Voice-over-IP (VoIP) telephony becomes more and more popular in the wired Internet because of easy-to-use applications with high sound quality like Skype. UMTS operators promise to offer large data rates which should also make VoIP possible in a mobile environment. However, the success of those application strongly depends on the user perceived voice quality. In this paper, we therefore analyze the achievable and the actual quality of IP-based telephony calls using Skype. This is done performing measurements in both a real UMTS network and a test environment. The latter is used to emulate rate control mechanisms and changing system conditions of UMTS networks. The results show whether Skype over UMTS is able to keep pace with existing mobile telephony systems and how it reacts to different network characteristics. The investigated performance measures comprise the Perceptual Evaluation of Speech Quality (PESQ) to evaluate the voice quality, the packet loss, the inter-packet delay, and the throughput to capture networkbased factors. In this context, the concept of the Network Utility Function (NUF) is applied to describe the impact of the network on the voice quality as perceived by the end-user.

En studie om talkvaliten av Skype via UMTS med konkreta värden som demonstrerar priset för mobilitetn samt skillnaden mellan upp- och nedlänken. VoIP, Skype, UMTS, mätningar, Network Utility Function