Abstract:
An apparatus and method for maintaining access to lifeline services through telephone sets provided with telephone service from a voice over digital subscriber loop (VoDSL) transceiver during power interruptions are described. All telephone sets associated with the transceiver are connected to a wire loop which supports the VoDSL service in the event of a power interruption to the transceiver. The advantage is the economical provision of lifeline service access to all telephone sets when power is interrupted to the transceiver. Thus, confusion is reduced, safety is enhanced, and access to lifeline services is ensured during emergency situations.

Description:
TECHNICAL FIELD 
     This invention relates to the provision of telephone services at a customer premises over a wideband service channel and, in particular, to a method and apparatus for maintaining access to telephone services during power outages at the customer&#39;s premises on telephone sets connected to voice over digital subscriber loop (VoDSL) derived telephone lines. 
     BACKGROUND OF THE INVENTION 
     In the art of telephony, until relatively recently twisted pair copper loops have been used to provide a physical connection for single directory number terminations on the Public Switched Telephone Network (PSTN). This type of service is known in the art as a Plain Old Telephone Service (POTS) connection and provides a termination to which at least one telephone set is connected. 
     Recently the telecommunications industry has experienced an increase in the utilisation of telecommunications services which requires more bandwidth for service delivery to customer&#39;s premises. One way to deliver increased bandwidth to a customer is to install more local loops between the customer&#39;s premises and a servicing central office. Another way is to install higher bandwidth connections, such as optical fibre. However, any solution involving the installation of new infrastructure typically proves to be very costly. Considering the downward pressure on service pricing due to increased competition in the telecommunications market, large capital investments in new infrastructure are generally not practical. 
     Solutions have been developed for providing increased bandwidth over existing subscriber loops. One successful solution is digital subscriber loop (DSL) service which provides good data transfer rates for customers located in proximity of a central office. Several DSL service protocols have been developed. They include asymmetric (ADSL); symmetric (SDSL), rate adaptive (RADSL) and very high speed (VDSL) which are collectively referred to as “XDSL” services. This technology permits the provision of wide frequency bandwidth which provides a second communications channel over the same twisted pair subscriber loop used for telephone service delivery. Various service applications have been developed and deployed using xDSL technology, of which Internet access is a prime example. xDSL devices installed at a customer location or on the customer premises are respectively referred to as Customer Located Equipment and Customer Premises Equipment (CLE/CPE) 
     There is an increasing interest in providing multiple telephone line terminations at a customer&#39;s premises using xDSL services. This interest is fuelled by, for example, an expanding small business workforce requiring office equipment that uses the PSTN as an interconnection medium; an increase in home-based businesses; and a demand for multiple telephone lines for family use. 
     The provision and deployment of multiple POTS terminations at the customers premises has to date largely been accommodated by installing multiple local loops between the customer&#39;s premises and a servicing central office. The deployment of VoDSL, in which multiple telephone line terminations are derived from the DSL channel, has now enabled multiple telephone lines using a single subscriber loop. However, VoDSL has a disadvantage because during power interruptions the DSL channel derived lines are lost. Consequently, telephones connected to those lines are disabled and offer no access to lifeline services during the power interruption. 
     In the event of power interruption at the customer&#39;s premises, current implementations of VoDSL CLEs/CPEs do not provide a contingency solution for maintaining service on the VoDSL derived lines. Nonetheless, in a VoDSL service offering in which VoDSL derived telephone lines are provided, in the event of power interruption at the customer&#39;s premises, the telephone set connected to the wire loop termination remains in service because it is provided with power from the central office. However, the VoDSL derived telephone lines become non-functional and cannot be used to place calls. Consequently, the only way the customer is able to place an emergency call is to find the active telephone set connected to the wire loop termination. This is obviously not a desirable situation. 
     It is known in the art to provide power to telephone equipment in event of power interruption. U.S. Pat. No. 4,381,427 which issued Apr. 26, 1983 to the Applicant describes a local loop system for providing voice and data communications which enables signalling between a customer&#39;s telephone and the central office in the event of power interruption. The system is located at the central office and only provides a return path for a local loop in the event of power interruption. The system is not adapted to maintain access to lifeline services through telephone sets connected to VoDSL derived line terminations because it is not adapted to supply power to the VoDSL CLE/CPE. 
     U.S. Pat. No. 4,730,311 which issued Mar. 8, 1988 to Carse et al. describes a system in which a battery backup is provided at the customer&#39;s premises. There are shortcomings in providing backup power in the event of power interruption at a customer&#39;s premises using devices such as un-interruptible power supplies or battery backups. Providing batteries or uninterruptible power supplies significantly increases the cost of the deployed CLE/CPE. Backup power supplies can only operate only for a limited period of time before the batteries employed are exhausted. Furthermore, batteries employed in providing backup power also have a limited operational life, and must be serviced and periodically replaced. 
