CCCH Grouping

 The GSM system supports various kinds of channel combinations (GPRS not taken into account), in which the main BCCH, extended BCCH, combined BCCH, and the BCCH+CBCH combination contain the CCCH, i.e. all of the four combinations support the MS access. The MS are distributed to different CCCH groups based on this fact.

The number of CCCH supported by the system depends on the parameters of BS_CC_CHANS, CCCH type and the number of channels. These message are broadcast in the control channel description domain of system information type 3.

  

    The GSM specifies that the CCCH can be mapped to timeslots 0, 2, 4 and 6 but the extended BCCH combination can only be mapped to timeslots 2, 4 and 6 because it does not contain FCCH and SCH. Therefore, all MS synchronize with the base station at timeslot 0 and access the network via different CCCH.