Abstract:
In an Optical Network Termination (ONT), a software controlled system, method and computer readable medium includes measuring a modulation current of an upstream laser transmission. The measured modulation current is processed to determine if a continuous transmission state is present, in response to which, a processor of the ONT sends a signal to shut down the upstream laser transmission. The software solution allows reconfigurable parameters including sample rate and shut down procedure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present patent application is related to and claims the benefit of provisional patent application No. 60/869,264, filed 8 Dec. 2006, entitled Controller Detection, the entire contents of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a system, method and computer readable medium for controlling components in an optical network. In preferred embodiments, the invention relates to a system, method and computer readable medium for detecting and controlling specific transmission conditions in an Optical Network Termination (ONT) of an optical network. 
       BACKGROUND OF THE INVENTION 
       [0003]    ONT (Optical Network Termination), also called ONU (Optical Network Unit), refer to the consumer end equipment in an optical Fiber to the Home (FTTH) link. The ONT/ONU receives downstream data from the OLT (Optical Line Termination) through the passive optical splitters and provides video, voice, and broadband services to the consumer. 
         [0004]    In the FTTH Passive Optical Network (PON) applications, ONT&#39;s are granted permission under control of the OLT to transmit upstream on a shared PON medium at specific assigned time slots. There exists the possibility of an ONT operating it&#39;s upstream transmit laser in an always on state operating within unassigned transmit timeslots. Detection and alleviation of this continuous transmission state is essential. 
         [0005]    Various hardware methods exist to detect laser on times such as resettable “watchdog timers” which are reset by the normal laser enable control signal. If the control signal does not reset the watchdog timer then the timer times out and inhibits the transmit laser from coming on. 
         [0006]    The known solutions require a hardware implementation and are not flexible as a software driven solution. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to overcome the disadvantages of the present invention by providing a software solution that allows predetermined transmission conditions, such as a continuous transmission state, to be detected and alleviated if necessary. Transmission states of the ONT can be determined by random sampling of the laser transmission via a software controlled processor within the ONT. 
         [0008]    In one embodiment of the disclosure, there is provided an Optical Network Termination (ONT) comprising at least one processor, at least one transmission module and at least one transmission monitor. The at least one transmission module transmits upstream on an optical network, the transmission monitor is configured to measure at least one parameter of an upstream transmission, the at least one processor is configured to process the at least one measured parameter to determine whether the measured parameter indicates a predetermined transmission condition and the processor is adapted to adjust the operation of the transmission module if the predetermined transmission condition is indicated. 
         [0009]    In one embodiment of the disclosure, there is provided a method of operating an Optical Network Termination comprising measuring at least one parameter of an upstream transmission, determining whether the measured parameter is indicative of a predetermined transmission condition, and adjusting the operation of the Optical Network Termination if the predetermined transmission condition is indicated. 
         [0010]    In one embodiment of the disclosure, there is provided a computer readable medium comprising instructions executable in at least one processor of an Optical Network Termination for sampling at least one parameter of a laser transmission module, determining whether the sampled parameter is indicative of a predetermined transmission condition; and providing a signal to a laser transmission module to adjust the operation of the laser transmission module if the predetermined transmission condition is indicated. 
         [0011]    In one embodiment, the predetermined transmission condition is a continuous transmission condition, in response to which, the upstream transmission is shut down. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will now be described by way of example with reference to preferred embodiments and to the accompanying drawings in which: 
           [0013]      FIG. 1  provides a schematic representation of an Optical Network Termination; 
           [0014]      FIG. 2  provides a flow chart representing a method of operation of the Optical Network Termination of  FIG. 1 ; 
           [0015]      FIG. 3  provides a flow chart representing a method of detecting a continuous transmission state; and 
           [0016]      FIG. 4  provides a flow chart representing a method of operating a processor of the Optical Network Termination. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]      FIG. 1  shows an Optical Network Termination (ONT)  10  in accordance with one embodiment of the invention. The ONT  10  has a controller  11  including a processor  18  and a programmable memory  20 . The programmable memory  20  stores the operating instructions in software which are run by the processor  18  for controlling the operation of the ONT. The controller  11  controls operation of the ONT laser modules, of which an upstream transmitting laser module  12  is shown, via any appropriate communication interface  13 , for example an I 2 C line. 
