GB2263846A

GB2263846A - Method and system for interfacing a computer to a digital telephone network or to other digital transmission systems

Info

Publication number: GB2263846A
Application number: GB9301765A
Authority: GB
Inventors: Pekka Lahtinen; Esko T Rautanen
Original assignee: Nokia Telecommunications Oy
Current assignee: Nokia Oyj
Priority date: 1992-01-31
Filing date: 1993-01-29
Publication date: 1993-08-04
Anticipated expiration: 2013-01-29
Also published as: FI920444A0; GB9301765D0; FI90173C; DE4301733A1; FI90173B; GB2263846B

Description

2263846 1 Method and system for interfacing a computer to a digital

telephone network or to other digital transmission systems This invention relates to a method and a system for interfacing a computer to a digital telephone network or to other digital transmission systems by an interface unit connectable to a computer interface bus.

At present, computers are connected to an analog telephone network by a voltage interface, i.e. a modem, which is connected to the analog subscriber interface of the analog telephone network. The modems establish voice-based connections to another subscriber equipment in the network.

In practice, computers are able to transfer only codeword-based data in an analog telephone network, which data must be transferred acoustically. The transmission rates so obtained are low. New digital transmission systems require an essentially different architecture to fully benefit from the digital connections. One example of digital transmission systems is the integration of different electric subscriber services, such as telephone, cable television, etc., into a single subscriber connection. An international ISDN standard (Integrated Services Digital Network) has been developed for digital signal transmission. In the basic ISDN connection, a so-called S interface bus connects a network terminal to one or more terminal equipments. The S interface of the terminal equipment connection is defined in the CCITT specifications 1.411, 1.412 and 1.430, and it employs a 2B+D channel configuration, where the rate of the B channel is 64 kbit/s and the rate of the D channel 16 kbit/s.

2 The ISDN digital interface thus enables a computer, such as a PC, to transmit data directly in digital form and voice coded into digital form, typically at a rate of at leat 64 kbit/s. Connections can be established both to digital-and analog terminal equipments. Accordingly, the computer is able to receive, transmit and process digital voice, such as speech, at the transmission rate offered by the ISDN interface under the control of its own processor or a control processor located in the interface board.

The object of the present invention is to provide a method and a system for interfacing a computer or a similar workstation to a digital telephone network, such as an ISDN network or a similar digital transmission system comprising an ISDN interface. The method according to the invention is characterized in that the traffic is arranged to take place on the time-division principle in a digital serial bus system of the interface unit by means of a switching field, whereby the digital voice, data and/or signalling channels of the digital telephone network or transmission system are connected to the serial bus system so that digital voice, data and/or signalling information can be read from/written to the serial bus system by the computer over the computer interface bus, and that the interface unit is able to transmit or receive data independently in desired timeslots.

According to another aspect of the present invention, there is provided a system for interfacing a computer to a digital telephone network or to other digital transmission systems by an interface unit connectable to a computer interface bus, characterized in that.the interface unit comprises a digital serial bus system and a switching field, by means of which traffic in the serial bus system takes place on the time-division principle, and that the digital voice, data and/or signalling channels of said network or transmission 3 system are connected to the serial bus system so that digital voice, data and/or signalling information can be read from/written to the serial bus system by the computer connected to it over the computer interface bus, if required, via electronics of the interface unit, which interface unit is also able to independently transmit data to or receive data from the channels of the digital telephone network or transmission network in desired time-slots.

Other preferred.embodiments of the invention and the system according to the invention are characterized by what is disclosed in the claims below.

In the following the invention will be described more closely by means of examples with reference to the attached drawings, in which 21 .P 4 Figure 1 shows a prior art configuration for interfacing a computer to a public telephone network;

Figure 2 shows, in the same manner as Figure 1, a computer connected to a digital interface in accordance with the invention; Figure 3 is a block diagram illustrating a digital interface according to the invention based on the time-div sion technique; Figure 4 illustrates one way of transmitting data or digital voice in the interface according to the invention; Figure 5 shows an embodiment of the invention for realizing a digital telephone; Figure 6 shows an embodiment of the invention for connecting the interface circuit of a computer to a digital hterface; Figure 7 shows an embodiment of the invention for expanding the architecture of a digital interface; and Figure 8 shows an example of the division of tasks between a computer and an interf ace according to the invention.

