Intelligent Network Application Part (INAP) is the signaling protocol used in Intelligent Networking. Developed by the International Telecommunications Union [1] (ITU), IN is recognized as a global standard. Within the International Telecommunications Union, a total functionality of the IN has been defined and implemented in digestible segments called capability sets. The first version to be released was Capability Set 1 (CS-1). Currently CS-2 is defined and available. The CAMEL Application Part (CAP) is a derivative of INAP and enables the use of INAP in mobile GSM networks.

INAP is a signaling protocol between a service switching point (SSP), network media resources (intelligent peripherals), and a centralized network database called a service control point (SCP). The SCP consists of operator or 3rd party derived service logic programs and data.

• Service Switching Point (SSP) is a physical entity in the Intelligent Network that provides the switching functionality. SSP the point of subscription for the service user, and is responsible for detecting special conditions during call processing that cause a query for instructions to be issued to the SCP.

  The SSP contains Detection Capability to detect requests for IN services. It also contains capabilities to communicate with other physical entities containing SCF, such as SCP, and to respond to instructions from the other physical entities. Functionally, an SSP contains a Call Control Function, a Service Switching Function, and, if the SSP is a local exchange, a Call Control Agent Function. It also may optionally contain Service Control Function, and/or a Specialized Resource Function, and/or a Service Data Function. The SSP may provide IN services to users connected to subtending Network Access Points.

  The SSP is usually provided by the traditional switch manufacturers. These switches are programmable and they can be implemented using multipurpose processors. The main difference of SSP from an ordinary switch is in the software where the service control of IN is separated from the basic call control.

• Service Control Point (SCP) validates and authenticates information from the service user, processing requests from the SSP and issuing responses.The SCP stores the service provider instructions and data that direct switch processing and provide call control. At predefined points during processing an incoming or outgoing call, the switch suspends what it is doing, packages up information it has regarding the processing of the call, and queries the SCP for further instruction. The SCP executes user-defined programs that analyze the current state of the call and the information received from the switch. The programs can then modify or create the call data that is sent back to the switch. The switch then analyzes the information received from the SCP and follows the provided instruction to further process the call.

  Functionally, an SCP contains Service Control Function (SCF) and optionally also Service Data Function (SDF). The SCF is implemented in Service Logic Programs (SLP). The SCP is connected to SSPs by a signalling network. Multiple SCPs may contain the same SLPs and data to improve service reliability and to facilitate load sharing between SCPs. In case of external Service Data Point (SDP) the SCF can access data through a signalling network. The SDP may be in the same network as the SCP, or in another network. The SCP can be connected to SSPs, and optionally to IPs, through the signalling network. The SCP can also be connected to an IP via an SSP relay function. The SCP comprises the SCP node, the SCP platform, and applications. The node performs functions common to applications, or independent of any application; it provides all functions for handling service-related, administrative, and network messages. These functions include message discrimination, distribution, routing, and network management and testing. For example, when the SCP node receives a service-related message, it distributes the incoming message to the proper application. In turn, the application issues a response message to the node, which routes it to the appropriate network elements. The SCP node gathers data on all incoming and outgoing messages to assist in network administration and cost allocation. This data is collected at the node, and transmitted to an administrative system for processing.

• Intelligent Peripheral (IP) provides resources such as customized and concatenated voice announcements, voice recognition, and Dual Tone Multi-Frequencies (DTMF) digit collection, and contains switching matrix to connect users to these resources. The IP supports flexible information interactions between a user and the network. Functionally, the IP contains the Special Resource Function. The IP may directly connect to one or more SSPs, and/or may connect to the signalling network.

• Service Management Point (SMP) performs service management control, service provision control, and service deployment control. Examples of functions it can perform are database administration, network surveillance and testing, network traffic management, and network data collection. Functionally, the SMP contains the Service Management Function and, optionally, the Service Management Access Function and the Service Creation Environment
  Function. The SMP can access all other Physical Entities.

Conceptual model of the Intelligent Network :

The IN standards present a conceptual model of the Intelligent Network that model and abstract the IN functionality in four planes:

• The Service Plane (SP): This plane is of primary interest to service users and providers. It describes services and service features from a user perspective, and is not concerned with how the services are implemented within the network.
• The  Global Functional Plane (GFP): The GFP is of primary interest to the service designer. It describes units of functionality, known as service independent building blocks (SIBs) and it is not concerned with how the functionality is distributed in the network. Services and service features can be realised in the service plane by combining SIBs in the GFP.
• The Distributed Functional Plane (DFP): This plane is of primary interest to network providers and designers. It defines the functional architecture of an IN-structured network in terms of network functionality, known as functional entities (FEs). SIBs in the GFP are realised in the DFP by a sequence of functional entity actions (FEAs) and their resulting information flows.
• The  Physical Plane (PP): Real view of the physical network.The PP is of primary interest to equipment providers. It describes the physical architecture for an IN-structured network in terms of physical entities (PEs) and the interfaces between them. The functional entities from the DFP are realised by physical entities in the physical plane.

Services that can be defined with INAP include:

• Single number service: one number reaches a local number associated with the service
• Personal access service: provide end user management of incoming calls
• Disaster recovery service: define backup call destinations in case of disaster
• Do not disturb service: call forward
• Virtual private network short digit extension dialing service

Advantages created by the IN architecture:

• extensive use of information processing techniques;
• efficient use of network resources;
• modularization of network functions;
• integrated service creation and implementation by means of reusable standard network functions;
• flexible allocation of network functions to physical entities;
• portability of network functions among physical entities;
• standardised communication between network functions via service independent interfaces;
• customer control over their specific service attributes;
• standardised management of service logic.

References:

SS7 Discussion Forum [2]

http://www.item.ntnu.no/fag/ttm4130/stottelitteratur/IN.pdf

http://www.doc.ic.ac.uk/~nd/surprise_97/journal/vol4/vra/