ime slots assigned to GPRS. The allocated packet data channels can be shared by every GPRS user in the cell. A GPRS network can be seen as an extension of a GSM system. The main new nodes in the core network are the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN). Both are edge nodes as seen in Figure 13.23. Their initial task is to support data traffic. When the control network has evolved to UMTS and has been provided with IP multimedia support (see Chapter 14), all types of traffic will be supported. More information is found in Chapter 11. Theoretically, data speeds could increase to 115 kbit/s. The real figure depends on how many time slots are available, and how much traffic is occupying the network. Since packet mode is used for data transfer over the radio interface it is natural to proceed with packet mode through the core network part. In GPRS, therefore, data traffic is separated from voice in the base station controller and the data traffic continues in packet mode through a new IP packet-switched core network. From the packet-switched core network we can reach the Internet and other data networks via GGSN. With packet mode several users can share the same physical channels and make use of statistical multiplexing. We can stay online and pay only for the packets we send instead of paying for the time being connected. Figure 13.24 gives an overview of architecture and terminology in GPRS. Other network Terminal if any Content Content Applications: QoS aware Service enablers Server Server Access Core connectivity Figure 13.23 The new nodes SGSN and GGSN initially take care of data traffic, later on multi- media traffic is also included Access Network Terminal equipment Mobile terminal Mobile station Base station system Regarding interfaces GPRS model network Base transceiver station see also figure8-6 Base station controller Gateway mobile services switching center External Mobile switching centre networks network Visitor location register Home location register Authentication 