event detection points Interaction between a user and a service using announcements, voice prompting and information collection via in-band interaction or Unstructured Supplementary Service Data (USSD) interaction Control of call duration and transfer of Advice of Charge Information to the mobile station; The ability to inform the gsmSCF about the invocation of the supplementary services Explicit Call Transfer (ECT), Call Deflection (CD) and Multi-Party Calls (MPTY) The ability, for easier post-processing, of integrating charging information from a serving node in normal call records Phase 2 was defined as part of 3GPP Releases 97 and 98, in 1998, although it is referenced in the stage 1 specification of Release 96. Phase 3 The third phase of CAMEL enhanced the capabilities of phase 2. The following capabilities were added: Support of facilities to avoid overload Capabilities to support Dialed Services Capabilities to handle mobility events, such as (Not-)reachability and roaming; Control of GPRS sessions and PDP contexts Control of Mobile Originated SMS through both circuit-switched and packet-switched serving network entities Interworking with SoLSA (Support of Localised Service Area). Support for this interworking is optional; The gsmSCF can be informed about the invocation of the supplementary service Call Completion to Busy Subscriber (CCBS) Phase 3 was released as part of 3GPP Releases 99 and 4 in 1999. Phase 4 The fourth phase of CAMEL built on the capabilities of phase 3. The following features were defined: Support for Optimal Routing of circuit-switched mobile-to-mobile calls The capability for the gsmSCF to create additional parties in an existing call (Call Party Handling) The capability for the gsmSCF to create a new call unrelated to any other existing call (Call Party Handling - new call) Capabilities for the enhanced handling of call party connections (Call Party Handling) Control of Mobile Terminated SMS through both circuit-switched and packet-switched serving network entities The capability for the gsmSCF to control sessions in the IP Multimedia Subsystem (IMS) The gsmSCF can request the gsmSSF to play a fixed or a variable sequence of tones With CAMEL Phase 4, it is possible that only a limited subset of the new functionalities is supported, in addition to the complete support of CAMEL Phase 3. Phase 4 was released as part of 3GPP Release 5 in 2002. See also Open Services Architecture IP Multimedia Subsystem Service layer Camel References Signaling System 7 GSM standard