BCCH Packet Broadcast Control CH (can be combined with BCCH) MS CONTINUOUSLY MONITORS PAGCH Packet Paging CH Packet Access Grant CH Packet Random Access CH BSS WANTS TO PDCH IS MS ASKS FOR CONTACT MS ALLOCATED TO MS PDCHs. Figure 2.33 GPRS radio interface channels In Release 1, the GPRS common control channels are combined with the corresponding logical chan- nels. Therefore, with the introduction of the GPRS extra load will be placed on the Random Access Channel (RACH), the Access Grant Channel (AGCH) and the Paging Channel (PCH). Data Transfer In the downlink direction, the BS uses the packet PPCH and PAGCH for the call assignment, with the PPCH being used for the paging of a terminal and the PAGCH providing the information of the assigned traffic channel to the terminal. In the uplink direction, a terminal sends information to the BS by using just one broadcasting channel, which is called PAGCH. On this channel, the mobile sends a request for service to the BS (or to the network) in both mobile originating and mobile terminating cases. The GPRS packet data transfer protocols for both the uplink and downlink data transfers are presented in Figure 2.34. Both uplink and downlink initiated data transfers will require extensive use of the RACH and AGCH. The load on these channels will be highly dependent on the traffic model. An email message can usually be transferred with a single reservation of the radio resource, whereas a WWW type of application may produce a bursty sequence of data packets that require several reservations, therefore generating a lot of extra load on the signalling channels (Figure 2.35). In addition to the packet data traffic, mobility management procedures such as routing area updates and cell re-selections as well as GPRS attach and detach generate common control signalling. The resource required on the RACH and AGCH is given for every GPRS event in Table 2.18. Therefore the parameters associated with the above events (ready timers, periodic routing area updates) and implementation of the 