. Because of the introduction of packet switching, the new network elements are those capable of performing packet switching. The main ones are the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN). The GSM system is orientated towards providing a voice service. So, apart from the addition of new elements such as SGSN and GGSN, there are only minor changes required in the GSM network elements in the BSS and HLR. These are both hardware- and software- related changes and are due to the higher-level coding schemes that are being used in the GPRS technology. The most important change is the addition of a PCU (packet control unit) at the base station controller. The GPRS system with all these elements looks the same as the GSM except for the addition of the packet-handling core part, as shown in Figure 5.1. As all the network elements of the GSM have been explained in earlier chapters, here only the new elements will be discussed. But first let us look at the changes in the mobile station. SMS-GMSC Network HLR/AuC GPRS IP PTM SC Backbone Network Corporate Inter-PLMN Intranet Backbone Corporate Operator B Intranet Internet Figure 5.1 GPRS network GPRS Mobile Station The fundamental difference between a GSM mobile and GPRS mobile (shown in Figure 5.2) is that the GPRS mobile is able to handle the packet data at a higher speed. GPRS mobile stations have been classified into three classes, A, B and C, based on their ability to handle cellular networks. Class A mobiles are connected to both the GSM and GPRS networks and can use them simultaneously. Class B mobiles are connected to both the networks, but they can use only one at a time. Class C mobiles can be connected to either one of the networks. THE GPRS SYSTEM GSM Mobile Base Band Network GPRS Mobile Network Base-Band Network Figure 5.2 GSM and GPRS mobile station Serving GPRS Support Node (SGSN) SGSN is the most important element in a GPRS network. It is the service access point for the mobile station. Its main functions include mobility manag