nce of QoS is very much associated with the transition from circuit switching to packet switching, with the success of the IP technology, with the development towards multimedia and finally with the success of mobile systems. One consequence is the appearance of voice, video and multimedia over IP, basically a best-effort technology. Going one step further we get voice/multimedia over IP over wireless, 'VoIPoWL', the real challenge. IP was not designed for voice traffic, and wireless was not designed to carry IP traffic. Therefore the most critical QoS terms have become delay, delay variations/jitter and packet loss. This has indeed led to a semantic change of the meaning of the term QoS. Today, some people tend to use the expression in a narrow sense, such as: 'QoS is a necessity for (packetized) real-time services' or 'A specific QoS can be described as a set of parameters that describe quality requirements of a stream of data'. The QoS of IP telephony (or VoIP, voice over IP) and associated charging, in relation to subscriber perception has been a hot question ever since the birth of the 'IP paradigm'. What is then SO attractive about real time services over IP? IP technology enables unification of the private or public network by allowing voice to be treated as a data application. Once achieved, the unification enables us to decrease network operating cost, and opens up the door for innovation and fast service creation. For rational reasons VoIP is already a reality, especially in the local area network of many enterprises. For residents it could for example be combined with ADSL subscrip- tions (VoIPoADSL). The main advantage of running IP all the way over the air interface is service flexibility. To date, cellular-access networks have been optimized in a two-dimensional space Understanding Changing Telecommunications - Building a Successful Telecom Business VolPoW IP service flexibility WCDMA with ROHC Pure IP Ideal solution Spectrum efficiency WCDMA circuit switched voice Speech quality Figure 7.3 A main t