Abstract:
An apparatus or corresponding method of managing Plain Old Telephone Service (POTS) lines in a Passive Optical Network (PON) to prevent an alarm system from generating an alarm during a software upgrade or maintenance of an Optical Network Terminal (ONT), Optical Line Terminal (OLT), or PON while maintaining the effectiveness of the alarm system. The ONT may store data related to a POTS line in nonvolatile memory. The ONT may activate the POTS line based on the data from the nonvolatile memory in an event of interruption in communications with an OLT prior to reestablishing communications with the OLT. The interruption in communications may be caused by an ONT reboot to complete an installation of a software upgrade. The ONT may energize the POTS line with a voltage in response to activating the POTS line to prevent the alarm system from generating the alarm.

Description:
BACKGROUND OF THE INVENTION 
     In Fiber-To-The-Premises (FTTP) networks, software or hardware upgrades to or maintenance of Optical Network Terminals (ONTs) and Optical Line Terminals (OLTs) may cause brief interruptions in communications between the ONTs and OLTs. For example, in a software upgrade to the ONT, the ONT loses communication with the OLT during a reboot process used to initialize the ONT with the software upgrade. In some systems, these interruptions in communications, in turn, cause Plain Old Telephone System (POTS) lines of the ONTs to deactivate. An alarm system, such as a burglar alarm system, connected to the ONT via a POTS line may generate an alarm in response to detecting a deactivated POTS line. 
     SUMMARY OF THE INVENTION 
     A method in accordance with an embodiment of the present invention prevents an alarm system from generating an alarm during a software upgrade or maintenance of an ONT, OLT, or PON while, at the same time, maintaining the effectiveness of the alarm system. The method may include storing data related to a POTS line in memory connected to the ONT. The method may further include activating the POTS line based on the data from the memory in an event of interruption in communications between the ONT and OLT prior to reestablishing communications between the ONT and OLT. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  is a network diagram of an optical communications system employing an embodiment of the present invention; 
         FIG. 2  is a network diagram of a portion of the optical communications system of  FIG. 1  employing an embodiment of the present invention; and 
         FIGS. 3-8  are example flow diagrams performed by elements of the optical communications system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of preferred embodiments of the invention follows. 
       FIG. 1  is a network diagram of an example optical communications system  100  employing an embodiment of the present invention. The optical communications system  100  includes a central office  120  connected to a plurality of ONTs  135   a ,  135   b , . . .  135   n  via Passive Optical Networks (PON) communications links  125   a ,  125   b , . . . ,  125   n . As shown in  FIG. 1 , the PON communications links  125   a ,  125   b , . . . ,  125   n  are deployed for Fiber-To-The-Home (FTTH) or Fiber-To-The-Premises (FTTP) applications. In other embodiments, the PON communications links  125   a ,  125   b , . . . ,  125   n  may be deployed for Fiber-To-The-Business (FTTB) or Fiber-To-The-Curb (FTTC) applications. 
     The central office  120  includes an OLT  122  with multiple PON cards  124   a ,  124   b , . . . ,  124   n . Each PON card  124   a ,  124   b , . . . ,  124   n  may connect to multiple ONTs, including respective ONTs  135   a ,  135   b , . . . ,  135   n . As described above, an ONT  135   a  may be deployed at a subscriber&#39;s premises  130 . The example ONT  135 a may support any number of Plain Old Telephone Service (POTS) lines. For example, the ONT  135   a  may support POTS service to a telephone device  132  via port  2  and a POTS line  142 . The ONT  135   a  may also support POTS service to an alarm system  131 , such as a home security system or any similar alarm system, via port  1  and a POTS line  141 . In other embodiments, the alarm system  131  may share POTS line  142  with the telephone device  132 . The ONT  135   a  may further support video services (e.g., RF Video) and data services (LAN Data) to a television  133  and a computer  134 , respectively, via respective dedicated ports  3  and  4  designed for these services. The OLT  122  in the central office  120  also connects to a Wide Area Network (WAN)  110 . 
     In prior art communications systems, a subscriber&#39;s premises connected directly to a central office through POTS lines. The POTS lines are configured as Tip and Ring lines with a differential 48 volt output. Home security systems are connected to the POTS lines in order to automatically alert law enforcement agencies of a break-in. The home security systems are designed to detect the differential 48 volts on the POTS line so that the home security system can know whether or not a burglar had disabled communications by cutting the POTS lines. 
