To uniquely identify each cell in the GSM PLMN, the network operator needs to allocate one code for each cell, which is the cell identity (CI). Cell identity, together with LAI, is used for identity of each cell in the world.
CI is composed of 16 bits, The available range is 0~65535

Cell Identity (CI) is one part of Cell Global Identity (CGI), transmitted in system information of each cell.

There is generally no restriction for the allocation of CI. Value from 0 to 65535 (decimal) can be obtained. But it should be ensured that one location area cannot have two cells with the same CI.

CI is usually determined in the network design. Except for some special cases, CI value should not be changed during the operation of the system.

Please note that one location area is not permitted to have two or more cells using the same CI. CI on MSC should be the same as that on BSC. Otherwise, MS cannot make calls in this cell.