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3.1 Introduction

This chapter describes the AG Access call control functions. These functions manage telephone network signaling, and the procedures required for establishing and maintaining calls. There are two methods for establishing calls - answering inbound calls, and placing outbound calls. In either case, AG Access and the application exchange commands and events to advance the port to a call-connected state. Eventually, AG Access and the application cooperatively release the call.
The AG Access call control functions manage the following operations: Answering inbound calls Placing outbound calls Releasing calls Blocking calls Transferring calls
This chapter presents a summary of events sent by the telephone network, how these events are used with call control, and a detailed explanation of how to perform call control operations in response to telephone network events. Each section explains how to perform the operation, how to manage the parameters that govern the behavior of the operation, and how to use the events generated by AG Access. The call control functions and events are closely incorporated into the AG Access state machine, as is illustrated in this chapter with detailed diagrams.
The call control operations are performed by the corresponding AG Access call control functions, as follows: To... Use... Answer an incoming call adiAnswerCall Block subsequent calls adiBlockCalls Retrieve the current call status adiGetCallStatus Place an outbound call adiPlaceCall Place the first call on hold and dial a second number or extension adiPlaceSecondCall Reject an incoming call adiRejectCall Release a call adiReleaseCall Release a second call and retrieve a first call adiReleaseSecondCall Transfer a call adiTransferCall Unblock previously blocked calls adiUnBlockCalls

To...	Use...
Answer an incoming call	`adiAnswerCall`
Block subsequent calls	`adiBlockCalls`
Retrieve the current call status	`adiGetCallStatus`
Place an outbound call	`adiPlaceCall`
Place the first call on hold and dial a second number or extension	`adiPlaceSecondCall`
Reject an incoming call	`adiRejectCall`
Release a call	`adiReleaseCall`
Release a second call and retrieve a first call	`adiReleaseSecondCall`
Transfer a call	`adiTransferCall`
Unblock previously blocked calls	`adiUnBlockCalls`

3.1.1 Call Control and Protocol-Independence

The AG Access call control functions are protocol-independent. Your application must be running a specific telephony protocol on each open port, but it uses the same AG Access call control functions regardless of which telephony protocol is running on the port. In AG Access, a protocol is embodied by a Trunk Control Program (TCP), which must be started on a port using adiStartProtocol. Refer to Section 10.2.3, for details about starting up telephony protocols.
Telephone network events and protocol-specific events are mapped to AG Access call control events, which are semantically identical across all protocols. This independence promotes application portability and accelerates application development.

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