Function	Description/Associated Events
briAcceptCall	Directs the ISDN stack to accept an incoming call without answering it. The application can then perform other operations before answering or rejecting the call. Associated Events: · `BRIEVN_ACCEPTING_CALL`: The ISDN stack is accepting the call. An `ALERTING` message is sent to the network. · `BRIEVN_CALL_DISCONNECTED`: A `DISCONNECT` message was received from the network, indicating that the remote party has hung up. The event `value` field contains the reason.
briAnswerCall	Directs the ISDN stack to answer a call immediately. Associated Events: · `BRIEVN_ANSWERING_CALL`: A `CONNECT` message is sent to the network. · `BRIEVN_CALL_CONNECTED`: The `CONNECT` message was acknowledged by the network, and the connection is established. · `BRIEVN_CALL_DISCONNECTED`: A `DISCONNECT` message was received from the network, indicating that the remote party has hung up. The event `value` field contains the reason. · `BRIEVN_STATUS_UPDATE`: Asynchronous information regarding the call (UUI information) has arrived. The event `value` field contains the information type.
briBlockCalls	Requests the BRI service to block all incoming calls and outgoing calls. The line remains in the blocked state until briUnBlockCalls is called. Associated Events: · `BRIEVN_CALLS_BLOCKED`: Returns when the request has been granted.
briGetCallStatus	Retrieves call status information. Associated Events: None.
briPlaceCall	Directs the ISDN stack to place a call to a specified number. Associated Events: · `BRIEVN_PLACING_CALL`: This informational event is generated after the trunk has been seized, and an acknowledgement has been received from the network. (This implies that glare has been resolved.) The network is sent a `SETUP` message. This event also indicates that a B channel has been chosen for the call. The stream and timeslot for this B channel can be determined by calling briGetCallStatus. · `BRIEVN_CALL_PROCEEDING`: This low-level event is enabled only if the `BRI_CC_REPTPROCEEDING` bit is set in the `BRI_START_PARMS` `eventmask` passed to briStartProtocol (refer to the source code for `briswi` for an example). This event follows `BRIEVN_PLACING_CALL`. · `BRIEVN_REMOTE_ALERTING`: This low-level event is enabled only if the `BRI_CC_REPTALERTING` bit is set in the `BRI_START_PARMS` `eventmask` passed to briStartProtocol (refer to the source code for `briswi` for an example). It means that the network has sent an `ALERTING` message, indicating that the remote party is being alerted of the call, or that a ring back tone has been detected. · `BRIEVN_REMOTE_ANSWERED`: This low-level event is enabled only if the `BRI_CC_REPTANSWERED` bit is set in the `BRI_START_PARMS` `eventmask` passed to briStartProtocol (refer to the source code for `briswi` for an example). It means that the network has sent a `CONNECT` message, indicating that the remote party has answered. · `BRIEVN_CALL_CONNECTED:` The call has been established. This occurs when a `CONNECT` message is received by the network. The application can now play and record voice files, generate and detect DTMF tones, etc. · `BRIEVN_CALL_DISCONNECTED`: The call could not be placed. This occurs when a `DISCONNECT` message is received from the network. · `BRIEVN_INCOMING_CALL`: A call is arriving on the B channel. Call placement is aborted. This message occurs when a `SETUP` message is received. · `BRIEVN_STATUS_UPDATE`: Asynchronous information regarding the call (UUI information) has arrived. The event `value` field contains the information type.
briRejectCall	Directs the ISDN stack to reject an incoming call immediately. Associated Events: · `BRIEVN_REJECTING_CALL`: The reject sequence has started. · `BRIEVN_CALL_DISCONNECTED`: A `RELEASE` message has been received from the network. · `BRIEVN_STATUS_UPDATE`: Asynchronous information regarding the call (UUI information) has arrived. The event `value` field contains the information type.
briReleaseCall	Directs the ISDN stack to perform one of the following actions: initiate connection teardown, abandon call placement, or acknowledge a network disconnect event. Associated Events: · `BRIEVN_CALL_RELEASED:` The call has been released. A `DISCONNECT` message was sent to the network, and a `RELEASE` message was received. · `BRIEVN_CALL_DISCONNECTED`: A disconnect occurred while the release is taking place. This means that a `DISCONNECT` message has been received from the network. A `RELEASE` message is sent in response, terminating the call. · `BRIEVN_STATUS_UPDATE`: Asynchronous information regarding the call (UUI information) has arrived. The event `value` field contains the information type.
briSetExtendedArgs	Sets new arguments for the call control function that immediately follows it. Associated Events: None.
briStartProtocol	Starts the ISDN protocol. Associated Events: · `BRIEVN_STARTPROTOCOL_DONE`: The function has finished. The event `value` field indicates if the protocol started successfully. `CTA_REASON_ FINISHED` means a successful completion. Any other value implies an error.
briStopProtocol	Stops the ISDN protocol. Associated Events: `BRIEVN_STOPPROTOCOL_DONE`: Indicates that the protocol has been halted. The `value` field is set to `CTA_REASON_FINISHED`.
briUnBlockCalls	Requests the BRI service to stop blocking calls. Associated Events: · `BRIEVN_CALLS_UNBLOCKED`: The request to unblock the line is granted.

