Section: 4.3.2 Base Station Identify Code (BSIC)
Content: The base station identity code is a local colour code that allows an MS to distinguish between different neighbouring base stations. BSIC is a 6 bit code which is structured as shown in Figure 6. Exceptions apply to networks supporting EC-GSM-IoT or PEO and for mobile stations in EC or PEO operation (see 3GPP TS 43.064[ None ]  [112]) where the BSIC is a 9 bit code which is structured as shown in Figure 6a. Figure 6: Structure of 6 bit BSIC Figure 6a: Structure of 9 bit BSIC In the definition of the NCC, care should be taken to ensure that the same NCC is not used in adjacent PLMNs which may use the same BCCH carrier frequencies in neighbouring areas. Therefore, to prevent potential deadlocks, a definition of the NCC appears in annex A. This annex will be reviewed in a co-ordinated manner when a PLMN is created. In addition to the above, the GERAN networks should be configured so that: - in a cell shared between different PLMNs as per GERAN network sharing (see 3GPP TS 44.018[ None ]  [99] and 3GPP TS 44.060[ None ]  [100]), the NCC used in this cell is different from the NCC used in the neighbouring non-shared cells of these PLMNs; and that - these PLMNs use different NCCs in non-shared cells neighbouring this shared cell. Furthermore, GERAN networks supporting the 9 bit BSIC shall also support the 6 bit BSIC field and when supporting both the 6 bit BSIC and 9 bit BSIC the network shall ensure that the NCC and BCC parts are identical between the 6 bit and 9 bit BSIC fields.