# HCI/CTI Telephony Description

The HOST COMMAND INTERFACE (HCI) / Computer Telephony Integration (CTI) specification is a MITEL protocol that allows integration of host computer-based applications with system-based telecommunications services.

## HCI/CTI - Basic Telephony

HCI/CTI - Basic Telephony is the base software required for HCI applications. The software allows a host computer to instruct the system to set up and clear down calls on behalf of the system's devices.

HCI/CTI - Basic Telephony resolves external naming and addressing schemes into logical addresses which identify system resources. The addressing schemes include:

- directory numbers

- physical location identifiers (cabinet, shelf, slot and circuit)

- user names

- trunk numbers.

When the host computer specifies one of the above, the system returns a logical address, which can then be used in subsequent operations.

## HCI/CTI Advanced Telephony

HCI/CTI-Advanced Telephony is an enhancement of HCI/CTI - Basic Telephony functionality. The software allows a host computer to interrogate and monitor the state of devices and calls within the system and host computer environment. The host computer can then take action (such as invoking a feature) on the basis of the information returned to it.

HCI/CTI-Advanced Telephony also allows remote access to a user's messages on a system via an HCI application.

HCI/CTI-Advanced Telephony allows the host computer to:

- Initiate a call monitor on any station, any line appearance on a multiline telephone set, or on any trunk. ACD events may be monitored. All changes of state on the line or device result in call status messages being transmitted from the system to the host computer. Only the host computer can invoke a monitor request.

- The host computer provides a filter for the particular call processing states it is interested in. A filter has three components: a call state, a flag indicating whether all call events are to be reported or not, and a flag indicating whether name information (if available) is to be given in the call status messages.

- Stop a call monitor. A system application could issue the stop-monitor request if an error condition arose, to permit re-synchronization of the host computer with the system.

- Interrogate the monitor to verify that a monitor has been set against an extension if no call status messages have been received for a period of time. If the device is currently being monitored, then the filter in use will be returned to the host computer. Otherwise, no filter will be sent. The host computer may respond to the message (for example, raise a log). Either the host computer or the system applications can initiate an interrogation request.

- Return the call status, to inform the host computer each time there is a state change in the monitored device.

- Invoke a call event, to activate a feature on behalf of a call identified by the call reference number.

- Send, retrieve, or delete messages from a user's telephone set. A message password may be set from the host computer for a specific telephone set on the system.

- Program or de-program a system feature.

The following steps describe an application of HCI Telephony:

1. With an RS-232 cable connecting the telephone to the computer, and a suitable software application running, you can place a call from the computer.

2. The computer initiates a call request over the HCI link and provides the destination digits. The call request is processed by the system.

3. The appearance at the desktop depends on the type and state of your telephone. See Desktop Appearance of an HCI Call Request.

4. At the end of the call, send a disconnect request from the computer to clear down the call.

Related Topics

- HCI/CTI Telephony Conditions

- HCI/CTI Telephony Operation

- HCI/CTI Telephony Programming