GB2344967A

GB2344967A - An information transmission system and more precisely a telephone system

Info

Publication number: GB2344967A
Application number: GB0005611A
Authority: GB
Inventors: Gerhard Prochazka
Original assignee: Ericsson Austria GmbH
Current assignee: Ericsson Austria GmbH
Priority date: 1997-08-19
Filing date: 1998-08-12
Publication date: 2000-06-21
Anticipated expiration: 2018-08-12
Also published as: BR9811915A; AT408297B; WO1999009727A2; GB2344967B; GB0005611D0; ES2190863A1; ATA138897A; AU8718098A; PL338916A1; WO1999009727A3; HK1027699A1; ES2190863B1

Abstract

The present invention relates to a system for transmitting information from a central station such as an automatic exchange (1) to a peripheral station such as a subscriber's terminal (4). The central station (1) is connected to a bi-directional analog-digital converter (7) on the exchange side through a central bi-directional analog-digital converter (5) and an analog transmission line (11). The bi-directional analog-digital converter (7) on the exchange side has its corresponding output or input connected to a bi-directional analog-digital converter (8) on the peripheral side via a digital transmission line and interfaces associated to the line terminals. The bi-directional analog-digital converter (8) is connected on the output or input side to the peripheral station via another analog transmission line (30). The characteristic curve of the bi-directional analog-digital converter (7) on the exchange side and that of the bi-directional analog-digital converter (8) on the peripheral side are linear. The transmission line consists in a high-speed transmission line (12, 21, 31).

Description

z 2344967 -1 Information transmission system and more Precisely a

telephone system The invention relates to an information transmission system and more precisely a telephone system for transmitting information, more precisely voice and data information, from a central station, for example an automatic exchange, to a peripheral station, for example a subscriber's terminal, in which the central station is connected, by way of a central bi directional analog-digital converter and an analog transmission line, to a bi-directional analog-digital converter on the exchange side, for example in the exchange portion of a remote installation, of a further automatic exchange, of a private automatic branch exchange or the like, which bi-directional analog digital converter on the exchange side has its corresponding output or input connected, by way of a digital transmission link and interfaces associated with the line ends, to a bi-directional analog-digital converter that is on the peripheral side, for example in the local portion of the remote installation, of the further automatic exchange, of the private automatic branch exchange or the like, which on the output side or input side is connected to the peripheral station by way of a further analog transmission line, with a converter characteristic curve being associated with the bi-directional analog-digital converter on the exchange side and the bi-directional analog-digital converter on the peripheral side.

Using such known transmission systems it is possible to transmit both digital data and voice information, which was originally analog voice information, by means of the digital transmission line. Embodiments of a telephone system are possible in all sorts of switching unit arrays, for example from automatic exchange to automatic exchange, from the automatic exchange by way of a remote installation to the subscriber's terminal, or from a private automatic branch exchange to a subscriber's terminal. Although such systems are designed for bi-directional data transmission, in many cases of application the major part of the volume of data - one is thinking here of Internet applications - is only transmitted in one direction, that is, from the central station to the peripheral subscriber.

In order to achieve a high transmission speed on the digital transmission line or in order to enable there to be the highest possible number of transmission channels, hitherto it has always been necessary to compress the digitized voice information according to various international standards, for example by means of ADPCM, A-law or p-law, in such a way that wh lst the intelligibility of the voice certainly suffers little from this, the quality of the transmission of data information is impaired instead. The latter effect sets in owing to the fact that each, more precisely, non-linear analog-digital and digital-analog conversion respectively gives rise to quantization errors which add up from stage to stage. As a result, in practice from a certain transmission rate onwards data transmission is no longer possible.

The non-linear conversion for the purpose of achieving a companding effect is thereby made possible by means of the converter characteristic curves that are associated with the analog-digital converters and which are either converted in the converters themselves or in associated functional groups, such as, for example, compressors.

In the case of remote installations which partly also in multiplex operation operate a plurality of subscribers, for example PCM-4, the voice signals are usually coded after the analog-digital conversion according to A-law or p-law and thereby coded to 8 bits. The companding by means of ADPCM even enables there to be compression to 4 bits. The digital transmission is therefore advantageously organized in time slots each for 8 bits (= 1 byte).

