GB1603898A

GB1603898A - Telecommunications system

Info

Publication number: GB1603898A
Application number: GB23289/78A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1977-06-30
Filing date: 1978-05-26
Publication date: 1981-12-02
Also published as: SE7807377L; SE423588B; NO148658B; YU155478A; AU518649B2; NO148658C; IE46933B1; CH634702A5; BE868634A; BR7804167A; CA1108325A; FR2396478B1; LU79894A1; NL7806930A; ATA474678A; FI782046A; ZA783426B; DE2729689B1; NO782243L; IE781186L

Abstract

This information transmission system for speech, music, text, images and data has a basic telecommunications network (I), in particular for analog transmission, and an additional digital overlay network (II). The two networks are interconnected between their terminating exchanges (6, 7, 9, 11) via analog-digital or digital-analog converters (10, 12). Current communications facilities are retained thanks to the continued existence of the basic telecommunications network (I), while a user group interested in new, high-speed forms of communication can be served via the digital network (II). <IMAGE>

Description

(54) A TELECOMMUNICATIONS SYSTEM (71) We, SIEMENS AKTIENGESELL SCHAFT, a German Company of Berlin and Munich, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a telecommunications system for line and/or wireless transmission of speech, music, text, images or data.

The current telecommunications network of the German Post Office and other postal administrations fundamentally consists of telephone channels each having a band width of 3.1 kHz. Digital transmission links across which 3.1-kHz-signals each comprising 64 kbit/s can be transmitted are also individually interposed to form a section-by-section data transmission arrangement.

The "Nachrichtentechnische Zeitschrift", Vol. 29 (1976) No. 3, pages 190 to 210 deals with a series of useful communications facilities such as office teleprinters, telecopying, telephone-individual image- or electronic letter-transmission which, when a conventional analogue telecommunications network is employed, are either too slow or must be discarded as uneconomical due to too great a band width requirement.

Pulse code modulation transmission devices which are to some extent used in conventional telecommunications networks and which transmit one 64-kbit/s-signal per speech channel, would in themselves be suitable for eliminating the major part of the abovementioned disadvantages.

However for this purpose the individual subscriber would have to be directly connected to the .64-kbit/s-network and the 64-kbit/s-signal would have to be able to reach the corresponding subscriber without interruption due to digital-analogue and analogue-digital conversions. Furthermore the subscribers would also require a four wire terminal or quasi-four-wire terminal in order to be able to exploit all the ad vantages of this connection. Since, in the foreseeable future digital connections will consist merely of intermediate sections within the analogue network, their advantages cannot be exploited.

According to this invention there is provided a telecommunications system for line transmission and/or wireless transmission of speech, music, text, images or data, said system containing a conventional telecommunioations analogue exchange network for analogue transmission and having local exchanges and transit exchanges, said system also including a digital exchange network for purely digital transmission which is coextensive with the analogue exchange network and which is provided with its own local and transit exchanges, all digital exchange network subscriber stations being directly connected for digital transmission to the digital local exchanges and possessing analogue-digital and digital-analogue converters, this system being such that each connection emanating from a digital subscriber station and extending between digital local exchanges can be switched via converting means including digitalanalogue and analogue-digital converters, through local and transit exchanges of the analogue network.

In one practical embodiment it is advantageous to arrange that at least some of the digital local exchanges selectively, as a result of a pre-dialling signal, switch the signals emanating from the digital subscriber stations either to the analogue exchange network or to the digital exchange network.

It is also advantageous if the digital local exchanges are connected to their digital subscriber stations via subscriber lines which have four-wire properties and which can be constructed using time hybrids, two wire-four wire hybrids and/or frequency switches.

A "time hybrid" as referred to herein is to be understood as comprising å switching arrangement for providing transmission in opposite directions during alternate time intervals.

A "frequency switch" as referred to herein is to be understood as comprising a frequency-separating filter (used where transmission in opposite directions takes place in respective different frequency ranges).

