Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Testing of subscriber loop or terminal
Reexamination Certificate
2001-07-23
2003-01-21
Kuntz, Curtis (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Testing of subscriber loop or terminal
C379S001030, C379S009050, C379S022040, C379S027010, C379S027060, C379S029010
Reexamination Certificate
active
06510204
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for transferring digital voice signals together with high speed data, and particularly to an all digital loop possessing a mode of low-power transfer of such signals. Additionally, the present invention relates to a telephone network comprising such apparatus.
With the proliferation of digital data transmission across telecommunications networks and inter-networks, it has become common practice to integrate the transmission of analogue telephone signals, associated with a ‘Plain Old Telephone Service’ (POTS), with the transmission of other digital data, upon such networks (e.g. xDSL transmission). In many cases, the latter type of data may well be transmitted via the same transmission medium as the former signals (i.e. via a telephone line).
It is well known that analogue signals associated with POTS and, for example, the digital signal associated with an xDSL (Digital Subscriber Line) data stream, may be simultaneously transmitted via a twisted-pair transmission line.
Such simultaneous data transmission is clearly desirable and its realisation may typically involve the technique of frequency-division multiplexing of the two signals. According to such a technique, a low-frequency transmission band (i.e. 300 Hz-3400 Hz) is assigned to the transmission of analogue telephony signals and a high-frequency transmission band (i.e. band of high-frequency carriers modulated with signal data) is assigned to transmission of the xDSL data stream. Consequently, simultaneous transmission of digital xDSL data and independent analogue telephone signals may be provided via the same twisted-pair transmission line of a telecommunications network.
Such a transmission technique is known, generally, as ‘out of band’ transmission since telephone signals are transmitted outside of the xDSL transmission band.
A recognised deficiency of this technique lies in the necessity of employing suitable multiplexing/de-multiplexing equipment capable of accepting the relatively high voltage levels typically present in analogue telephone signals (e.g. the ringing signal). Consequently, this equipment (POTS splitter) is often prohibitively expensive (operator dependent) and/or bulky. Born of this realisation came the incentive to develop systems for the simultaneous transmission of digitized telephone signals, together with other independent xDSL digital data, over a twisted pair telephone line.
Such a system, known as an ‘all digital loop’, thereby obviates the need to employ such expensive/bulky equipment by transmitting telephone signals, together with other digital data, in a digital format only and thereby removing the high-voltage components associated with the analogue telephone signal. For example, digitized telephone signals may be embedded within the frames associated with an xDSL data stream. In such a case, ‘in-bond’ transmission is achieved since the digitized telephone signals are thereby transmitted within the same transmission band (of carriers) as the xDSL data stream.
In the case of ADSL or VDSL (Very High Speed Digital Subscriber Line) this implies that, in contrast to the traditional ‘overlay scenario’ where POTS or ISDN are transported ‘out of band’, the telephony signals are transmitted ‘in-band’. That is to say, analogue telephone signals originating from a telephone set are transmitted therefrom to an xDSL network termination node containing xDSL equipment operable to digitise and subsequently transmit those signals to an xDSL line termination in the access node providing the gateway to the PSTN (Publicly Switched Telephone Network) network. This is one way to realise the all digital loop. Alternatively, the telephone signals may be digitized before being supplied to an xDSL network termination to be transmitted subsequently over the all digital loop.
However, a potential weakness of an approach such as this lies in the need to digitise the telephone signals and embed them, via the xDSL equipment, into the xDSL data stream prior to simultaneous transmission thereof. Should xDSL equipment fail due, for example, to a loss of power then both xDSL and (more importantly) telephone communications along the all digital loop would break down.
Clearly, such a loss in telephone communications would be inconvenient at the very least and, conceivably, precipitate disastrous consequences should POTS telephone services be urgently required. Thus, the provision of an emergency ‘lifeline’ within such all digital loops, which would guarantee continued telephone communications services (POTS) is therefore paramount.
A common prior art technique of providing continued POTS under such circumstances involves the step of reverting to independent analogue transmission of telephone signals. Analogue telephone signals (or digital telephone signals via for instance an ISDN interface) are received at a telephone network termination (NT) node (from a telephone set) for subsequent digital transmission therefrom to a line termination (LT) access node providing a gateway to the PSTN network. Under normal operating conditions ‘in-band’ transmission of those telephone signals with digital data streams simultaneously input to the xDSL equipment (at the NT node), would then take place in accordance with all digital loop transmission techniques as outlined above.
As discussed above, in the event of power failure at the NT node of the digital loop, ‘in-band’ digital transmission of neither the telephone signal nor the xDSL data could take place and POTS would be lost. However, when failure occurs, a series of switches may be switched at each node of the digital loop (i.e. the NT and LT nodes) so as to provide a bypass circuit which permits the analogue/digital telephone signal (input to the NT node) to bypass all xDSL equipment in the respective node. Consequently, a direct POTS lifeline from the NT node to the LT node, and thence to the PSTN, is thereby provided.
Unfortunately, as will be readily apparent, such a system requires the use of additional circuitry to bypass the xDSL equipment at both nodes. Furthermore, old existing linecards are required at the LT (access) node to operate the additional circuitry. These linecards must be kept in place at all times so as to guarantee a POTS lifeline and, therefore, cannot be replaced with other equipment should the need, or desire, arise.
SUMMARY OF THE INVENTION
The present invention aims to overcome at least some of the above identified deficiencies of the prior art by providing an all digital loop in which a POTS lifeline is provided without recourse to switching/bypass circuitry and the corresponding linecards associated therewith.
Accordingly, in a first of its aspects the present invention provides apparatus for use in a digital telecommunications network, the apparatus including:
a first network node;
a second network node; and
a data transmission line connecting the first network node to the second network node;
wherein each one of said first and second network nodes is operable to transmit to the other of said first and second network nodes, at least one digitized telephone signal with other digital data via a set of carriers, the apparatus being characterised in that:
one of said first and second said network nodes includes or is associated with means which in the event of power failure at the first said network node, is operable selectively to provide power to the first node such that the first node operates only via a limited subset of said carriers which limited subset is such as to minimize the power required for the transmission thereof so as to provide transmission of a telephone lifeline signal between the first and second nodes.
Thus, it will be understood that the present invention, in its first aspect, aims to guarantee a POTS lifeline by means of providing an emergency power supply operable to selectively power the continued digital transmission of telephone signals between two nodes of e.g. an all digital loop using minimal power. Preferably, the limited subset of carriers p
De Clercq Luc Josephine Theoduul
Ploumen Franciscus Maria
Reusens Peter Paul Frans
Van Bladel Marc Maria Marcel
Verbiest Willem Jules Antoine
Alcatel
Kuntz Curtis
Tran Quoc D.
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