Telecom knowledge and experience sharing: An Introduction CAMEL

CAMEL: An Introduction

by Zahid Ghadialy

Introduction

Customised Applications for Mobile network Enhanced Logic also known as CAMEL was developed as a standard for mobile intelligence across different vendor equipment for GSM network. What this means is that the end user should be able to roam between different networks (maybe in different countries) and be reachable at the same number and should receive only one bill from the original service provider (Home Operator).

Before CAMEL, the GSM networks used INAP (Intelligent Network Application Part) for injecting intelligence in GSM networks. The limitations of INAP was that it did not support mobility management. CAMEL solved the mobility management problem and provided with much more functionality. With the evolution of 3G standards, CAMEL has evolved to provide new functionality that will be discussed later.

CAMEL has been divided into Phases. The last section in this primer lists the functionality of each phases. The latest Phase is Phase 4. If an IPLMN (Interrogating PLMN) or VPLMN (Visiting PLMN) supports CAMEL Phase 4, it shall also provide the functionality of all previous CAMEL phases.

The first commercial implementation of CAMEL (phase 1) was in August 2000 by France Telecom Mobiles (France), Mobistar (Belgium) and Dutchtone (The Netherlands).

NOTE: CAMEL feature is a network feature and not a supplementary service. It is a tool to help the network operator

Applicability of CAMEL procedures

· The CAMEL feature is applicable to Mobile Originated and Mobile Terminated Call Related Activities. CAMEL procedures are applicable to all circuit switched basic services without distinction (except Emergency calls).

· The CAMEL feature is applicable to Supplementary Services Invocation

· CAMEL procedures are applicable to GPRS sessions and PDP contexts

· CAMEL procedures are applicable to Mobile Originating/Terminating short message service through both circuit switched and packet switched serving network entities

· CAMEL procedures are applicable to IP multimedia services (except Emergency calls) to support legacy services

· CAMEL shall support IPMM sessions which are based on the same charging paradigm as CS/PS calls. This applies most probably to VoIP and Video over IP.

· CAMEL procedures are applicable to IP multimedia sessions addressed by either E.164 numbers or SIP URLs.

Example of CAMEL procedure

Before we proceed further and use more technical terms, it would be wise to understand CAMEL procedure with the help of some examples.

Take a simple scenario of a voice call being made. When a subscriber starts to make a call, this request is received by the network's Mobile Switching Centre (MSC). The MSC then sends a message that 'queries' the SCP's database. Note that the essential element of any CAMEL solution is a Service Control Point (SCP). This unit effectively hosts a database which holds the instructions needed for an intelligent application.

The SCP processes that query, comes up with an appropriate response and then sends a message back to the MSC telling what action it should take with the subscriber’s request for a specific service. The call is then connected in the most appropriate manner, a process which is transparent to the customer. A very good example of this process in action is short code dialling over a VPN (Virtual Private Network) where the user calls a colleague’s internal extension telephone number but is, in fact, routed to that person’s mobile phone which is roaming abroad.

The main addition in CAMEL phase 2 which phase 1 omitted is support for a Specialised Resource Function (SRF) a component most often found in Voice Response Units (VRUs). For example, when an account balance reaches zero for a pre-paid customer under phase 1, the customer will simply be cut off. With phase 2 thanks to support for SRF, the customer will hear automatically generated messages from the Voice Response Unit warning that the balance is dangerously low before a call and even during the call. Naturally this leads to greater customer satisfaction.

Technical Terms

For any further discussions we would need to use some technical terms. They are discussed in this section.

· Interrogating PLMN (IPLMN): The PLMN that interrogates the Home PLMN (HPLMN) for information to handle mobile terminating call.

· CAMEL Service Environment (CSE): A CSE is a logical entity which processes activities related to Operator Specific Services (OSS).

· CAMEL Subscription Information (CSI): Identifies that CAMEL support is required for the subscriber and the identities of the CSEs to be used for that support.

· Service Control Function (SCF): SCF contains the actual independent service logic to apply to the call.

· Basic Call State Model (BCSM): BSCM represents an abstract view of call processing, seen from the perspective of service feature control performed by the SCF. The BCSM consists of two sets of call processing logic, Originating BCSM (O-BCSM) and Terminating BCSM (T-BCSM).

· Points in Call (PIC): PIC are defined by standards to represent those points in which action might be taken. They provide a view of a state or event in which call processing logic may initiate an action, such as suspension of call processing while a database is queried.

