Abstract:
To initiate the transmission of electrical power over a telecommunications connection from a power-collecting telecommunications interface unit o such as a customer premises equipment, connectable to a power supply, to a power-receiving unit such as a curbside electrical/optical interface, when a connection is first established, or the collecting unit is first powered up, or in order to re-establish connection alter a power outage, control signals are transmitted between low-power modems in the interlace units using a low-power communications protocol. This allows the controlled initiation of a larger power output and a higher speed exchange of data once the full telecommunications connection has been established. A low-powered beacon signal is transmitted over the telecommunications connection by the power-collecting telecommunications interface unit on connection to a power supply, for detection by the power-receiving telecommunications interface unit. In the event of a loss of power at the input, the low power modem initiates power management control signals to cause the power-receiving telecommunications interface to shut down certain functions in order to preserve backup power for essential “lifeline” services.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is a National Phase entry of PCT Application No. PCT/GB2014/000214, filed Jun. 5, 2014, which claims the benefit of EP Application No. 13250085.1, filed Jul. 23, 2013, each of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments relate to a reverse powering system for telecommunications nodes. Embodiments provide a signaling mechanism between a power sink (ANU) and a power source arranged such that sufficient power is always available in a remote unit both from an individual line perspective and the global powering requirement of the ANU. 
       BACKGROUND 
       [0003]    In a Fiber-to-the-Distribution Point (FttDP) system each remote node (Access Network Unit ANU, also known as Distribution Point Unit—DPU), which provides the interface between the optical domain and the wired electrical connection into the customer premises, may be powered from an electricity supply located in the customers&#39; premises, using the wired electrical connection. Several customers may be connected to the ANU and each could be operating under different power sink conditions depending upon the services that each customer is consuming. 
         [0004]    International Patent specifications WO2009/138710, WO2009/138711, and WO2010/082016 describe a power supply system in which the power supply to be delivered by each user connected to an ANU is controlled such that users connected over short drop lengths provide proportionately more power to the ANU than those connected over longer drops. This reduces energy losses, because of the lower power losses on shorter (lower resistance) electrical connections (Power loss =I 2  R, with R (resistance) proportional to the length of wire through which the current passes). 
         [0005]    The reduced power draw on the longer connections also compensates those customers on the longer connections for the generally slower DSL service possible over the longer lines. However, the system described in the earlier references was isolated from the element management of the ANU and the state of the CPE (battery backup). 
         [0006]    It is common for the ANU or distribution point to be located in a relatively inaccessible location such as on a pole, or in a locked curbside cabinet, and only accessible to trained and authorized personnel of the telecommunications service provider. It is therefore not practical to make adjustments to their settings manually, so a setting procedure is required that can be operated using control signals transmitted from a remote location. 
         [0007]    When a connection is operational, signaling between the customer premises equipment and the ANU can be achieved using a management channel in the xDSL (digital subscriber line) protocols. However, at system start-up or following an interruption in connection there is no xDSL operating, and therefore no means of controlling the power collection function. Without power, the xDSL protocols cannot be used to communicate with the customer premises equipment to initiate the power collection function. 
       SUMMARY 
       [0008]    Embodiments provide for much greater control of the reverse powering system, in particular during start-up. According to a first aspect of embodiments, there is provided a power insertion system for a telecommunications interface unit for controlling the transmission of electrical power over a telecommunications connection between the interface unit and another interface unit, the power insertion unit comprising a control system for processing control signals controlling the power delivered over the telecommunications connection, and comprising a modem for the transmission of control messages between the interface units, the modem being configured to operate during a dormant phase using a communications protocol capable of operation on power scavenged by one of the interface units from the other interface unit over a high impedance connection indicative that the connection is intact, to allow the transmission of control messages between the interface units to initiate an active phase in which a larger power output can be transmitted over the telecommunications connection from the power-collecting telecommunications interface unit to the power-receiving telecommunications interface unit. 
         [0009]    Two interface units, each having such a modem, can communicate with each other to deliver power to one of them from a power supply connected to the other. These will be referred to respectively as the power-receiving unit (or “sink”) and the power-collecting unit (or “source”). The power-receiving unit (“sink”) may be an optical network termination point for converting between electrical signals and optical signals. In use, during the dormant phase, the “sink” is not connected to an electricity supply other than the very low power (high impedance) connection from the source unit, and its modem operates on power scavenged from the telecommunications connection to power the modem. The source modem is connected to a power supply, but its modem should nevertheless operate on the low power protocol in order that the sink modem can co-operate with it. 
