national number (X.121) (NN)
The ITU standardX.121 standardizes the international telephone numbers for public and private data networks and telephone networks.
As far as public data networks are concerned, the International Telecommunication Union (ITU) has specified the International Data Number( IDN) for this purpose.
This network number can consist of the Data Country Code( DCC) and the National Number (NN). In this formation, the Data Country Code consists of three digits and the National Number of up to 11 digits, starting with the 4th digit of the Data Network Identification Code( DNIC).