Communication system with signal converter between networks

An information transmission system with a first user network in which pulse code modulation is used, with transition points connecting the networks. There are also signal preparation and data format adaptation devices in the terminals and in the transition point there is a source network recognition device by which a source network identification symbol is added to the call number from the other user network.

BACKGROUND OF THE INVENTION 
The invention relates to a communication system according to the preamble 
of patent claim 1, and also to interfaces matched thereto. 
A system of this type is known from German Offenlegungsschrift 3,033,871. 
This communication system consists of a first subscriber network in which 
the voice processing is executed with pulse code modulation and of a 
second subscriber network in which the voice processing is executed with 
delta modulation. The subscribers of the networks are connected to one 
another across an interface, with a signaling converter being provided in 
the interface. The subscriber terminals of the first network, which are 
equipped with a cryptogenerator, additionally have a delta modulation 
device corresponding to the second network for voice processing. 
SUMMARY OF THE INVENTION 
The object of the invention is to disclose a communication system or 
interfaces of the type mentioned at the beginning in which it is possible 
to connect networks having different bit rates in a simple manner. 
This object is achieved according to the invention by a communication 
system, having a first subscriber network in which the subscriber 
terminals have a voice processing device employing pulse code modulation, 
having at least one further subscriber network in which the subscriber 
terminals have voice processing devices and in which the bit transmission 
rate is not greater than that in the first subscriber network, having at 
least one interface with signaling converter connecting the networks, 
having predetermined subscriber terminals of the first subscriber network, 
which additionally have a voice processing device in accordance with each 
of the further subscriber networks. The subscriber terminals have data 
format adaptation devices connected downstream of the additional voice 
processing devices. The interfaces have data format adaptation devices, 
and each of the interfaces has a source network identification device with 
which a source network identifier is appended to the call number from the 
further subscriber network, by means of which one of the additional voice 
processing and data format adaptation devices is switched on in the 
subscriber terminal of the first network. One of the interfaces has a data 
format adaptation device and a source network identification device, with 
which a source network identifier is appended to the call number from a 
further network, by means of which one of the additional voice processing 
and data format adaptation devices is switched on in the subscriber 
terminal of the first network. Another of the interfaces has a data format 
adaptation device and a modem for digital signal transmission in an analog 
network. A source network identification device is provided, with which a 
source network identifier is appended to the call number from the analog 
network, by means of which one of the additional voice processing and data 
format adaptation devices is switched on in the subscriber terminal of the 
first network. 
A great advantage of the communication system according to the invention is 
that it is also possible to exchange encrypted messages between 
subscribers on different networks without the message appearing in the 
interface without encryption. 
A further advantage is conferred by the fact that it is not necessary to 
alter the existing networks in the communication system according to the 
invention. 
Likewise it is not necessary to alter any of the subscriber terminals in 
the corresponding networks (Eurocom network and IVSN Nato network). 
An extension of the communication system according to the invention to 
further digital or analog networks is readily possible.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates three subscriber networks: 
A first network N1, a so-called ISDN network, in which the data are 
transmitted at a bit rate of 64 kbits per second. For voice processing, 
that is to say for digitizing the analog voice signal or, in the opposite 
direction, for converting the incoming digital voice signal into an analog 
signal, pulse code modulation is employed in the subscriber terminals 
Tn11, 12, . . . . 
A second network N2, a so-called Eurocom network, in which the data are 
transmitted at a bit rate of 16 kbits per second. Delta modulation is 
employed for voice processing in the subscriber terminals Tn21, 22. 
A third network N3, a so-called IVSN Nato network. This is an analog 
network in which the voice signal is transmitted as an analog signal 
between the subscriber terminals Tn31, 32. If so-called vocoders are 
employed for voice processing in the subscriber terminals Tn31, 32, the 
digital voice signal is transmitted at a transmission rate of 2.4 kbits 
per second instead of the analog voice signal. 
In all of the networks N1, N2, N3, the digital voice signals are normally 
transmitted without encryption, but they are also transmitted encrypted if 
cryptogenerators are employed in selected subscriber terminals. 
