ontain the necessary HW/SW (including protocols) enabling features for inter-working. Today, for example, the SMG (ETSI) and 3GPP organization have the task of making 2nd and 3rd generation elements inter-work seamlessly through specification and recommenda- tions. The technical specifications for practical reasons are issued in releases, e.g. the contents of the 1st edition of this book will be based on Release 1999 covering the evo- lution of GSM and the introduction of UMTS. The UMTS Network and Radio Access Technology Existing Circuit Short Message Network Switched (CS) Network Service Centre GSM and UMTS Home Location Handsets Register Integrated Billing (O & M) System Charging Gateway Serving GPRS Support Node UMTS UTRAN Firewall Backbone IP Network Internet Gateway. GPRS Support Node Border Legal Gateway Intercept Intranet Future Air-Interface Domain Name System Enhancements InterPLMN Network Packet Switched (PS) Network Figure 3.3 Coexistence of 2nd and 3rd generation mobile network elements. THE CORE NETWORK DOMAIN 3.2.1 Network Evolution Towards UMTS Evolution here implies seamless and dynamic interoperability of 2G (2.5G) and 3G technologies in the Core Network (CN) and Radio Network (RN) sides. We will thus cover these evolution implications next taking into account the integrated network ele- ments illustrated in Figure 3.3, i.e. the PS and CS building blocks in the CN side and UTRAN and EDGE in the RN side. To structure the presentation following the domain concept, we first cover the core net- work domain. Forthcoming chapters address the access network and mobile equipment The UMTS Development Platform domains. Furthermore, for completeness we also define the basic functions of the CN building blocks. The UMTS platform as illustrated in Figure 3.3, will incorporate a number of 2G/3G1 functional elements joined by standard interfaces. Together these network elements will route multifarious information traffic and provide: resource allocation; mobility management; radio link management; call process