Common channel signaling processes

The state transitions shown in Figure 1 show the events visible to the user of the signaling interface.

Common channel signaling processes are responsible for all the signaling information for a trunk. Therefore all the flows required to set up and clear a call must be handled by the signaling process.

Figure 1. Common channel signaling model

The diagram shows flows between the Idle state and the Connected state, passing through either the Off-hook state or the Ringing state. From Idle to Off-hook the action is SL_CALL_SETUP_REQ. From Off-hook to Connected the action is SL_CALL_SETUP_CNF success but, if the connection fails Off-hook returns the SL_CALL_SETUP_CNF fail action to the Idle state. To end the call, the flow from Connected state back to Idle is SL_CALL_TERMINATE_IND (or SL_CALL_TERMINATE_REQ and SL_CALL_TERMINATE_CNF. From Idle to Ringing the action is SL_CALL_SETUP_IND. If the call is successful the flow continues to Connected state by SL_CALL_ANSWER_REQ and SL_CALL_ANSWER_CNF success. If unsuccessful, Ringing state returns SL_CALL_TERMINATE_REQ and SL_CALL_TERMINATE_CNF to the Idle state (alternatively, it can return SL_CALL_ANSWER_REQ and SL_CALL_ANSWER_CNF fail).

See Call transfer model for details of how a Blueworx Voice Response signaling process implements call transfer. See Message waiting indicator for details of how a Blueworx Voice Response signaling process implements message waiting indicators.