The PSTN is the ultimate benchmark for voice quality in communication networks. When the first VoIP solution was introduced in 1996, the Internet’s audio transport capabilities were far below the benchmark set by public-network standards and therefore much lower per-forming than traditional telephony. Considering that Internet Telephony is constantly being promoted as the next killer application in Next Generation Networks and as the potential substitute for current telephony technologies, voice quality however needs to at least be equal to the level ISDN telephony provides at the moment. The following comparison of VoIP and traditional telephony QoS levels and their corresponding performance development revealed the following: QoS of Internet Telephony was intolerably low when first introduced, compared to the standards set by the traditional telephony. However, these shortcomings were largely factored out and optimised through numerous QoS enhancing methods, meaningful traffic engineering and network planning. This paper proves that QoS of today’s VoIP solutions is fully satisfactory for end-users and that VoIP therefore constitutes a potential substitute for traditional telehpony services. Index Terms - QoS, Real-time traffic engineering, Protocols, Standardization, VoIP I. INTRODUCTION nternet Telephony first broke into public view in 1996, with the Israeli firm VocalTec (www.vocaltec.com) offering the first solution for the transmission of voice signals through the public Internet using the Internet Protocol. Ever since its first appearance, it was a common belief among journalists and researchers that Internet Telephony was about to fundamentally change the status quo in the telecommunications industry. For all its trillion-dollar heft, the telecommunications sector seemed vulnerable because the price difference between Internet Telephony and the traditional wire-line telephony was tremendously high. At that time, a call – regardless if national or international - was literally free, if it was handled via a flat- rate ISP subscription. This cost advantage was the driving force for the continuous development of Internet Telephony services. While the initial “greenfield” solution by VocalTec was limited to PC-to-PC calls, companies like Net2Phone (www.net2phone.com) and Deltathree (www.deltathree.com) Manuscript received January 30, 2008. Justus Broß is PhD student at the Hasso-Plattner Institute at the University of Potsdam. (tel: +49 331 5509-524, fax: +49 331 5509-325, justus.bross@hpi.uni-potsdam.de ) Christoph Meinel is a full professor and scientific and managing director of the Hasso-Plattner Institute (meinel@hpi.uni-potsdam.de ). expanded upon this technical development in the middle of the 1990’s by installing gateways into the public telephone network. This allowed them to offer low-priced overseas calls in the traditional telephone networks, thus enabling both PC- to-Telephone and Telephone-to-PC calls. The quality of IP telephony at that time was not high, but cellular and speaker phones degraded voice quality as well, and the blatant price difference between the two transmission technologies adjusted this imbalance for many users. During the following years, however, this story became a moot point, since telecommunications carriers dramatically lowered the costs of national and international calls. One important reason for this development in the European perspective was the intervening role of EU institutions, which employed their increasing powers and sense of legitimacy to prod member states in the direction of liberalization and privatization. The quality differences between Internet Telephony and the traditional wire-line service turned out to be much harder to tolerate than expected; however, the technology continued to improve as the quality problems of what came to be called Voice over IP (VoIP) telephony began to diminish as voice packets traveled more and more frequently through fast and well-managed networks. Since then the growth of broadband Internet access in homes worldwide, coupled with improved software and increased user awareness, has enabled both equipment makers and service providers alike to offer much better voice services using less expensive hardware. If however VoIP development has ultimately shifted from only providing the price sensitive Internet community with cheap calls over the public Internet, to providing fully- functional telephony services over IP-based networks as a real alternative to traditional telephony services for both business users and the private mass market alike will be the central aspect of this paper. The most important service performances attribute in the voice arena of both the traditional telecommunications industry and Internet Telephony is Quality of Service (QoS). QoS is the only real technical performance characteristic of voice transmission services and is therefore attributed special importance in this paper. The ultimate goal of this paper is therefore to assess whether calls over broadband Internet connections are nowadays indistinguishable from most ordinary phone voice calls and maybe even better than the wireless service quality consumers have come to accept. The paper is organized as follows. Section 2 shortly introduces the concept of QoS, and its importance for telecommunication services in general. While Section 3 and 4 quantify and assess the QoS-levels of the traditional wireline telephony, sections 5 and 6 elaborate upon the QoS of Internet telephony. The paper is rounded off by a comparison of both transmission techniques regarding the provision of satisfactory Can VoIP Live up to the QoS Standards of Traditional Wireline Telephony? Justus F.M. Broß, Christoph Meinel, Hasso-Plattner Institute, University of Potsdam I The Fourth Advanced International Conference on Telecommunications 978-0-7695-3162-5/08 $25.00 © 2008 IEEE DOI 10.1109/AICT.2008.75 126