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566 INTELLIGENT NETWORK APPLICATION PARTFigure 18.4-1 INAP protocol stacks.ISDN protocol, may be used between an IP and a SCP (relayed via SSP).Figure 18.4-1 shows how INAP fits in the SS7 and the DSS1 protocol stacks.ITU-T recommendations describe INAP signaling in terms of three areas:1. Rules for single and multiple interactions between PEs2. Operations3. Procedures (i.e., actions taken after receiving a request for an operation)A physical entity may have a single interaction with another PE in relation to agiven call, in which case the rules controlling the execution of operations aremanaged by the single association control function (SACF)—see Fig. 18.4-2. A PEmay also have multiple linked interactions with other PEs in relation to a given call,in which case the rules are managed by the multiple association control function(MACF). A typical example of the latter is a SCP interacting with a SSP, a SDP,and an IP on behalf of the same call. The MACF works in concert with theFigure 18.4-2 INAP architecture in a physical entity.