Research : Robust Audio Tool

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 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...]

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.


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.

Opinions expressed are my own, and do not represent those of my employers or the organisations that fund my research.