BCSM (Basic Call State Model)

The Basic Call State Model (BCSM) is a framework used in telecommunications networks to define the states and transitions that occur during a call setup and call control process. It is an essential component of the Intelligent Network (IN) architecture, which enables the development of advanced call management services and applications.

The BCSM provides a standardized approach to call control and signaling, which simplifies the development and deployment of IN services across different network types and vendors. It defines the events and triggers that occur during a call's lifecycle, such as call establishment, termination, redirection, and transfer. This information is used by IN service logic to determine how a call should be handled and what actions should be taken based on the user's preferences and network conditions.

The BCSM is divided into two main categories: call-independent and call-dependent states. The call-independent states refer to the network's condition that is not related to a specific call, such as idle or congested. The call-dependent states are those that are related to a specific call, such as ringing or connected.

The BCSM also defines various parameters that are used to describe the state of a call, such as the call state, call direction, call type, and call progress. These parameters are used to exchange signaling messages between the network elements involved in a call, such as switches, gateways, and service control points.

Let's now examine the various call states and transitions that occur during a typical call setup and call control process, according to the BCSM framework:

1. Idle State: This is the initial state of a call when there is no ongoing call activity. The network is available to receive and initiate new calls.
2. Originating State: When a user initiates a call, the network moves into the originating state. In this state, the network starts the call setup process by selecting a route to the called party and sending a call request to the destination switch.
3. Call Proceeding State: Once the call request is received by the destination switch, the network moves into the call proceeding state. In this state, the destination switch analyzes the call request and generates a call progress message back to the originating switch to indicate that the call is being processed.
4. Alerting State: After the call proceeding state, the network moves into the alerting state. In this state, the called party's telephone rings or otherwise alerts the user that a call is incoming.
5. Connected State: If the called party answers the call, the network moves into the connected state. In this state, the two parties can communicate with each other.
6. Clearing State: Once the call is terminated by either party, the network moves into the clearing state. In this state, the network releases the call resources and sends a call release message to both parties to indicate that the call is terminated.
7. Released State: After the clearing state, the network moves into the released state, where all call resources have been released, and the network is again available to initiate or receive new calls.

In addition to these basic call states, the BCSM also defines various call-related events and actions that can occur during a call setup and call control process. Some of these events and actions include:

1. Call Transfer: The transfer of a call from one network element to another, such as transferring a call from a mobile phone to a landline phone.
2. Call Hold: The temporary suspension of a call to allow the user to perform other tasks.
3. Call Waiting: The notification of an incoming call while the user is already on another call.
4. Call Diversion: The forwarding of a call to another number, such as forwarding calls to a voicemail box or an alternate phone number.
5. Call Screening: The ability to screen incoming calls based on
6. Caller ID: The display of the calling party's phone number or name on the recipient's phone or device.
7. Call Blocking: The ability to block incoming calls from specific numbers or types of calls.
8. Call Forwarding: The forwarding of incoming calls to another number or device.
9. Call Waiting with Caller ID: The notification of an incoming call while the user is already on another call, with the display of the calling party's phone number or name.
10. Three-Way Calling: The ability to add a third party to an ongoing call.
11. Call Pickup: The ability to answer a call that is ringing on another phone within the same group or department.
12. Call Completion: The ability to connect a call that could not be connected due to a network or user-related issue.

These events and actions are supported by the BCSM framework, which provides the necessary signaling and call control functions to implement them. For example, call forwarding is implemented using BCSM functions that allow the network to redirect incoming calls to a specified number or device.

The BCSM also defines various call types that can be used to classify different types of calls based on their characteristics and requirements. Some of the call types defined by the BCSM include:

1. Voice Call: A call that is used for two-way voice communication between two or more parties.
2. Data Call: A call that is used for data transmission, such as fax or modem transmission.
3. Video Call: A call that is used for two-way video communication between two or more parties.
4. Multimedia Call: A call that supports multiple media types, such as voice, video, and data.
5. Emergency Call: A call that is used to request emergency assistance from a public safety answering point (PSAP).
6. Information Call: A call that is used to retrieve information, such as weather updates or stock prices.

These call types are used by the network to determine the appropriate call routing and call handling procedures based on the user's preferences and network conditions.

In conclusion, the Basic Call State Model (BCSM) is a critical component of the Intelligent Network (IN) architecture, which provides a standardized approach to call control and signaling in telecommunications networks. It defines the various call states and transitions that occur during a call setup and call control process, as well as the events and actions that can be supported by the network. The BCSM also defines various call types that can be used to classify different types of calls based on their characteristics and requirements. The BCSM framework enables the development and deployment of advanced call management services and applications, such as call forwarding, call waiting, and call screening, across different network types and vendors.