· Detection Points (DP): DP represent transitional events that occur between some PICs.

· Triggers: A trigger is the term used to define specific call-processing logic associated with a given point in call. Triggers are nothing more than software logic that is loaded in a network element to carry out instructions to initiate an intelligent network process based on analysis of conditions at a detection point.

· Events: Unlike a trigger, which depends on some form of input criteria, an event is simply a call occurrence such as no answer, busy signal or call termination.

· Arming of detection points: Detection points have two classifications: Trigger Detection Points (TDP) and Event Detection Point (EDP). A detection point is armed if control logic is established to initiate service control based on a trigger or event.

· GSM Service Control Function (gsmSCF): functional entity that contains the CAMEL service logic to implement OSS. It interfaces with the gsmSSF, the gsmSRF, the GMLC and the HLR.

· GSM Service Switching Function (gsmSSF): functional entity that interfaces the MSC or GMSC to the gsmSCF. The concept of the gsmSSF is derived from the IN SSF, but uses different triggering mechanisms because of the nature of the mobile network.

· GSM Specialised Resource Function (gsmSRF): functional entity which provides various specialized resources. It interfaces with the gsmSCF and with the MSC.

Examples of Signalling procedures

[13] gives example of Signalling procedures using CAMEL for originating and terminating calls and has been described below.

Mobile Originating Calls:

If an active originating CAMEL Subscription Information (CSI) is found in the VLR during the call set up of a MS, the Visited Service Switching Function (VSSF) sends an InitialDetectionPoint message to the gsmSCF and the VMSC suspends the call processing. The InitialDetectionPoint shall always contain the service key, called and calling party number, calling party’s category, location number, bearer capability, event type Basic Call State Model (BCSM), location information and the International Mobile Station Identity (IMSI). After the service logic processing CAMEL specific handling is initiated from the gsmSCF, see figure above.

Mobile Terminating Calls:

In the case of mobile terminating call, the Gateway MSC (GMSC) in the interrogating PLMN identifies the HLR of the called party with the help of the MSISDN. Then the GMSC sends a Routing Information-Request to the HLR. The HLR checks the CSI of the called party and sends the information stored in the subscriber record back to the GMSC. Now, the GMSC acts according to CSI. If the terminating CSI is active the trigger criteria of a Detection Point (DP) is fulfilled and the call processing is suspended. An Initial DP message, which shall always contain the service key, called party number, event type BCSM and the IMSI is sent to the CSE and the service logic execution is started. Thereafter CAMEL specific handling is initiated, see figure above.

Contents of each CAMEL Phase

CAMEL phase 1:

1.1 CAMEL phase 1 functionality:

Functionality	Purpose / supports	Restrictions
Triggering on MO, MT and forwarded calls.	Call screening Simple VPN Call Forwarding Call Redirection Call Rerouting Homing of pre-paid calls to HPLMN	No IN announcements supported No charging operations Limited set of detection points, e.g. the hunting services are not possible. MT calls trigger in the GMSC only. Not possible to activate Call Forwardings with VPN short codes.
Any Time Interrogation	The CSE may request HLR to provide subscriber status and/or location information at any time.	The exact location may not be up-to-date unless the mobile has an active call ongoing. CS only

CAMEL phase 2:

2.1 CAMEL phase 2 functionality:

Functionality	Purpose / supports	Restrictions
Triggering on MO, MT and forwarded calls.	Call screening VPN for calls Call Forwarding Call Redirection Call Rerouting Follow-on calls In-band user interaction (DTMF) Tones and announcements	MT calls trigger in the GMSC only.
Charging operations	Pre-paid (MO, MT, CF) Free-phone Premium rate Personal Discount Location Dependent discount Reverse Charging	-
CSE provided e-parameters	MO AoC	-
New detection points (Abandon, Busy, NotReachable, NoAnswer, RouteSelectFailure cases)	Cleaner termination of relationship. Better pre-paid service. Hunting type of services.	-
Triggering criteria	To reduce CSE & SSP load	-
Any Time Interrogation	The CSE may request HLR to provide subscriber status and/or location information at any time.	The exact location may not be up-to-date unless the mobile has an active call ongoing. No call supervision
USSD communication between MS and CSE	USSD call-back for pre-paid roaming Control & enquiry of IN services
Control of north American carrier information	Enhances pre-paid CSE based carrier selection Selecting correct long distance network for user interaction
Notification of supplementary service (CCBS, ECT, CD and MPTY) invocation to CSE	Fraud control