It is ,advantageous to provide a delta modulator for the analogue-digital conversion of speech where appropriate in the subscriber stations.

Although the magazine "AIEE, Part I, Communications and Electronics", May 1957, pages 142 to 147 has already disclosed a communications transmission system wherein delta modulation is used between subscribers that disclosure relates to a purely digital network and not a hybrid network as described herein.

It is also advantageous to transmit additional data modes on the subscriber line by a modulation or additional coding or by multiplex processes.

It is likewise advantageous if a part of the bit flow available for speech transmission is constantly or periodically used for data transmission and/or signalling purposes.

It is also advantageous to provide enciphering and deciphering for purposes of secrecy in the digital local exchanges and/or in the digital subscriber stations.

It is also advantageous to provide a change-over switch with the aid of which the entire bit flow can be switched over between a terminal for speech devices and a terminal for data devices. A data word can serve to control the change-over switch.

Different data words serve to distinguish between different types of data signals.

It is likewise advantageous to provide a switch which can switch on a data transmission unit in the naturally existing speech pauses either under manual control or automatically.

It is also advantageous, in the case of services using lower bit rates than is available in the digital network to provide stores which are read out in bursts with the highest bit rate of the digital network, for example in the speech pauses.

Finally it is advantageous to provide a micro-processor for store control, multiplex formation, code conversion, data word analysis, speech pause recognition and/or monitoring.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic block diagram of a telecommunications system embodying the invention: Fig. 2 is a schematic diagram of two digital subscriber stations of the system shown in Fig. 1; Fig. 3 is a schematic block diagram of a digital local exchange and two digital subscriber stations of the system shown in Fig. 1; Fig. 4 is a schematic block diagram of a digital subscriber station of the system shown in Fig. 1; Fig. 5 is a schematic block diagram of a connection between two digital subscriber stations of the system shown in Fig. 1; and Fig. 6 is a schematic block diagram of a data adaptor for a digital subscriber station of the system shown in Fig. 1.

Fig. 1 is a schematic block circuit diagram of a telecommunications system which contains a conventional analogue network I, a digital network II, two local exchange ranges 7 and 1' and 3 and 3', in which subscriber stations are located, and a longdistance network and transit exchange range 2 and 2'. The boxes without a diagonal line represent telephone exchanges.

If the box contains a reference letter A, it represents an analogue exchange, and if it contains a reference letter D it represents a digital exchange. The schematic illustrations of telephones and the circles represent subscriber stations. Where they are marked with an A they represent analogue subscriber stations, and where they are marked with a ;I} they represent digital subscriber stations. Subscriber stations of the latter kind contain a commercially available analogue-digital and a digitalanalogue converter for speech signals.

In the analogue network I, a connection can be established in the conventional manner for example between a subscriber station 4 connected to the analogue local exchange 6 and a subscriber station 5 connected to the analogue local exchange 7.

In this case the telecommunications transmission occurs only in the analogue network I via the appropriate analogue exchanges A and the analogue long-distance network 2.

The same is possible in the digital network II between a subscriber station 8 connected to the digital local exchange 9 and a subscriber station 13 connected to the digital local exchange 1E For a connection between the digital subscriber stations 8 and 13, in dependence upon a pre-dialling signal, the connection is established either via the digital local exchange 9, the digital long-distance network 2', and the digital local exchange 11, or via the digital local exchange 9, a commercially available conventional digital-analogue converter 10, the analogue network I, a commercially available analogue-digital converter 12, and the digital local exchange 11. If, however, the analogue network l is unsuitable for the desired communication, transmission takes place only via the digital longdistance network 2'.

If a connection is to be established from the digital subscriber station 8 to the analogue subscriber station 5, this is established via the digital local exchange 9, via the digital-analogue converter 10 and the analogue network I.

If, on the other hand a connection is to be established from the analogue subscriber station 5 to the digital subscriber station 8, this is established without special predialling signals via the analogue network I to the last analogue exchange, the local exchange 6, and from there via the analogue-digital converter 10 and via the digital local exchange 9.

