domain, which is the CN part between the SN and the remote party. 3.1.1.2 The IMT 2000 Family The UMTS high level architecture integrates the physical aspects through the domain concept and functional aspects through the strata concept. The separation according to [1] allows a UMTS network to fit within the context of the IMT 2000 family of net- works as illustrated in Figure 3.2. Basically there are two CN options for the air interface of the IMT 2000 family of net- works, i.e. GSM and IS-41 networks. The first one, which also includes the IP packet The UMTS Development Platform network, will serve the UTRA modes and the UWC-136 (packet) evolving based on EDGE. While GPRS may become an IP core network on its own, where UMTS and other air interfaces will directly connect to it, today it is part of the GSM infrastructure. IS-41 will serve primarily USA regions in the evolution of IS-136 in TDMA and IS-95 in CDMA. 3G Air Interfaces Core Networks CS & PS FDD: WCDMA Evolving cores TDD: TD-CDMA IP-CORE UWC-1361 EDGE IS-41 CDMA2000: Multi-carrier IS-41 CORE Figure 3.2 The IMT 2000 family of networks. 3.1.2 Coexistence of Present and Future Networks While UMTS will bring new services and allow new access options, its deployment and introduction will be in several phases. The first no doubt will evolve within a mixed environment where coexistence with 2nd generation systems like GSM (including GPRS) will be predominant. Figure 3.3 illustrates the main network elements of a typi- cal GSM network incorporating the Circuit Switched (CS) segment and the GPRS enti- ties as part of the Packet Switched (PS) segment. It also includes the future UMTS ele- ments on the radio interface side. Hence while some operators or service providers will deploy completely new network infrastructures, others will use GSM architecture as the basis for UMTS or 3G systems. This means that UMTS will complement the existing GSM system in some cases, not replace it. Clearly for all the elements to coexist as illustrated in Figure 3.3 they must all c