 available hard- ware, the network infrastructure, the offered services/applications, etc. As usual, in this process influenced by many factors (which may appear to be different to different users of the same telecommunication service), some differences may arise between perceived and assessed QoS. QoS is important for all parties involved with the telecommunication services, includ- ing both customers (or end-users) and service providers. Therefore there is a need for QoS standards that can form a basis for establishing QoS policies in each country - this is the remit of the appropriate authority in the telecommunication/ICT area (e.g. the national regulatory authority (NRA), ICT ministry, or other ministry or government body). Then the QoS provisioning for the services offered to the customers should be monitored as well as encouraged and/or enforced when necessary. 1.2 Convergence of the Telecom and Internet Worlds and QoS The telecom and Internet worlds developed in parallel in the 1970s and 1980s. On one side, the telecom world was focused on traditional telecommunication services, tele- phony (i.e. voice) and television (i.e. TV), which were primary telecommunication ser- vices during most of the twentieth century. Traditional telephony was initially fixed based, which refers to the fixed access network via so-called twisted pairs (a pair of two copper wires twisted with the aim of reducing the echo in the opposite direction). A pair of wires also is needed to create a circuit between the telephone (as end-user terminal) and the telecom operator's equipment (e.g. the exchange), therefore such communica- tion was also referred to as circuit-switching (exchanges are network nodes placed on the operator's side, and they provide switching between number of channels on their input and their output). The first condition for the appearance of the Internet on a global scale was the digital- ization of the telecommunication networks built for telephony as the primary service. The process of digitalization of initial