     No solution is currently known in which VoDSL equipment provides access to lifeline services from telephone sets connected to VoDSL derived telephone lines in the event of a power interruption to the transceiver. Therefore, there remains a need to provide a method and apparatus in which all telephone sets connected to VoDSL derived telephone lines are enabled to maintain access to lifeline services in the event of a power interruption at the customer&#39;s premises. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method and apparatus which maintains access to lifeline services for telephone sets connected to line terminations derived from a wideband service channel in the event of a power interruption to a transceiver providing the services. 
     The invention therefore provides a transceiver adapted to maintain access to lifeline services over telephones sharing a physical link with a wire loop termination in the event of a power interruption to the transceiver. If operating power to the transceiver is interrupted, the transceiver is adapted to connect a plurality of telephone interfaces associated with the wideband derived line terminations to the wire loop termination, thereby providing power to the interfaces so that access to lifeline services through all telephone sets associated with the transceiver is maintained. 
     In accordance with the invention, the transceiver is provided with switchover circuitry. While provided with operating power from the customer&#39;s premises, the switchover circuitry decouples the telephone interfaces associated with the wideband derived line terminations from the wire loop termination. In the event of a power interruption, the switchover circuitry couples the telephone interfaces associated with the wideband derived line terminations to the wire loop termination, thereby providing operating power to maintain access to lifeline services to all telephone sets associated with the transceiver. 
     The switchover circuitry preferably automatically transitions from a first state to a second state when operating power is supplied to the transceiver. In the first state, the switchover circuitry couples the telephone interfaces derived from the wideband derived telephone lines in parallel to the wire loop. This permits outbound calls to be placed from any one of the telephones. In the second state, the switchover circuitry couples the telephone interfaces to respective circuits associated with the wideband derived telephone lines so that normal, multi-line operation is restored. 
     The switchover circuitry may be, for example, one or more electromechanical relays or solid state relays. 
     The wideband channel may be, for example, a digital subscriber loop (DSL) service channel such as a voice over digital subscriber loop (VoDSL) service channel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing a VoDSL transceiver in accordance with a preferred embodiment of the invention during power interruption conditions; and 
     FIG. 2 is a schematic diagram showing the VoDSL transceiver shown in FIG. 1 in a normal operations mode in which operating power is provided to the transceiver. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention provides a method and apparatus for providing access to lifeline services over telephone lines derived from a wideband channel, such as VoDSL, using a transceiver connected to a wire loop when operating power to the transceiver is interrupted. 
     A VoDSL transceiver  10  in accordance with a preferred embodiment of the invention is schematically illustrated in FIG.  1 . The VoDSL transceiver is shown in power interruption mode. The VoDSL transceiver  10  normally draws operating power from a customer&#39;s premises. Communications payload is exchanged between the VoDSL transceiver  10  and a servicing central office (not shown) via a connector  12  to which a subscriber loop is connected. Received communications signals are routed to a POTS filter  14  via internal connections  16  and to an xDSL transceiver  20  via internal connections  18 . The POTS filter  14 , also commonly referred to as a “splitter”, reduces noise induced by the wideband channel. The POTS filter is optional and may not be included in the VoDSL transceiver  10 , in which case the tip and ring pair  22 ,  24  are directly connected to the internal connections  16 . A telephone (not shown) is connected to the legacy POTS termination via telephone interface  26 , typically an RJ 11  standard connector. 
     In the embodiment of the VoDSL transceiver shown in FIG. 1, four line cards  28  provide telephone line terminations  34   a-d  derived from the DSL service channel. A person skilled in the art will appreciate that the VoDSL transceiver  10  can support a number of telephone line terminations limited only by a bandwidth of the DSL service channel and multiplexing efficiency of the DSL receiver. VoDSL derived telephone line terminations also provide tip and ring conductors  30   a-d  and  32   a-d , respectively. The customer can access the VoDSL derived telephone line terminations via telephone interfaces  34   a-d  to which telephone sets (not shown) may be connected. Under normal operating conditions, each of the telephone line interfaces  26 ,  34   a-d  are adapted to support a variety of telephony interfaces that are known standards in the art. Consequently, the customer cannot distinguish between telephone sets connected to the two types of telephone lines (wire loop and VoDSL derived). 
