The presence of a PBCCH channel in the cell is indicated by a PBCCH channel description in the SI 13 broadcast on the BCCH (providing GPRS-specific information). If the mobile station receives a SI 13 message without any PBCCH description, it will assume that PBCCH is not present in this cell (this was the case in GPRS Phase I), and the only PDCHs used for GPRS are the PDTCH and the associated control channels PACCH and PTCCH. Figure 6-7 shows a representation of the PBCCH.

Figure 6-7: The PBCH in GPRS.

All the CCCHs are the GSM logical channels (RACH, AGCH, and PCH). In this case, all the necessary GPRS information is transmitted on SI 13 (SI 15 messages are no longer used for this). If PBCCH is used in a cell, a single PDCH carries PBCCH, but this PDCH may have several PBCCH blocks (between one and four). Each block is made up of four consecutive time slots (PDCH carried by four consecutive TDMA frames).

The number of PBCCH blocks existing in the cell is given by the parameter BS_PBCCH_BLKS, which is broadcast on the PSI of the first PBCCH block (block 0). If many PCCCHs are declared for the cell (this number is provided by the parameter BS_PCC_CHANS transmitted on SI 13), only one of them carries PBCCH (between one and four PBCCH blocks in total, on the same PDCH).

PBCCH, if used, carries the PSI 1, 2, 3bis, 4, 5, and 13. PBCCH,...