The facilities which are offered by the telecommunications system shown in Fig.

1 will be described with reference to Fig. 2.

Fig. 2 schematically illustrates the digital subscriber stations 8 and 13 from Fig. 1.

In the digital subscriber station 8, a telephone 19, for example having unrestricted speech facilities, a business teleprinter 14, a display device 15, for example for displaying text or still pictures, or a facsimile device 16 can be connected via the switch 17 to the transmission line. The digital subscriber station 13 contains corresponding devices, whose references have been provided with an apostrophe for differentiation. A coding device 18, 18' can be optionally interposed, each coding device containing an EXCLUSIVE-OR-gate 181, 181' for modulo-2-addition and a commercially available quasi-random generator 182, 182' which consists for example of a shift register with feedback.

The entire speech spectrum can be trans mitten unrestrictedly with 64-kbit/s delta modulation from the telephone 19 to the telephone 19'. In comparison to bandlimit transmission in the CCITT speech channel (300 Hz to 3400 Hz), the delta modulation provides a considerable improvement in speech quality and an increase in intelligibility, of particular importance in the case of foreign languages.

Delta modulation is better adapted to the speech spectrum than pulse code modulation so that even with the considerably extended low-frequency band only a very few quantising distortions occur. Due to the hlgh scanning frequency, the low-pass filters required at the transmitting and receiving ends in the case of pulse code modulation can be dispensed with. In addition, a delta codec is very much simpler and cheaper than a pulse code modulation codec. The four-wire connection to the subscriber facilitates genpine unrestricted conversation. Echo suppressors can be dispensed with. Purthermore in the case of digital transmission no attenuation fluctuations occur.

Conference connections are possible.

Subscriber stations having priority can be achieved by the digital connection without additional lines. As a result of the delta modulation band width which is greater than for PCM, the quality of a domestic: wireless receiver can be achieved in music transmission. As a result services such as "Dial a Hit" are feasible (Popular record success of the week via telephone).

A very high-speed data transmission is possible between the business teleprinters 14 and 14' (e.g. I DIN-A-4-page in approxi- mately 0.3 s).

A high-speed data communication between monitors and computers is also possible.

The monitors 15 and 15' can be used to transmit still pictures with an accompanying text. The transmission of a screen image with 625-line resolution in colour lasts approximately 25 s, High-speed telecopying is possible between facsimile devices 16 and 16'.

Approximately 15 s are required to transmit one DIN-A-4-page with a resolution of 8 lines/mm. The redundancy resolution required in current high-speed facsimile transmission using speech channels can be dispensed with, saving outlay and reducing the sensitivity to transmission disturbances.

In addition the use of expensive 4.8-kbit/s modems which partially operate with adaptive distortion correctlon can avoided.

Telephone conversations and telecopying can also be selectively carried out simultaneously in parallel channels to each of which 32 kbit/s are allocated, in which case the speech quality is still good and it is possible to transmit simultaneously one DIN-A-4-page in approximately 30 s.

The possibility of using high-speed and cheap telecopying devices is considered to be an important advantage of the tele communications system described here.

Material in image form or text form can.

be immediately supplied to accompany a telephone conversation. Eyen in the first stage of development of a PBX network, the local postal system of the area can be relieved of load.

Fig. 3 is a more detailed view of the digital local exchange 9 illustrated in Fig.

1, which is provided with two digital su- scriber stations 8' and 8".

One terminal of the exchange serves as output into the digital long-distanc network 2', and a further terminal serves as output into the analogue network I. Smce in this example two,wire lines have been assumed to form the connections into the analogue network I and into the digital long-distance network 2', two wire-four wire hybrids must be provided for the fourwire connection. Therefore a circuit 27 having a digital hybrid unit 271 and a two-wire duplex transmission unit 272 has been provided in the output to the digital long-distance network 2'. A circuit 20 having a commercially available codec 201.

