The Packet Traffic Channels are the only ones used in GPRS Phase I. Figure 6-11 provides an example of the Packet Traffic Channel configurations.

Figure 6-11: Packet Traffic Channels.

PDTCH: Packet Data Traffic Channel

PACCH: Packet Associated Control Channel

PTCCH: Packet Timing Advance Control Channel

The main difference between the PDTCH and the TCH logical channels in GSM consists of two points:

• PDTCH is allocated either for downlink or for uplink, but not for both (simplex channel).

• The control signaling (PACCH) associated with the assigned PDTCH is described only by its PDCH , but has no fixed position on this PDCH (radio blocks). As a conclusion, the mobile station may transmit a PACCH whenever UL, even by preempting the block position of a PDTCH , and the mobile station has to continuously monitor the DL of the DL control time slot indicated in the Packet Resource or Immediate Assignment.

Up to eight PDTCHs may be allocated to one subscriber (on the same TDMA) and up to eight mobile stations may share the same PDCH. Currently, the actual numbers are no more than three total time slots (two downlinks and one uplink for most manufacturers). Some manufacturers mobile stations can support four downlink and one uplink time slots (for example, Motorola). Many of the network resources (aside from the mobile stations) are limited to the two downlink and one uplink time slots due to timing advance situations regardless of the capability of the mobile...