Two interfaces U1, U2 are used to connect the networks N1 to N3. The first 
interface U1 is connected between the first N1 and the second network N2, 
and the second interface U2 is connected between the first network N1 and 
the third network N3. The interfaces U1 and U2 are explained more fully 
later with reference to FIGS. 4 and 5. 
A subscriber terminal Tn1 for an ISDN network (first network N1) is 
illustrated in FIG. 2. It has here a voice processor 1 employing pulse 
code modulation, a subscriber line device 2 for the ISDN format, and a 
line terminating device 3 in accordance with the ISDN transmission 
protocol. In addition, the subscriber terminal Tn1 contains a 
cryptogenerator 4 for encrypting the digital voice signal. 
According to the invention, the subscriber terminal Tn1 has additional 
devices matched to the second network (N2) (Eurocom network). These are a 
voice processing device 8 employing delta modulation (16 kbit/sec), a 
subscriber line device 9 in accordance with the Eurocom format, and also a 
data format adaptation device 10 for converting the voice signal digitized 
according to the Eurocom format into a voice signal digitized according to 
the ISDN protocol. 
According to the invention, the subscriber terminal Tn1 has further 
additional devices matched to the third network N3 (IVSN Nato network). 
These are an LPC vocoder 5 (2.4 kbit/sec) for voice processing, a 
subscriber line device 6 for matching to the IVSN format, and also a data 
format adaptation device 7 for converting the voice signal digitized 
according to the IVSN protocol into a voice signal digitized according to 
the ISDN protocol. 
The analog voice signal is thus digitized with three different methods in 
the subscriber terminal Tn1 and output to the first network N1. The one of 
the voice processing devices 1, 5, 8 corresponding to the network where 
the called subscriber is located is always switched on here. Likewise, 
each of the voice signals can be encrypted using the cryptogenerator 4. 
The bit rate of the cryptogenerator 4 is matched to the bit rate of the 
voice processing device 1, 5, 8 that is switched on and is connected 
directly downstream of the voice digitizer (delta modulator 8, LPC vocoder 
5) with associated subscriber line device 6, 9. 
Such a connection establishment is described below with reference to FIG. 
3. 
To start with, the receiver is usually lifted and a number is dialled to 
establish a connection between one subscriber in the first network N1 and 
the called subscriber. This dialling also entails a network exit in the 
case of a subscriber located outside the network. 
If the dialling does not entail a network exit (network exit n), the voice 
processing device 2 employing pulse code modulation is switched on, the 
cryptogenerator 4 may be connected if desired, and the conversation 
between the two subscribers takes place. 
If the dialling does entail a network exit (network exit y), in one case 
the connection is established to the second network N2 (Eurocom network) 
to the subscriber there (Eurocom y) via the transition point U1. The voice 
processing device 8 employing delta modulation is switched on in the 
subscriber terminal Tn1, the cryptogenerator 4 (matched to 16 kbit/sec) 
may be connected if desired, and the Eurocom/ISDN format adaptation device 
10 is activated. If the dialling entails a network exit (via the second 
interface U2) to the third network N3 (Eurocom n), then the LPC vocoder 5 
is switched on in the subscriber terminal Tn1 for voice processing, if 
necessary the cryptogenerator 4 (matched to 2.4 kbit/sec) is connected, 
and the IVSN/ISDN format adaptation device is activated. 
According to the invention, therefore, quite normal voice signals 
(non-encrypted or encrypted text) digitized and formatted in accordance 
with the ISDN network are transmitted in the first network N1. Moreover, 
so-called pseudo-ISDN messages are also transmitted in this ISDN network. 
These are the analog voice signals processed with a vocoder or in 
accordance with the delta modulation method, which were converted using 
the data adaptation devices 7, 10 into the ISDN format and are transmitted 
in the first network 1 like normal ISDN signals. 
The establishment of the connection between a calling subscriber in one of 
the networks N2, N3 and a called subscriber in the first network N1 will 
be discussed later. 
