authority and format identifier (OSI) (AFI)
Authority and Format Identifier (AFI) is a header field for the OSI address.
Because of the non-uniform addressing worldwide and the associated multiple assignment of addresses, three data fields are used in the network service access points( NSAP) in the network layer. The first, the Authority and Format Identifier (AFI), is part of an NSAP format for the ATM address.
The AFI identifier identifies the type and format of the Initial Domain Identifier( IDI) in the ATM address. In public networks with Data Country Code( DCC) the AFI field has the number 39, with the International Code Designator( ICD) the value 47 is entered and with ATM addresses according to the E.164 the Authority and Format Identifier has the value 45. These addresses can be used for ISDN connections.