202 and an analogue hybrid 203 is arranged in the output to the analogue network.

Also provided are a timing pulse train supply unit 21, and a signalling tone generator 22 which consist for example of an analogue-digital converter 221, a scanner 222 and a tone generator 223. The subscriber stations 8' and 8" contain digital adaptors 23' and 23" (as described in greater detail in relation to Fig. 4), telephones 25' and 25", data device adaptors 24 and 24" (as described in greater detail in relation to Fig. 6 with regard to the items having reference numerals 39 and 40) and data devices 26' and 26".

Fig. 4 is a detailed view of a digital subscriber station 8' as illustrated in Fig. 3.

The digital adaptor 23' contains a commercially available speech signal codec 34, a speech/data switch-over device 28, which fundamentally corresponds to the switch 17 in Fig. 2, (and is described in greater detail in relation to Fig. 6 with regard to the item having reference numeral 45) and an arrangement 29 comprising a demultiplexer 291, a multiplexer 292 in the form of a change-over switch, a digital hybrid 293 and a two-wire duplex transmission unit 294 for two-wire duplex transmission.

The telephone 25' has an ear-piece 30, a microphone 31, a signalling tone receiver 32 and a dialling signal generator 33. The data device adaptor 24' and the data device 26' have also been illustrated.

Fig. 5 illustrates a connection for speech transmissin and high-speed data transmission between two digital subscriber stations 8 and 13 as illustrated in Fig. 1, the elements of the digital subscriber stations being as illustrated in Fig. 4. The digital subscriber stations also contain a first, commercially available data store 37, 37', a second commercially available data store 35, 35', such as a RAM (random access memory) for example, and a commercially available data printer 36, 36'.

The function of the switch-over device 28, 28' is to facilitate signal exchange via the 64-kbitls transmission channel for various services. In the case of pure speech transmission, an appropriate setting of the change-over switch 28, 28' ensures that the microphone 31 of the codec 34 and the transmission channel are connected to the codec 34 and the ear-piece 30'. For transmission in the opposite direction there are corresponding connections (3 1'-34'-34-30).

When only data is to be transmitted, the switch 28, 28' is reversed. The 64-kbit/s- trans mission channel is then connected to the data stores 37, 35 and 37', 35'. Here the data stores have been provided in order to facilitate optimum data exchange via the 64-kbit/s-transmission channel for slower data sources and data sinks. Such slower data sources and data sinks could for example consist of business teleprinters which have been referenced 14 and 14' in Fig. 2.

However, data bursts can also be transmitted in speech pauses during a conversation. This is possible since, generally speaking, information only requires to be transmitted in one direction at a time.

Thus data can be transmitted in the opposite direction. This has been assumed in the case of the setting of the switches 28, 28' illustrated in Fig. 5.

The automatic switch-over to data transmission can be controlled, for example, by speech signal coding circuits which have been in use for many years in the TAST- devices of sea cable systems.

In the illustrated position of the switches 28, 28', signals are transmitted from the microphone 31 to the ear-piece 30' via the modulator of the speech signal codec 34, via the switch 28, via the transmission channel, via the switch 28' and via the demodulator of the speech signal code 34'. At the same time data is transmitted from the data store 37' via the transmission line to the data store 35 and the data printer 36. When the switches 28, 28' are reversed the respective transmissions take place in the opposite directions.

Fig. 6 illustrates a combination of the data adaptor 24' shown in Fig. 4 with a switch-over device 45 which fundamentally corresponds to the change-over switches 28, 28' shown in Fig. 5, in an embodiment which does not employ a micro-processor.

The circuit contains a data transmitting component 39 and a data receiving component 40.

A basic portion of the data transmitting component 39 includes a commercially available transmitting store 41, into which the data are input at the generally slow speed of the data device 38, and can be kept available for transmission at 64 kbit/s.