     The home security systems are further designed to trigger an alarm after detecting either a loss of voltage or a short in the POTS line. The home security systems use a timer to ride out momentary service disruptions. The length of the timer could be different for the loss of voltage and the short in the POTS lines. For example, the timer for the short could be quicker than for the loss of voltage. 
     With the deployment of ONTs in FTTP and FTTB applications, however, the ONTs  135   a ,  135   b , . . . ,  135   n , instead of the central office  120 , provide POTS service. Often the ONT  135   a  or the OLT  122  is upgraded with new software. In order to activate new software on either the OLT  122  or ONT  135   a , the OLT  122  or ONT  135   a  must reboot. If the ONT reboot causes a loss of the differential 48 volts to the alarm system  131  (e.g., a home security system) for more than a short time window, such as seven seconds, then the alarm system  131  determines that the POTS line has been cut and sounds an alarm. When a PON card  124   a  is upgraded with new software, it too must reboot to activate the new software. The PON card reboot causes a loss of communications between it and the ONT(s) and may further cause the ONT(s) to reboot. 
     According to an embodiment of the present invention, the subscriber&#39;s premises  130  include nonvolatile memory  136  connected to or integral with the ONT  135   a . The nonvolatile memory  136 , such as FLASH memory, may store information indicating whether or not ports  1  and  2  are enabled. When the ONT  135   a  reboots, ports  1  and  2  immediately output a differential 48 volts within a time window, such as a seven second window. This prevents the alarm system from issuing a false alarm. However, if a burglar cuts a fiber in the PON communications link  125   a , ports  1  and  2  maintain the differential 48 volt output and the alarm system  131  does not issue an alarm. 
       FIG. 2  is a network diagram of a portion  200  of the optical communications system  100  of  FIG. 1  employing embodiments of the present invention. In one embodiment, an ONT  235  includes a timer  237 . In some embodiments, when the ONT  235  loses communications with an OLT ( 122 ) at a Central Office ( 120 ) ( FIG. 1 ) through an optical fiber  201 , the ONT processor  251 : (1) reboots, (2) starts the timer  237 , and (3) maintains a differential voltage on a POTS line  241  supporting an alarm system  231 . In other embodiments, the ONT processor  251  may not reboot when the ONT  253  loses communications with the OLT ( 122 ), but the POTS line may be treated in a manner disclosed herein to prevent the alarm system from generating an alarm. The differential voltage on the POTS line  241  may be maintained by closing a switch  238  connected between a POTS line power source  239 , such as an integrated power-supply unit or a battery, and the POTS line  241 . 
     The timer  237  may operate according to a timer value, such as two minutes, defining a time window within which the software upgrade or maintenance of the ONT  235 , OLT ( 122 ), or PON communications link ( 125   a ) is to be completed. Maintenance of the PON communications link ( 125   a ) may include cleaning optical connectors or moving connections at an optical splitter. If the ONT  235  regains communications with the OLT ( 122 ) within the time window, the timer  237  retains the switch  238  closed so that the POTS line power source continues to provide power to the alarm system  231 . In this manner, an ONT or OLT reboot or a planned interruption in communications do not cause the alarm system  231  to issue a false alarm. 
     If, however, the ONT  235  does not regain communications with the OLT ( 122 ) within the time window (possibly indicating that the optical fiber  201  has been severed), the timer  237  may cause the switch  238  to open in order to remove power from the alarm system  231  and allow the alarm system  231  to issue an alarm. 
     The timer  237  may be a configurable timer that may be configured by a user through the ONT processor  251 . The timer  237  may be configured with any time value, for example, any time value from zero to six minutes in ten second increments. The OLT ( 122 ) may also provision the ONT  235  with a timer value, which the ONT may store in nonvolatile memory  236 . Thus, if the ONT reboots, such as during an upgrade of the ONT&#39;s  235  software, then the ONT  235  may use the user-configured or provisioned timer value rather than a default timer value, such as two minutes. 
     The example ONT  235  may also include a light detector  250  which detects light, such as an optical communications signal, on the optical fiber  201 . The ONT  235  may further include a transceiver  252  for sending and receiving optical communications signals between the OLT ( 122 ) and the ONT  235 . In this embodiment, if the ONT  235  loses communications with the OLT ( 122 ), the ONT  235  detects at the light detector  250  whether or not it has lost a received optical communications signals. In the case where the OLT ( 122 ) receives software upgrades, the OLT ( 122 ) (or PON card  124   a ) reboots, but keeps its optical transmitter running. As a result, the light detector  250  continues to detect an optical communication signal. 
