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18.4 INAP SIGNALING 567SACF. MACF and SACF are a set of rules that apply to the INAP protocol; for moredetails we refer the reader to the Q.12x8 set of Recommendations.INAP provides for backward compatibility with future changes to the protocol bytaking advantage of two recent improvements in protocol design: extensions andcontext negotiation. Minor additions to the protocol are handled via the extensionmechanism, which consists of embedding in message formats optional fields thatare left open for future additions, and of defining rules that specify behavior (bythe current version) when messages containing the new fields are received. Majoradditions to the protocol are handled via the application context negotiation mechanismof TCAP, described in Chapter 16.An example of the INAP protocol architecture in a physical entity is shown inFig. 18.4-2. The figure shows a case with multiple interactions. For single interactionthe MACF is absent or bypassed.18.4.2 INAP, TCAP, and SCCPINAP, as a TC-user, uses the structured dialog facility, dialog-handling primitives,and component-handling primitives to communicate with TCAP (Chapter 16).Unstructured dialog is not used [29–33]. Primitives are exchanged under thecontrol of the SACF (Fig. 18.4-2).An INAP AE conveys the address of the destination AE to TCAP in adialog-handling TC primitive such as TC-UNI or TC-BEGIN (Section 16.1.3). Asexplained in Section 14.2.4, the address takes the form of a point code (PC),which identifies the PE, and a subsystem number (SSN), which identifies the AEwithin the PE. The Operation code parameter identifies the ASE within the AE,since an operation is unique within an AE.18.4.3 INAP OperationsThe following paragraphs show examples of operations for various types of functionalelement interfaces standardized by ITU-T. Since INAP messages areexchanged between physical entities, the actual messages exchanged can varywith the implementation, depending on which FEs are located in each PE.ITU-T recommendations define operations using the ASN.1 notation [34–36]and define procedures using state diagrams (SDL). Due to the complexity of therequirements and of the notations, we refer the reader to the Q.12 8 series of recommendationsfor the detailed formats.INAP Operations for CS-1. Examples of CS-1 operations are listed inTable 18.4-1 [37,38]. INAP signaling is used for the following interfaces: SCF–SDF, SCF–SSF, and SCF–SRF.INAP Operations for CS-2. A selection of additional operations is listed inTable 18.4-2 [39,40]. The following additional interfaces are supported:SDF–SDF, SCF–SCF, and SCF–CUSF.