AU748305B2

AU748305B2 - ISDN communication process and device

Info

Publication number: AU748305B2
Application number: AU25110/99A
Authority: AU
Inventors: Michael Zirpel
Original assignee: RVS DATENTECHNIK GmbH
Current assignee: RVS DATENTECHNIK GmbH
Priority date: 1998-02-11
Filing date: 1999-01-04
Publication date: 2002-05-30
Anticipated expiration: 2019-01-04
Also published as: BR9907873A; DE19805555A1; EP1055349A2; EP1055349B1; JP2002503933A; DE59914252D1; CN1290466A; AU2511099A; WO1999041935A3; WO1999041935A2

Description

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Process and device for ISDN communication In modern telecommunications, the ISDN (Integrated Services Digital Network) standard is becoming more and more prevalent. The new standard is eminently suitable not only for communications by telephone but in particular for data transmission, since it offers a higher transmission speed and better data security than previous mechanisms used for data transmission.

For data transmission on the ISDN network, various standardised protocols are used X.75 and ISO 8208 for file transfer in accordance with the Euro-File Transfer standard and fax sending in accordance with ISDN Group 4) A common feature of most different ISDN protocols is that they are packet-oriented protocols for data transmission, that is to say the useful data to be transmitted is divided up into individual packets, with specification, check or other data relating to the communication in each case being placed before or after the useful data.

For communication over the ISDN network, the useful data to be transmitted then has to be formatted in accordance with the ISDN protocol to be used, that is to say it has to be "packed" into the appropriate packets.

Conventionally, this protocol processing is carried out by an ISDN adapter (terminal adapter) or the associated driver software. The protocols are implemented in the adapter by the adapter manufacturer, so that the functions or transmission standards available are determined by the protocols implemented in the adapter and are dependent thereon. The application software running on a computer to which the adapter is connected then uses a standardised interface the Hayes modem compatible AT instruction set or the ISDN CAPI (common ISDN application interface))

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O r ~G a 2 to use these protocols for file or fax transfer.

However, the fact that the possible functionalities depend on the protocols implemented in the adapter creates a problem. A large number of ISDN adapters do not have, or have only an inadequate number of, the protocols required by the application software. In most cases, only a small number of the protocols which are in principle possible are implemented; there is no possibility of extending the range, since the protocols available are predetermined by the adapter manufacturer and cannot be modified.

Although the problem above is not so acute when using ISDN cards which are installed in a PC, since the ISDN protocols are not processed in an external device but in the PC itself and so from this point of view there is greater flexibility, here too it is necessary to carry out processing or linking to the hardware via the CAPI. This entails the disadvantage that, when a call comes in, the ISDN card is often unable to determine the desired protocol and the desired application automatically, since when a call is to be received, because of the specifications of the CAPI, it is first necessary to communicate to the latter which ISDN protocol is to be used.

It is therefore an object of the present invention to provide a process and a device for ISDN communication by means of which a large number of ISDN protocols can be processed.

In particular, it is an object of the present invention to increase flexibility as regards the ISDN protocols which can be used and to provide the possibility of extending the range of protocols available hitherto to include new transmission protocols.

A further object of the present invention is to provide a process and a device for ISDN communication by means of which, when data comes in, there is automatic recognition of which ISDN protocol is to be used to perform successful communication.

A process and a device for ISDN communication according to the present invention are described in Claims 1, 7 and 13. The other claims describe particular example embodiments of the invention.

According to one aspect of the present invention, the data, which is packed in accordance with an ISDN protocol by means of software running on a computer, is transmitted using a second data processing unit, which may for example be an ISDN terminal adapter or a (passive) ISDN card, using an operating mode in which the second data processing unit is capable of HDLC-transparent transmission of the data it receives. HDLC (high level data link control) is a packetoriented protocol onto which the ISDN protocols etc.) are built up.

The use of an HDLC-transparent transmission mode by the second data processing unit makes it possible for the procedures involving the ISDN protocol to run completely in the application or communications software.

The only task remaining to the terminal adapter (or ISDN card) is to pass on in HDLC-transparent manner the data it receives.

In a further embodiment, the computer communicates to the adapter or CAPI interface of the ISDN card connected thereto that the latter should from now on operate in the HDLC-transparent mode. Admittedly, in the case of a terminal adapter for example, this initially restricts the functionality thereof (it cannot now itself process the ISDN protocols which in principle it is to perform), but the protocol processing is thereby shifted to the communications software running on the computer. This means that ultimately, because of the greater flexibility of the communications software, which is built up such that it can process a plurality of ISDN protocols, the flexibility of the overall system is increased.

