3.6.2 Advanced Call States for Hold and Transfer

Two advanced call states are appended to the basic call model to support call hold and transfer. These advanced call states are as follows:

On-Hold State (GCST_ONHOLD)

A call must be in the Connected call state to be put on hold. When a call is put on hold, the remote party is often routed via the local switch or network to receive background music while temporarily suspended from conversing with the local party. The call remains on hold until the application retrieves the call, effectively re-transitioning it into the Connected, "conversational" state. The application may not issue a gc_MakeCall( ) or receive another call while a call is in the On-hold state.

There is no limit to the number of times a call may be placed in and retrieved from the On-hold state. In addition, either the called party or the calling party can put the call in the On-hold state.

The On-hold call state applies only to call scenarios where a single call is present on the specified channel. The On-hold call state does not apply to call transfer scenarios that use the On-Hold Pending Transfer call state instead.

On-Hold Pending Transfer State (GCST_ONHOLDPENDINGTRANSFER)

During a supervised call transfer, two calls are made accessible to the local channel. Both calls must be in the Connected call state. The call that is temporarily suspended from conversing is considered to be in the On-hold Pending Transfer call state. This call is often routed via the local switch or network to receive background music while awaiting completion of the call transfer.

Both the suspended call and the currently active call may be swapped at any time so that the call that was in the On-hold Pending Transfer state is now actively connected, while the former active call is placed in the On-hold Pending Transfer state. There is no limit to the number of times two calls may be swapped between the On-hold Pending Transfer and "Connected" states. The completion of the call transfer is independent of which call is active or on hold.

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