AU2020100949A4 - Off-hook detection in a reverse-powered environment - Google Patents

Abstract

A method is suggested for detecting an off-hook phone, comprising (i) determining a change in a loop current of a loop connected to the phone and a reverse-powered network element, (ii) changing a source impedance for a short duration and determining a response, and (iii) depending on the response either detecting the off-hook phone and dropping the power delivery towards the network element or not detecting the off-hook phone and not dropping the power delivery towards the network element. Also, an according device for detecting an off-hook phone and a computer program product that enables performing the steps of the method are provided. Fig. 3 4/5 SZt Z 0- 0 o: a, 0o (a) ~~ (1 F- ) 0 3: d) = Cb ) 0~ 0~ a,) 0 0- s U -~~ 0o l - C o 0CDU 75 o0 o0 CUD - - - C =~ U) U) (10 CO) C- co 0 >P (1 0 a, -T 0~ a (1 0 C) U) C- C- a ,- 7a5 0 CU 0a) -M 0 E D- C~ 0- UC ) CD 70 -0 '- M~ 0 > a,)l DCD 0 - CD a,) U) E aU ) - ~ C) 0JC~ CD mt 0) 0 C C ) 0) IC) 0 U) X0I I II 0)) a, Co C/)o CD- U) U)- (1 - > C C- a, U) 72 0 ,- C- aa 0~~ 0o c CU) 2 _ -CD o Co 0 0 ~~d 0~ CU ECU Cl) a, C)N a,1-t0 -a 0 '-) C- C- t3 CU a, -0a 0 :3 00- 0C) 0 U CU >, CU a, U C) U) U) U) Clo 0- Zc 3: C) C ) CD-a CNJ C)) SI =0o o ( 1 ) =) C) 0 m(0 U) U)0 m 0 0) cJ) c ) E 0 U :7

Description

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Off-hook detection in a reverse-powered environment

Description

Solutions described herein refer to detecting an off-hook phone in a reverse powered system using a network element like a DPU.

Some telecom services use power supplied from customer premises. This configuration is called "reverse powering". One particular example refers to a DPU, which has a fiber or coax-fed network data connection, and relatively short copper loops that are connected to the customers. Electrical power is fed back from at least one customer box towards the DPU.

There exists a requirement that allows a system fallback to providing normal POTS in particular in an emergency situation. In such scenario, an off-hook telephone is detected across the reverse-powered customer loop.

The objective is to provide an efficient solution to enable such fallback to POTS in case an off-hook telephone is detected.

This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims.

The examples suggested herein may in particular be based on at least one of the following solutions. In particular combinations of the following features could be utilized in order to reach a desired result. The features of the method could be combined with any feature(s) of the device, apparatus, or system or vice versa.

In order to overcome this problem, a method is provided for detecting an off-hook phone, the method comprising - determining a change in a loop current of a loop connected to the phone and a reverse-powered network element, - changing a source impedance for a short duration and determining a response,

- depending on the response either detecting the off-hook phone and dropping the power delivery towards the network element or not detecting the off hook phone and not dropping the power delivery towards the network element.

It is noted that there are many ways to change the source impedance. One example is turning off or reducing power emitted by a power source (e.g., a voltage source).

Hence, "changing the source impedance" may include removing or reducing power that is made available to a port or line. This may be achieved either by increasing a resistance value or by reducing the power source output.

The response may in particular be directed to determining if there is a load (change) on the line or not. In addition, or as an alternative, a change of voltage (in particular a voltage drop) may be determined as response.

According to an embodiment, the method is run on a network communication device.

According to an embodiment, the network element is reversed powered by the network communication device.

According to an embodiment, the network element is a distribution point unit.

According to an embodiment, the change in the loop current is determined by monitoring a current at one port to the network element.

According to an embodiment, the source impedance increases the resistance in the loop towards the network element and induces a power interruption for a predetermined amount of time.

According to an embodiment, - the response is based on a voltage drop, and - if the voltage drop is below a threshold, the off-hook status of the phone is detected and the power delivery towards the network element is dropped,

- if the voltage drop is not below the threshold, the off-hook status of the phone is not detected and the power delivery towards the network element is not dropped.