4.4 Inbound Calls

This section describes how a typical BRI service call control application receives and processes calls, once it has been initialized as described in Chapter 3.
The following is a summary of the steps to establishing an inbound call:

The network offers the call.

The application takes one of the following actions:

Action

What Happens

It answers the call, by invoking briAnswerCall.

The call is immediately connected.

It rejects the call, by invoking briRejectCall.

The call is immediately cleared.

It accepts the call without answering, by invoking briAcceptCall.

The BRI service accepts the call, but the call is not connected yet. The application can then invoke briAnswerCall or briRejectCall as needed.
Figure 9 is a state diagram for inbound calls. The sequence diagrams on the following pages can be correlated with this diagram to gain a comprehensive understanding of the inbound call states and events. Figure 9. Inbound Call State

Action	What Happens
It answers the call, by invoking briAnswerCall.	The call is immediately connected.
It rejects the call, by invoking briRejectCall.	The call is immediately cleared.
It accepts the call without answering, by invoking briAcceptCall.	The BRI service accepts the call, but the call is not connected yet. The application can then invoke briAnswerCall or briRejectCall as needed.

4.4.1 Retrieving Call Information

When the network first sends a SETUP message, the ISDN stack handles the setup of an incoming call, and collects incoming digits (including ANI and subaddress digits), and other setup information. When all initial phases of call setup are complete, and the digits and other setup information are available, a BRIEVN_INCOMING_CALL event is generated.
The application must call briGetCallStatus to retrieve the digits (calledaddr and callingaddr) and other information (stream and timeslot). For more information about the stream and timeslot, refer to the BX 2000 Installation and Developer's Manual. The call status information is stored in the BRI_CALL_STATUS data structure:

typedef struct
{ DWORD size; /* Size returned by briGetCallStatus */
DWORD state; /* Call states (BRI_CC_STATE_xxx) */
INT32 reason; /* Reason for going back to IDLE state */
char calledaddr [BRI_MAX_DIGITS+1];
/* DNIS info, called number */
/* (null-terminated string) */
char callingaddr[BRI_MAX_DIGITS+1];
/* ANI info, calling number */
/* (null-terminated string) */
DWORD pendingcommand; /* Current unacknowledged command */
char usercategory; /* User category of the calling party */
/* (for future use) */
char tollcategory; /* Toll category. Generally, same as */
/* usercategory (for future use) */
BYTE stream; /* MVIP address of B channel */
BYTE timeslot; /* MVIP address of B channel */
WORD billingrate; /* Billing rate of the call */
/* (for future use) */
char callednumplan; /* Q.931 numbering plan ID of */
/* called number */
char callednumtype; /* Q.931 number type of */
/* called number */
char callingnumplan; /* Q.931 numbering plan ID of */
/* calling number */
char callingnumtype; /* Q.931 number type of calling number */
char callingpres; /* Caller ID presentation indicator */
char callingscreen; /* Q.931 ANI screening indicator */
char progressdescr; /* Progress descriptor */
char releasecause; /* Cause for call release */
WORD service; /* Service for the current call */
char UUI[BRI_MAX_UUI]; /* UUI message received */
} BRI_CALL_STATUS;
Refer to briGetCallStatus in Chapter 6 for a description of the fields in the BRI_CALL_STATUS structure.

4.4.2 Answering the Call

To immediately answer the call, the application calls briAnswerCall.
The following events are associated with briAnswerCall:

Event

Description

BRIEVN_ANSWERING_CALL

A CONNECT message is sent to the network.

BRIEVN_CALL_CONNECTED

Indicates that the CONNECT message has been acknowledged by the network, and the connection is established.

BRIEVN_CALL_DISCONNECTED

Occurs if a DISCONNECT message is received from the network, indicating that the remote party has hung up.