3 CAMEL phase 3:

3.1 CAMEL phase 3 functionality:

Functionality	Purpose / supports	Restrictions
Triggering on MO, MT and forwarded calls.	Call screening Full VPN Call Forwarding Call Redirection Call Rerouting Follow-on calls In-band user interaction (DTMF) Tones and announcements	adv
Charging operations	Pre-paid (MO, MT, CF) Free-phone Premium rate Personal Discount Location Dependent discount Reverse Charging
CSE provided e-parameters
CAMEL2 new detection points (Abandon, Busy, NotReachable, NoAnswer, RouteSelectFailure cases)	Cleaner termination of relationship. Better pre-paid service. Hunting type of services.
CAMEL3 new trigger detection points.	To trigger on demand only, e.g. for hunting services.
Triggering criteria	To reduce CSE & SSP load
Any Time Interrogation. Enhanced with CAMEL3 current location retrieval, and ATI for GMLC.	The CSE may request HLR to provide subscriber status and/or location information at any time.	CS only
USSD communication between MS and CSE	USSD call-back for pre-paid roaming Control & enquiry of IN services
Control of north American carrier information	Enhances pre-paid CSE based carrier selection Selecting correct long distance network for user interaction
Notification of supplementary service (CCBS, ECT, CD and MPTY) invocation to CSE	Fraud control
Call Gapping	To control CSE overload situations within HPLMN	For CS calls only. Not for SMS or GPRS.
MT call triggering in VMSC-B	To control MT supplementary services (CW, hold, CF, CD, ECT, MPTY) Pre-paid for MT air-time charge (1^st minute free, e.g. in USA)
Abandon as an EDP-R	Improves charging
Enhanced FreeFormatCharging data (40 octets -> 160 octets)	Makes the CSE service logic easier
Reporting of MSRN/FTN to CSE	Charging control of optimally routed calls
CSE-HLR interface: ATM/ATSI/NSDC	Multiple Subscriber Profile phase 2 CSE can control CF, barring supplementary services. Off-line subscription control based on VPLMN / time-of-day Virtual operators
Subscribed dialled services (D-CSI)	HPLMN specific service numbers	No call supervision
Serving Network Dialled services (N-CSI)	VPLMN specific service numbers	No call supervision
MO SMS control (CS+PS)	Enhances pre-paid. Enhances VPN	No MT SMS control. Not content based
Inter-working with GPRS	GPRS pre-paid	Not content based
CS Mobility management notifications	CSE can monitor location / reachability
Service Interaction Indicators	CSE can control inter-working with supplementary services (CW, hold, CF, CD, ECT, MPTY). Multiple subscriber profile phase 2

CAMEL phase 4:

