HCI/CTI - Basic Telephony does not inform the host computer of the state of the user device or the success of a call attempt. The call progress tones returned to the call originator's set allow the originator to judge the success of the call request. HCI/CTI - Advanced Telephony does pass this call state information to the host computer.
Database changes, such as moving a directory number to a different circuit, are not automatically reflected in the host computer's database. The host computer application must be instructed to query the system to obtain current information associated with directory number or a physical location identifier.
The HCI specification is an application-to-application protocol based on the following communications standards:
CCITT X.409
CCITT X.410
LAPB (CCITT X.25).