BRIEVN_STATUS_UPDATE

Asynchronous information regarding the call (UUI information) has arrived. The event value field contains the information type.
Figure 10 is a sequence diagram for answering an inbound call. This diagram depicts the normal exchange of commands and events among the network, the BRI service, CT Access, and the application. Figure 10. Sequence Diagram for Answering Inbound Call

Event	Description
`BRIEVN_ANSWERING_CALL`	A `CONNECT` message is sent to the network.
`BRIEVN_CALL_CONNECTED`	Indicates that the `CONNECT` message has been acknowledged by the network, and the connection is established.
`BRIEVN_CALL_DISCONNECTED`	Occurs if a `DISCONNECT` message is received from the network, indicating that the remote party has hung up.
`BRIEVN_STATUS_UPDATE`	Asynchronous information regarding the call (UUI information) has arrived. The event `value` field contains the information type.

4.4.3 Rejecting the Call

To reject the call, the application can call briRejectCall. It causes the ISDN protocol stack to actively clear a rejected call by sending a RELEASE message. No tone is played.
The following events are associated with briRejectCall:

Event

Description

BRIEVN_REJECTING_CALL

The ISDN stack is rejecting the call.

BRIEVN_CALL_DISCONNECTED

Occurs when the RELEASE message is received from the network. Call rejection is completed.

BRIEVN_STATUS_UPDATE

Asynchronous information regarding the call (UUI information) has arrived. The event value field contains the information type.
Figure 11 illustrates rejection of an inbound call: Figure 11. Sequence Diagram for Rejecting Inbound Call

Event	Description
`BRIEVN_REJECTING_CALL`	The ISDN stack is rejecting the call.
`BRIEVN_CALL_DISCONNECTED`	Occurs when the `RELEASE` message is received from the network. Call rejection is completed.
`BRIEVN_STATUS_UPDATE`	Asynchronous information regarding the call (UUI information) has arrived. The event `value` field contains the information type.

4.4.4 Accepting the Call Without Answering

An application can accept an inbound call without answering, by calling briAcceptCall. briAcceptCall directs the ISDN stack to accept an incoming call without answering it. In response to this function call, the ISDN protocol stack sends an ALERTING message on the trunk. No further action is taken until the application calls briAnswerCall or briRejectCall, or the remote party disconnects.
The following events are associated with briAcceptCall:

Event

Description

BRIEVN_ACCEPTING_CALL

The BRI service has accepted the call, and is waiting for further instructions from the application.

BRIEVN_CALL_DISCONNECTED

The remote party has disconnected.
Figure 12 illustrates accepting an inbound call and then rejecting it: Figure 12. Sequence Diagram for Accepting and then Rejecting Inbound Call Note: When accepting and then rejecting a call, the remote party may first receive a ring back tone (when the call is accepted) and then a busy tone (when the call is rejected).
Figure 13 illustrates accepting an inbound call and then answering it: Figure 13. Sequence Diagram for Accepting and then Answering Inbound Call

Event	Description
`BRIEVN_ACCEPTING_CALL`	The BRI service has accepted the call, and is waiting for further instructions from the application.
`BRIEVN_CALL_DISCONNECTED`	The remote party has disconnected.

4.5 Outbound Calls

This section describes how a typical BRI service call control application places calls, once it has been initialized as described in Chapter 3.
Once the ISDN protocol is started on the CTA context with briStartProtocol, the application can place outgoing calls. Outbound calls are established as follows:

The application invokes briPlaceCall.

The ISDN stack causes a SETUP message to be sent to the network. This message contains the information necessary to place the call.

If the network does not accept the call placement, the BRI service abandons it and sends a BRIEVN_CALL_DISCONNECTED event.

If the network accepts the call, it sends a call proceeding message.

After the call proceeding message has been sent, the BRI service generates a BRIEVN_PLACING_CALL event.

It then waits for the remote party to accept or reject the call.

If a network connection is established, the BRI service generates a BRIEVN_CALL_CONNECTED event.

If the call request is rejected by the network (e.g., a DISCONNECT message from the network), the BRI service abandons call placement.
Figure 14 is a state diagram for placing outbound calls. This diagram can be correlated with the sequence diagram in Figure 15 to gain an understanding of outbound call states and events. Figure 14. Outbound Call State Diagram
Figure 15 is a sequence diagram depicting, at several levels, the command and event interchange for placing an outbound call. Figure 15. Sequence Diagram for Outbound Call

4.5.1 Initiating an Outbound Call

To initiate an outbound call, the application calls briPlaceCall. This function tells the BRI service to deliver a digit string to the network switch. Refer to briPlaceCall in Chapter 6 for more information about how the BRI service expects the digit string to be formatted.