         [0010]    In one advantageous arrangement, the low-power protocol is only used to set up the power delivery system, to allow a second, high speed, connection to then operate once the full power supply has been initiated. 
         [0011]    In one advantageous arrangement, the power collecting unit transmits a beacon signal when it is connected to a power supply, and the power receiving unit, when in a standby mode, monitors the telecommunications connection for such beacons and responds when it detects one. The power-collecting unit is therefore required to use only a small amount of power when in the “standby” mode, until it is connected to a power supply. This can typically be provided by a battery. 
         [0012]    The control system may also be configured to exchange signals in the event of a loss of power, either intentional or otherwise, at the power-collecting unit, in order to manage a “graceful” shutdown and return the power-receiving unit into the standby mode. 
         [0013]    According to another aspect of embodiments, there is provided a method of controlling transmission of electrical power, over a telecommunications connection, to a power-receiving telecommunications interface unit from a power-collecting telecommunications interface unit connectable to a power supply, wherein during a dormant phase a high impedance connection is provided between the interface units indicative that the connection is intact, and an active phase is initiated by transmitting control messages between the interface units using a communications protocol capable of operation on power scavenged by the power-receiving interface unit from the high impedance circuit, the control messages initiating the transmission of a larger power output over the telecommunications connection from the power-collecting telecommunications interface unit to the power-receiving telecommunications interface unit. 
         [0014]    In one advantageous arrangement, the power signaling system is integrated into the start-up protocol and also into the element management of the ANU so that OSS systems are aware of the current state of ANU system power, for example if the CPE has lost its local mains power feed and is currently operating in standby battery backup mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    An embodiment will now be described, by way of example, with reference to the accompanying drawings in which: 
           [0016]      FIG. 1  illustrates a Fiber-to-the-Distribution-Point installation. 
           [0017]      FIG. 2  shows a conventional distribution point in more detail. 
           [0018]      FIG. 3  shows a conventional customer premises system in more detail. 
           [0019]      FIG. 4  shows a distribution point modified according to an embodiment. 
           [0020]      FIG. 5  shows a customer premises system modified according to an embodiment. 
           [0021]      FIG. 6  shows a variant of the distribution point modified according to an embodiment. 
           [0022]      FIG. 7  is a sequence diagram depicting a start-up process performed by an embodiment. 
           [0023]      FIG. 8  is a sequence diagram depicting power-down processes performed by an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  shows a typical a Fiber-to-the-Distribution-Point (FttDP) architecture with a Gigabit Passive Optical Network (GPON) backhaul. The optical line termination (OLT)  11  of the GPON is located in a Central Office  12  and is connected to a remote distribution point (DPU)  22  via the optical fiber/PON infrastructure  10 . The DPU is typically located on a pole, with an overhead drop wire  14  connecting to the individual customer premises  15 . 
         [0025]    The DPU  22  is connected to the network-side of the master-socket (network termination equipment—NTE)  16  in the customers&#39; premises (NTE) via the existing copper drop wire  14 . The customer premises equipment  32  is connected to the customer-side of the NTE. The customer premises equipment  32  comprises a number of elements  33 - 39  (shown in more detail in  FIG. 3 ) communicating with each other and the DPU  22  through the home wiring network  17 . These include a Reverse Power Feed (RPF) source  38  and a baseband voice service which is generated by an Analogue Terminal Adapter (ATA)  33 . 
         [0026]    Typically, a remote power feed will conflict with the d.c. signaling which is usually used in analogue telephony (“plain old telephone service”—POTS) to signal off-hook and on-hook telephone conditions, so when such a power feed is provided, it is necessary to provide a special adapter  30  known as a POTS Signaling Dongle (PSD) to each normal telephone handset  13 . These devices co-operate with the ATA  33  in order to allow the POTS signaling to be carried in the presence of a d.c. remote power feed. Some versions also generate the ringing signal for the attached telephone handset  13 . 
         [0027]    Throughout  FIGS. 2 to 5 , the suffixes “O” and “R” are used respectively for the network (“Office”) end and the customer (“Remote”) end. 
         [0028]      FIG. 2  shows the distribution point  22  of  FIG. 1  in more detail, and  FIG. 3  likewise depicts the customer premises equipment  32 . These are connected to each other by the drop wire  14 , at the interfaces marked respectively U O  and U r . In particular,  FIGS. 2 and 3  depict the management entities located respectively in the DPU  22  and the Customer Premises  32 . 
