Phase 2: Data over PSTN or leased lines using modem. Phase 3: Introduction of dedicated switched data networks: X.21, X.25, and later frame relay and ATM. Mainly used for business (intra-company) traffic. Phase 4: A connectionless datacom technique, IP, appeared. Universities and defence were among the users. Phase 5: ISDN was the first attempt to integrate voice and data. At that time (mid-1980s) no killer data application was available to fill the capacity. Phase 6: Mobile voice was introduced early, but the real worldwide break-through came during the 1990s. Phase 7: ATM was developed during the 1980s as next integrating system. The initial deployment concerned data. During the 1990s the technology found a fixed-voice appli- cation in backbone networks and was used in some mobile systems from the terminal. Utilization: data over ATM and voice over ATM rather than integration. Phase 8: The killer application, WWW, changes the telecom world during the 1990s. E-mail supports. Suddenly all accesses need to find a path to the WWW servers and acquire an e-mail address. See Figure 13.5. Phase 9: Now the killer applications are in place and dedicated broadband data accesses are developed, such as 3G mobile systems and WLAN. On the wired side cable modems and xDSL systems find a large number of subscribers and Ethernet over fibre solutions offer even more bandwidth and promises. Phase 10: Nation-wide transitions to broadband radio access coverage require a lot of investments. WLAN is installed in hot spots. The business case for such broad extensions of the radio access infrastructure is not clear, causing some delay. Among the reasons for uncertainty are: There is no linearity between revenue and bandwidth, rather between cost and band- width. Instead of increasing, the ARPU has been fairly stable during recent years. The income from voice per user declines in many countries. The issue of radiation is frequently discussed. A development towards smaller abun- dant (low cost) base stations would solve the problem. This 