At present, computers are connected to an analog telephone network in a manner shown in Figure 1. A personal computer 1 is connected by a voltage interface E to a modem 2, which is connected to an analog subscriber interface F of an analog telephone network 3. The modem 2 establishes an acoustic connection to another subscriber equipment 4 in the net- work 3. The voltage interface E is usually realized by a circuit which converts a TTL-level signal into a V.28-level signal ( 12V).

In the computer's own architecture, this interface may be realized as shown in Figure 1. The computer (PC) comprises a processor 5 which controls a bus 6. The bus 6 has associated memory circuits 7 containing a program code required by the processor 5 and data processed by it. The bus 6 also has an associated interface circuit 8 having registers processed by the processor 5. The interface circuit 8 transmits data to and receives data from the registers interface separate provided f rom the interface by means of the voltage interface E. The circuit 8 may also be connected to a interf ace bus (such as an ISA or EISA bus) for the interface circuits and separated internal processor bus of the processor by circuits. The bus is located in the address space of the processor, but it may have its own clock frequency, for instance.

Figure 2 shows a computer 1 connected to a digital ISDN interface in the same manner as in Figure 1. In an ISDN network 13, data can be transmitted directly in digital form via an interface G at a transmission rate offered by it, typically at least 64 kbit/s. Voice, such as speech, coded into digital form can be received, transmitted and processed in the connections both with a digital and an analog terminal equipment 4.

A connection to the digital transmission system is established by an interface unit mounted in the computer 1. This may be a printed circuit board mounted in the expansion interface of the computer bus, called an interface board 9 in this example. An essential feature of the architecture of the inter- f ace unit of the invention is that the bit stream supplied by the digital interface G is passed on to an internal serial bus system 15 of the interface board, where the buses can be switched together as desired by a switching field 14. Furthermore, the buses can be switched by appropriate interface cir- 6 cuits 16 to an internal parallel bus 17 of the interface board, which parallel bus is controlled by a processor 12. In Figure 3, the means indicated by the reference numerals 14 to 16 are drawn in outline in the absence of established graphic symbols. The operation and purpose of the means 14 to 16 will be described more closely below. The processor 5 and the bus 6 of the computer have the following type of interfaces to the. interface board: an interface cir- cuit system 10 corresponding to the interface circuit 8 of Figure 1, and a two-port memory 11; data and voice can be supplied from these e.g. to the processor 12 over the bus 17.

In the method according to the invention, to interconnect the computer and the digital transmission network, it is essential that the interface board 9 of f ers a platform for a wide range of dif ferent applications offering digital transmission, where application features can be programmed to be performed both by the processor 5 and the processor 12. Flexibility is in a key position, which is due to the different serial and parallel buses and their interconnection.

The interface shown in Figures 2 and 3, by way of example an ISDN interface, typically comprises a plurality of digital channels implemented with timedivision techniques, such as channels D, Bl and B2 in Figure 3. The speeds of these channels in the S interface of the basic ISDN are 16, 64 and 64 kbit/s.

The D channel is used for call control, and the B channels for transferring data or voice transparently through the ISDN network 13.

Similarly as in Figure 3, the serial bus system 15 in Figure 2 may comprise a number of conductors Jl 35... Jn, each having a number of time-slots A realized 7 by the time-division technique. Time-division (such as TDM) is a well- known technique, and will not be described 'more closely herein. The time- division techniques of different serial buses are supported by one or several manufacturers of integrated circuits, so that data or digital voice can be connected to/from the time-slots of the serial bus system 15 from/to different sources by utilizing commercially available integrated circuits, which will be called 10 serial bus circuits hereinbelow.

Figure 3 shows a serial connects the digital channels digital telephone interface G and transmission direction to bus circuit 18, which D, Bl and B2 of the both in the reception the time- slots of the serial bus system 15. An arrangement according to the basic idea of the invention, where the switching field 14 enables the time-slots to be configured as desired, is also well-suited to interfaces other than the 2B + D interf ace, e.g. to the 30B + D structure.

In addition, there are applications where one channel may reserve several time-slots, which is illustrated in this specific case by a channel B2, which has reserved two successive time-slots. In this way, data from the interface G is available to any other serial bus circuit 16 associated with the serial bus system 15 by reading the data from the appropriate time-slot of the appropriate conductor Jl... Jn; on the other hand, one such other serial bus circuit at a time may control the data to be transmitted to a certain chan- nel of the interface G by writing the desired data in the appropriate time-slot of the appropriate conductor Jl... Jn.

