Customised Applications for Mobile networks Enhanced Logic

Customised Applications for Mobile networks Enhanced Logic, or CAMEL (ETSI TS 123 078) for short, is a set of standards designed to work on either a GSM core network or UMTS network. They allow an operator to define services over and above standard GSM services/UMTS services. The CAMEL architecture is based on the Intelligent network (IN) standards, and uses the CAP protocol.

Many services can be created using CAMEL, and it is particularly effective in allowing these services to be offered when a subscriber is roaming, like, for instance, no-prefix dialing (the number the user dials is the same no matter the country where the call is placed) or seamless MMS message access from abroad.

CAMEL entities

• gsmSCF: GSM Service Control Function
• gsmSSF: GSM Service Switching Function
• gsmSRF: GSM Specialized Resource Function
• gprsSSF: GPRS Service Switching Function

Phases

CAMEL was always intended to be specified in phases.^[1] As of 2007^[update], there have been 4 phases specified, each building on the previous phase.^[2] Phases 1 and 2 were defined before 3G networks were specified, and as such support adding IN services to a GSM network, although they are equally applicable to 2.5G and 3G networks. Phase 3 was defined for 3GPP Releases 99 and 4, and hence is a GSM and UMTS common specification, while Phase 4 was defined as part of 3GPP Release 5.

In line with other GSM specifications, later phases should be fully backwards compatible with earlier phases; this is achieved by means of the Transaction Capabilities Application Part (TCAP) Application Context (AC) negotiation procedure, with each CAMEL phase being allocated its own AC version.^[3]

Phase 1

CAMEL Phase 1 defined only very basic call control services, but introduced the concept of a CAMEL Basic call state model (BCSM) to the Intelligent Network (IN). Phase 1 gave the gsmSCF the ability to bar calls (release the call prior to connection), allow a call to continue unchanged, or to modify a limited number of call parameters before allowing it to continue. The gsmSCF could also monitor the status of a call for certain events (call connection and disconnection), and take appropriate action on being informed of the event.^[1]

Phase 1 was defined as part of Release 96 in 1997.

Phase 2

CAMEL Phase 2 enhanced the capabilities defined in Phase 1. In addition to supporting the facilities of Phase 1, Phase 2 included the following:

• Additional 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^[1]

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)^[2]

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:

• CAMEL 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)^[2]
• 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

References

1. ^ ^{a b c} 3GPP TS 02.78 Release 96 specification for the service aspects of CAMEL Phase 1 & 2 (zip file).
2. ^ ^{a b c} 3GPP TS 22.078 Release 5 specification for CAMEL phase 4 (zip file).
3. ^ 3GPP TS 29.078 CAMEL Application Part specification for Release 5 (zipped Word document).