Multi-Tech MultiModem ISDN MT128ISA-UV, User Manual

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Appendix B - Application Programming Interface
MT128ISA/PCI
Appendix B - APIs
This Appendix describes the APIs (Application Program Interfaces) used with the MT128ISA
and MT128PCI ISDN terminal adapters.
An API is a set of routines, protocols, and tools for building software applications. A good API
makes it easier to develop a application by providing all the building blocks for a programmer
to use in the development process. Most operating environments, such as MS-Windows,
provide an API so that programmers can write applications consistent with the operating
environment. Programs developed using a common API will have a similar user interface,
making it easier to learn the new program.
The three basic APIs used with the MT128ISA and MT128PCI ISDN terminal adapters are
VCOMM, CAPI and NDIS. The support provided for each API by the ISDN drivers is
dependent upon the operating system you are using. A description of these three
communication APIs follow.
VCOMM
Multi-Tech’s ISDN adapters support the VCOMM (Microsoft Windows Comm) API interface.
VCOMM is essentially a virtual communications port emulator (a virtual modem) which
provides protected-mode services allowing Windows-based applications and drivers to use
ports and modems. To conserve system resources, communications drivers are loaded into
memory only when in use by applications.
This interface is similar to a modem interface and enables existing applications based on AT
commands to access ISDN. This feature is called the Comport Emulator and allows AT
commands to enable ISDN features such as HDLC, X.75, V.120, or Async to Sync PPP
(note this emulation does NOT support fax features).
In Windows 3.1 the VCOMM API is enabled only after running the atloader.exe program.
The AT Console will not be activated automatically at boot time unless you add it to the
StartUp group in Windows 3.1.
Windows 95 and Windows 98 have the VCOMM API enabled automatically. VCOMM can
only provide AT-emulation if the application requests its COM port services from
Windows. It cannot support the application if it tries to access the COM port hardware
directly or if your software does not use the standard VCOMM driver interface.
Windows NT and Windows 2000 do not support VCOMM.
CAPI
CAPI (Common ISDN application programming interface) is an application programming
interface standard used to access ISDN equipment. When an application wants to
communicate with an ISDN card it sends a standard series of commands to the card. These
commands form the CAPI standard and give developers and users a chance to use a well-
defined mechanism for communications over ISDN lines without being forced to adjust to
hardware idiosyncrasies.
CAPI drivers take over total control of your COM port and act as a switch for any other CAPI
compatible applications. While in CAPI mode, instead of DUN (Dial-up Networking) opening
and using the “real” COM port, your system uses a “virtual” COM port. A common CAPI
application which creates this “virtual” COM port is RVS-COM. To DUN, this virtual COM
port looks like a physical COM port. If your machine has two physical COM ports (COM1
and COM2), RVS-COM creates the first virtual port as the next available port (COM3).