The time slot configuration is declared for each time slot at the operations maintenance center for radio (OMC-R), initially found in GPRS Phase I. As shown in Figure 6-5, some time slots are reserved for the GSM system only (circuit-switched time slot); others are reserved for the GPRS system only (packet-switched time slot: PDCH); and some are used for a mix of each (first come first served). Future GPRS phases will likely have a dynamic time slot configuration, so that all the channels may be allocated either for a circuit-switched logical channel or for a packet-switched logical channel, based on the capacity-on-demand principle (TCH/PDTCH configuration of the time slot at the OMC). The PDCH may be temporarily allocated (they share the same physical resource as circuit-switched services) due to their fast release.

Figure 6-5: The sharing of time slots between GSM and GPRS.

A cell supporting GPRS may allocate resources on one or several physical channels in order to support the GPRS traffic. The physical channels shared by GPRS mobile stations are taken from a common pool of physical channels available within the cell. This allocation of physical channels to switched services and GPRS is carried out somewhat dynamically according to the capacity-on-demand principle.

The capacity-on-demand principle means that PDCHs do not need to be permanently allocated to support GPRS and the network allocates available channels as required. Common control signaling required by GPRS in the initial phase of packet transfer is conveyed on the...