effort by the network, and without any guarantees regarding quality of service. However, from the beginning the Internet designers allocated for QoS support even in the fundamental Internet Protocol in both versions, IPv4 (IP version 4, which is also simply referred to as IP) and IPv6 (IP version 6). That was done because it was known that different type of media such as audio, video, and data, have different requirements on certain quality metrics (bitrate in downlink and uplink, delay, losses, etc.). Those protocols are standardized by the IETF, the main standardization body for Internet tech- nologies (i.e. it includes protocols and architectures from the network protocol layer up to the application layer, which are used in hosts and nodes attached to the Internet network). Since the beginning of the twenty-first century the whole telecommunication world has been transiting to the Internet as a single networking platform for all telecommu- nication services, including native Internet services (e.g. Web, email) and traditional telecommunication services (e.g. telephony, television). That makes for different QoS techniques which are standardized for legacy telecommunication networks (e.g. PSTNs) to be implemented in a certain manner in IP networks (here, an IP network is based on the Internet networking principles and has IP protocol implemented in all hosts and nodes in the given network). Also, there were certain QoS solutions specifically stan- dardized for the Internet by the IETF, and such solutions have further influenced QoS mechanisms in the telecommunication/Information and Communication Technologies (ICTs) world based on Internet technology protocols. It has been said that the long-term goal of networking is to design a network that has the flexibility and low cost of the Internet and at the same time can provide the end-to-end QoS guarantees of the telephone network. However, that is not a simple process when there are many services with different quality requirements over a single network. 2.1 Overvi