     Power is provided to the VoDSL transceiver  20  and therefore to the line cards  28  and from a power connector  36  via power conductors  38  and  40 . Power conductors  38  also provide operating power to a switchover circuit  42 , for example a coil of a relay. A power supply (not shown) for the VoDSL transceiver  20  may be internal or external to the transceiver. 
     The VoDSL transceiver  10  shown in FIG. 1 is operating under power interruption conditions at the customer&#39;s premises. Switchover circuit  42  is de-energized during periods that power is unavailable from power connector  36 . The switchover circuit  42  has centre leads  44   a-d  that correspond to each of the tip and ring conductors  30   a-d  and  32   a-d . Under power interruption conditions, the centre leads  44   a-d  are normally-closed width leads  46   a-d , respectively. In this state, all tip and ring leads associated with the telephone interfaces  34   a-d  are connected to a tip and ring bus  48  formed by conductors  50  and  52 , as shown in FIG.  1 . The tip and ring bus  48  is derived from the tip and ring leads  22  and  24  associated with the wire loop termination. Under power interruption conditions, telephone interfaces  26  and  34   a-d  are connected in parallel. 
     In an emergency situation in which power is interrupted at the customer&#39;s premises, the VoDSL transceiver  10  in accordance with the invention has the following characteristics: all telephone sets connected to VoDSL derived telephone line terminations via connectors  34   a-d  are automatically coupled to the wire loop termination. This provides a customer with access to lifeline services available on the PSTN from any of the telephone sets by making the wire loop termination available to all telephone sets. Thus the VoDSL connected telephone sets behave as extension telephones on the wire loop termination. 
     Out-of-box characteristics of the VoDSL transceiver  10 , as enabled by the invention, are such that all connected telephone sets are operational—albeit sharing the wire loop termination—in the event of improper installation or configuration of the VoDSL transceiver  10  or improper provision of power to the VoDSL transceiver. 
     As an additional feature, the VoDSL transceiver  10  preferably further includes a control device  56  which controls power to the switchover circuit  42 . The control device is connected to the xDSL transceiver  20  by a control line  58 . The xDSL transceiver uses the control line  58  to control the control device  56  so that power only flows to the switchover circuit  42  under control of the xDSL transceiver  20 . The xDSL transceiver is preferably programmed to run a process which enables power to the switchover circuit  42  only when the xDSL transceiver  20  is fully operational and telephone service on the wideband channel is functional. Consequently, if communications on the DSL service channel are lost, the telephone(s) connected to telephone interfaces  34   a-d  are connected to the tip and ring leads  22 ,  24 , as explained above, even though power to the VoDSL transceiver  10  is not interrupted. Likewise, during a reboot, or other transition from a power interruption to a normal operating condition, the xDSL transceiver  20  interrupts power to the switchover circuit  56  using the control line  58  and the control device  56 , until normal operation is restored on the DSL service channel. This ensures that all telephones connected to the VoDSL transceiver  10  are enabled for access to lifeline services at all times. 
     FIG. 2 shows the VoDSL transceiver  10 , according to the invention, under normal operating conditions in which the VoDSL transceiver  10  is provided with operating power. Switchover circuit  42  is energised for as long as power is provided from power supply connector  36 . While the switchover circuit  42  is energized, the centre leads  44  maintain the switches  54   a-d  in their normally-open condition. This provides, under normal operating conditions, connectivity between each line card  28   a-d  and its respective telephone interface  34   a-d . 
     A person skilled in the art will appreciate that the invention may also be applied to CLE/CPE devices employing VoDSL techniques or CLE/CPE devices which carry voice subchannels over a wideband channel using other protocols such as, but not limited to, frequency division multiplexing, time division multiplexing, code division multiplexing etc., all of which are well known in the art. 
     Persons skilled in the art will also appreciate that the switchover circuit  42  may be any mechanical or solid state switching device. A relay provides an economical solution for switching all telephone sets associated with the VoDSL derived telephone interfaces over to the wire loop termination. However, there exist a multitude of workable electrical component combinations known in the art for providing reliable switchover circuitry. For example, solid state relays provide one practical alternative for the switchover circuit  42 . 
     Persons skilled in the art will also understand that although the number of telephone interfaces that may be supported by the transceivers in accordance with the invention is limited only by bandwidth and multiplexing efficiency, as described above, there is a practical limit on the number of telephones that can be supported by the wire loop termination for inbound call ringing. Nonetheless, outbound call capability is enabled on all telephones connected to a transceiver in accordance with the invention. As explained above, when power to the transceiver is interrupted, each of the telephones connected to the transceiver perform and behave as extension sets, which are referred to by persons skilled in the art as parallel mode extension telephones. 
     The embodiment of the invention described above is intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.