What is T-BCSM Terminating Basic Call State Model

Unveiling the T-BCSM: The Conductor of Terminating Calls in a Network

In the realm of telecommunications, the Terminating Basic Call State Model (T-BCSM) plays a vital role in managing the terminating leg of a mobile call within a network based on the Intelligent Network (IN) architecture. Think of it as the conductor on the receiving end, ensuring everything is in place to handle the incoming call and connect the recipient.

Understanding the Big Picture:

• The overall call setup and teardown process is governed by a set of state models called Basic Call State Models (BCSMs).
• There are two primary BCSMs:
  • Originating Basic Call State Model (O-BCSM): Manages the call setup process from the initiating subscriber's network.
  • Terminating Basic Call State Model (T-BCSM): Handles the call termination process at the recipient subscriber's network.

The T-BCSM in Action:

The T-BCSM defines a series of states and events that the network traverses when a call is being directed towards a specific mobile subscriber. Here's a breakdown of the key stages:

1. T_Null & Authorize Termination Attempt: The T-BCSM starts in the "T_Null" state, where the network receives an indication that a call is being routed towards a specific subscriber. This is followed by an authorization check to ensure the network can proceed with the termination attempt.
2. Select Facility & Present Call: Based on the called subscriber's information and network configuration, the T-BCSM selects the appropriate network facility (e.g., base station) to deliver the call. The call is then presented to the selected facility, initiating procedures to locate and notify the recipient subscriber.
3. T_Alerting (Merged with 8. in CAMEL Ph1): The network attempts to alert the called subscriber about the incoming call. This might involve ringing the subscriber's phone or sending a notification depending on the network technology and subscriber settings. In some implementations, this state might be merged with the following state (T_Active) in simplified network architectures like CAMEL Phase 1.
4. T_Active: If the subscriber answers the call, the T-BCSM enters the "T_Active" state. This indicates an established communication channel between the caller and the called subscriber.
5. T_Exception: If any unexpected events occur during the termination process (e.g., network congestion, subscriber unavailable), the T-BCSM transitions to the "T_Exception" state. Here, the network might initiate call failure procedures or attempt recovery mechanisms.

Additional Points to Consider:

• The T-BCSM interacts with various network elements like the Mobile Switching Center (MSC) and the Service Control Point (SCP) to exchange information and execute call control procedures.
• Detection Points (DPs) are defined within the T-BCSM states. These DPs act as trigger points for specific actions based on network events or subscriber responses.
• The specific implementation and interaction of the T-BCSM might vary slightly depending on the network technology and signaling protocols used (e.g., ISUP, Diameter).

Benefits of T-BCSM:

• Structured Call Termination: The T-BCSM provides a structured and standardized approach for managing the terminating leg of a mobile call, ensuring efficient routing and connection establishment.
• Error Handling: The T-BCSM incorporates exception handling mechanisms to address unexpected events during call termination.
• Service Integration: The T-BCSM can interact with the Intelligent Network (IN) to enable advanced call services like call forwarding or voicemail.

Conclusion:

The T-BCSM serves as a critical element within the network infrastructure, ensuring the smooth and efficient termination of mobile calls. By adhering to a defined set of states and events, the T-BCSM paves the way for reliable communication experiences for end users. While technological advancements might lead to variations in implementation details, understanding the core principles of the T-BCSM remains essential for appreciating the complexities of call management within mobile networks.