The CAMEL Application Part (CAP) portable, software provides mechanisms to support operator services beyond the standard GSM services for subscribers roaming within or outside the Home PLMN (HPLMN). The CAP product extends the IN framework to the GSM/3G networks for implementing IN-based services within GSM/3G networks.
CAMEL is used when the subscriber is roaming between networks, allowing the home network to monitor and control calls made by the subscriber. CAMEL provides services such as prepaid roaming services, fraud control, special numbers (e.g., 123 for voicemail that works everywhere) and closed user groups (e.g., office extension numbers that work everywhere).
As with CAMEL, CAP has been defined in four phases, each of which has an accompanying specification that builds upon the previous phase. Each CAP phase provides the message set and procedures needed to support the corresponding CAMEL phase requirements, as defined in 3GPP TS 22.078 (service aspects) and 3GPP TS 23.078 (technical realization).
The definition of the protocol may be considered to be split into three sections:
3GPP TS 29.078 - The 3GPP specification for CAP http://www.3gpp.org/ftp/Specs/html-info/29078.htm ↩