     If the optical fiber  201  is cut, the light detector  250  senses a loss of an optical communications signal and starts the timer  237 . Logic (not shown) may be coupled to the light detector  250  and timer  237  to cause the timer  237  to start in event of loss of light on the optical fiber  201 . When the timer  237  exceeds a default or user-configured timer value, the switch  238  opens to cause the alarm system to issue an electronic representation of an alarm (e.g., via a wireless network path) or sound an audible alarm. 
     If the ONT  235  reboots, the light detector  250  may not detect an optical communications signal from the OLT ( 122 ). In this case, the light detector  250  may activate the timer  237 . The timer  237  preferably provides sufficient time for the ONT to regain communications with the OLT ( 122 ) so that the timer does not open the switch  238  to cause the alarm system  231  to sound an alarm. 
     In another embodiment of the present invention, the ONT  235  may include two timers configured by the user. For example, the first timer may be associated with the light detector  250  and may be activated by the loss of an optical communications signal, and the second timer may be associated with the transceiver  252  and may be activated when the transceiver  252  loses communications with the OLT ( 122 ). The first timer associated with the loss of an optical communication signal may be configured with a timer value shorter than the second timer associated with the loss of communications with the OLT ( 122 ). For example, the first timer associated with the loss of an optical communications signal may use a ten second timer value, and the second timer associated with the loss of communications may use a five minute timer value. The ONT  235  uses one of these two timer values depending on whether a loss of the optical communications signal or the loss of communications with the OLT ( 122 ) is encountered. Thus, an embodiment using a light detector  250  provides a way to more quickly sound an alarm if a burglar cuts the optical fiber  201  by actually sensing the optical communications signal on the optical fiber  201 . 
     In yet another embodiment, the timer  237  may be automatically configured with another timer value during an upgrade. A user may configure the timer  237  associated with the light detector  250  with a short time window, such as ten seconds or thirty seconds. When the software upgrades are performed on the OLT or the ONT, the OLT may send a special message to the ONT to inform it that an upgrade is in progress. In this case, the message may indicate that the timer value is configured with a longer time window, such as two minutes. In this way, the ONT  235  knows that if it loses communication with the OLT or if the ONT reboots, it is most likely because of a software upgrade or other scheduled maintenance event (e.g., fiber plant service) and not because the optical fiber  201  has been severed. 
     After the software upgrade, the timer may revert back to the timer value associated with the light detector  250 . Likewise, if a PON card at the OLT needs to be replaced, the OLT may send a message to the ONT informing it to configure the timer with a timer value sufficient to allow the PON card to be replaced. For example, the time value may be set to five minutes and then revert back to a shorter time window, such as two minutes, after the PON card is replaced. 
       FIG. 3  is an example flow diagram that may be performed by elements of the optical communication system of  FIG. 1 . After a service provider installs a POTS line ( 302 ), such as a POTS line supporting a security system  331 , a second PON system, such an OLT  320 , sends a message to a first PON system, such as an ONT  335 , to enable the POTS line ( 304 ). The ONT  335  may store a value in FLASH memory ( 306 ), indicating that the POTS line has been enabled by the OLT  320 . The ONT  335  then provides a differential 48 volts through a power source ( 308 ) to the POTS line and security system  331 . 
     After a period of time, such as two months, the OLT software may be upgraded ( 310 ), which causes the PON card to reboot ( 312 ). As a result, the OLT ( 320 ) loses communications ( 314 ) with the ONT  335 , and the ONT  335  reboots ( 316 ) and removes the differential 48 volts ( 318 ) from the security system  331 . The ONT  335  reads from FLASH memory ( 324 ), determines that the POTS line is enabled, provides the differential 48 volts ( 326 ) to the security system  331 , and starts the timer ( 328 ). If, for example, the timer is configured with a timer value of two minutes and the OLT  320  regains communications ( 330 ) with the ONT  335  after ninety (90) seconds ( 322 ), then the ONT  335  stops the timer  332 . 