According to an embodiment, the method further comprises: - upon detecting the off-hook phone switching, by the network element, to POTS thereby connecting the off-hook phone with the POTS.

Also, a device is suggested for detecting an off-hook phone, - wherein the device is connected via a loop to the phone and to a network element, - wherein in normal operation the device at least partially reverse powers the network element, - wherein the device is arranged to - determine a change in a current of the loop, - change a source impedance for a short duration and determine the response, - depending on the response either detect the off-hook phone and drop the power delivery towards the network element or not detect the off-hook phone and not drop the power delivery towards the network element.

According to an embodiment, the device is a network communication device and the network element is a distribution point unit, which is reversed powered by at least one network communication device.

Further, a computer program product is provided, which is directly loadable into a memory of a digital processing device, comprising software code portions for performing the steps of the method as described herein.

Embodiments are shown and illustrated with reference to the drawings. The drawings serve to illustrate the basic principle, so that only aspects necessary for understanding the basic principle are illustrated. The drawings are not to scale. In the drawings the same reference characters denote like features.

Fig.1 shows an exemplary block diagram comprising a DPU that is connected via a copper pair to an NCD and to a phone;

Fig.2 shows an exemplary flow chart that illustrates the operation at the NCD;

Fig.3 shows an exemplary diagram comprising two NCDs, which are connected to a DPU;

Fig.4 shows a diagram for illustrating the operation between the components shown in Fig.3;

Fig.5 shows an exemplary implementation of the rectifier bridge indicated in Fig.3.

Fig.1 shows an exemplary block diagram comprising a DPU 101 that is connected via a copper pair 107 (which might be a twisted copper pair) to an NCD 102 and to a (tele)phone 103. The DPU 101 is also connected to a GPON 104 (via fiber or coax cable) and to a POTS 105 (via another (twisted) copper pair).

The DPU 101 comprises a modem 106 that is connected to the GPON 104. The modem 106 allows data conversion between the fiber (or coax cable) and the copper pair 107. Data may be conveyed across the copper pair 107 using G.fast or any DSL standard (referred to herein as "xDSL"). In addition, the NCD 102 supplies power to ("reverse powers") the DPU 101, which is indicated by an arrow 108.

The DPU 101 also comprises a switch 109 (electronic switch, relay, or the like) to connect the copper pair 107 either to the modem 106 (for utilizing GPON services) or to the copper pair towards the POTS 105.

The copper pair 107 can be used to convey signals pursuant to xDSL, G.fast or POTS (depending also on the selection conducted by the switch 109).

The NCD 102 comprises a modem 110 that supplies Ethernet towards a computer 111. Also, the NCD 102 comprises a Reverse Power Feed (RPF) 112 that supplies said reverse power 108 (over the copper pair 107) to the DPU 101.

If the phone 103 enters its off-hook state, the switch 109 of the DPU 101 connects the POTS 105 to the phone 103. This will be described in more detail below.

In an exemplary installation (a residence) there may already exist POTS wiring with typically a phone jack in several locations. The jack may or may not have a POTS splitter installed. When a customer activates the G.fast service, the NCD 102 may be plugged into one of the phone jacks which may be located anywhere in the house. Also, the customer may plug the phone 103 into one of the other jacks available. This could be accidental or deliberate to revert back to POTS, e.g., in case of an emergency used by a security system or fire alarm that is wired into the existing POTS. An on-hook phone or non-active emergency service does not disrupt the G.fast signaling. However, if a POTS device goes off hook, the NCD 102 should stop injecting power into the POTS wiring. Hence, the NCD 102 may stop reverse powering the DPU 101 (by stopping delivering power to the DPU port that is connected to the NCD 102) and thereby enable the DPU 101 to fall back (revert) to POTS. The other ports of the DPU 101 that are connected to other NCDs may not be affected by this.

The phone 103 may in this regard represent an entire POTS wiring inside the residence or location where G.fast is installed, i.e. more than a mere phone or even any phones.

The NCD 102 may have an additional dedicated POTS output (not shown in Fig.1). This allows traditional POTS service to be simultaneously supported with xDSL at the premise without disrupting the xDSL service. If the xDSL service connects to existing structural POTS wiring this dedicated POTS output on the NCD 102 remains separate from the structural POTS wiring. If the xDSL service does not connect to the structural wiring this POTS port can be connected to the structural wiring and provide POTS throughout the premise.