A modem-transmission of data from an Internet provider by way of an automatic exchange and a remote installation to a subscriber may be outlined in order to illustrate the problem that is posed. With the ADPCM-companding (4 bits) a rate of 9600 bit/s already makes it difficult for the subscriber to receive the digital data, whilst with A- or p-law companding (8 bits) it is no longer possible to attain the data rate of over 50 kbit/s that is striven for, since the three successive analog-digital conversions in the automatic exchange and in the remote installation on account of the companding effect increase the quantization distortions to such a great extent that it is no longer possible to reconstruct the information that reaches the subscriber.

The object of the invention is therefore to specify an information transmission system of the kind mentioned at the beginning, with which system it is possible to attain a high data transmission rate between the central station and the peripheral station.

According to the invention this object is achieved in that the converter characteristic curve of the bi directional analog-digital converter on the exchange side and also of the bi-directional analog-digital converter on the peripheral side is linear, and in that the digital transmission link is formed by means of a high-speed transmission link.

On account of the exclusively linear conversion of the voice signals, voice compression is foregone in favour of the higher data transmission rate that can be attained. As a result of the discontinuation of the companding and expanding the quantization distortions are greatly reduced SO that it is Possible to transmit large volumes of data, for example for Internet applications.

In a further development of the invention it can be provided that the bi-directional analog-digital converter on the exchange side and the bi-directional analog-digital converter on the peripheral side each be formed as a 12 bit to 16 bit resolving converter, preferably as a 13 bit resolving converter.

As a result of the high resolution in comparison with that of standard analog-digital converters that are used with companding, the quality of the voice information that is transmitted is improved.

According to a further feature of the invention it can be provided that the high-speed transmission link between the exchange portion and the local portion of the remote installation be formed by means of an HDSL transmission line and HDSL-interfaces associated with the line ends.

The great advantage of the HDSL-transmission method (High Digital Subscriber Line) lies in the fact that this has already been standardized (for example ETSI Standard ETR 152, Bellcore-Standard TA-NWT-012 10) and the components that are required to set up an appropriate transmission line are therefore already provided. Furthermore, the HDSL makes a technology available with which the necessary high data rates can also be controlled. In the various standards the bit rate of the transmission is fixed at a fixed value, yet in the case of the application in accordance with the invention the bit rate can also be adjusted as a function of the number of subscribers, that is, increased or lowered in relation to the standard.

In this connection it can be particularly advantageous that the data rate on the HDSL-transmission line (12) amounts to between 280 kbit/s and 2.2 Mbit/s. As a result, a clear increase in the data transmission rate in comparison with, for example, an ISDN-transmission is possible, with it being possible to make allowance for different conditions on account of the comparatively large frequency operating range.

According to a further variant of the invention, the high-speed transmission link between the exchange portion and the local portion of the remote installation can be formed by means of a DMT transmission line and DMT-interfaces associated with the line ends.

Besides the HDSL, DMT (Discrete Multi Tone) is a method that is suitable for the transmission on copper lines and with which it is possible to attain very high data rates, although some technological development work still needs to be carried out in order to increase the reliability of the same.

In a further development of the invention it can be provided that the high-speed transmission link between the exchange portion and the local portion of the remote installation be formed by means of a fibre-optic line or by means of a radio link.

As a result, a rapid Internet transmission is rendered possible in a simple manner for automatic exchanges and telephone networks that already exist.

In a further development of the invention it can be provided that the high-speed transmission link be formed by means of internal digital lines and the switching matrix of a private automatic branch exchange (PABX) or an automatic exchange (PSTN), in which case the through-connection in the switching matrix is effected with 12 to 16 bits, preferably with 16 bits.

As a result, it is also possible to achieve routing of very high densities of information within already existing private automatic branch exchanges and automatic exchanges.

In this connection, it can further be provided that in order to transmit by way of the high-speed transmission link in two transmission channels in each case 8 bits be combined in parallel or serially to form a respective 16 bit word.