         [0029]    The DPU  22  comprises an optical network unit (ONU)  21  for converting between optical signals conveyed over the optical fiber backhaul  10  through a backhaul termination  20  and xDSL signaling conveyed through an “xDSL terminating unit O” (XTU-O)  24  to the drop wire  14 . 
         [0030]    In the CPE  32  corresponding components are used to convert xDSL signals into signals usable by the end-user. In particular, the xDSL terminating unit-R (XTU-R)  34  acts as a modem for the xDSL service whilst the Analog terminal adapter (ATA)  33  in the xDSL network termination unit  31  co-operates with the POTS adapter  30  connected to a standard telephone  31  to allow normal voiceband traffic. A service splitter  39  separates traffic for the ATA  33  and traffic for the network termination  34   
         [0031]    Electrical power is required to operate the ONU  21 . As the connection to the central office  12  is by way of an optical, not electrical, connection it is not possible to power the DPU, nor the customer premises equipment  32 , from the central office  12  as is conventional. Nor is it generally convenient to install a dedicated supply to the DPU  22 , which may be located at some distance from a suitable mains feed. Instead, electrical power is drawn from an input  18  connected to a power insertion unit  38  in the customer premises equipment  32 , and used to power both the XTU-R  34  in the network termination  31  of the customer premises equipment  32 , and the XTU-O  24  in the optical network unit  21  of the distribution point  22 . 
         [0032]    Power is delivered to the DPU  22  from the power insertion unit  38  in the customer premises equipment  32  by way of the same electrical drop wire  14  that carries communications data. At each end of the drop wire  14  a respective power splitter  27 ,  37  is provided which separates the power supply from the xDSL or other communications streams. In a typical arrangement, the xDSL is carried as an ac modulation summed with a dc power supply. 
         [0033]    The power drawn by the DPU  22  is extracted by an extraction unit  28 . 
         [0034]    The CPE  32  is provided with a battery  36  to maintain service in the event of failure of the power input  18 . Similarly, the DPU  22  is provided with a battery  26  and power combiner  23  to maintain service in the event of failure of the customer premises equipment  32  or the connection  14 . Respective power management systems  25 ,  35  control the flow of electrical power between the various electrical components. In particular they may be used to control how much of the power required to operate the equipment in the distribution point  22  should be drawn from each of several customer premises  32 , taking into account factors such as the number of operational customer premises equipments currently capable of delivering power, the volume of traffic each is carrying, and electrical losses in each of the respective drop wire connections  14 . 
         [0035]    In normal use, management information can be transmitted between the power management systems  25 ,  35  of the DPU  22  and the or each customer premises equipment  32  via the same DSL service that is used for data transmission, i.e., using the “xDSL terminating unit  0 ” (XTU-O)  24  and “xDSL terminating unit R” (XTU-R)  34 . 
         [0036]    This same system can also be used to monitor and control power usage from the CPE  32  to DPU  22  and also interface generally the RPF sub-system with the element management of the system. This power control/monitoring system is especially useful in the case of mains power failure at the CPE and operating is occurring under battery power, i.e., the power system can ‘tell’ the XTU-O  24  and XTU-R  34  to operate in a low-power state. 
         [0037]    However, the power management system cannot be operated over the xDSL system unless that system is in operation. When the customer premises equipment is first started up, or restarted after being switched off, or after reconnection of the drop wire  14 , the xDSL system cannot operate until the DPU  22  is drawing power through the power extraction unit. In particular, when the system is in the initiation phase another signaling and transmission system is required to coordinate the delivery of electrical power from the CPE  32  to the DPU  22 . Such an arrangement is depicted in  FIGS. 4 and 5 , which respectively illustrate the modifications made to the distribution point of  FIG. 2  and the customer equipment of  FIG. 3  in order to put embodiments into effect. 
         [0038]    A principal difference is the provision of a respective secondary communications modem  45 ,  55  in each of the power extraction unit  28  in the distribution point  22  and the power insertion unit  38  in the customer premises equipment  32 . 
         [0039]      FIGS. 4 and 5  show the respective power signaling modems  45 ,  55  in the DPU  22  and the CPE  32 . Both modems are connected via the respective power splitters  27 ,  37  which perform a frequency division duplexing arrangement to split/merge the signaling from the DSL systems  21 ,  31  used for data transport and the d.c. powering arrangement  28 ,  38 . Both signaling modems are also connected to the respective management entities  25 ,  35  at each location. 
