External equipment provides additional features to the system
in their own right. These are features that are not otherwise
present on the system. Examples are the Voicemail systems
covered earlier in this book, voice announce units and music
on hold sources.
Computer Telephony Integration (CTI) is a relatively new facility
becoming available on a widening range of telephone systems.
In simple terms it is a method of connecting the system to
a computer and for these to work as an integrated unit. Using
these interfaces has made it possible to provide much enhanced
functionality to the users. These new facilities have begun
to open up new application areas whose limits will be defined
only by the ingenuity of the developers and willingness of
the customers to pay for them.
The link is achieved with a combination of hardware and software
provided by or in association with the system
manufacturer. The hardware is usually an interface card for
the system and/or the PC. The system software will be able
to operate the card when it is installed, and there will be
software for the computer to allow it to communicate with
the system via the interface.
The most basic of these is the Telephone Applications Programming
Interface (TAPI) which connects individual
computers to the system, usually using the proprietary extension
port and allowing the computer to have access to basic system
functions and control of the extension port when required.
TAPI is a Microsoft protocol, which is currently at version
2, with version 3 due to become available in early 2000.
The protocol is a series of software functions and calls which
allow the application to use the operating system to interact
with the telephony connection.
The Telephone System Applications Programming Interface (TSAPI)
is more sophisticated link between the telephone system and
a computer. In this case the link is directly from the CCU
of the telephone system to a network server which allows integration
of the functions of the telephones and computer network on
a system wide basis from the one connection.
The level of integration is such that Unified Messaging System
functions can be combined in a single application. Control
can be from the users computer and/or extensions. It
can also enable transmission of call data such as Calling
Line Identity (CLI) from system to system so that as the users
phone rings their terminal presents them with a database
record containing information about the caller if they have
TAPI and TSAPI are 'open' interface protocols. Developers
can obtain and use the specifications and be confident that
the applications they create will be compatible with other
equipment following the standard. Proprietary Application
Interfaces (PAPI) are created for a single system, usually
by the manufacturer. They have the advantage of being more
highly integrated with the system than TAPI and TSAPI as they
are not required to adhere to the standards defined for these
interfaces. The disadvantage is that the applications developed
for them cannot be used on other platforms and the programmers
will need to learn them before creating the applications.