The dedicated POTS port provides analog POTS service to one or more phones or other POTS devices (not shown) connected to this POTS port on the NCD 102. The NCD 102 converts the analog POTS signal into digital Voice over Internet Protocol (VoIP) and sends this VOIP data to the DPU 101 via the xDSL service. The DPU 101 can either forward the VOIP data up the GPON/coax connection 104 or the DPU 101 can convert the digital VOIP data back to analog POTS 105.

Fig.2 shows an exemplary flow chart that illustrates the operation at the NCD 102.

In a step 201, the NCD 102 monitors a load current at one of its ports (which is connected to the DPU 101), which is connected to the phone 103.

In a subsequent step 202, the NCD 102 determines whether a change in load current over a predetermined amount of time (reaches or) exceeds a predetermined threshold. This may be perceived as a comparison with a predetermined current pattern indicating a significant change of the load current.

If this is not the case, a loop to step 201 is entered.

If the (e.g., sudden) increase in the load current (reaches or) exceeds the threshold current, in a step 203 a short power outage is induced by the NCD 102 at its port towards the DPU 101. This power outage is preferably of less than 2ms duration. It is noted, however, that 2ms is only an exemplary figure, which may vary according to different use-case scenarios. As the DPU 101 is reverse powered by the NCD 102, such power outage may be recognized by (e.g., the operating system of) the DPU 101. The power interruption may be short compared to a hold-up time of the DPU to ensure the DPU remains operational.

Then, in a step 204, it is checked by the NCD 102 whether a voltage drop exceeding a predetermined threshold ("large voltage drop") can be detected of the NCD output port voltage. If this is the case, it is branched to a step 206; otherwise it is assumed that the phone is on-hook in a step 205. Power is re-applied and the loop towards step 201 is closed.

Step 206 detects that the phone 103 is off-hook and in a subsequent step 207 the NCD continues with NCD port outage and the NCD 102 cuts off the reverse power towards the DPU 101. Based on the loss of reverse power, the DPU 101 via the switch 109 connects the POTS 105 with the copper pair 107 thereby providing the POTS to the phone 103.

In a next step 208, the NCD 102 detects that the phone has re-entered the on-hook state. The NCD 102 thus provides its reverse power to the DPU 101. The DPU 101 conducts a re-initialization thereby connecting the modem 106 via the switch 109 to the NCD 102 entering the G.fast or the xDSL service. After step 208 it is continued with step 201.

Fig.3 shows an exemplary diagram comprising two NCDs 301, 302, which are connected to a DPU 310. The connection to the DPU 310 is established via copper pairs and each of the NCDs 301, 302 is able to reverse power the DPU 310 (see also Fig.1 and explanations).

It is noted that more than two NCDs may be connected to the DPU 310.

The NCD 301 is connected to a first port (comprising terminals 311, 312) of the DPU 310 and the NCD 302 is connected to a second port (comprising terminals 313, 314) of the DPU 310.

The terminal 311 is connected via a rectifier bridge 304a to a first input of a power supply unit 303a and the terminal 312 is connected via the rectifier bridge 304a to a second input of the power supply unit 303a.

The rectifier bridge 304a may be implemented as a full wave rectifier as is shown in Fig.5. The terminal 311 is connected to the cathode of a diode 501a and to the anode of a diode 502a. The terminal 312 is connected to the cathode of a diode 503a and to the anode of a diode 504a. The anode of the diode 501a and the anode of the diode 503a are connected together and to the second input of the power supply unit 303a. The cathode of the diode 502a and the cathode of the diode 504a are connected together and to the first input of the power supply unit 303a.

The implementation of the rectifier bridge as full wave rectifier allows the DPU 310 to operate with voltages of either polarity, since the tip ring pair connections could be reversed.

The terminal 313 is connected via a rectifier bridge 304b to a first input of a power supply unit 303b and the terminal 314 is connected via the rectifier bridge 304b to a second input of the power supply unit 303b. A capacitor C22 is connected across the first and second input terminals of the power supply unit 303b.

