Multiplex communications – Wide area network – Packet switching
Patent
1996-05-14
1998-08-18
Rinehart, Mark H.
Multiplex communications
Wide area network
Packet switching
395841, 395309, 370463, G06F 1300, H04Q 1104, H04M 1106
Patent
active
057969582
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention pertains to a passive ISDN adapter card for data transfer with a computer and to a process for making a passive ISDN adapter card compatible with a data communications device to be run on a serial port of a computer.
By means of passive ISDN adapter cards, computers connected to each other in a wide variety of different ways can exchange information over great distances. Usually a network, a computer, a communications program, and possibly a device for converting the data to the proper form are required for this exchange of data.
If the data are to be transmitted over the telephone lines, for example, modems and acoustic couplers are used to convert the data in the manner required for connecting the personal computer to the telephone network. Before the data can be fed into the telephone network, the digital data in the computer must first be converted into analog data, and then the analog data must to be converted back into digital data at the receiving end. The invention, however, pertains to data transmission over the ISDN network, ISDN standing for "Integrated Services Digital Network". In a network such as this, both active and passive ISDN adapter cards are used; the passive cards differ from the active ones in that they do not have their own processor for handling the communications protocols. The protocols are handled in the case of these passive cards by the CPU (central processing unit) of the terminal (personal computer), which is always present.
So that communication with the connected device, whether this be a modem or an ISDN adapter card, can be carried out successfully, a long-distance data transmission applications program ("communications program") is required. So that the communications programs already existing for modems can continue to be used for passive ISDN cards as well, it is essential that the system for controlling the passive ISDN adapter card be completely compatible with a modem connected to the serial interface of the data terminal.
Only two approaches are known so far in the state of the art for making an ISDN adapter card compatible with a modem connected to the serial port.
The first approach uses an active ISDN PC adapter card, i.e., a card with its own processor. In this case, the ISDN adapter card behaves in fact like an external modem connected to the serial interface. Complete compatibility can be achieved. The active design of the ISDN adapter card, which, in addition to the appropriate peripheral components, also requires a CPU, RAM, and ROM, is frequently neither desirable for cost reasons nor even necessary.
Because ultimately the complete compatibility of the ISDN adapter card with a modem connected to the serial port can be produced only by hardware compatibility with the known serial controllers such as those normally used for connecting to external data communications devices, and because many communications programs respond directly on the register plane to this serial controller, a so-called UART, there is usually no longer any internal software interface which would allow a further evaluation process for monitoring the data stream from the application to the ISDN adapter card and for filtering out the appropriate control information such as the dialing commands.
A conceivable solution would be to resort to the INT 14 H interface in the BIOS. In general, there should be the possibility of "hooking" an evaluation process in at INT 14 H for the control of an ISDN adapter card so that, for example, dialing information could be received.
Because this software interface present in the BIOS is not very powerful, however, it is not supported by most communications programs. They make direct use of the serial controller.
A solution which would be based on the use of INT 14 H would therefore suffer from the disadvantage of not being suitable for all communications programs.
SUMMARY OF THE INVENTION
The invention is therefore based on the task of making a passive ISDN adapter card compatible with a modem connected to a s
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patent: 5450412 (1995-09-01), Takebayashi et al.
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ELSA GmbH
Rinehart Mark H.
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