IDP – Initial Detection Point contains A party number, B party number, MSC Number, Call type (MO call or MT call), Service Key, Camel version and IMSI Details (A Party).
The gsmSSF sends CAP IDP to the gsmSCF to start a CAMEL service. The sending of CAP IDP results from successful TDP processing during call establishment. The argument of CAP IDP contains a number of parameters that are used by the CAMEL service for its service processing. These parameters are filled with information from various sources:
- Subscriber-specific – the parameter is obtained from the subscription data. Examples are service key, which is obtained from the CSI, calling party number for an MO call and called party number for an MT call.
- MSC-generated – the parameter is determined by the MSC or by the gsmSSF. Examples are call reference number and MSC address.
- Call-specific – the parameter is obtained from the signalling flow in the access network. For an MO call, the access network is the Radio Access Network. For an MF call and an MT call, the access network is ISUP.