CGI and eCGI
The CGI or Cell Global Identification is used in GSM/UMTS standard and it is defined as the concatenation of the MCC (Mobile Country Code), MNC (Mobile Network Code), LAC (Location Area Code) , and the CI (Cell Identity). Cell Identity shall be unique within a location area.
The eCGI or extendend CGI, is used in LTE/LTE-A standards and it defined as the concatenation of MCC, MNC and the eCI. The MCC and MNC are the same as included in the CGI, while the eCI is build by a concatenation of the eNodeB and the CI
Both lengths are 15 decimal digit code and for 2G, 3G & 4G Networks the first 5 digits are always the MCC (Mobile Country Code) and the MNC (Mobile Network Code)
The CGI structure is shown in the following figure. For 2G and 3G networks the next 5 digits are the LAC (Location Area Code) and the last five the Cell ID within the LAC. Note that the LAC/CI can be represented by 4 hexadecimal bytes (eventually BCD converted), but in some systems they are separated out into two 5-digit decimal numbers. This will give a very different result depending on which method is used. Any user should first know exactly which presentation is being used.
For 4G Networks the CGI is named eCGI and, while first 5 digits are still MCC & MNC, the last digits are split in eNB-ID (6 digits) and CI (max 3 digits).
The binary size of the eNB-ID is 20 bit while that of CI is 8 bit.
The point is that some systems or applications works with the whole CGI or eCGI and other systems works with the separate blocks: MCC-MNC-LAC-CID or MCC-MNC-eNB. In order to translate the 15 digit code received into blocks it is a need to know the right cell technology to correctly split the digits.