In a preferred embodiment, the transparent mode is the PPP (point-to-point protocol) mode. Since almost all terminal adapters and almost all passive ISDN cards are capable of processing the PPP protocol, this example embodiment provides the possibility of using virtually all ISDN protocols by means of a commercially available terminal adapter, since these protocols are not processed by the terminal adapter itself but by the software connected upstream thereof. The PPP protocol is in this case used to pass on the data received by the computer (or ISDN network) in HDLC-transparent manner.

In a further preferred example embodiment, the incoming packets have their signatures of the possible ISDN protocols checked and corresponding response packets are sent until the desired protocol is determined. This provides the possibility of receiving and processing all ISDN protocols by means of a commercially available terminal adapter, without a previously defined pre-setting.

This makes it unnecessary to communicate to the CAPI of the ISDN card which protocol is to be used for a call to be received, since the protocol to be used is determined by data exchange between the receiving communications software and the sender, with the CAPI operating only in HDLCtransparent mode.

The flexibility and functionality of the overall system thus depends only on the communications software which receives and/or sends the data by means of the HDLCtransparent transmission mode of a data processing unit connected to the computer. However, there is no longer a restriction in relation to the functionality or the protocols to be used as a result of predetermined hardware limitations (terminal adapter) or software standards (CAPI interface of the ISDN card).

In a further preferred example embodiment, the communication between the computer and the terminal adapter runs asynchronously, for example via an RS 232 interface, using the asynchronous PPP protocol, while the terminal adapter converts the packets received on the ISDN network side into synchronous ones, that is to say it sends and receives packets which are HDLC-transparent.

In the above case, a second packet-oriented protocol is therefore "overlaid" onto the ISDN protocol actually to be used for communication, namely the PPP protocol, which however serves only to transmit and receive in transparent manner the actual ISDN protocol and/or the data formatted in accordance with this ISDN protocol. In this way, the ISDN protocol processing can be shifted to a higher level, namely the level of communications or application software.

The terminal adapter itself here performs only the role of transparently passing on the data packed in accordance with the ISDN protocol.

In the description below, the present invention is described in more detail with reference to the attached drawings, using some preferred example embodiments. In the drawings: Fig. 1 is a diagrammatic representation of the attachment of a PC to the ISDN network by means of a terminal adapter.

Fig. 2 is a diagrammatic representation of transmission over the ISDN network by means of a terminal 6 adapter in conventional manner.

Fig. 3 is a diagrammatic representation of transmission over the ISDN network by means of a terminal adapter according to the present invention.

Fig. 4 is a diagrammatic representation of the attachment of a PC to the ISDN network by means of a passive ISDN card.

Fig. 1 is a diagrammatic representation of the attachment of a personal computer (PC) 100 to an ISDN network 110 by means of a terminal adapter (TA) 120. A communications program 130 runs on the PC 100 and transmits data to the terminal adapter 120 by way of an interface 140. This is for example an interface which transmits data only serially and asynchronously, e.g. an RS 232 interface, a parallel port, an IRDA interface, a USB interface with COM port emulation, etc. Formatting in accordance with the ISDN protocol used is carried out by the communications software. This formatted data is then transmitted to the terminal adapter 120 by way of the interface 140, for example using the PPP protocol. The terminal adapter 120 then further p.rocesses the incoming data by using its PPP functionality to transmit the packet structure transmitted to it by the interface 140 over the ISDN network 110 in HDLC-transparent manner.

Whereas in the prior art, as shown in diagrammatic representation in Fig. 2, the ISDN protocol is processed in the terminal adapter, in the case of the example embodiment according to the present invention, as shown in diagrammatic representation in Fig. 3, thanks to the use of PPP mode in the terminal adapter the ISDN protocol processing can be shifted to the communications software of the PC.

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i The PPP protocol is a serial transmission protocol for point-to-point connections used for example on the Internet. Almost all the ISDN adapters on the market have PPP functions for Internet and remote (RAS) access. Using the PPP functions, HDLC (high-level data link control)based ISDN B channel protocols are thus implemented in the (communications) software as a field modification, without the adapter itself having been equipped with these protocols by the manufacturer. Using the PPP functionality, the adapter can then also be used for such "retrofitted" ISDN applications as Group 4 fax and Euro-File Transfer.

An HDLC-transparent transmission of the packets is thus carried out on the ISDN network. Here, HDLCtransparent means that the structure according to the HDLC protocol is passed on unchanged from one communication end point to the next. The PPP stage connected in between passes the HDLC packets on "transparently", i.e. unchanged.

