The Cell Allocation (CA) is a list of all the frequencies allocated to a cell. The CA is transmitted regularly on the BCCH. Usually it is also included in the signaling messages that command the mobile to start using a frequency hopping logical channel. The cell allocation may be different for each cell.
In GSM 900 the CA list may include all the 124 available frequencies . However, the practical limit is 64, since the MA-list can only point to 64 frequencies that are included in the CA list as presented in the next section. The only signaling method allowed in the GSM 900 systems to transmit the CA list is the “bit map 0” method presented in below Table.
In GSM 1800 and GSM 1900 systems the frequency band is so large that the CA list cannot include all the frequencies available in a system. In these systems the “bit map 0” method is not available, but five other methods can be used. Each of these methods has different limitations that limit the maximum frequency range and the maximum number of frequencies. The CA list is always automatically generated and it includes the BCCH frequency and the frequencies that are defined for the MA-list.