CA1108325A - Telecommunications system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

It is the object of the present invention to provide service for a group of subscribers having a particular interest in digital transmission, without cancelling the conventional substantially analogue telephone network. According to the present invention the subscriber group is provided with digital subscriber stations connected to digital terminal exchanges which, for con-nections to be set up beyond the range of the terminal exchange area, are adapted to be selectively connectable with the convention-al analogue network either through digital/analogue converters and analogue/digital converters, or through a new digital long distance network which is connectable with the analogue network through the digital/analogue and analogue/digital converters. The invention can be used in the transmission of speech, music, textcopy, images or data.

Description

This invention relates to a telecommunications system ror line and/or ~,~/irQless trar~.smlssi.cn of speech., mus~c~ 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 kHæ.
Digital transmission links across which 3.1-~Hz-sjgnals 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, tele-copying, telephone-individual image- or electronic letter-transmission which, when a conventional analogue telecommuni- ;
cations network is employed, are either too slo~ or must be discarded as uneconomical due to too great a barld 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 9 would in themselves be suitable ror eliminating the major part of the abovementioned disadvantagesO However or this purpose the individual subscriber would have to be directly connecte.d ~o cne 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

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3,~i conversions. Furthermore the subscribers would also require a four-wire terminal or quas1-~o~lr-wire terminal in order to be able to exploit all the advantages 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 tele-communications system for line transmission and/or wireless ~^;` transmission of speech, music, text9 images or data, said system containing a conventional telecommunications analogue network for analogue transmission and having local exchanges and transit exchanges, said system also including a long distance network for purely digital transmission which is coextensive with the analogue network and which is provided with its own transit exchanges, digltal local exchanges being provided which on the one hand are directly connected to digital subscriber stations possessing analogue-digital and digital-analogue converters, and on the other hand~ for each connection -to be established which extends beyond the local exchange range, can be connected either to the digital long~distance network directly, or to the analogue network via analogue-digital and digital-analogue converters.
In one practical embodiment it is advantageous to arrange that at least of some of the digital local exchanges selectively, as a result of a pre-dialling signal, switcn the signaIs . ~
emanatlng from the digital subscriber stations either to the analogue network or to the digital network.

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It is also advantageous if the digital lccal exchangesare connected to their digital subscriber stations via subscriber lines which have four-wire properties and which can be constructed using time hybrids two wire-~our wire h~brids and/or frequency switches.
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 1~ 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 or data transmission and/or signallLng purposes.
It is also advantageous to provide encryption and decryption devices for p~rposes of secrecy in the digital local exchanges andlor in the digital subscriber stations.
It is also advantageous to provide a change-over switch ~5 ~ith the alu o~ ihich th~ entir~ ~it flow can be switched over between a terminal for speech devices and a terminal for data devlces. A data wo.d can serve to control the chang~-over switchO
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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 au-to-matically.
It is also advantageous 9 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 }nvention;
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 sub-scriber station of the system shown in Fig. 1;
Fig. 5 is a schematic block diagram of a connection - ~ :

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between two digital subscriber stations of the system shown in Fig. 1; and Fig. 6 is a schematic block diagram of a data adaptor ~or a ditital subscriber station of the system shown in Fig. 1.
Fig. 1 is a schematic block circuit diagram of a tele-communications system which contains a conventional analogue network I, a digital network II, two local exchange ranges 1 and 1' and 3 and 3', in which subscriber stations are located, and a long-distance 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 9 and if it contains a reference letter D it represents a digital exchange. The schematlc 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 D they represe~t digital subscriber stations. Subscriber stations of the latter kind contain a commercially availa~le analogue-digital and a digital-analogue converter ~or speech signals.
In the~analogue network I, a connection can be established in the conventional manner ~or 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 net~ork I via the appropriate analogue exchanges A and the analogue long-dist'ance network 2.
The same is possible in the digital network II between - : . . - . : . i.,.
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a subscriber station 8 connected to the digital local exchange 9 and a subscriber station 13 connected to the~digital local exchange ~1. For a connection betwePn 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 27 ~ and the digital local exchange 11 7 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 exhange If, however, the analogue network I is unsuitable for the desired communication, transmission takes place only vla the digital long-distance 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~ sub~scriber station 5 to the digital subscriber ~:
'~ station 8, this is established without special pre-dialling : 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.
: 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.
The ~acilities which are offered by thë telecommunications system shown in Fig. 1 will be described with reference to Fig. 2. ~-~

