New applications like VoIP and video conferencing are sensitive to network performance, therefore making the network capacity provide quality of service is increasingly important. IPv6 was developed to solve some of the problems of IPv4, such as QoS, security and the IPv4 addresses reduction. Current IP networks provide better traffic delivery effort providing partial guarantees in terms of Quality of Service. However, there are services, including voice, with strong requirements for delay and delay variation (jitter), which makes it necessary to add functionality to IPv4 networks in order to gain support for such services. In this paper we describe the mechanisms and architectures that are used to provide QoS on a network. Then, we specify the features that use both IPv4 and IPv6 to implement QoS. Finally, we present the results of the comparison of 2 scenarios in which basic QoS features of IPv6 and IPv4 are assessed.