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288 ISDN USER PARTFigure 11.2-5. Format of parameters. Par.4: backward call indicators. Par.14: forward callindicators. Par.15: information indicators. Par.16: information request indicators. Par.22redirection information.Figure 11.2-6. Format of Par.5: call reference. (From Rec. Q.763. Courtesy of ITU-T.)The combination of bits H, G, J, and K is known as the protocol control indicator.Par.5 Call Reference. This is an optional parameter in IAM, ACM, CPG, REL,SUS, RES, FOT, INF, and INR messages (Fig. 11.2-6). The parameter identifies aparticular ISUP call at an exchange and consists of a call identity (assigned bythe exchange that sends the message) and the point code of that exchange (twooctets in ITU-T-ISUP; three octets in ANSI-ISUP). It is used in one form ofend-to-end signaling (Section 11.5).Par.6 Called Party Number. This is a mandatory variable-length parameter inIAM (Fig. 11.2-7). The parameter field consists of several subfields:Odd/even indicator (O/E):0 Even number of address digits1 Odd number of address digitsNature of address:000 0001 Subscriber (directory)number000 0011 National number000 0100 International numberNumbering plan (only one value used):001 ISDN/telephony numbering plan(see Section 1.2)Bits H and D through A are not used.