The ITU defines several "capability levels" for this protocol, starting with Capability Set 1 (CS-1). A typical application for the IN is a Number Translation service. For example, in the United Kingdom, 0800 numbers are freephone numbers and are translated to a geographic number using an IN platform. The Telephone exchanges decode the 0800 numbers to an IN trigger and the exchange connects to the IN.
The Telephone exchange uses TCAP, SCCP and INAP and in IN terms is a Service Switching Point. It sends an INAP Initial Detection Point (IDP) message to the Service Control Point. The SCP returns an INAP Connect message, which contains a geographic number to forward the call to.
INAP messages are defined using ASN.1 encoding. SCCP is used for the routing. Extended form of INAP is Customised Applications for Mobile Enhanced Logic. TCAP is used to separate the transactions into discrete units.