The rectifier bridge 304b may be implemented as a full wave rectifier according to the example described above with regard to the rectifier bridge 304a. In order to adapt the rectifier bridge 304b to the example shown in Fig.5, the input terminals 313 and 314 replace the input terminals 311 and 312 and the output is connected to the power supply unit 303b instead of the power supply unit 303a.

The NCDs 301, 302 are preferably galvanically isolated from each other and from a secondary side of the DPU 310, which handles digital signal processing. The power supply units 303a, 303b may share a common power. Also, the power supply units 303a, 303b may be controlled via digital and/or analog signal processing, which is indicated by a connection 308 between the power supply units 303a, 303b of the DPU 310.

The NCD 301 comprises a voltage source VI with one pole connected across a resistor RI to a first terminal of the NCD 301. The voltage source VI is connected via its other pole across a diode D1 to a second terminal of the NCD 301, wherein the cathode of the diode D1 points towards the voltage source VI. The first and the second terminal of the NCD 301 are connected via a copper pair to the first port of the DPU 310. A capacitor C1Iis connected between the first terminal and the second terminal of the NCD 301.

The NCD 301 further comprises a switch SWi that is arranged in parallel to the resistor RI. When activated, the switch SWi shortcuts the resistor RI.

Also, a phone 306 can be connected to the first and second terminal of the NCD 301, optionally via a splitter or bridge tap 304.

The NCD 302 comprises a voltage source V2 with one pole connected across a resistor R2 to a first terminal of the NCD 302. The voltage source V2 is connected via its other pole across a diode D2 to a second terminal of the NCD 302, wherein the cathode of the diode D2 points towards the voltage source V2. The first and the second terminal of the NCD 302 are connected via a copper pair to the second port of the DPU 310. A capacitor C21 is connected between the first terminal and the second terminal of the NCD 302.

The capacitors C1Iand C21 are used to maintain a tip ring voltage during the power interruption when there the phone of the respective NCD is on hook. It is an option to use the capacitor C1Iinstead of the resistor RI and the capacitor C21 instead of the resistor R2. Also, these capacitors may be used in addition to the resistors as depicted in Fig.3.

The diodes D Iand D2 act as blocking diodes to protect the respective NCD when reverse polarity voltage is present on the tip ring pair.

The NCD 302 further comprises a switch SW2 that is arranged in parallel to the resistor R2. When activated, the switch SW2 shortcuts the resistor R2.

Also, a phone 307 can be connected to the first and second terminal of the NCD 302, optionally via a splitter of bridge tap 305.

Reference is made in particular to the following exemplary states:

State 1: The phones 306 and 307 are on-hook. The NCDs 301, 302 provide approximately equal power (by the voltage sources VI and V2) to the DPU 310. The switches SW Iand SW2 are closed. After State 1 either State 2 or State 3 may be entered.

State 2: The phone 306 goes off-hook, the phone 307 remains on-hook. The current delivered by the voltage source VI changes because of the reduced resistance of the phone 306. In the on-hook state the phone has a very high resistance and in the off-hook state the resistance is reduced, e.g., to 500 ohms.

State 3: The voltage source V2 is turned off. Phones 306 and 307 are on-hook. The voltage source Vi provides all power to the DPU 310.

Each of State 2 or State 3 results in a fluctuation of current that can be determined by the NCD 301. However, States 2 and 3, i.e. the phone 306 going off-hook and the NCD 302 being deactivated, need to be differentiated in a reliable manner.

This can be achieved by monitoring the voltage between the terminals of the NCD 301 while opening the switch SWI for a short period of time, e.g., less than 2ms. If the voltage drop is large, i.e. more than half of the voltage provided by the voltage source VI, the phone 306 is off-hook (State 2), otherwise State 3 has been entered.

It is noted that instead of opening the switch SWI for a short period of time, any measure to increase the impedance may be used. One example is shutting off or reducing the power delivery by the voltage source VI.

It is noted that the resistors RI, R2 and switches SWI and SW2 are mere examples. Other means may be used to achieve the same effect as described herein. In one exemplary embodiment, the resistor RI and switch SWI may not exist and instead the voltage source VI may be turned off or reduced. In this case, the capacitor C Imay help maintain the NCD output voltage during the time of the reduction of the voltage supplied by the voltage source VI if the phone is on-hook. This may apply accordingly to the resistor R2, the switch SW2 and the voltage source V2.