For transmission which can be manually or automatically introduced into the conversation pauses, the transmitting store 41 is switched through to the transmission channel in place of the speech signal codec 34 and subsequently an initial data word from a commercially available data word generator 42 is read out by means of switch 45b.

In the receiving component 40, a commercially available data word decoder 43 recognises the beginning of the data burst and for a short length of time, for example until the store 44 is full, switches over from the speech signal codec 34 to a commercially available data receiving store 44.

Then the data device 37 at the receiving end can read out the receiving store 44 at its own data speed.

The embodiments described above enable a predominantly analogue network to include subscriber circuits which are particularly concerned with digital transmission and for which application may be found in particular in the business world.

The embodiments provide for example a high-speed facsimile transmission, an electronic postal system, extended display services and a high-grade cryptographic unit with improved speech quality in the speech circuits.

WHAT WE CLAIM IS: 1, A telecommunications system for line transmission and/or wireless transmission of speech, music, text, images or data, said system containing a conventional telecommunications analogue exchange network for analogue transmission and having local exchanges and transit exchanges, said system also including a digital exchange network for purely digital transmission which is coextensive with the analogue exchange network and which is provided with its own local and transit exchanges, all digital exchange network subscriber stations being directly connected for digital transmission to the digital local exchanges and possessing analogue-digital and digitalanalogue converters, this system being such that each connection emanating from a digital subscriber station and extending between digital local exchanges can be switched via converting means including digital-analogue and analogue-digital converters, through local and transit exchanges of the analogue network.

2. A system as claimed in claim 1, wherein the analogue exchange network includes an arrangement for providing section-by-section digital transmission, a code converter being provided for enabling connection of the digital exchange network to said section-by-section digital transmission arrangement.

3. A system as claimed in claim 1 or claim 2 wherein at least some of the digital local exchanges selectively, on the basis of a pre-dialling signal, switch signals emanating from the digital subscriber stations either into the analogue exchange network or into the digital exchange network.

4. A system as claimed in any one of the preceding claims wherein the digital local exchanges are connected to their digital subscriber stations via subscriber lines having four-wire properties.

5. A system as claimed in Claim 4, wherein the four-wire properties are achieved by means of time hybrids.

6. A system as claimed in Claim 4, wherein the four-wire properties are achieved by two wire-four wire hybrids and/or frequency switches.

7. A system as claimed in any one of the preceding claims wherein a delta modulator is provided for analogue-digital conversion of speech in the subscriber stations.

8. A system as claimed in any one of the preceding Claims, wherein additional data forms can be transmitted on the subscriber lines by modulation or additional coding or multiplex processes.

9. A system as claimed in any one of the preceding claims, wherein a part of the bit flow available for speech transmission is used constantly or periodically for data transmission and/or signalling purposes.

10. A system as claimed in any one of the preceding Claims, wherein enciphering and deciphering devices are provided in the digital local exchanges or in the digital subscriber stations for purposes of secrecy.

11. A system as claimed in any one of the preceding claims, wherein a changeover switch is provided with which it is possible to switch over the entire available bit flow between a terminal for speech devices and a terminal for data devices and vice versa.

12. A system as claimed in Claim 11, wherein there is provided a device for producing a data word which controls the change-over switch.

13. A system as claimed in Claim 12, wherein said data word device is arranged for producing different data words in order to distinguish between different types of data signals.

14. A system as claimed in any one of the preceding Claims, wherein a switch is arranged for initiating data transmission in the naturally existing speech pauses under manual control or automatically.

15. A system as claimed in any one of the preceding Claims, wherein in the digital exchange network, for services employing lower bit rates than is available, stores are provided which are arranged to be read out with the higher bit rate of the digital exchange network in the form of bursts.

16. A system according to Claim 15, wherein said bursts are arranged to occur in the speech pauses.

17. A system as claimed in any one of the preceding Claims, wherein a microprocessor is provided for store control, multiplex formation, code conversion, data

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

45b.

