Child OIDs identify distinct public network codes for packet switching, a.k.a. Data Network Identification Code (DNIC). For more information, see Recommendation ITU-T X.121.
A DNIC could be assigned as follows:
a) to each Public Data Network (PDN) within a country;
b) to a global service, such as the public mobile satellite system and to global public data networks;
c) to a Public Switched Telephone Network (PSTN) or to an Integrated Services Digital Network (ISDN) for the purpose of making calls from Digital Terminal Equipments (DTEs) connected to a PDN to DTEs connected to that PSTN or ISDN;
d) to a group of PDNs within a country, when permitted by national regulations;
e) to a group of private data networks connected to PDNs within a country, where permitted by national regulations.
All Data Network Identification Codes (DNICs) shall consist of four digits. There are two categories of DNICs. If the first digit of the DNIC is the digit 1, the DNIC identifies a public mobile satellite system or a global public data network. If the first digit of the DNIC is any digit 2 through 7, the DNIC identifies a public data network in a specific country or geographic region. In this case the first three digits will always identify a country and are to be regarded as a Data Country Code (DCC). The fourth, or network digit, should identify a specific data network in the country.
The system of Data Network Identification Codes (DNICs) will provide for 600 Data Country Codes (DCCs) with a theoretical maximum of 6000 DNICs plus 1000 Global DNICs.
In the case where a country requires more than 10 DNICs, multiple Data Country Codes (DCCs) could be assigned to the country if spare DCC codes (within the geographic zone) exist.
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