Basic call state model

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In Intelligent Network and CAMEL switching, a BCSM is a Basic Call State Model. [1]

The Intelligent Network (IN) is the standard network architecture specified in the ITU-T Q.1200 series recommendations. It is intended 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 on fixed networks, and GSM services on mobile phones or other mobile devices.

Contents

Types

A fundamental concept for IN control is the basic call state model (BCSM). When a call is processed by an exchange, the call goes through a number of pre-defined phases. These phases of the call are described in the BCSM. The BCSM generally follows the ISUP signalling of a call

State machine description

In the following IN BCSMs, bold Detection Points and Points In Call are also present in the CAMEL Ph1 subset.

TODO: Expand to Ph2,3,4

O-BCSM

Points in call

  • 1. O_Null & Authorize Origination Attempt
  • 2. Collected_info (Merged with 1. in CAMEL Ph1)
  • 3. Analyze_Info
  • 4. Routing & Alerting (Merged with 3. in CAMEL Ph1)
  • 5. O_Active
  • 6. O_Exception

Detection Points

  • 1 Origination_Attempt_Authorized
  • 2 Collected_Info
  • 3 Analyzed_Info (this is the only Statically armed DP, others are dynamically armed using "Request Report BCSM (RRBE)" message by the SCP)
  • 4 Route_Select_Failure
  • 5 O_Called_Party_Busy
  • 6 O_No_Answer
  • 7 O_Answer
  • 8 O_Mid_Call
  • 9 O_Disconnect
  • 10 O_Abandon

T-BCSM

Points in call

  • 7. T_Null & Authorize Termination_Attempt
  • 8. Select_Facility & Present_Call
  • 9. T_Alerting (Merged with 8. in CAMEL Ph1)
  • 10. T_Active
  • 11. T_Exception

Detection Points

  • 12 Termination_Attempt_Authorized
  • 13 T_Called_Party_Busy
  • 14 T_No_Answer
  • 15 T_Answer
  • 16 T_Mid_Call
  • 17 T_Disconnect
  • 18 T_Abandon

Messages

basic INAP call example Simple call example (INAP) for BCSM.jpg
basic INAP call example

The IDP receives a message initiated by the SSP and transmitted to the service control point SCP via the INAP protocol. The Service Switching Point (SSP) receives a message (ISUP Message) initiated by the Calling Party, this could be an IAM. The SSP evaluates the nature of the message, in the case of the IAM the called and calling party numbers. From this it determines whether it can route the call or whether it needs further instructions. In this case if the SSP does require further instructions it sends an IDP to a service control point SCP via an IN protocol. The protocol may be INAP but could be CAMEL, or bespoke INAP flavours such as Ericsson INAP, Nokia INAP, Siemens INAP or Huawei INAP.

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