Quality aspects of internet telephony
Internet telephony has had a tremendous impact on how people communicate.Many now maintain contact using some form of Internet telephony.Therefore the motivation for this work has been to address the quality aspectsof real-world Internet telephony for both fixed and wireless telecommunication.The focus has been on the quality aspects of voice communication,since poor quality leads often to user dissatisfaction. The scope of the workhas been broad in order to address the main factors within IP-based voicecommunication.
The first four chapters of this dissertation constitute the backgroundmaterial. The first chapter outlines where Internet telephony is deployedtoday. It also motivates the topics and techniques used in this research.The second chapter provides the background on Internet telephony includingsignalling, speech coding and voice Internetworking. The third chapterfocuses solely on quality measures for packetised voice systems and finallythe fourth chapter is devoted to the history of voice research.
The appendix of this dissertation constitutes the research contributions.It includes an examination of the access network, focusing on how calls aremultiplexed in wired and wireless systems. Subsequently in the wirelesscase, we consider how to handover calls from 802.11 networks to the cellularinfrastructure. We then consider the Internet backbone where most of ourwork is devoted to measurements specifically for Internet telephony. Theapplications of these measurements have been estimating telephony arrivalprocesses, measuring call quality, and quantifying the trend in Internet telephonyquality over several years. We also consider the end systems, sincethey are responsible for reconstructing a voice stream given loss and delayconstraints. Finally we estimate voice quality using the ITU proposal PESQand the packet loss process.
The main contribution of this work is a systematic examination of Internettelephony. We describe several methods to enable adaptable solutionsfor maintaining consistent voice quality. We have also found that relativelysmall technical changes can lead to substantial user quality improvements.A second contribution of this work is a suite of software tools designed toascertain voice quality in IP networks. Some of these tools are in use withincommercial systems today.
School:Kungliga Tekniska högskolan
Source Type:Doctoral Dissertation
Keywords:TECHNOLOGY; Information technology; Telecommunication
Date of Publication:01/01/2009