Figure 3 shows one such other serial bus circuit 16, which realizes one way of interconnecting the parallel interface bus 17 and the serial bus 8 system 15 (cf. Figure 2). The serial bus circuit 16 contains registers R which can be read and written from the interface bus 17. Part of the registers R are control registers controlling the operation -of the serial bus circuit 16, while part of them are data registers the content of which is either written in a time-slot or is derived from a time-slot A (possibly determined by the control register). In this way, data can be transferred exactly in a desired manner between the interface bus 17 and the serial bus system 15, and further between the interf ace bus 17 and the channels D, B1 and B2 of the interface G.

The flexibility and versatility of this electronic switching arrangement is further improved by the switching f ield 14, which is able to switch any time-slot of the serial bus system 15 to any other time-slot. These switchings can be controlled from the interface bus 17 by writing into the control registers of the switching field 14 (not shown).

Accordingly, each one of the serial bus circuits 18 and 16 may operate e.g. in predetermined f ixed time slots, and the transfer of data between these time slots and thus between the serial bus circuits is controlled by the switching field 14. A time-slot based switching f ield is well-known in the art, and there are several manufacturers of s7itching field microcircuits (e.g. Mitel and Siemens), wherefore the operation of the switching field, being known to one skilled in the art, will not be described more close ly herein.

What has been stated above and will be stated below concerning data processing in the serial bus system 15 also applies to digital voice as the serial bus system 15 does not make difference between dif- 9 ferent kinds of digital information transferred in the time-slots. It is further to be noted that the channels Bl, B2 and D of the interface G are only examples of a selection of channels which may be contained in an interface, a digital telephone network or other such digital transmission system.

Timing is of vital importance in the switching arrangement shown in Figure 3, as the interface G is operated in synchronization with the clock of the ISDN network 13, whereas the bus 17 operates in synchronization with the processor 12 of Figure 2. Serial bus synchronization is the timing prevailing in the serial bus system 15, in the switching field 14, and in that portion of the serial bus circuit 18 located between the serial bus system and the interface which is associated with the serial bus system 15. Serial bus synchronization can be obtained from the interface G, or the interface board may comprise a crystal or the like providing serial bus syn- chronization; the interface board may thus operate even without a connection to the ISDN network 13.

Figure 4 shows one way of transferring data or digital voice between the interface circuit system 10 and the two-port memory 11 shown in Figures 2 and 3 and serial bus circuits 16a and 16b similar to the serial bus circuit 16. The processor circuit 12 and a DMA circuit 19 controlled by it transfer data between the circuits 10 and 11 and the circuits 16a and 16b. The interface circuit 10 may contain e.g. registers Rl... Rn addressable both f rom the bus 6 of the computer and the bus 17 of the interface board. The twoport memory circuit 11 contains a number of memory positions M addressable from both buses. Essential is the transfer of data and digital voice from the computer bus 6 to the serial bus circuits 16a and 16b, to the serial bus system 15 and further to the ISDN interface G (cf. Figures 2 and 3), and vice versa.

It appears from the above technical specification how the digital channels of e.g. the ISDN network are connected to the interface board, how they can be switched as desired to the time-slots in the serial bus system of the board, and how data or digital voice can be read from or written into the time-slots from the computer bus. It is especially important to note that the interface of the ISDN network in the computer does not depend on the applications used, and that the processors 5 and 12 of the computer and the interface board can both be programmed to serve digital data transmission between the computer and the ISDN.

Figure 5 shows how an external equipment, in this specific case an analog telephone handset, can be connected to the interface board. Various other external equipments can be used in different applica- tions. The analog handset 20 is connected by an analog speech interface A to an adapter circuit 21, such as a commercially available serial bus circuit referred to in the description above. The circuit 21 contains a digital/analog converter 22, which converts the digital voice extracted by the circuit 21 from a certain time-slot of the serial bus system 15 into analog form to the loudspeaker of the handset 20. Correspondingly, the circuit 21 contains an analog/digital converter 23, which converts the analog voice from the microphone of the handset 20 into digital form to be written in a certain timeslot of the serial bus system 15. This operation (as well as other functions of the circuit 21) are controlled by control registers 24, which can be read and written by the interface board processor 12 over the internal interface bus 17 of the interface board. In this way, a digital telephone can be achieved by the interface board.

If required, the processor 5 of the computer (Figure, 2) may control this procedure by forwarding commands directly to the processor 12, e.g. via the two-port memory 11 shown in Figure 2.