The packets are transferred to the application or communications software or passed on from it with their packet structure maintained. To go into detail, with adapters which are controlled by AT instructions (instructions of a Hayes-compatible modem) this is conventionally performed in that an asynchronous PPP protocol is used for -the data exchange between the computer 100 and the adapter 120.

For this purpose, the packets are marked with certain frame markers (marking characters for the start and end of the packet). These characters are converted using an escape sequence in the actual data to be transmitted. Finally, for error recognition, the packets are also provided with check information (CRC). Packets with errors can then be rejected, once the CRC check has been performed, by both the adapter and the application software.

Finally, the terminal adapter 120 converts the 111 8 asynchronous PPP data into synchronous data on the ISDN network side, that is to say it sends and receives HDLCtransparent packets. The application software thus performs the HDLC-based ISDN protocols (X.75, V.120, ISO 8208, etc.) by sending the suitable packets, or evaluating the received packets appropriately.

During the processing in accordance with the PPP protocol, however, packets which correspond to the usual PPP contents are not processed, but rather those packets which are based on ISDN B channel protocols. This means that for example a PPP header is replaced by an header. Some terminal adapters now perform a check on the receiving side so that the received packets are checked for their standardised PPP components. If a check of this kind results in failure, the packets are rejected. Since, according to the present invention, however, there is no PPP communication, properly speaking, but rather the PPP protocol functions merely as an "overlaid" addition to the ISDN protocol, which is actually used, the PPP implementation of the adapter may have to be modified such that the contents of the (received) packets are not checked for the standardised PPP components but are passed on in transparent manner. With commercially available terminal adapters which carry out a PPP check of this kind, a slight modification is therefore necessary in order to use the PPP functionality of these terminal adapters for transmission in accordance with ISDN protocols.

Fig. 2 shows a diagrammatic representation of the "packing" of the useful data to be sent, in a conventional system comprising a terminal adapter (TA) and a PC on the sending and on the receiving side. The data sent from the PC to the terminal adapter is in this case sent in a manner based on the ISDN protocol to be used (here X.75), and on the receiving side it is in turned unpacked by the terminal adapter, using the appropriate ISDN protocol, and passed on to its target destination, for example a file in the receiving PC, or to a port of software running on this PC.

Fig. 3, in contrast, shows in diagrammatic representation the procedure according to the present invention. The ISDN protocol processing is carried out in the PC. The data formatted in accordance with the ISDN protocol is passed on to the terminal adapter (TA) using the asynchronous PPP protocol, and there it is converted by the terminal adapter to synchronous packets using the HDLCtransparent transmission mode providing the PPP functionality of the terminal adapter, and transmitted over the network in HDLC-transparent manner. On the receiving side, once again all that is required is for the terminal adapter to pass on the data in HDLC-transparent manner, and the actual ISDN packets are passed on in HDLC-transparent manner to the receiving terminal device (PC) using the PPP mode of the adapter.

Fig. 4 shows a further example embodiment according to the present invention, in which the hardware implementation is not carried out by means of a terminal adapter but by means of a PC 200 and a passive ISDN card 220.

Conventionally, these ISDN cards provide a software interface, CAPI, for communication with the communications software or application software 230 overlaid onto it. In conventional operation, the data to be sent is transferred to the ISDN card via the CAPI. The corresponding ISDN protocols are processed there, and the data is transmitted over the ISDN network.

In the example embodiment according to Fig. 4, however, the ISDN protocol processing is no longer carried out once the data to be sent has been transferred to the CAPI, but before this, on the level of a communications program 230. This communications program processes the ISDN protocols and then, for sending on the data packed in this way, uses the mode of HDLC-transparent transmission to the CAPI. The rest of the procedure otherwise corresponds to the example embodiment of Fig. 1.

In the example embodiment of Fig. 4, therefore, the ISDN protocol processing is shifted "up" a level, that is to say to the level of the communications program 230 placed upstream of the CAPI software interface. This has a number of advantages. Although, in the case of passive ISDN cards, there is no longer a limitation to certain protocol implementations, since with these ISDN cards the ISDN protocols run on the PC, and thus there is no hardware limitation as in the case of the terminal adapter in this form, on the other hand there is a limitation in that use has to be made of the CAPI specifications for communication with application software or a communications program overlaid thereon. If, however, an incoming call is to be assessed, with the conventional configuration, for example, it is necessary to communicate to the CAPI which protocol must be used for receiving.

According to the present invention, however, the CAPI is not used to access the ISDN protocols running at a lower level, but is used merely to allow HDLC-transparent transmission to be performed. For this transmission functionality, however, it is not necessary to communicate to the CAPI which protocol must be used for receiving.