     If, after a period of time, such as a few months, the ONT software is upgraded ( 340 ), the OLT  320  downloads software ( 341 ) and activates the software ( 342 ) by rebooting the ONT ( 343 ). The ONT reboot ( 343 ) causes the ONT ( 335 ) to remove the differential 48 volts ( 344 ) on the POTS line. Within a short time frame of, for example, seven seconds, the ONT  335  provides the differential 48 volts ( 345 ) to the security system  331  and starts the timer ( 346 ). If the ONT  335  regains communications ( 347 ) with the OLT  320  before the timer exceeds the timer value, the ONT  335  stops the timer ( 348 ). In the case where the optical fiber is cut ( 350 ), the ONT  335  loses communications ( 351 ) with the OLT  320 . When the ONT  335  determines that it has lost communications with the OLT, it starts the timer ( 353 ). When the timer expires ( 355 ) (after the timer exceeds a timer value, such as two minutes), the ONT  335  removes the differential 48 volts ( 357 ) from the security system  331 . After the security system  331  detects a loss of power from the ONT  335 , it triggers an alarm ( 359 ). 
     In the general field of POTS line technology, the term “activating” is often understood to mean that a service provider has enabled a POTS line by associating a telephone number with the POTS line. From the perspective of the service provider, the POTS line is always activated once the telephone number has been assigned to it. However, with respect to the present invention, the term “activating” refers to enabling, energizing or configuring, depending on the embodiment, the POTS line (i.e., a port associated with the POTS line) based on data stored in memory, in some embodiments, prior to reestablishing communications between PON systems on either side of the POTS line. For example, activating the POTS line may include energizing the POTS line with a voltage based on the data or may include applying configuration data associated with a port connected to the POTS line. 
       FIG. 4  is an example flow diagram performed by elements of an optical communications system, such as the optical communications system of  FIG. 1 . After starting ( 401 ), an ONT stores POTS line data in nonvolatile memory ( 402 ). The POTS line data may include configuration data, timer values, or a parameter or other representation indicating whether a POTS line is enabled. The ONT may then monitor for an interruption in communications ( 404 ,  405 ) between an OLT and the ONT. If the ONT detects an interruption in communications, the ONT activates the POTS line with the POTS line data prior to reestablishing communications with the OLT ( 406 ). Finally, the foregoing ONT process ends ( 408 ). 
     There may be embodiments where the POTS line data can be stored in RAM and not need to be loaded from nonvolatile memory. In other embodiments, the POTS line data can be stored in nonvolatile memory and loaded into RAM. Thus, in the event of interruption in communications between the ONT and OLT, the ONT can activate the POTS line based on data from nonvolatile memory or RAM. 
       FIG. 5  is another example flow diagram of an example process  500  performed by elements of the optical communication system of  FIG. 1 . After starting ( 501 ), an ONT stores POTS line data in nonvolatile memory ( 502 ). The ONT proceeds to determine whether the PON system has rebooted ( 504 ). If not, the ONT continues to determine whether the PON system has rebooted ( 505 ). If the ONT determines that the PON system has rebooted, the ONT activates the POTS line with POTS line data ( 506 ) and energizes the POTS line with a voltage based on the POTS line data ( 509 ) prior to reestablishing communications with the OLT. The ONT may energize the POTS line with a voltage to prevent an alarm system connected to the POTS line from generating an alarm. Then, the foregoing ONT process ends ( 510 ). 
       FIG. 6  is another example flow diagram performed by elements of the optical communications system of  FIG. 1 . After starting ( 601 ), a user sets a timer value ( 602 ) for a timer. The timer value may be a value known to be sufficient to allow an ONT to reestablish communications with an OLT, but not so long as to ineffectuate an alarm system connected to the ONT via a POTS line. For example, the timer value may be a fixed value between about one and a half and three minutes. The ONT may then proceed to monitor for an interruption in communications ( 604 ). If the ONT detects an interruption in communications between the ONT and the OLT ( 605 ), the ONT starts the timer ( 606 ). If there is no interruption in communications, the ONT continues to monitor for an interruption in communications. ( 605 ). 
     The ONT may next determine whether the timer has expired ( 608 ). If the timer has not expired ( 608 ), the ONT maintains a POTS line voltage ( 609 ) and proceeds to determine whether uninterrupted communications have been reestablished ( 610 ). If uninterrupted communications have been reestablished, the ONT continues to determine whether the ONT has expired ( 611 ). When uninterrupted communications are reestablished, the ONT resets the timer ( 612 ) and resumes monitoring for an interruption in communications ( 604 ). If the timer has expired ( 608 ), the ONT removes the POTS line voltage( 614 ) and ends the preceding process ( 615 ) by removing the POTS line voltage. An alarm system, such as a home security system, connected to the POTS line may then sound an alarm. 