In Figure 6, the external equipment is the computer's own interface circuit, i.e. an integrated circuit connected to the bus of a PC, for instance. In Figure 6, the connection of the conventional serial interface circuit 8 according to Figure 1 to the digital transmission system is realized by a commercially available serial bus circuit 25, which adapts the TTL level voltage interface Eb of the circuit 8 to the time- slots of the serial bus system 15. A framing is employed which is assembled by an internal connection SF of the circuit 25 on transmission and disassembled by a connection FS on reception. In this way the conventional data transmission rate of the interface circuit 8 can be adapted to the higher transmission rate of the serial bus system and the ISDN.

As concerns the interface circuits, the inter- face circuit 8 may be mounted in the interface board 9, as in Figure 7, or the interface board may comprise a TTL level connector for the Eh interface or even a modem-emulating connector for a V.28 level (±12 V) serial interface (cf. the interface F in Figure 1). In this way the computer's own equipment or software may use the switching arrangement of Figure 6 in the same way and with the same software as it uses the switching arrangement of Figure 1.

To sum up, it can be stated that a large number of external equipment can be connected to the basic 12 architecture of Figures 2 to 4 by using existing commercially available serial bus circuits; such "external equipment" may also be internal equipment of the computer, in which case full software compatibility is ensured by emulating protocols and external connections known to the computer.

According to one embodiment of the invention, the architecture of the computer can be easily expanded as shown in Figure 7 by designing various expansion boards 26. In the example of Figure 7, for instance, from the interface board 9, by means of connectors Cl and C2 (having e.g. a flat cable C3 therebetween) has been transferred to the expansion board 26 the conventional TTL-level serial interface Eb shown in Figure 6, which continues on the expansion board as a serial interface Ex; one or more data conductor pairs Jx of the serial bus system 15, which enable certain time-slots of the serial bus system to be used in the expansion board; and the internal interface bus 17 of the board (17b on the expansion board).

Due to this expansion, any connector or device 27 on the expansion board may transfer conventional serial interface data utilizing the switching arrangement of Figure 6 (device 27 in Figure 7 replaces device 8 in Figure 6). In addition, any serial bus circuit 28 operating in -ffie serial bus system time-slots may be located on the expansion board. Through the expansion 17b of the bus 17 the interface board processor 12 may control any circuits 29 on the expansion board.

It is especially important to note that the serial bus circuit 28 may connect to the interface board an interface Gb of an ISDN network 13b which is not supported by the normal ISDN interface located on 13 the board (shown in Figures 2 and 3). This is of importance as there are technically different interf aces even for the same digital transmission service, and these require different serial bus circuits 28. This expandability makes the interface board compatible with several future digital networks and transmission systems.

Naturally, the circuits 27, 28 and/or 29 in Figure 7 may be one and the same circuit. Only an example of the flexible expansion of the architecture of the basic interface board by using expansion boards in accordance with the invention has been presented; practically all interface board buses and interfaces can be expanded by means of expansion boards.

The connection and interaction between the computer and the ISDN network and other devices behind the ISDN connections are thus based on a program code executed both by the processor 5 of the computer and the processor 12 of the interface board, and on the interaction between the program codes. The processor 12 of the interface board in particular is able to nearly independently take care of the establishment of connections through the ISDN network 13 to other equipment 4 (cf. Figure 2) by means of the software stored in the memories of the interface board.

This is a very important feature'distinguishing the present invention from prior art systems where the equipment corresponding to the ISDN interface board is directly controlled by the processor of the computer.

Figure 8 illustrates this principle. The processor 5 of the computer executes application programs Al... An, and the processor 12 of the interface board executes e.g. switching and signalling 14 programs Bl... Bn. The buses 6 and 17 and the electronics - provided therebetween, such as the circuits 10 and 11, of fer a data transmission link between the processors 5 and 12, that is, they provide a flexible way of implementing exactly the desired communication between the program groups Al... An and Bl... Bn. The switching and signalling programs Bl... Bn may perform e.g. the following functions, indicated by the references i... iv in Figure 8:

1: controlling the switching f ield 14 to switch time-slots in the serial bus system 15; ii: transmitting and receiving data through the serial bus circuits 16; iii: one important special case of ii is an independent processing of the signalling protocols with the exchange of the ISDN 13 by using the signalling channel D (Figure 3) to set up calls; and iv: another important special case of ii is the processing of data transmission protocols with other subscriber equipments 4 by using the data transmission channels Bl and B2 (Figure 3), e.g. to transfer data from the computer to the equipment 4.