4.5.2 Outbound Call Events

The following events are generated while the call is being set up:

Event

Description

BRIEVN_PLACING_CALL

This informational event is generated after the ISDN stack has seized the trunk, and an acknowledgement has been received from the network. (This implies that glare has been resolved and that the digit string has been delivered.)
This event also indicates that a B channel is now available. At this point, the application should determine which outbound channel has been assigned to the call, and connect this channel to the CTA context. The stream and timeslot corresponding to this channel can be determined by calling briGetCallStatus. For more information, refer to Section 4.4.1, Retrieving Call Information.

BRIEVN_CALL_PROCEEDING

This is a low-level event which is enabled only if the BRI_CC_REPTPROCEEDING bit is set in the BRI_START_PARMS eventmask passed to briStartProtocol (refer to briswi in Chapter 7 for an example of this). With the BRI service, this event will immediately follow BRIEVN_PLACING_CALL, because, in addition to glare resolution, the digits have been delivered to the network.

BRIEVN_REMOTE_ALERTING

This is a low-level event which is enabled only if the BRI_CC_REPTALERTING bit is set in the BRI_START_PARMS eventmask passed to briStartProtocol (refer to briswi in Chapter 7 for an example of this). It means that the network has sent an ALERTING message indicating that the remote party is being alerted of the call, or that ring back tone has been detected.

BRIEVN_REMOTE_ANSWERED

This is a low-level event which is enabled only if the BRI_CC_REPTANSWERED bit is set in the BRI_START_PARMS eventmask passed to briStartProtocol (refer to briswi in Chapter 7 for an example of this). It means that the network has sent a CONNECT message, indicating that the remote party has answered.

BRIEVN_CALL_CONNECTED

This event indicates that the connection has been established. This happens when a CONNECT message is received by the network. The application can now play and record voice files, generate and detect DTMF tones, etc.

BRIEVN_CALL_DISCONNECTED

This event indicates that the call is disconnected because a release event has been received from the network.

BRIEVN_INCOMING_CALL

A call is coming in on the B channel. The call placement is aborted. This message results from the receipt of a SETUP message.

Event	Description
`BRIEVN_PLACING_CALL`	This informational event is generated after the ISDN stack has seized the trunk, and an acknowledgement has been received from the network. (This implies that glare has been resolved and that the digit string has been delivered.) This event also indicates that a B channel is now available. At this point, the application should determine which outbound channel has been assigned to the call, and connect this channel to the CTA context. The stream and timeslot corresponding to this channel can be determined by calling briGetCallStatus. For more information, refer to Section 4.4.1, Retrieving Call Information.
`BRIEVN_CALL_PROCEEDING`	This is a low-level event which is enabled only if the `BRI_CC_REPTPROCEEDING` bit is set in the `BRI_START_PARMS` `eventmask` passed to briStartProtocol (refer to `briswi` in Chapter 7 for an example of this). With the BRI service, this event will immediately follow `BRIEVN_PLACING_CALL`, because, in addition to glare resolution, the digits have been delivered to the network.
`BRIEVN_REMOTE_ALERTING`	This is a low-level event which is enabled only if the `BRI_CC_REPTALERTING` bit is set in the `BRI_START_PARMS` `eventmask` passed to briStartProtocol (refer to `briswi` in Chapter 7 for an example of this). It means that the network has sent an `ALERTING` message indicating that the remote party is being alerted of the call, or that ring back tone has been detected.
`BRIEVN_REMOTE_ANSWERED`	This is a low-level event which is enabled only if the `BRI_CC_REPTANSWERED` bit is set in the `BRI_START_PARMS` `eventmask` passed to briStartProtocol (refer to `briswi` in Chapter 7 for an example of this). It means that the network has sent a `CONNECT` message, indicating that the remote party has answered.
`BRIEVN_CALL_CONNECTED`	This event indicates that the connection has been established. This happens when a `CONNECT` message is received by the network. The application can now play and record voice files, generate and detect DTMF tones, etc.
`BRIEVN_CALL_DISCONNECTED`	This event indicates that the call is disconnected because a release event has been received from the network.
`BRIEVN_INCOMING_CALL`	A call is coming in on the B channel. The call placement is aborted. This message results from the receipt of a `SETUP` message.