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Fig. 2 schematicallv illustrates the digital subscriber stations and 13 -2m Fis. 1 In the disital subscri~e. staticns 8, a telephone 19, for example having unrestricted speech facilities, a business teleprinter la, a display device 15, S for example for displaying text or still p~ctures, 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 EXCLUSIV~-OR-gate 181, 181' for modulo-2-addition and a commercially available quasi-random generator 182, 18Z' which consists for example of a shift register with feedback.
The entire speech spectrum can be transmitted unrestrict-edly with 64-kbit/s delta modulation from the telephone 19 to the telephone 19l. In comparison to band-limit trans~ission in the CCITT speech channel (300 Hz to 3400 Hz~, the del~a modulation provides a considerable irnpro~ement in speech quality and an increase in intelligibility, of particular 2~ importance in the case of foreign languages.
Delta modulation is better adapted to the speech spectrum than pulse code modulation so;~hat even with the considerably extended low-frequency band only a very few quantising distortions occur. Due to the high scanning frequency, the Z5 low-pass filters required at the transmitting and receiving ends in the case of pulse code modulation can be dispensed with.
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than a pulse code modulation codec. The four-wire connection to the subscriber facilitates genuine unrestricted conversationO
Ech~ suppreSsors canbe d~enged with.~urthermore in the case o~
digital transmission no attenuation fluctuations occur.
Conference connections are possible. Subscriber stations having priority can be achieved by the digital connection ?
without additiona 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 ~easible (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. 1 DIN-A-4-page in approximately 0.3 s).
A high-speed data communication between monitors and ., ~ .
computers is also posslble.
The monitors 15 and 15' can be used to transmit still piC~ with an accompanying text. The transmission of a screen image with 625-line resolution in colour lasts approx~
imately 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 resoIution of ~ llnes/mm. The redund-ancy resolution required in current high-speed facsimile transmission~using speech channels can be dispensed with, saving outlay and reducing the sensitivity to transmlssion disturbances. In addition the use of expensi~e 4.8-kbit/s ., ;;

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moderns which partially operate with adaptive distortion correction can be avoided.
Telephone conversations and telecopying can also be selectively carried out simultaneously in parallel channels to each of which 32 kbit/s are allocated, ln which case the speech quality is still good and it is possible to transmit simultaneously one DIN~A-4~page in approYimately 30 s.
The possibility of using high-speed and cheap telecopying devices is considered to be an important advantage of the telecommunications system described here. Material in image form or text form can be immediately supplied to accompany a telephone conversation. Even in the first stage of development of a PBX ne-twork, the local postal system of the area can be relieved of load.
~ig. 3 is a more detailed view of the digital local exchange 9 illustrated in Fig. 1, which is provided with two digital subscriber stations 8' and 8''.
One terminal of the exchange serves as output into the digital long-distance network 2', and a further terminal serves as output lnto the an~logue network I~ Since 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' 9 two wire-~our wirehy~ds must be provided for the four-wire~connection. Therefore a circuit 27 having a digital hybrid unit 271 and a two-wire duplex transmission unit 272 have been provided in the output to the digital long-distance network 2'. A circuit 20 having a commercially available codec - .

