multiple sampling rates and stereo, a new conference bus for remote control, improved receiver based repair improved support for novel channel coding schemes and an improved user interface.
I was part of a team responsible for transmitting the proceedings of the IEEE Globecom'96 conference, held in London in the week of 17-22 November 1996, live over the Mbone. Two papers, published in the IEEE Communications Magazine and presented at the IEEE Engineer's Conference at Networld+Interop in May 1997 describe how this was done.
RAT v3.0.3 was released on 3 November 1996. This was the first release in the RAT v3.0 series, which was the result of a significant effort to internally restructure and modularise the code, after Orion Hodson and I joined the project.
- Project Management: Vicky Hardman, Peter Kirstein, and Angela Sasse.
- RAT 4 Development Team: Orion Hodson and Colin Perkins.
- RAT 3 Development Team: Vicky Hardman, Orion Hodson, Isidor Kouvelas, and Colin Perkins.
- RAT 1 & 2 Hackers: Vicky Hardman and 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, and Anna Watson.
The RAT project was funded by the EPSRC under the Multimedia and Networked Applications Programme, British Telecommunications plc, and the European Commission (Telematics Applications Programme, Research Sector, Project 1007; Telematics for Research Programme, Project 4007). The project 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.