       FIG. 7  is another example flow diagram that may be performed by elements of, for example, the optical communications system of  FIG. 1 . After starting ( 701 ), an ONT sets first and second timer values ( 702 ). These timer values may be stored in nonvolatile memory in the ONT. The ONT may then monitor for an interruption in communications with an OLT ( 704 ). If the ONT detects an interruption in communications with the OLT, the ONT proceeds to determine whether an interruption in communications is expected ( 704 ). For example, the ONT may determine whether an interruption due to a software upgrade or other maintenance activities has been scheduled. 
     If an interruption in communications is expected, the ONT may start the timer using the second timer value. If an interruption in communications is not expected ( 704 ), the ONT starts the timer using the first timer value ( 705 ). Whether or not the ONT has started the timer using the first or second timer values, the ONT determines whether the timer has expired ( 708 ). If the timer has not expired, the ONT ( 709 ) maintains the POTS line voltage and proceeds to determine whether uninterrupted communications have been reestablished ( 710 ). 
     If uninterrupted communications have not been reestablished, the ONT continues to determine whether the timer has expired ( 711 ). If uninterrupted communications have been established, the ONT resets the timer ( 712 ) and returns to monitor whether there has been an interruption in communications between the ONT and the OLT. If there has been no interruption in communications between the ONT and the OLT, the ONT continues to monitor for an interruption in communications ( 705 ). If the timer value has expired, the ONT removes the POTS line voltage ( 714 ) and ends the above process ( 715 ). 
       FIG. 8  is another example flow diagram that may be performed by components of the optical communications system of  FIG. 1 . After starting ( 801 ), an ONT sets a first timer value, such as less than or equal to 30 seconds, and a second timer value such as greater than 30 seconds ( 802 ). The ONT may then monitor for the loss of light on the fiber connecting the ONT to an OLT or a PON card ( 804 ). If the ONT has not detected a loss of light on the fiber, the ONT continues to monitor for a loss of light on the fiber ( 805 ). If the ONT detects loss of light on the fiber, the ONT next detects whether the loss of light is expected ( 804 ). If the loss of light is not expected, the ONT starts a timer using the first timer value ( 805 ). If the loss of light is expected, the ONT starts the timer using the second value ( 806 ). 
     The ONT may next determine whether the timer has expired ( 808 ). If the timer has not expired, the ONT maintains the POTS line voltage ( 809 ) and determines whether light has once again been detected ( 810 ). If light has not been detected ( 811 ), the ONT continues to determine whether the timer has expired ( 808 ). If light has been detected, the ONT returns to monitor for the loss of light on the fiber. If the timer has expired ( 808 ), then the ONT removes the POTS line voltage ( 814 ) and ends the above process ( 815 ). 
     The POTS line data may include configuration data used to configure the POTS lines to operate as loop start or ground start on a per POTS line basis. For businesses or other commercial facilities, ONTs may use ground start. Non-businesses or other non-commercial facilities generally use loop start. When the POTS lines operate as loop start, the tip and ring are shorted and a current is detected in the loop. Tip and ring are wires used in a typical POTS line. Thus, an ONT may energize a POTS line operating as loop start (e.g., provide loop current feed by grounding the tip and applying a POTS line power source to the ring on a loop start port) as soon as possible after initialization of a software upgrade to prevent an alarm system connected to the POTS line from generating an alarm. On the other hand, when the POTS lines operate as ground start, the tip is grounded and a current is detected. Energizing a POTS line operating as ground start, however, indicates an incoming call. Thus, a POTS line operating as ground start may not be used to prevent an alarm system connected to the POTS line from generating an alarm in accordance with principles of the present invention. 
     By including configuration data, used to configure the POTS line to operate as loop start or ground start on a per POTS line basis, the ONT can be activated with the applicable configured POTS analog interface on a per POTS line basis when the ONT reboots. In this manner, the configuration data is not lost through a reboot. 
     It should be understood that the OLT and ONT may communicate using Broadband PON (BPON) or a Gigabit PON (GPON) protocols. It should also be understood that the OLT may be configured to transmit Operations, Maintenance, and Control Interface (OMCI) data to the ONT. The OMCI data may include timer values and settings for the method of seizing the POTS lines (e.g., loop start or ground start). 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. 
     For example, the flow diagrams of  FIGS. 3-8  may include a subset of the flow diagrams, a different order of the flow diagrams, additional sections of the flow diagrams, and so forth, on a per application basis. The flow diagrams may be implemented in hardware, firmware, or software. If software, the software may be stored locally or remotely on a machine-readable medium, loaded (locally or via a network communications path), and executed by a general purpose or application-specific processor.