In the receiving component 40, a commercially available data word decoder 43 recognises the beginning of the data burst and for a short length of time, for example until the store 44 is full, switches over from the speech signal codec 34 to a commercially available data receiving store 44.

Then the data device 37 at the receiving end can read out the receiving store 44 at its own data speed.

The embodiments described above enable a predominantly analogue network to include subscriber circuits which are particularly concerned with digital transmission and for which application may be found in particular in the business world.

The embodiments provide for example a high-speed facsimile transmission, an electronic postal system, extended display services and a high-grade cryptographic unit with improved speech quality in the speech circuits.

WHAT WE CLAIM IS: 1, A telecommunications system for line transmission and/or wireless transmission of speech, music, text, images or data, said system containing a conventional telecommunications analogue exchange network for analogue transmission and having local exchanges and transit exchanges, said system also including a digital exchange network for purely digital transmission which is coextensive with the analogue exchange network and which is provided with its own local and transit exchanges, all digital exchange network subscriber stations being directly connected for digital transmission to the digital local exchanges and possessing analogue-digital and digitalanalogue converters, this system being such that each connection emanating from a digital subscriber station and extending between digital local exchanges can be switched via converting means including digital-analogue and analogue-digital converters, through local and transit exchanges of the analogue network.
2. A system as claimed in claim 1, wherein the analogue exchange network includes an arrangement for providing section-by-section digital transmission, a code converter being provided for enabling connection of the digital exchange network to said section-by-section digital transmission arrangement.
3. A system as claimed in claim 1 or claim 2 wherein at least some of the digital local exchanges selectively, on the basis of a pre-dialling signal, switch signals emanating from the digital subscriber stations either into the analogue exchange network or into the digital exchange network.
4. A system as claimed in any one of the preceding claims wherein the digital local exchanges are connected to their digital subscriber stations via subscriber lines having four-wire properties.
5. A system as claimed in Claim 4, wherein the four-wire properties are achieved by means of time hybrids.
6. A system as claimed in Claim 4, wherein the four-wire properties are achieved by two wire-four wire hybrids and/or frequency switches.
7. A system as claimed in any one of the preceding claims wherein a delta modulator is provided for analogue-digital conversion of speech in the subscriber stations.
8. A system as claimed in any one of the preceding Claims, wherein additional data forms can be transmitted on the subscriber lines by modulation or additional coding or multiplex processes.
9. A system as claimed in any one of the preceding claims, wherein a part of the bit flow available for speech transmission is used constantly or periodically for data transmission and/or signalling purposes.
10. A system as claimed in any one of the preceding Claims, wherein enciphering and deciphering devices are provided in the digital local exchanges or in the digital subscriber stations for purposes of secrecy.
11. A system as claimed in any one of the preceding claims, wherein a changeover switch is provided with which it is possible to switch over the entire available bit flow between a terminal for speech devices and a terminal for data devices and vice versa.
12. A system as claimed in Claim 11, wherein there is provided a device for producing a data word which controls the change-over switch.
13. A system as claimed in Claim 12, wherein said data word device is arranged for producing different data words in order to distinguish between different types of data signals.
14. A system as claimed in any one of the preceding Claims, wherein a switch is arranged for initiating data transmission in the naturally existing speech pauses under manual control or automatically.
15. A system as claimed in any one of the preceding Claims, wherein in the digital exchange network, for services employing lower bit rates than is available, stores are provided which are arranged to be read out with the higher bit rate of the digital exchange network in the form of bursts.
16. A system according to Claim 15, wherein said bursts are arranged to occur in the speech pauses.
17. A system as claimed in any one of the preceding Claims, wherein a microprocessor is provided for store control, multiplex formation, code conversion, data

word analysis, speech pause recognition and/or monitoring.
18. A telecommunications system for line transmission and/or wireless transmission of speech, music, text, images or data, said system being substantially as described herein with reference to figure 1 or figure 1 in combination with any of the figures of the accompanying drawings.