         [0040]    Until the power initialization system is fully operational, the remote power signaling modem  45  in the DPU can only operate in a low power mode using scavenged power, that is power transmitted from the CPE to the remote unit before the remote unit has ‘officially’ come to life. Typically the CPE would might supply a small current and voltage (a few milliwatts—i.e., the remote node presents a very high impedance) to indicate that the connection is present. The secondary communications modem  45  in the remote unit  22  is arranged to operate on the low power available in such a situation. The secondary communications modem  55  in the customer premises equipment  32  is not subject to such power constraints, as it will only be required to operate when the user requires it, at which time it is connected to a power supply  18 . It is therefore convenient for the customer premises system to control the operation of embodiments, and to transmit instructions to the distribution point, rather than vice versa. 
         [0041]    An alternative approach is depicted in  FIG. 6 , and is possible if a POTS (traditional telephony) connection  40  is available on the network side  11  of the distribution point  22 , as is often the case in the legacy network. In this approach, the POTS line  40  can be connected to the remote unit  22 . This is connected to the drop wire connection  14  through the power splitter  27 . As shown, a POTS adapter  43  and service splitter  29  are also provided so that traditional voice calls can be carried over the “copper” POTS service if desired, or as a contingency to ensure basic telephony service is still available in the event of a power failure. 
         [0042]    The signaling modems  45 ,  55  may communicate between each other using any suitable protocol, for example the “1-wire protocol” developed by Dallas Semiconductor Corp. This system includes a parasitic powering capability at the remote device, so no separate power supply is required at the remote end in order for communication to commence. This signaling could be used to communicate to the CPE that a suitable device is present at the remote end and that reverse powering can commence. The data-rate of this technique is sufficiently low that it would not interfere with the G.hs (handshake) signaling that the G.fast or VDSL2 would use in establishing the full xDSL connection. 
         [0043]    Alternatively, G.hs tones could be used for the remote power signaling system. In this case the protocol would have to be incorporated into the xDSL chipsets. 
         [0044]    A method of operation is depicted in  FIG. 7  and  FIG. 8 . As depicted in  FIG. 7 , when the CPE is first powered up (at  70 ), the CPE secondary modem  55  sends out a scan signal  71  to the DPU  22  seeking a response from the corresponding secondary modem  45  in the DPU. At this stage only a low voltage is applied to the line (say 20 V) which is current limited to say 60 mA. If no response is received, the scan signal is repeated ( 710 ,  711  . . . ), until either a response is received or the system is powered down again. 
         [0045]    If a secondary modem  45  is present in the DPU, it returns an acknowledgement signal  72  to the CPE secondary modem  55 . This acknowledgement  72  indicates to the modem  55  that the modem  45  (and thus the power extraction unit  28 ) is present on the line, and that the power output across the connection  14  can safely be increased without damage to other components in the DPU or further into the network (as would be the case, for example, if only a standard POTS connection were connected to the DPU  22 ) 
         [0046]    The secondary modem  55  in the CPE  32  next increases the source voltage and increases its current limit (e.g., 60 V, 350 mA), thus allowing normal operation of the remote unit  45 . The remote unit  45 , detecting the increased voltage, initiates a training process  74  to initiate the power insertion and extraction processors  38 ,  28 , in particular to match the impedances so that the power drawn matches the power delivered. The signaling system monitors the power that is being transmitted over the link  14  and reports this to the element management system  35 . 
         [0047]      FIG. 8  depicts processes that occur should the CPE power insertion unit  38  detect a failure of the power supply  19  (at  75 ), it switches to battery backup mode ( 76 ), and transmits a signal ( 77 ) to the DPU  22  to cause the XTU-O  24  to switch into a ‘Low Power Mode’, in which the data rate is reduced significantly in order to save power consumption in both the CPE  32  and the DPU  22 . This will allow the battery life to be extended to allow a low bitrate (or analogue) ‘lifeline’ service to be maintained either using the POTS connection  40  ( FIG. 6 ) if one is present or, otherwise, using the optical link  10 ,  20 ,  24  in a low power mode. When the power  18  is restored to the CPE  32  this is signaled from the CPE to the DPU  22  ( 79 ) to allow the remote unit  24  to revert back to normal operating conditions. 
         [0048]    During deliberate power-down of the CPE  32  (step  75 ), sufficient energy is stored in its battery  36  or a capacitor to enable a message  777  to be sent to the remote unit  28  which causes it to be powered down gracefully, and also instructs the element manager  45  to switch to the standby listening mode, to await a beacon  71  from the CPE  32  indicating that it has powered up again.