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558 INTELLIGENT NETWORK APPLICATION PARTFigure 18.1-1 Conceptual model of IN processes.in the BCP (called detection points—DPs) transfer control to the SLP, from where itis returned to the BCP to complete the connection process (Fig. 18.1-1).18.1.1 The Four Planes of the IN Conceptual ModelFigure 18.1-2 shows the four IN planes and how they relate to each other.Service Plane. The service plane defines IN-based services from a user’s viewpoint,without any awareness of network components, internal components, orimplementation details. Services are built around service features [3]. Examplesof services are internetwork freephone (IFPH), conference calling (CONF), and universalpersonal telecommunications (UPT). Examples of service features are callwaiting (CW), call forwarding (CF), and call transfer (CT).Global Functional Plane. The GFP decomposes services into a collection ofservice-independent building blocks (SIBs) that can be chained together to build servicesand service features [4].SIBs are service-independent and global. Service independence means that a SIBcan be used to build different services. Global means that SIBs are network-wideconcepts, unaware of the network elements used to implement them, and of howtheir functionality may be distributed across those elements. Examples of SIBsare charge, compare, and basic call process.In this plane a service is realized by linking together multiple SIBs under thecontrol of a subset of the service logic program. The SLP is broken into packages(one per service) called global service logic (GSL), which interact with instancesof the basic call process (BCP), as shown in Fig. 18.1-3. The BCP is a specialSIB that controls building and releasing connections and is an abstract monolithicprocess, unaware of how it may be distributed among functional entities. Instancesof the BCP typically run in local exchanges (access nodes) that provide access tousers.