The following section will explain how the PDCH is allocated. Traffic Channels and packet data channels basically create a common pool of resources, utilizing the existing resources in an efficient way. See Figure 26
Figure 26 Common Recourse
Pool
The PDCHs are allocated to the PCU,
the PCU is responsible for assigning channels to different GPRS
MSs. The PDCHs can be allocated in different ways:
Dedicated
PDCHs are allocated and released by operator command.
On-demand PDCHs, serving as temporary dynamic GPRS recourses,
are allocated and released depending on GPRS traffic demand.
The channels that are allocated for GPRS (PDCH) are allocated
in sets of maximum four consecutive time slots, such a set is
called a PEST (Shown in Figure 27), a PEST can consist of both
dedicated and on demand PDCH. All PESTS are on the same frequency
or hop the same frequency hopping set. An MS can only be assigned
PDCHs from one PEST, at present this limits the maximum number
of assigned time slots to four, there is no additional limit
on the number of PDCHs that can be allocated in a cell, except
the number of available TCHs.
