Patent Publication Number: US-2004057576-A1

Title: System and method for on-demand battery backup for cable telephony device

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to cable telephony, and more particularly to a system and method for on-demand battery backup of cable telephony devices.  
       [0003] 2. Discussion of Related Art  
       [0004] Telephone services over cable networks, also known as Voice over Internet Protocol (“VoIP”) on cable, are susceptible to primary AC power outages because first generation cable VoIP devices are powered from the AC main and must respond to periodic polling signals from the Cable Modem Termination System (“CMTS”) in order to remain registered on the cable network.  
       [0005] Existing battery-backed power supplies simply work for as long as the battery can provide normal operating power to the telephony device, then turn off their output when the battery is depleted. Power conserving schemes have been proposed for the interface device to extend the backup time by putting nonessential circuitry into an idle or sleep mode during a AC main power outage. With existing Data Over Cable Service Interface Specification (“DOCSIS”) cable modem device protocols, this scheme is of limited success because the cable modem device must continue to respond to polling messages from the CMTS in order to remain registered on the cable network. The polling response requires that the most power-consuming circuits in the cable modem device remain in normal operation.  
       [0006] Existing commercial backup power supplies provide sufficient energy for about 10 hours of cable modem device operation (about 400 kilo Joules). In cases of extended power outages, this backup time can be exceeded and the subscriber will then lose the ability to make outgoing calls.  
       [0007] Therefore, a need exists for a system and method for providing on-demand battery backup to cable telephony devices.  
       SUMMARY OF THE INVENTION  
       [0008] A system and method for providing on-demand battery backup to cable telephony devices comprising converting AC main power to DC, charging a battery, providing regulated power to the cable modem device, providing a signal to the cable modem device to indicate that AC main power is not present, and provisioning telephony service for the cable telephony device. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] Preferred embodiments of the present invention will be described below in more detail, with reference to the accompanying drawings:  
     [0010]FIG. 1 is a flow chart of a method for supplying on-demand battery backup to cable telephony devices according to an embodiment of the present invention; and  
     [0011]FIG. 2 is a diagram of a system comprising a cable telephony device adapted to operate using on-demand battery backup according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0012] According to an embodiment of the present invention, a system and method that provides a battery-backup power supply having a converter that converts AC main power to DC, having a charger that charges a battery, having a power source that provides regulated power to the cable modem device, having a AC main power detector that detects when AC main power is not present, and having a signal provider that provides a power loss signal to the cable modem device to indicate when AC main power is not present.  
     [0013] The cable modem device includes a signal detector that detects the power loss signal provided to the cable modem device from the on-demand battery backup. Additionally, the cable modem device has a sleep mode circuit such as, power gating circuitry that disables selected circuitry to provide a low power consumption sleep mode. In this mode, the cable modem device does not communicate with the CMTS and does not provide data or telephony service.  
     [0014] The cable modem device also has wake up circuitry that exits sleep mode upon activation of a telephony device. For example, the subscriber can activate an activation switch indicating that the subscriber desires to make an outgoing telephone call. Additionally, the cable modem device has a circuit that provisions a telephony interface upon activation of a telephony device. If the activation switch is activated, the cable modem device wakes up. Wake up can occur for example, by having the power gating circuitry enable the circuitry that has been switched off and having the cable modem device initialize itself on the cable network thereby provisioning the telephony interface. This process takes approximately one minute. Additionally, the cable modem device can have a telephony service indicator that signals that telephony service is available for example, by illuminating an LED or activating an audible beep.  
     [0015] The cable modem device power gating circuitry also includes a first timer so that after occurrence of a main power outage, as indicated by the power loss signal from the on-demand battery backup, the cable modem device does not enter sleep mode until the first timer has elapsed. This enables the cable modem device to function normally during the short power outages that make up the majority of power interruptions. After the first timer expires, the cable modem device will enter its sleep mode and continue in that mode until it senses that the cable modem device wake up circuitry has detected that a cable telephony device has been activated. It will wake up as described previously, and will continue in normal operating mode until either a second timer expires occurring when there is no activity from attached telephony devices, an active telephone call is ended, or the battery is depleted. Upon occurrence of any of these events, the cable modem device will reenter sleep mode.  
     [0016] In another embodiment of the invention, the cable modem device&#39;s power gating circuitry provides power to a section of the telephony interface circuit that monitors the hook state of attached telephony devices. If a telephony device is taken off hook, the cable modem device wakes up and re-enables normal functionality of the cable telephony device. The primary advantage of this embodiment is that the subscriber can simply pick up any attached telephony device to begin the process which enables an outgoing call to be placed.  
     [0017] Referring to FIGS. 1 and 2, wherein FIG. 1 illustrates a method for on-demand battery backup for a cable telephony device and FIG. 2 illustrates a system for on-demand battery backup for a cable telephony device. As shown in the figures, a cable telephony device such as a telephone  226  is connected to a cable modem device  216 . The cable modem device  216  is powered by an on-demand battery backup  204 . The battery backup  204  is powered by AC main current  202  and has a AC/DC Converter/Charger/Power Regulator  206 . The AC/DC Converter/Charger/Power Regulator  206  converts AC main power to DC power (step  102 ), charges the battery (step  104 ), and supplies regulated power (step  106 ) to the cable modem device  216 . The on-demand battery backup has a battery pack  208  for battery power and an AC power monitor/signal provider  210  to indicate AC main power unavailability (step  108 ).  
     [0018] The on-demand battery backup  204  provides a power loss signal  214  to the signal detector  218  that indicates the absence of AC main current (step  110 ), e.g. during a AC main power outage. When the signal detector  218  detects (step  112 ) the power loss signal  214  that was generated by the on-demand battery backup  204 , the DOCSIS cable modem device with sleep circuit  220  enters sleep mode (step  114 ), i.e. disables the telephony interface  222  thereby rendering telephone service unavailable. In the event that the AC main power outage is of short duration (step  114 ), the cable modem device  216  can also be equipped with a first timer  217  that prevents entering sleep mode until the first timer  217  elapses.  
     [0019] The cable modem device  216  is connected to a network  232  by a Cable Modem Termination System  230  to allow communications with the network  232 . The cable modem device  216  uses a Data Over Cable System Interface Specification (DOCSIS) protocol  220  that has a telephony interface  222 , an activation switch  224  for activating telephony service, and a telephony service indicator  228  for indicating service availability. When the activation switch  224  has been depressed, i.e. activated, sleep mode is exited and the telephony interface is enabled (step  116 ), thereby allowing a subscriber to place a telephone call. After the telephony service is made available, the cable modem device  216  signals telephony service availability (step  118 ) using a telephony service indicator  228 , e.g. a LED or audible alarm.  
     [0020] Upon ending an active telephone call, the cable modem device  216  reenters sleep mode (step  120 ). The cable modem device  216  can also reenter sleep mode if the battery pack  208  is depleted (step  120 ) or no active telephone call is placed by a subscriber and a second timer  225  elapses (step  120 ).  
     [0021] Having described embodiments for a system and method for on-demand battery backup for cable telephony devices, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as defined by the appended claims.