ly analogue telecommunication networks (which used to carry analogue voice signals end-to-end) happened in the 1970s and 1980s, supported by the appearance and development of computers. The telecommunication networks were among the first to accept computers in place of the older analogue tech- nology (based on electrical equipment), with the new digital equipment being based on hardware (i.e. electronics) and software. Digitalization changed the design of telecom- munication networks SO they started to carry digits as signals (instead of analogue audio for telephony or analogue video and audio for TV), where typically the digits were bits (i.e. ones and zeros) as the most appropriate form for representing different types of media (only a single threshold was needed to distinguish between one and zero at the receiving end of the transmission link, and also computers' architectures are based on 1.2 Convergence of the Telecom and Internet Worlds and QoS storing and processing the data in a digital form, consisting of ones and zeros). With digitalization, the path was traced to transmit all types of information (audio, video, data) over the same network because all signals were in fact converted into ones and zeros before the transmission (at the sender's end) and vice versa (to the original form of the information) at the receiver's end. So, after the digitalization of telecom networks, data services started to increase in importance; however, there was also a need for a new technology which would suit all types of services, including voice, television, and various data. The next technology was packet-switching. Unlike with circuit-switching where a given channel is occupied all the time during the connection between two ends (e.g. between two telephones), regardless of whether or not there is information to trans- mit (e.g. voice), the new technology was thought to be based on a different approach. That approach was transmitting a chunk of information in a unit called a packet where each packet has a header (which 