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i~/n~8325 201, 2Q2 and an analogue hybrid unit ~Q3 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'l, 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' con-tains 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 rela-; tion to Fig. 6 with regard to the item having reference numeral 45) and an arrangement 29 comprising a demuItiplexer 291, a multi-plexer 293 in the form of a change-over switch, a digital hybrid unit 293 (time hybrid) and a two-wire duplex transmission unit 294 ` 20 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 transmission and high-speed data transmission between two digital subscriber ~ stations 8 and 13 as illustrated in Fig. 1, the elements of the :
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digital subscriber statiorls being as illustrated in Fig. 4 The digltal subscriber stations also contain a first, commercially available data ~tore 37t 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 2~, 28' is to facilitate signal exchange via the 64-kbit/s transmission channel for various services. In the case of pure speech transmission, an appropriate setting of the change-over swi~ch - 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 t ~ opposite direction there are corresponding connections ~31'-34'-34-30).
When only data is to be transmitted, the switch 28~28 is reversed. The 64-kbit/s-transmission channel is then connected to the data stores 37, 35 and 37', 35'. ilere the data stores have been provided in order to facilitate opt~lmum 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 whicn 9 .
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 sincè, 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.
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The automatic switch-over to data transmission can be controlled, fcr example, by speech signal coding circuits which have been in use for many years in the TASI-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, l;
via the switch 28, via the transmission channel, via the switch i 28' and via the demodulator of the speech signal codec 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 ! I
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, ln an embodiment which does not employ a micro-processor. The circuit contains a data transmitting ';
component 39 and a~data receiving component 40r A basic portion of the data transmitting component 39 includes a commercially available transmitting store 4'1, into whic-h the ~ata are input at the generally slow speed of the data device 38, and can be kep~ available for transmission at 64 kbit~so For transmission which can be manually or auto-matically introduced into the conversatlon pauses, the trans- ;~
mitting store 41 is swltched through to the transmission channel ;~
in place of the speech signal codec 34 and subsequently an -J

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initial data word from a commercially available data word generator 4~ is read out by means of swi~ch 45b~
In the receiving component 40, a com~ercially available data word decoder 43 recognises the beginning o~ the data burst and for a short length of time, for example until the store 44 is full, switches over ~rom 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 ln particular in the business world~
The embodiments provide for exampIe a high-speed facsimile transmission, an electronic postal syst~em, extended display services and a high-grade cryptographic unit with improved speech quality in the speech circuits.

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Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

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 network for analogue transmission and having local exchanges and transit exchanges, said system also including a long distance net-work for purely digital transmission which is coextensive with the analogue network and which is provided with its own transit ex-changes, digital local exchanges being provided which on the one hand are directly connected to digital subscriber stations possess-ing analogue-digital and digital-analogue converters, and on the other hand, for each connection to be established which extends beyond the local exchange range, can be connected either to the digital long-distance network directly, or to the analogue network via analogue-digital and digital-analogue converters.

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

3. A system as claimed in claim 1 wherein the digital local exchanges are connected to their digital subscriber stations via subscriber lines having four-wire properties.

4. A system as claimed in claim 3, wherein the four-wire properties are achieved by means of time hybrids.

5. A system as claimed in claim 3, wherein the four-wire properties are achieved by two wire-four wire hybrids.

6. A system as claimed in Claim 1, 2 or 4 wherein a delta modulator is provided for analogue-digital conversion of speech in the subscriber stations.

7. A system as claimed in Claim 1, 2 or 4 wherein additional data forms can be transmitted on the subscriber lines by modulation or addition-al coding or multiplex processes.

8. A system as claimed in Claim 1, 2 or 4 wherein a part of the bit flow available for speech transmission is used constantly or periodically for data transmission and/or signalling purposes.

9. A system as claimed in Claim 1, 2 or 4 wherein encryption and de-cryption devices are provided in the digital local exchanges or in the digital subscriber stations for purposes of secrecy.

10. A system as claimed in claim 1 wherein a change-over 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.

11. A system as claimed in Claim 10 wherein there is provided a device for producing a data word which controls the change-over switch.

12. A system as claimed in Claim 11 wherein said data word device is arranged for producing different data words in order to distinguish between different types of data signals.

13. A system as claimed in Claim 1 wherein a switch is arranged for initiating data transmission in naturally existing speech pauses under manual control or automatically.

14. A system as claimed in claim 1 wherein the digital long-distance network, for services employing low bit rates, stores are provided which are arranged to be read out at a high bit rate by the digital long-distance network in the form of bursts.

15. A system according to claim 13 wherein said bursts are arranged to occur during speech pauses.

16. A system as claimed in claim 1, 4 or 15 wherein a micro-processor is provided for store control, multiplex formation, code conversion, data word analysis, speech pause recognition and monitoring.