Note: Descriptions are shown in the official language in which they were submitted.
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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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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
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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
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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
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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.
- In addition, a delta codec is very much simpler and cheaper
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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
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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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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
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sinks could for example consist of business teleprinters whicn
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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
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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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