6.2 Voice in the 3GPP Release 1999 Network

Release 1999 is the first phase of the 3GPP standards for UMTS. This is a completed set of standards that defines a UMTS network able to provide users with voice and data services fully compatible with those of GSM and GPRS. The standards allow users to migrate on to the UMTS and to roam seamlessly between UMTS and GSM/GPRS networks without any loss of capability. It also has the benefit to the network operator of being able to target the introduction of UMTS to specific geographical areas, while relying on existing GSM and GPRS networks to provide coverage in other areas.

Specifically, current GSM networks support voice and low-speed data services that are circuit-switched, so called because the voice or data is carried between users in bearer circuits that are switched into place across the network for a time period, under the control of signalling from the users. In contrast, the GPRS network supports packet-switched data services. For the purposes of this chapter, only the voice services in Release 1999 are described, but the descriptions also apply to low-speed circuit-switched data services.

Figure 6.1 shows the overall network for the support of voice services in the 3GPP Release 1999 standards, and is more fully described in Chapter 5.

Figure 6.1: 3GPP Release 1999 voice network overview.

To achieve compatibility with GSM, the Release 1999 network effectively adopts the GSM core network and service architecture. This has a significant benefit to the network...