Fig.4 shows a diagram for illustrating the operation between the components shown in Fig.3.

In an exemplary starting step 401 the phone 306 is present and it is on-hook.

In a step 402 the phone 306 goes off-hook.

In a step 403 the NCD 301 recognizes a change (in particular an increase) in a loop current (or load current). This fluctuation of loop current could be due to the phone 306 going off-hook or due to a load change in another NCD, e.g., NCD 302. Hence, the NCD 301 increases its source impedance for a short duration and monitors a voltage Vp I at its terminals.

In a subsequent step 405, the NCD 301 determines that the voltage Vp I does not drop below a predetermined threshold. This corresponds to the phone 306 being on-hook. Hence, the NCD 301 restores normal source impedance and continues to provide power to the DPU 310 thereby entering normal operation and reverting to step 401.

A different alternative is shown in a step 404 that may follow on step 403: If the voltage Vpl drops below the predetermined threshold, the phone 306 is determined to be off hook. The NCD 301 thus drops power delivery to the DPU 310. It is branched off to a step 406 or to a step 407.

Step 406 refers to a multi-line mode scenario, i.e. in case the DPU 310 is powered by more than one NCD (in the example shown in Fig.3, the DPU 310 is still powered by the NCD 302 even if the NCD 301 drops power delivery to the DPU 310). In such multi-line mode scenario, the DPU remains powered.

The DPU 310 recognizes power loss at the port connected to the NCD 301. Next, the DPU 310 switches this port to POTS, i.e. it disconnects the G.fast/xDSL service and reconnects the subscriber to POTS. Hence, POTS is provided to the phone 306 that is off-hook. The G.fast/xDSL (or any other) service may still be provided to any other NCD, here to NCD 302.

Step 407 refers to an alternative, the so-called single-line mode scenario with only a single NCD 301 (reverse) powering the DPU 310. The DPU 310 remains powered for a short period of time by the energy stored within the DPU 310, i.e. the energy stored in the capacitor C12. During that time the DPU 310 is able to recognize the power loss at the port connected to the NCD 301. Next, the DPU 310 switches this port to POTS, i.e. it disconnects the G.fast/xDSL service and reconnects the subscriber to POTS. Hence, POTS is provided to the phone 306 that is off-hook. Then the DPU 310 powers down.

Hence, the phone 306 being off-hook puts an additional load on the reverse powering power supplies, and this additional load can be detected. The approach presented allows differentiating between the load of an off-hook telephone, and variations in the load resulting from changes in the number of customer premises equipment that are back feeding power to the DPU. This approach thus enables a reliable detection of an off hook telephone in spite of variation of load current.

Although various exemplary embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the spirit and scope of the invention. It will be obvious to those reasonably skilled in the art that other components performing the same functions may be suitably substituted. It should be mentioned that features explained with reference to a specific figure may be combined with features of other figures, even in those cases in which this has not explicitly been mentioned. Further, the methods of the invention may be achieved in either all software implementations, using the appropriate processor instructions, or in hybrid implementations that utilize a combination of hardware logic and software logic to achieve the same results. Such modifications to the inventive concept are intended to be covered by the appended claims.

List of Abbreviations:

CPE Customer Premises Equipment (terminal) DPU Distribution Point Unit DSL Digital Subscriber Line DSLAM DSL Access Multiplexer G.fast is a digital subscriber line (DSL) protocol standard, wherein "G." stands for ITU-T G.97xx series of recommendations, "fast" is an acronym for fast access to subscriber terminals GPON Gigabit Passive Optical Network NCD Network Communication Device POTS Plain Old Telephone Service RPF Reverse Power Feed VoIP Voice over Internet Protocol xDSL any DSL Service, e.g., VDSL, VDSL2, etc.

Claims (11)

Claims:

1. Method for detecting an off-hook phone, comprising - determining a change in a loop current of a loop connected to the phone and a reverse-powered network element, - changing a source impedance for a short duration and determining a response, - depending on the response either detecting the off-hook phone and dropping the power delivery towards the network element or not detecting the off hook phone and not dropping the power delivery towards the network element.