As a result, existing transmission channels, for example for fibre-optic links or radio links, can be used for the high-speed transmission.

The invention is explained in detail in the following with reference to the exemplary embodiments that are shown in the drawings, in which:

Figure 1 shows a diagrammatic representation of an information transmission system in accordance with the prior art;

Figure 2 shows a diagrammatic representation of an embodiment of the invention; Figure 3 shows a block diagram of an information transmission system in accordance with the prior art;

Figure 4 shows a block diagram of an embodiment of an information system in accordance with the invention; Figures 5 and 6 each show a block diagram of further embodiments of the information system in accordance with the invention.

The representations in Figures 3 to 6 for the purposes of simplification and better illustration are not provided with bi-directional analog-digital converters, but with unidirectional analog-digital converters, and only the transmission of the data or voice information from the respective central station 1 to the respective peripheral station 4 is shown. In actual fact, however, it is intended that there also be transmissions for such in both directions, that is, that there be bi-directional transmission, as will be explained with reference to Figures 1 and 2.

A telephone system arrangement in accordance with the prior art that is used to transmit information, more precisely voice and data information, from an automatic exchange 1, which represents a central station, to a peripheral station, in this exemplary embodiment a subscriber's terminal 4, is represented in Figure 3.

Besides telephone systems, other functionally equivalent systems are also understood by information transmission systems.

By way of a provider 10, for example an Internet provider, a video-on-demand-provider or the like, digital data reaches a central digital-analog converter 5, the analog output of which is connected to the one end of an analog transmission line 11, the other end of which communicates with an analog-digital converter 7 on the exchange side. The compander 6 connected downstream of-the analog-digital converter 7 compresses the converted data, whereby a general non-linear characteristic curve of the analog-digital converter 7 and compander 6 results.

The analog-digital converter 7 and the compander 6 are accommodated in an exchange portion 2 of a remote installation 15 which on the output side is connected by way of a digital transmission link 12, for example a two-wire copper line, to the local portion 3 of this remote installation 15.

An application is shown in Figure 3 that does not contain a multiplexer/demultiplexer, that is, it only contains one single forward and backward channel.

However, even if it is not explicitly shown, such applications in which the transmission is effected in multiplex operation can also be contained in all the embodiments in accordance with the invention.

However, not only data information, but also analog voice information is transmitted by way of the central exchange 1 in the direction of the subscriber's terminal 4. Besides conventional telephone apparatus, facsimile installations, computer modems or the like are also to be understood by subscriber's terminals.

The compander 6, on account of its non-linear transmission function, has a greater resolution in the case of signals with a small amplitude than in the case of signals with a large amplitude. Usually, the compression is effected by means of the compander 6 in accordance with the A- or p-law standard (ITU-T G.711).

According to the known solutions of the prior art, the digital transmission method is developed in accordance with the ISDN-standard on the line 12. The line 12 has the corresponding ISDN-interfaces at its line ends.

An expander 9 and a digital-analog converter 8 on the peripheral side are arranged in the local portion 3 of the remote installation 15 for the purpose of reconverting the signal that is transmitted on the ISDN-UkO-line. The expander 9 decompresses the digital signal that is received so that the digital-analog converter 8 on the peripheral side can supply to the subscriber 4 an analog signal from which distortions have been eliminated.

The analog-digital converter 8 on the output side is then connected to the subscriber by way of a further analog transmission line 30, in which case the expander 9, as already described above, can also be contained in the converter 8 itself.

The embodiment shown in Figure 3 has been prior art for a comparatively long time and has the disadvantage that on account of the companding which is effected after the analog-digital conversion or before the digital analog conversion respectively, quantization distortions result in the analog-digital and digital analog converters and this reduces the maximum data transmission rate that can be attained. In the case of ADPCM, problems are already noticeable in the range of kbit/s and in the case of A- and p-law from 50 kbit/s onwards with more than one analog-digital or digital-analog conversion.

