MCC (Mobile country code) - mobile country code in which operator operates.
MNC (Mobile network code) - mobile operator code.
After these codes are combined together, we get a full E.212 code or MCC-MNC code.
For example, MCC code 255 has been assigned to Ukraine.
MNC code 01 has been assigned to mobile operator Kyivstar.
Therefore, E.212 code (MCC-MNC code) for Kyivstar subscribers would be 25501.
MCC-MNC codes are used for Billing and Routing, because more than 50% mobile subscribers all over the world use feature Number portability, and E.164 telephony number no longer identifies operator, to which subscriber is connected.