The communications software overlaid onto the CAPI therefore receives in ISDN format the data which is passed on in transparent manner by the CAPI using its HDLCtransparent transmission mode. The communications software is in this case constructed such that it checks the incoming packets for the appropriate signatures of the ISDN protocols and sends corresponding response packets until the desired protocol is determined. Because the signatures f the desired application are searched for within the packets received, it is possible to process a large number of ISDN protocols, for example G4 fax, Euro-File Transfer, video telephony, simple data transmission, etc. For this purpose, only the appropriate components of the communications software overlaid onto the CAPI are activated.

The invention according to the second example embodiment is thus similar to that of the first example embodiment, although, unlike the case of the first example embodiment where there is in principle a limitation present as regards possible protocols, rather an actually present multifunctionality of the passive ISDN card is "artificially" suppressed by using the ISDN card only to process HDLC-transparent transmission. As a result of this, the limitations produced by using the CAPI with a conventional configuration are bypassed, since the communications program overlaid onto the CAPI can be constantly expanded in its range and adapted to the requirements.

Furthermore, the second example embodiment bypasses the necessity, when data is received by means of ISDN, of first communicating to the CAPI which protocol must be used to process the incoming data.

In the two example embodiments described, the present invention makes use of the fact that both commercially available terminal adapters and CAPI provide the function or processing of HDLC-transparent transmission. In the case of a terminal adapter, the PPP functionality used for this is not used for its actual purpose, making a PPP connection, however, but serves to "mask" the ISDN packets and transmit them over the ISDN network in HDLC-transparent manner. This makes it possible to shift processing of the ISDN protocols used for communication to a higher level, namely that of the communications software, as a result of RAz

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which both the flexibility and the functionality are markedly improved by comparison with the prior art.

It should be noted that the example embodiments above have a merely illustrative nature. Instead of the PPP functionality, any other mode which is suitable for HDLCtransparent transmission may also be used. In addition, the "transparent" transmission does not necessarily have to be HDLC-transparent; other comparable packet-oriented synchronous transmission standards may also be used for a transparent transmission of this type.

L -0 EDITORIAL NOTE NO.25110/99 The claim page numbering is not consecutive to the description. Claims pages are 1-3.

Claims

2. A process according to claim 1, which furthermore comprises the following steps: putting the terminal adapter in PPP mode by means of a signal from the data processing unit.
3. A process according to one of the preceding claims, in which instead of the terminal adapter, an ISDN card is used, N the functionality of the HDLC-transparent transmission of the CAPI (common ISDN application interface) being used for the mode of HDLC-transparent transmission.
4. A process according to one of the preceding claims, which furthermore comprises the following steps: checking incoming packets for the signatures of the possible ISDN protocols by means of the program running on the data processing unit, and sending corresponding response packets until the desired protocol is determined. A device for the transmission and/or receiving of data over an ISDN connection, which comprises: a unit for sending/receiving the data by a data processing unit by way of an ISDN terminal adapter by means of a program running on the data processing unit, the terminal adapter operating during the sending and receiving in a transparent mode in which it passes on the data received from the data processing unit or the ISDN network to the ISDN network or the data processing unit in HDLC-transparent manner, and the ISDN-B-channel protocols necessary for ISDN communication being processed by the program running on the data processing unit, the transparent mode is the PPP mode of the terminal adapter, and the data exchange between the data processing unit and the terminal adapter takes place via an asynchronous PPP protocol and on the ISDN network side the terminal adapter using its PPP functionality converts the packets received from the data processing unit into synchronous packets which are transmitted in HDLC-transparent manner, whereas the terminal adapter does not perform a check of the standardised PPP contents (PPP header).
6. A device according to Claim 5, which furthermore comprises the following: a unit for putting the terminal adapter in the PPP mode by means of a signal from the data processing unit.
7. A device according to one of claims 5 or 6, which instead of the terminal adapter has an ISDN card, the functionality of the HDLC-transparent transmission of the CAPI (common ISDN application interface) being used for the mode of HDLC-transparent transmission.
8. A device according to one of claims 5, 6 or 7, which furthermore comprises the following: a unit for checking incoming packets for the signatures of the possible ISDN protocols by means of the program running on the data processing unit, and a unit for sending corresponding response packets until the desired protocol is determined.
9. A computer program product which comprises computer- readable program code which allows the computer to transmit and/or receive data over an ISDN connection, the computer program product comprising the following: computer-readable program code in order to enable the computer to carry out a method according to one of claims 1 to 4.