The exemplary embodiment of the prior art that is shown in Figure 3 is diagrammatically represented in Figure 1 not only for the direction from the exchange to the subscriber, but also vice versa. Consequently, in the actual construction that is realized the analog-digital converters 5, 7 and 9 can also be understood to be bi directional converters.

Since there is a demand for ever higher transmission rates, which are pushed up ever higher as a result of applications such as the Internet, there is a great need to solve this problem.

According to the invention the object of solving this problem is achieved in that the converter characteristic curve of the bi-directional analog digital converter 7 on the exchange side and of the bi directional digital-analog converter 8 on the peripheral side is linear, and in that the digital transmission link 12 is formed by means of a high-speed transmission link.

An exemplary embodiment of the invention is shown in Figure 4, in which the provider 10 as the data source is connected to the automatic exchange 1, the retrieved data of which is converted into analog form by way of the digital-analog converter 5 and is transmitted thus on the analog transmission line 11 to the private automatic branch exchange 25 which contains the analog digital converter 7 on the exchange side that has a linear converter characteristic curve and is realized, for example, as a 13 bit converter. The companding of the voice can thus be replaced by comparatively high resolution of the sampling, in which case the comparatively large number of instances of sampling generated that is effected thereby is again compensated for by the high data transmission rate on the internal digital line 12 and a switching matrix 31 which constitute the high-speed transmission link of this embodiment. The corresponding output of the analog digital converter 7 is connected, by way of the digital transmission line 12, to the input of the digital analog converter 8 which on the output side is connected to the subscriber's terminal 4.

The digital-analog converter 8 on the peripheral side that converts the data transmitted by way of the digital line 12 back again also has a linear converter characteristic curve which renders possible the high data speed. The single subscriber's terminal 4 that is shown in the drawing is connected to the output of the digital-analog converter 8 and can receive both voice information and digital data, for example by modem.

The private automatic branch exchange 25, in accordance with its function, also connects a plurality of subscribers, which are not, however, shown separately in the drawing.

A further exemplary embodiment in accordance with the invention that is shown in Figure 5 relates to transmission by means of a remote installation 15, in which case provided between the exchange portion 2 and the local portion 3 there is an HDSL-transmission line 12 by way of which the high-speed transmission is performed. The corresponding associated interfaces at the line ends are not shown in Figure 5. The data transfer on this line preferably occurs with 280 kbit/s to 2.2 Mbit/s, in which case as the analog-digital converter 7 and as the digital-analog converter 8 in each case a bit rate in the range of 12 to 16 bits can be regarded as preferable.

The remote installation 15 can be operated in accordance with Figure 5 in all of the variants known hitherto, for example with a copper-line transmission link (copper in the loop) with HDSL-transmission or else even DMT-transmission with the corresponding associated interfaces, with a radio link (radio in the loop), a fibre-optic link (fibre in the loop) or the like. The transmission link 12 is therefore only to be understood as being a two-wire line in the conventional sense for those exemplary embodiments with HDSL- and DMT-transmission. A further terminal 40 is shown in Figure 5 for the purpose of illustrating the transmission to a subscriber that otherwise takes place in analog form.

With reference to Figure 5, a diagrammatic representation of the bi-directional information transmission system in accordance with the invention is shown in Figure 2, in which a respective termination set enables the transmitted and received signal to be split. By virtue of the fact that the compression and decompression respectively are discontinued, the signal in Figure 2 with 16 bits is only sampled linearly and is then transmitted digitally by way of two transmission channels with 8 bits in each case per transmitting direction.

Finally, in Figure 6 an analog connecting line 11, a so-called TRUNK line, is formed between a central automatic exchange 1 and a peripheral automatic exchange 20, in which case a linear analog-digital converter 7 on the exchange side and also a linear digital-analog converter 8 on the peripheral side are provided in the peripheral automatic exchange 20 and these can be connected by way of the internal digital 3D line 12 and a switching matrix 21 which together constitute the high-speed transmission link. A correspondingly large number of digital-analog converters 8 on the peripheral side can be formed in the automatic exchange 20 and these can route the information, which has been converted back into analog form, by way of respective analog lines 30 in the direction of the subscribers.

