title: Basic call state model
text: # Basic call state model
  
  In Intelligent Network and CAMEL switching, a BCSM is a Basic Call State Model.
  
  ## Types
  
  * O-BCSM (Originating BCSM)
  * T-BCSM (Terminating BCSM)
  
  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
  
  * Initial Detection Point (IDP)
  * RRBE (Request Report BCSM)
  * Event Report BCSM (ERB)
  * Connect (CON)
  * Continue (CUE)
  * Send Charging Information (SCI)
  * ACH (Apply Charging)
  * ACR (Apply Charging Report)
  