Arrangement for data transmission utilizing telephone network

[0002] 1. Field of the Invention

[0003] The present invention is directed to an arrangement for data transmission which utilizes a telephone network connection between modems for data terminal equipment that is connected to a telephone switching center via telephone subscriber lines.

[0004] 2. Description of the Related Art

[0005] In a telephone network that is utilized for data communications, modems (which include modulators and demodulators) provide a data transmission means that are arranged as a link for adapting between telephone voice paths and data terminal equipment and that serve the purpose of converting the digital signals supplied by the data terminal equipment into line signals which are advantageous for data transmission and which correspond to the electrical conditions for analog telephone connections or which undertake a back-conversion of such line signals into digital signals.

[0006] Different modulation methods, such as frequency modulation, phase-difference modulation and quadrature amplitude modulation, are applied in this context (see, for example, Handwörterbuch des elektrischen Fernmeldewesens, published on commission of the Bundesministerium für das Post- und Fernmeldewesen).

[0007] There are a multitude of different modem protocols for modem connections including, for example, those specified by the ITU-T (formerly CCITT) in what is referred to as the V-series.

[0008] FIG. 1 of the drawings shows how data transmission was previously sequenced over the telephone network.

[0009] Data signals which are derived from data terminal equipment, for example a personal computer PC1, are converted into line signals in a modulator MOD1 and are transmitted to a telephone switching center LE1 via a subscriber line TL1, which mainly serves for transmitting voice signals from and to telephone terminal equipment. In a subscriber line circuit TSCH1 to which the subscriber line TL1 is connected, the line signals experience the same handling as voice signals, namely a band limitation to 300 through 3400 Hz, an analog-to-digital conversion, a compression according to the A-law or the μ-law, and are ultimately transmitted via a PCM link PCM of the telephone network SPN, to which the switching center LE1 also belongs, to a destination switching center LE2 of the telephone network to which the other data terminal equipment that is in the form of the personal computer PC2 for the connection under consideration is connected. In the subscriber line circuit TSCH2 of the destination switching center LE2, the transmitted data experience a corresponding back-conversion, namely an A-law or μ-law expansion and a digital-to-analog conversion, before they are transmitted via the telephone subscriber line TL2 to the modem MOD2, in order to proceed therefrom to the data terminal equipment PC2 after conversion into digital signals.

[0010] Except for the data terminal equipment, the system parts mentioned in conjunction with the described data signal transmission, which mainly serve for voice signal transmission between telephone terminal equipment such as the illustrated terminal equipment Tel1 and Tel2, are accordingly optimized for the voice signal transmission and therefore have a limiting effect for the data transmission in view of the transmission rate and the transmission bandwidth. Highly complex modulation methods for the digital data are utilized in order to achieve an enhancement of the obtainable data rates, this, of course, resulting in correspondingly increased outlay.

[0011] Given the above-described, known way of sequencing data transmissions using the telephone network, there is a direct communication of the subscribers—as in voice signal connections—with one another. In this case, the subscribers are the modems. This requires that the subscribers must “understand one another”, i.e. that the same modem protocol must be employed at both modems at the two terminal equipment sides. A further demand arises when modem protocols are reformulated since these new protocols must also cover previous modem protocols so that modems which are already installed can continue to be employed.

[0012] An object of the present invention is to provide an arrangement for data transmission utilizing the telephone network between modems for data terminal equipment connected to a telephone switching center via analog telephone subscriber lines to such effect that such modem connections are possible without the aforementioned restrictions.

[0013] Given the present inventive arrangement, accordingly, a modem that works according to the same modem protocol as the modem connected to the respective telephone subscriber line at the subscriber side is arranged in the telephone switching centers at the interfaces to affected telephone subscriber lines, i.e. those that set up a connection to the modem of a data terminal equipment. This thus means that, given a data connection between two modems for data terminal equipment at the terminal equipment side, these modems of the terminal equipment side no longer have to communicate directly with one another but need only communicate with the modem located in the switching center. The modem protocols that are applied given such a communication and, in particular, the type of encoding method employed are thus only dependent on the properties of the transmission link between the terminal equipment modem and the switching center. This enables the definition of modem protocols that cover all previous standards and that are also in the position to transmit significantly higher data rates (such as data rates >>64 kbit/s).

[0014] According to a further development of the invention, the exchange-side modems are placed as close as possible to the interface to the telephone subscriber line. All voice-signal-specific equipment in the entry region of the switching center thus no longer have to be traversed, this, as indicated, having led to limitations under the previous practice. For example, the compression and expansion according to the A-law or μ-law provided for voice signals can be avoided by the present invention.

[0015] According to another development of the invention, the exchange-side modems are configured for optional operation according to different modem protocols, preferably according to all known protocols that are in practice, so that communication with any of the types of modems which may occur at the terminal equipment side is possible without further ado.

[0016] According to yet another development, the exchange-side modems are integrated in subscriber-individual physical subscriber line units or subscriber-group-individual subscriber line modules for the connection of the telephone subscriber lines.

[0017] According to yet a further development, the physical subscriber line units comprise a terminal to a data network in this case in addition to their terminal to the telephone switching center, whereby these terminals are alternatively activated for the data signals to be transmitted between the data terminal equipment. Given this construction, a subscriber equipped with an arbitrary, commercially available modem at the terminal equipment side can be conducted directly into the data network via the subscriber line of the switching center or its data network terminal. Connections to the data network, which often last for a relatively long period of time, for example, connections using Internet applications, are thus prevented from burdening the parts of the telephone network that are not individual to the subscriber, beyond the connection setup and the connection shutdown.