The most significant teaching of this example is that the functions i... iv are seen as automatic from the viewpoint of the application programs Al... An of the computer, and if required, the application programs are able to control them over an electronic connection consisting of buses and interfacing electronics provided between the buses (6, 17, 10, 11).

In the same way as the interface board programs Bl... Bn are able to provide flexible service to the computer programs Al...An, they are also able to provide service to the external equipment shown in Figures 5 and 6 and to the expansion boards shown in Figure 7.

It is obvious to one skilled in the art that the different embodiments of the invention are not restricted to the above examples but they may vary within the scope of the attached claims.

16

Claims

Claims:

1. A method for interfacing a computer to a digital - telephone network or to other digital trans mission systems by an interface unit connectable to a computer interface bus, c h a r a c t e r - i z e d in that the traffic is arranged to take place on the time-divislon principle in a digital serial bus system- of the interface unit by means of a switching f ield, whereby the digital voice, data and/or signalling channels of the digital telephone network or transmission system connected to the serial bus svstem are so that digital voice, data and/or signalling information can be read from/written to the serial bus system by the computer over the computer interface bus, and that the interface unit is able to transmit or receive data independently in desired time-slots.

2. A method according to claim 1, c h a r a c - t e r i z e d in that the interface unit is able to automatically establish a connection to the digital telephone network or transmission system through the channels of an interface of the digital telephone network by using its own processor and bus and various handshaking and/or data transmission protocols, and to accomplish time division switching of the serial bus system over said connections, and that the computer controls the operation of the connection through an interface cir cuit system and/or a two-port memory located in the interface unit.

3. A method according to claim 1 or 2, c h a r a c t e r i z e d in that external equipments that cannot be connected as such to the computer are connected to the digital telephone system or 17 transmission system unit.

4. A method according to claim 1, 2 or 3, c h a r a c t e r i z e d in that the computer is connected by means of said interface unit to the digital telephone network or transmission system by emulating external interfaces used by said computer and/or its software by means of the inter face unit.

5. A method according to any of claims 1 to 4, c h a r a c t e r i z e d in that one or more expansion boards - are connected to said interface unit for expanding the electronics and/or soft ware of the interface unit to a network or trans mission system - with which communication cannot take place by means of the interface unit only.

6. A system for interfacing a computer to a digital telephone network or to other digital transmission systems by an interface unit connectable to a computer interface bus, c h a r a c t e r - 1 z e d in that the interface unit comprises a digital serial bus system 1 and a switching f ield, by means of which traf f ic in the serial bus system takes place on the time-division principle, and that the digital voice, data and/or signalling channels of said network or transmission system are connected to the serial bus system so that digital voice, data and/or signalling information can be read from/written to the serial bus system by the computer connected to it over the computer inter face bus, if required, via electronics of the interf ace unit which interface unit is also able to independently transmit data to or receive data from the channels of the digital tele- phone network or transmission network in desired by means of said interf ace 18 time-slots.

7. A system according to claim 6, c h a r a c - t e r i z e d in that the interface unit has a processor and a bus to automatically establish a connection to the digital telephone net work or transmission system over the channels of an interface of the digital telephone network, and to accomplish time-division switching of the serial bus system over these connections, and that the interface unit has an interface circuit system and/or a two-port memory for transmitting information about the operation of the connection between the computer and the processor

8. A system according to claim 6 or 7, c h a r- a c t e r i z e d in that the interface unit has external connections to equipment not directly connected to said computer though connected to said network or transmission system.

9. A system according to claim 8, c h a r a c - t e r i z e d in that the external connection com prises a telephone interface to which an analog telephone handset is connected, the signals from the handset being adapted for the digital telephone network in the interface unit.

10. A system according to any of claims 6 to 9, characterized in that the interface unit has external interfaces emulating external inter faces used by said computer and/or its soft ware.

11. A system according to any of claims 6 to 10, c h a r a c t e r i z e d in that the interface unit comprises one or more connectors by means of which the electronics and/or software of the interface unit is expandable by one or more expansion boards having an interface to a network or 19 transmission system to which the interface unit itself is not connected.

12. A system according to any of claims 6 to 11, c h a r a c t e r i z e d in that the interface unit comprises a printed circuit board mountable in the expansion interface of the computer bus.

13. A method for interfacing a computer to a digital telephone network or to other digital transmission systems substantially as hereinbefore described with reference to the accompanying drawings.

14. A system for interfacing a computer to a digital telephone network or to other digital transmission systems substantially as hereinbefore described with reference to the accompanying drawings.