 charge a subscriber for network access and network usage. The system collects data, creates call detail records (CDR) and delivers them to external media, such as billing systems or a mediation system that can process the collected data for different purposes. Charging is treated in more depth in Chapter 5. 14.3.7 SECURITY AND QoS CSCF provides predefined PDP context parameters via SIP signaling to user equipment. Just as with dial-up roaming, proxy RADIUS is a common method for remote authen- tication for WISP roaming - at least in the short to medium term (See also Chapters 6 and 7). 14.3.8 ROUTING AND NUMBERING/ADDRESSING See Chapter 8. 14.3.9 IN SERVICES In general IN services were successful during the 1990s. However, many services have lost popularity with some exceptions, for example: cashless calling with prepaid, payment by card or billing afterwards. Prepaid is a 'killer application' access screening number portability freephone, which is a must in the USA premium rate information services with fixed charging. televoting universal access number A number of other IN services have been placed in 'maintenance mode'. The com- plicated IN-VPN service, with company internal telephony traffic at reduced rate as the main application, has often been replaced by special agreements with carriers. At least the successful IN services are migrating to IP based networks. The No 7 signalling system is a key enabler for IN, therefore VoIP systems must support and interoperate with SS7 in order to take advantage of what is already there. Interac- tions between IN and IP-based networks are subject to international standardization. See Section 14.9. 14.4 A SIMPLE TARGET CONTROL NETWORK SIGNALLING A target network example can look simple, if the network is homogeneous. See Figure 14.5. Control Network Service network IMS = IP multimedia subsystem SIP client IP network Figure 14.5 The future is simpler than the present convergence phase Audio & Video Coders H.323 IP v4, IP v6 Figure 14.6 Position of the SIP protocol The ses