4.1 CAMEL phase 4 functionality in Release 5:

Functionality	Purpose / supports	Restrictions
Triggering on MO, MT and forwarded calls.	Call screening Full VPN Call Forwarding Call Redirection Call Rerouting Follow-on calls In-band user interaction (DTMF) Tones and announcements
Charging operations	Pre-paid (MO, MT, CF) Free-phone Premium rate Personal Discount Location Dependent discount Reverse Charging
CSE provided e-parameters	MO & MT AoC
CAMEL2 new detection points (Abandon, Busy, NotReachable, NoAnswer, RouteSelectFailure cases)	· Cleaner termination of relationship. · Better pre-paid service. · Hunting type of services.
CAMEL3 new trigger detection points.	· To trigger on demand only, e.g. for hunting services.
Triggering criteria	· To reduce CSE & SSP load
Any Time Interrogation. Enhanced with CAMEL3 current location retrieval, and ATI for GMLC. CAMEL4 enhances this to PS domain.	The CSE may request HLR to provide subscriber status and/or location information at any time. ATI for GMLC
USSD communication between MS and CSE	USSD call-back for pre-paid roaming Control & enquiry of IN services
Control of north American carrier information	Enhances pre-paid· CSE based carrier selection Selecting correct long distance network for user interaction
Notification of supplementary service (CCBS, ECT, CD and MPTY) invocation to CSE	· Fraud control
Call Gapping	· To control CSE overload situations within HPLMN	For CS calls only. Not for SMS or GPRS.
MT call triggering in VMSC-B	· To control MT supplementary services (CW, hold, CF, CD, ECT, MPTY) · Pre-paid for MT air-time charge (1^st minute free, e.g. in USA)
Abandon as an EDP-R	· Improves charging
Enhanced FreeFormatCharging data (40 octets -> 160 octets)	· Makes the CSE service logic easier
Reporting of MSRN/FTN to CSE	· Charging control of optimally routed calls
CSE-HLR interface: ATM/ATSI/NSDC	Multiple Subscriber Profile phase 2 CSE can control CF, barring supplementary services. Off-line subscription control based on VPLMN / time-of-day Virtual operators
Subscribed dialled services (D-CSI)	· HPLMN specific service numbers	· No call supervision
Serving Network Dialled services (N-CSI)	· VPLMN specific service numbers	· No call supervision
SMS control (CS+PS)	· Enhances pre-paid. · Enhances VPN	· Not content based
Inter-working with GPRS	· GPRS pre-paid	· Not content based
CS Mobility management notifications	· CSE can monitor location / reachability
Service Interaction Indicators	· CSE can control inter-working with supplementary services (CW, hold, CF, CD, ECT, MPTY). · Multiple subscriber profile phase 2
Interactions with Optimal Routing	· CSE can control usage of OR
Call Party Handling	Wake-up calls Conference calling Parallel hunting Click-to dial IN based CCBS
Mid call procedure for MO and MT calls	Control CPH configuration during call. Automatic call collect
CAMEL for IMS	IMS pre-paid Convergence to CS and GPRS services
Inclusion of flexible tone injection	Enhancements of pre-paid warning tones Various informative tones

Provision of location information of called subscriber (Alerting phase)	The location of B-subscriber at the beginning of the call provided to service logic
Notification of GPRS mobility management to CSE	CSE can monitor location / reachability in PS side
Inclusion of ODB data in the CSE-HLR interface	Enhancement of MSP ph 2
Location information during an ongoing call (Handover DP)	Charging based on current location, for inter-PLMN and/or inter-system handovers
Transfer of the IMEI (with software version) and MS class mark to the CSE	allow the gsmSCF to determine information about the capabilities of the ME
Any Time Interrogation from CSE to MNP-SRF	Number portability query for prepay calls
Partial implementation of CAMEL phase 4	A functional entity (VMSC, GMSC or SGSN) may support the complete CAMEL phase4 functionality or, as a network option, it may support the complete CAMEL phase3 functionality and a partial implementation of CAMEL phase4.

4.2 CAMEL phase 4 additions in Release 6

Enhancements of Dialled Services	·Full control of Dialled Services	adv
Full CAMEL4 prepay support for SCUDIF	·The capability to report basic service code changes during ongoing call.
Change of position procedure armed with criteria	· Technical enhancement to reduce the signalling load

Concluding Remarks

We have covered some basic details of CAMEL in this tutorial. As mentioned in the beginning, this is just an introductory tutorial. Below is the list of references that an interested reader can use to expand their knowledge of the topic. [1] provides the basics of CAMEL procedures and the way they are applied during call processing. [7] gives ideas on how to implement VoIP in 3G networks based on CAMEL. Interested user can have a look at [7] for details. [3] gives details about CAMEL Application Part (CAP). [2] provides in-depth implementation related stuff for CAMEL.

References

[1] 3GPP TS 22.078: CAMEL Service Description; Stage 1

[2] 3GPP TS 23.078: CAMEL Phase 4; Stage 2

[3] 3GPP TS 29.078: CAMEL Phase 4; CAMEL Application Part (CAP) specification

[4] 3GPP: Contents of each CAMEL phase

[5] 3GPP TS 23.278: CAMEL Phase 4 - Stage 2; IM CN Interworking

[6] 3GPP TS 29.278: CAMEL Application Part (CAP) Specification for IP Multimedia Subsystems (IMS)

[7] 3GPP TR 21.978: Feasibility Technical Report - CAMEL Control of VoIP Services

[8] Wireless Intelligent Networking by G. Christensen, P. Florack and R. Duncan

[9] 3G service control; M.D.Cookson and D.G.Smith - BT Technological Journal, Vol 19, No. 1, Jan 2001

[10] IP Support in 3G systems; Snehamoy Banarjee and Dr. Dheeraj Sanghi - Indian Institute of Technology, Kanpur

[11] What is CAMEL? - WAP Insight