3.15 Closed user group interlock code The format of the closed user group interlock code parameter field is shown in Figure 16. 8 7 6 5 4 3 2 1 1 1st NI digit 2nd NI digit 2 3rd NI digit 4th NI digit 3 4 Binary code Figure 16/Q.763 - Closed user group interlock code parameter field The following codes are used in the subfields of the closed user group interlock code parameter field: a) Network Identity (NI) (octets 1 and 2) Each digit is coded in the binary coded decimal representation from 0 to 9. If the first digit of this field is coded 0 or 9, the TCC (Telephony Country Code) follows in the second to fourth NI digits (the most significant TCC digit is in the 2nd NI digit ). If the TCC is one or two digits long, the excess digit(s) is inserted with the code for RPOA or network identification, if necessary. If octet 2 is not required, it is coded all zeros. Coding of the first digit as 1 or 8 is excluded. If the first digit is not 0, 9, 1 or 8, this field contains a DNIC (Data Network Identification Code) as defined in Recommendation X.121. b) Binary code (octets 3 and 4) A code allocated to a closed user group administered by a particular ISDN or data network. Bit 8 of octet 3 is the most significant and bit 1 of octet 4 is the least significant.