NexGenVoIP - A Next Generation Telephone System

The speech quality of telephone system has hardly improved for decades. It has remained stagnant achieving only the so called "toll quality" which is referred to as narrow-band speech transmission having a Mean Opinion Source (MOS) of between average and good. But why should the telephone be limited to a quality so bad that no one would accept it for any kind of Hi-Fi system?

In the project "NexGenVoIP" we aim to bring the telephone system to the next evolutionary step making it sound perfectly. What is a perfect audio transmission? The goal of our work is based on the highest requirements regarding audio quality and latency. This results in musicians jamming over the internet and hence the problems we want to address are as follows:

The technology we develop may also be useful for e-sportsmen playing computer games in a team or those singing in chorus.. Any other user group that has lower quality requirements will also be satisfied with the solution. Thus, we see a sustainable rise in telephone systems supporting ensembles performing over a network. We are advancing an open-source softphone that would allow for simultaneous communication of musicians or any other group of persons.

This project is funded by the University of Tübingen in the "Nachwuchswissenschaftler" programme since 2007.


  1. Proposing Bluetooth Subband Codec (SBC), specified in Bluetooth SIG A2DP profile, for ultra-low latency audio transmission over the Internet
  2. Specification of an RTP payload format for Bluetooth's SBC Audio Codec, which allows SBC to be used for VoIP calls on the internet.
  3. Assessment of all coding modes of the SBC.
  4. Test procedure to verify the correctness of Linux kernel SBC implementation.
  5. Adding SBC to to the open-source phone "Ekiga" (we are still awaiting the approval from Philipps' legal department)
  6. Extending the ITU G.711 Appendix I packet loss concealment to full band stereo, which can be used in conduction with SBC.
  7. Adding ITU G.711 Appendix I packet loss concealment to the open-source phone "Ekiga".

Related Research

We are cooperating with

The following other research groups are or have been working on ensemble performances over the Internet:

The following user groups and software are relevant:


  1. Christian Hoene and Patrick Schreiner. A dtn mode for reliable internet telephony. In ACM Network and Operating System Support for Digital Audio and Video workshop (NOSSDAV), Vancouver, British Columbia, Canada, June 2011. [ .pdf ]
  2. Christian Hoene. Measuring the quality of an internet interactive audio codec. IETF draft-hoene-codec-quality-00.txt, work in progress, December 2010. [ .pdf ]
  3. Christian Hoene and Mansoor Hyder. Optimally using the bluetooth subband audio codec (SBC) over wireless links and on the internet. In the 35th Annual IEEE Conference on Local Computer Networks (LCN) (LCN 2010), Denver, Colorado, USA, October 2010. [ .pdf ]
  4. Joao Batista Pinto Neto, Edson N. Silva Jr., Edjair Mota, Christian Hoene, and Kleverson Santana Paixa. An alternative to data transmission in the amazon region. In The 2nd Extreme Workshop on Communication - The Himalayan Expedition (ExtremeCom 2010), September 2010. [ .pdf ]
  5. Christian Hoene and Michael Knappe. IETF audio codec: Quality testing. Presentation at the 78th IETF meeting, Maastricht, July 2010. [ .pdf ]
  6. Patrick Schreiner and Christian Hoene. Rate adaptation for the IETF IIAC. Presentation at the 78th IETF meeting, Maastricht, July 2010. [ .pdf ]
  7. Christian Hoene and Frans de Bont. RTP payload format for bluetooth's SBC audio codec. IETF draft-ietf-avt-rtp-sbc-00.txt, work in progress, June 2010. [ http ]
  8. Christian Hoene and Mansoor Hyder. Considering bluetooth's subband codec (SBC) for wideband speech and audio on the internet. Technical Report WSI-2009-3, Universität Tübingen - Wilhelm-Schickard-Institut für Informatik, 72076 Tübingen, Germany, October 2009. [ http ]
  9. Christian Hoene. Requirements of an audio communication system (acs). IETF draft-hoene-avt-acs-requirements-00.txt, work in progress, August 2009. [ .txt ]
  10. Christian Hoene and Frans de Bont. RTP payload format for bluetooth's SBC audio codec. IETF draft-hoene-avt-rtp-sbc-03.txt, work in progress, June 2009. [ .txt ]
  11. Joao Luis G. Moreira, Edjair Mota, Edson N. Silva Jr., Leandro Carvalho, Saulo Queiroz, and Christian Hoene. Voice over wireless mesh networks: A case study of voice codecs in the brazilian amazon region. In Fifth International Workshop on Heterogeneous Wireless Networks (HWISE), Bradford, UK, May 2009.
  12. Mansoor Hyder, Michael Haun, and Christian Hoene. Measurements of sound localization performance and speech quality in the context of 3d audio conference calls. In International Conference on Acoustics, Rotterdam, Netherlands, March 2009. NAG/DAGA. [ .pdf ]
  13. Christian Hoene. Conformance and quality tests of the SBC audio codec implementation in the linux kernel. online, December 2008. [ http ]
  14. Christian Hoene and Frans de Bont. RTP payload format for bluetooth's SBC audio codec. IETF draft-hoene-avt-rtp-sbc-02.txt, work in progress, December 2008. [ .txt ]
  15. Christian Hoene and Frans de Bont. RTP payload format for bluetooth's SBC audio codec. IETF draft-hoene-avt-rtp-sbc-00.txt, work in progress, October 2008. [ .txt ]
  16. Mathias Bartl and Christian Hoene. An open-source softphone for musicians playing over IP. ITU-T Workshop 'From Speech to Audio: bandwidth extension, binaural perception', September 2008. [ .pdf ]
  17. Christian Hoene, Kai Clüver, and Jan Weil. An architecture for a next generation VoIP transmission system. Praxis der Informationsverarbeitung und Kommunikation, 30(2), April-June 2007. [ http | .pdf ]