Within the private automatic branch exchange 25 (PABX - private automatic branch exchange) of the exemplary embodiment in accordance with Figure 4 or the automatic exchange 20 (PSTN = public switch telephone network) of the exemplary embodiment in accordance with Figure 6 - such a PSTN-system is described, for example, in the article "56Kbps Data Transmission Across the PSTN" by P. Michael Henderson, published on the Internet at "http:\\www.nb.rockwell.com/K56flex/whitepapers/56k_on PSTN.html" - it has proved to be particularly advantageous to effect the through-connection in the switching matrix with 12 to 16 bits, preferably with 16 bits. This digital through-connection in the automatic exchange 21 or in the private automatic branch exchange can, for example, either be effected serially with 16 bit words or with two times 8 bit words in two parallel digital voice paths. Consequently, in each case 8 bits from two transmission channels are combined for the purposes of transmission in parallel or serially to form a 16 bit word.

The analog TRUNK line 11 can also be in the form of various known embodiments, such as, for example, a directional radio link, satellite transmission, a fibre-optic link, but also as a copper line.

Claims

1. Information transmission system and more precisely a telephone system for transmitting information, more precisely voice and data information, from a central station, for example an automatic exchange, to a peripheral station, for example a subscriber's terminal, in which the central station is connected, by way of a central bi-directional analog-digital converter and an analog transmission line, to a bi directional analog-digital converter on the exchange side, for example in the exchange portion of a remote installation, of a further automatic exchange, of a private automatic branch exchange or the like, which bi-directional analog-digital converter on the exchange side has its corresponding output or input connected, by way of a digital transmission link and interfaces associated with the line ends, to a bi-directional analog-digital converter that is on the peripheral side, for example in the local portion of the remote installation, of the further automatic exchange, of the private automatic branch exchange or the like, which on the output side or input side is connected to the peripheral station by way of a further analog transmission line, with a converter characteristic curve being associated with the bi-directional analog digital converter on the exchange side and the bi directional analog-digital converter on the peripheral side, characterised in that the converter characteristic curve of the bi-directional analog digital converter (7) on the exchange side and also of the bi-directional analog-digital converter (8) on the peripheral side is linear, and in that the digital transmission link is formed by means of a high-speed transmission link (12, 21, 31).

2. Information transmission system according to claim 1, characterised in that the bi-directional analog digital converter (7) on the exchange side and the bi directional analog-digital converter (8) on the peripheral side are each formed as a 12 bit to 16 bit resolving converter, preferably as a 13 bit resolving converter.

3. Information transmission system according to claim 1 or 2, characterised in that the high-speed transmission link between the exchange portion and the local-portion of the remote installation (15) is formed by means of an HDSL-transmission line (12) and HDSL interfaces associated with the line ends.

4. Information transmission system according to claim 3, characterised in that the data rate on the HDSL transmission line (12) amounts to between 280 kbit/s and 2.2 Mbit/s.

5. Information transmission system according to claim 1 or 2, characterised in that the high-speed transmission link between the exchange portion and the local portion of the remote installation (15) is formed by means of a DMT-transmission line (12) and DMT interfaces associated with the line ends.

6. Information transmission system according to claim 1 or 2, characterised in that the high-speed transmission link between the exchange portion and the local portion of the remote installation is formed by means of a fibre-optic line.

7. Information transmission system according to claim 1 or 2, characterised in that the high-speed transmission link between the exchange portion and the local portion of the remote installation is formed by means of a radio link.

8. Information transmission system according to claim 1 or 2, characterised in that the high-speed transmission link is formed by means of internal digital lines (12) and the switching matrix (21, 31) of a private automatic branch exchange (PABX) (25) or an automatic exchange (PSTN) (20), in which case the through-connection in the switching matrix is effected with 12 to 16 bits, preferably with 16 bits.

9. Information transmission system according to one of claims 3 to 8, characterised in that in order to transmit by way of the high-speed transmission link in two transmission channels in each case 8 bits are combined in parallel or serially to form a respective 16 bit word.