international data number (X.121) (IDN)

The International Data Number(IDN) is the international identification of DTE/ DCE interfaces in public data networks. It is defined in the ITU standardX.121 and consists of two data fields: the Data Network Identification Code( DNIC) and the National Terminal Number( NTN).

The DNIC is an optional data field to identify the Public Switched Telephone Network( PSTN) in which the Data Terminal Equipment (DTE) is located. In a second scheme, the International Data Number consists of the Data Country Code( DCC) and the National Number( NN), which starts with the 4th digit of the DNIC code.

Structure of the International Data Number (IDN) according to X.121

The IDN number is used, among other things, to set up a switched virtual circuit( SVC) between public data networks( PDN) and connects two network user addresses( NUA).