[0018] In another aspect, the exchange-side modems are realized by employment of a digital processor system, for example a signal processor or microprocessor. The respective, selective modem protocol behavior can then be achieved in a simple way by loading appropriate software or by replacing or regrouping corresponding function blocks.

[0019] For realizing the modems in the case of the presence of subscriber line modules, it is provided that a signal processor pool be formed that comprises fewer signal processors than subscriber line circuits in a subscriber line module, whereby the processors can be dynamically allocated at will to the subscriber line circuits. A structurally compact and cost-beneficial solution thus derives.

[0020] According to a preferred embodiment, the modems work according to the DMT method (discrete multi-tone method). The lower transmission frequency range is thereby kept free for analog voice transmission of the telephone mode, which can thus ensue simultaneously with the data transmission which occurs in the higher transmission frequency range.

[0021] The present invention is explained in greater detail below on the basis of an exemplary embodiment with reference to the drawings.

[0022] FIG. 1 is a functional block diagram showing the conditions already discussed above for data transmissions via the telephone network which takes place by the use of modem connections;

[0023] FIG. 2 is a functional block diagram of an arrangement for data transmission which utilizes the telephone network according to the present invention, whereby the presence of a data network is assumed; and

[0024] FIG. 3 is a functional block diagram of a subscriber line module with equipment according to a specific embodiment of the invention.

[0025] In FIG. 2, parts that are the same as parts shown in FIG. 1 are provided with the same reference characters.

[0026] Differing from the apparatus shown in FIG. 1, the arrangement of FIG. 2 provides subscriber line units TSCH1 or TSCH2 of the telephone switching centers LE1 and LE2 to which modems MOD1 or, respectively, MOD2 of the terminal equipment side are connected via subscriber lines TL1 or, respectively, TL2 comprise an exchange-side modem MODCh1 or, respectively, MODCh2. These modems MODCh1 and MODCh2 are arranged as close as possible to the interface to the telephone subscriber line TL1 or, respectively, TL2, namely following a means AFE, which represents the analog part of the interface, in which the analog-to-digital conversion or, respectively, digital-to-analog conversion also occurs.

[0027] The modems MODCh1 and MODCh2 are connected to an interface circuit IFDN that leads to a data terminal at a data network DN.

[0028] The data network can, for example, be the Internet. An Internet connection will, thus, only occupy central parts of the switching centers LE1 and LE2 in the stage of the connection setup and only make use of parts individually associated with the subscriber line or, respectively, subscriber line group during the entire Internet connection. Modem communications during the course of such a connection between the personal computers PC1 and PC2 only have to occur between the modem MOD1 and the modem MODCh1, on the one hand, and the modem MOD2 and the modem MODCh2, on the other hand.

[0029] However, it also continues to be possible to conduct the data communication via the telephone network in its full scope or at least in a greater scope. This can be necessary when the switching center at the B-subscriber side of a data connection is not equipped according to the present invention.

[0030] With reference to FIG. 3, a subscriber line module SLMI:MSFM for subscriber lines TL that connect to data terminal equipment, such as a personal computer, PC constructed according to a specific development of the invention is shown in greater detail. Let such a subscriber line module SLMI:MSFM serve for the connection of 16 subscribers and therefore comprise 16 subscriber circuits TSCHG that essentially contain the analog part AFE of the line interface as also shown in FIG. 2. The digital interface part DFE (shown in FIG. 1) for the voice signals, in which—among other things—the compression or, respectively, expansion according to the A-law or, respectively, μ-law as well as the line impedance matching ensues, is provided here as a means shared by the 16 subscriber line circuits. The same is true of the interface IFSPN to the PCM line PCM leading to the central part of the switching center.

[0031] The compression or, respectively, expansion ensuing according to the A-law or μ-law and A/D or, respectively, D/A conversion are mixed analog-digital functions and are allocated here to the analog part AFE of the line interface. This allocation requires a drive of the analog line interface AFE in order to activate or suppress compression and expansion on request.

[0032] The modems which are referenced MODCh1 or, respectively, MODCh2 in FIG. 2 are realized here in the form of digital signal processors DSP that can work according to all known modem protocols, to which end the corresponding software is respectively loaded. When new protocols arise, the software merely has to be updated.

[0033] In the illustrated case, the signal processors are not permanently allocated to the individual subscriber circuits TSCH but form a pool that comprises fewer signal processors than subscriber line circuits TSCH in the subscriber line module SLMI:MSFM. They can be dynamically allocated to these subscriber line circuits.

[0034] The digital signal processors DSP as well as the interface IF are under the control influence of a control processor IOP that is influenced proceeding from a control network CN and with which—among other things—a determination is also made as to whether that data signals handled by one of the signal processors are supplied to the data network via the interface IFDN or to the voice network via the interface IFSPN.

[0035] According to a development of the invention, the modems work according to the DMT method (discrete multi-tone method). In this method, a plurality of carrier signals are utilized for the transmission, so that the transmission channel is subdivided into n sub-channels. In the modulation of the data, tones of a specific frequency are thereby generated, these are combined and sent over the line as “DMT symbol”.

[0036] In the embodiment of the present invention, the lower transmission frequency range is reserved for analog voice transmission of the telephony mode; the data transmission occurs in the higher transmission frequency range and can ensue simultaneously with the telephony mode.

[0037] Although other modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.