The interface U1 is illustrated as a block circuit diagram in FIG. 4. On 
the side facing the first network N1 it contains a line terminating device 
11 in accordance with the ISDN format, and on the side facing the second 
network N2 it contains a line terminating device 12 in accordance with the 
Eurocom format. According to the invention, a data format adaptation 
device 13 for converting these two data formats and a signaling converter 
14 for converting the signaling data (call number, busy and free tones, 
etc.) are connected in between. 
Furthermore, a source network identification device 15 is provided in the 
interface U1. In this source network identification device 15, in the 
event of signaling from the second network N2, a source network identifier 
is appended to the normal call number (the called subscriber is located in 
this case in the first network N1). By means of this source network 
identifier, the voice processing and formatting path (8, 9, 10) 
corresponding to the second network N2 is switched on in the subscriber 
terminal Tn1 of the called subscriber. 
FIG. 5 illustrates the second interface U2. On the side facing the first 
network N1 it contains a line terminating device 21 in accordance with the 
ISDN format, and on the side facing the analog third network N3 it 
contains a line terminating device 22 in accordance with the IVSN format. 
A PCM codec 23 (coder-decoder) is connected between these two line 
terminating devices 21, 22 for unencrypted voice transmission. Analog 
voice signals from the third network N3 are digitized in the PCM codec 23 
with the pulse code modulation method, and digital voice signals from the 
first network N1 are converted into the analog voice signal. 
As already explained with reference to FIG. 1, it is also possible to 
transmit digital voice signals, in particular encrypted digital voice 
signals, in the analog network N3. For this purpose, according to the 
invention a data format adaptation device 24, a signaling converter 25, 
and downstream of these last two a modem 27 are inserted between the two 
line terminating devices 21, 22. In this arrangement, the digital voice 
signals of the first network N1 and of the third network N3 are converted 
in the data format adaptation device 24 together with the modem 27. The 
signaling converter 25 likewise serves together with the modem 27 to 
convert the signaling used in the first network N1 and in the third 
network N3. 
Moreover, a source network identification device 26 is also provided here, 
by means of which a source network identifier is appended in the case of a 
call from the third network N3 (the called subscriber is located in the 
first network N1) to this call number. As a result of this source network 
identifier, the voice processing and formatting path (5, 6, 7) 
corresponding to the third network N3 is connected in the subscriber 
terminal. 
It is described with reference to FIG. 6 how a delta-modulated voice signal 
is converted into a PCM-modulated voice signal in the data format 
adaptation device 7 of the subscriber terminal Tn1, FIG. 2 (or in the data 
formatting device 13 in the interface U1, FIG. 4), and converted back from 
this into a delta-modulated voice signal. For this purpose, the 
delta-modulated voice signal is sampled with the PCM sampling clock, and a 
so-called pseudo-PCM signal is formed. In the line terminating device 3 of 
the subscriber terminal Tn1 (or in the line terminating device 11 in the 
interface U1, FIG. 4), this pseudo-PCM signal is handled and formatted 
exactly like a conventional PCM voice signal. 
In the data format adaptation device 13 of the interface U1, FIG. 4 (or in 
the data format adaptation device 7 of the subscriber terminal Tn1, FIG. 
2), this pseudo-PCM signal is sampled with the sampling clock 
corresponding to the delta modulation method, and the delta-modulated 
signal is recovered, as can be seen in the drawing, with a time offset. 
This delta-modulated signal is then output to the second network N2 (or to 
the subscriber line device 6, FIG. 2) via the line terminating device 12. 
The same procedure--conversion of the delta modulated signal into a 
pseudo-PCM signal and the recovery of the delta-modulated signal--is 
executed in the data format adaptation device 13 of the interface U1 when 
the digital voice signal is forwarded from the second network N2 into the 
first network N1. 
The conversions in the second interface U2, or in the signal processing 
path of the subscriber terminal corresponding to the third network N3, are 
executed analogously. 
The invention is not limited to the particular details of the apparatus 
depicted and other modifications and applications are contemplated. 
Certain other changes may be made in the above described apparatus without 
departing from the true spirit and scope of the invention herein involved. 
It is intended, therefore, that the subject matter in the above depiction 
shall be interpreted as illustrative and not in a limiting sense.