2. The method according to claim 1, wherein the method is run on a network communication device.

3. The method according to claim 2, wherein the network element is reversed powered by the network communication device.

4. The method according to any of the preceding claims, wherein the network element is a distribution point unit.

5. The method according to any of the preceding claims, wherein the change in the loop current is determined by monitoring a current at one port to the network element.

6. The method according to any of the preceding claims, wherein the source impedance increases the resistance in the loop towards the network element and induces a power interruption for a predetermined amount of time.

7. The method according to any of the preceding claims, - wherein the response is based on a voltage drop, and - if the voltage drop is below a threshold, the off-hook status of the phone is detected and the power delivery towards the network element is dropped,

- if the voltage drop is not below the threshold, the off-hook status of the phone is not detected and the power delivery towards the network element is not dropped.

8. The method according to any of the preceding claims, further comprising: - upon detecting the off-hook phone switching, by the network element, to POTS thereby connecting the off-hook phone with the POTS.

9. Device for detecting an off-hook phone, - wherein the device is connected via a loop to the phone and to a network element, - wherein in normal operation the device at least partially reverse powers the network element, - wherein the device is arranged to - determine a change in a current of the loop, - change a source impedance for a short duration and determine the response, - depending on the response either detect the off-hook phone and drop the power delivery towards the network element or not detect the off-hook phone and not drop the power delivery towards the network element.

10. The device according to claim 9, wherein the device is a network communication device and the network element is a distribution point unit, which is reversed powered by at least one network communication device.

11. A computer program product directly loadable into a memory of a digital processing device, comprising software code portions for performing the steps of the method according to any of claims I to 8.

Fig.1 103

Phone Fiber Copper (twisted) pair 102 104 Modem 106 107

GPON DPU xDSL, G.fast, etc. or POTS Network Communication 105 Device (NCD) POTS 110 1/5

109 Power MODEM 108 111 Ethernet Copper (twisted) pair 101 Reverse Power Feed (RPF)

Fig.2 201 Monitor load current at NCD port

202 Does the change in load current NO exceed threshold?

YES

Induce power interruption at NCD for 203 less than 2ms

205 2/5

204 Voltage drop Phone on-hook large? NO Re-apply power

YES

Phone off-hook detected 206

207 Continue with NCD port outage; 208 If the phone is put back on-hook, the DPU port will power off NCD provides power to the DPU and the DPU re-initializes providing DPU will switch to fallback POTS due xDSL/G.fast to the NCD. to lack of power supplied by the NCD.

Fig.3 304 301 SW1 310

311 R1 304a 303a C11 C12 V1 Vp1 D1 312 3/5

307 308 305 302 SW2

313 R2 304b 303b C21 C22 V2

D2

Fig.4 401 Phone 306 is present and on-hook

402 Phone 306 goes off-hook 405 • If voltage Vp1 does not drop below threshold, then the 403  NCD 301 recognizes an increase in loop phone 306 is determined to be on-hook current • NCD 301 restores normal source impedance and power is  NCD 301 increases source impedance for provided to the DPU 310 before service is dropped short duration and monitors voltage Vp1 • Operation is normal again

• If voltage Vp1 drops below threshold, then 4/5

404 the phone 306 is determined to be off-hook • NCD 301 drops power delivered to the DPU 310

406 Multi-line Mode Single-line mode 407  If the DPU 310 is powered by more than one NCD (multi-line  If the DPU 310 is powered only by NCD 301 (single-line mode), mode), then the DPU 310 remains powered then the DPU 310 remains powered by its stored energy  DPU 310 recognizes that power is lost at the port connected  DPU 310 recognizes that power is lost at the port connected to to NCD 301 NCD 301  DPU 310 switches that port to the POTS, i.e. disconnects  DPU 310 has enough energy stored to switch to POTS: DPU 310 xDSL/G.fast service and reconnects the subscriber to POTS disconnects xDSL/G.fast service and reconnects the subscriber to  POTS service is provided to the phone 306 that is off-hook POTS  POTS service is provided to the phone 306 that is off-hook  DPU 310 powers down

Fig.5 304a

311 501a 502a 303a

503a 504a C12 5/5