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Intelligent Network CAMEL & INAP

                                                  The Intelligent Network is network architecture intended both for fixed as well as mobile telecom networks. It allows operators to differentiate themselves by providing value-added services in addition to the standard telecom services such as PSTN, ISDN and GSM services on mobile phones.

In IN, the intelligence is provided by network nodes owned by telecom operators mostly called as SCP -Service Control Point.IN is based on the Signaling System #7 (SS7) protocol between telephone network switching centers and other network nodes owned by network operators.
Looking at the History, The IN concepts, architecture and protocols were originally developed as standards by the ITU-T which is the standardization committee of the International Telecommunication Union; prior to this a number of telecommunications providers had proprietary IN solutions. The primary aim of the IN was to enhance the core telephony services offered by traditional telecommunications networks.
A complete description of the IN emerged in a set of ITU-T standards named Q.1210 to Q.1219, or Capability Set One (CS-1).The major driver behind the development of the IN system was the need for a more flexible way of adding sophisticated services to the existing network. Before IN was developed, all new feature and/or services that were to be added had to be implemented directly in the core switch systems. i.e., intelligence is taken out of the switch and placed in computer nodes that are distributed throughout the network. This provides the network operator with the means to develop and control services more efficiently..This made for very long release cycles as the bug hunting and testing had to be extensive and thorough to prevent the network from failing. With the advent of IN, most of these services (such as toll free numbers and geographical number portability) were moved out of the core switch systems and into self serving nodes (IN) .The initial use of IN technology was for number translation services. But much more complex services have since been built on IN, such as  prepaid telephone calls.


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.

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.