         [0018]    A transmission monitor  14  measures one or more parameters of the upstream transmission by the laser module  12 . In one embodiment, the transmission monitor includes a bias current monitor  15  and a modulation current monitor  16 . The transmission monitor signals are provided to an analogue to digital converter (ADC)  17 . The digital values from the ADC  17  are made available on the I 2 C serial bus which can be read by the ONT controller  11  via a polling or interrupt mechanism. 
         [0019]      FIG. 2  provides a flow chart  200  for performing a method of operating the ONT  10  in accordance with one embodiment of the invention. The transmission monitor measures the upstream laser transmission (step  201 ). At step  202 , the transmission monitor signals are converted to digital signals by the ADC  17 . The controller processor  18  processes the digital signals to determine the state of operation of the upstream laser (step  203 ). 
         [0020]    If the processor  18  determines that the signals indicate the laser module  12  is operating in a predetermined state, then the controller software causes an interrupt signal  19  to be sent to the laser module  12  to adjust the operation of the laser module  12  (step  204 ). In one preferred embodiment, the predetermined state is an always on state which, when detected, causes the controller  11  to shut down the transmission laser of the laser module  12 . For example, if the level of transmission modulation current representing an “on” state is consistently detected in time equal to multiple 125 microsecond transmission frame intervals then the conclusion is the laser module is in an always on state. With this conclusion, the transmission laser is shut down by writing a transmit disable to the appropriate register of the laser module microcontroller (not shown). 
         [0021]    A specific example for detecting a continuous transmission state will now be described with reference to the flow diagram  300  shown in  FIG. 3 . The controller  11  reads the bias current and modulation current at step  301 . The values are stored (step  302 ) and the measurement process repeated for N loops, as indicated by loop  306 . Once N samples have been collected, the N samples are compared (step  303 ). If the samples are all equal, for example, digitally represented as all ones, then the controller determines that the samples indicate a continuous transmission state. Based on this determination, the ONT controller software will shut down the laser module  12  via the I 2 C serial bus by writing a transmit disable to the appropriate register (step  305 ). If the samples are not equal, then the transmission state of the laser is varying, as per standard operation which requires only that the controller  11  wait a time T seconds (step  304 ) before repeating the loop  307 . 
         [0022]    Additional or alternative transmit disable mechanisms are possible. For example, the laser module Reset can be used to shut down only the optical transmit section of the module. In one embodiment, only the upstream laser need be disabled. 
         [0023]    In the present example, the value for N representing the number of samples and the value T seconds representing the sample rate are both configurable parameters, as described below. 
         [0024]    Not being fixed in hardware, the above described embodiments provide the flexibility of software changes to reconfigure any suitable aspect of the controlling software run by the processor  18 .  FIG. 4  provides a flow chart  400  from the perspective of the processor. At step  401 , the processor  18  samples the output of the laser transmission module, ie the upstream laser transmission. In the present embodiments, the output of the laser transmission module is sampled via the transmission monitor  14  and ADC  17 , however the skilled addressee will readily understand that other systems and methods for sampling the upstream laser transmission are possible. The processor analyzes the sampled signal (step  402 ), for example using the method described above with reference to  FIG. 3 , though modifications and substitutions of this analysis method will be readily apparent to the skilled addressee. After analyzing the laser transmission signal, if the processor determines that a predetermined transmission state exists (step  403 ), such as a continuous transmission state, the processor sends an interrupt signal (step  404 ) to the laser module. At step  405 , the processor receives software updates, including any updates to the process routine parameters. For example, a software update may include changes to the sample rate, the method or range of values used in determining a predetermined transmission state, or the type of interrupt signal that is sent to the laser module. These software changes may be performed by downloading new software, ie new program instructions and storing the new instructions into the programmable memory of the ONT (step  406 ) through a suitable port (not shown). Alternatively, the reconfigurable parameters can be stored in distinct registers so that changes can be made by directly writing to those registers. 
         [0025]    In addition, the ONT controller software typically has multiple accessible control points which can be accessed, for example to control the transmit burst enable and transmit data stream. 
         [0026]    Although embodiments of the present invention have been illustrated in the accompanied drawings and described in the foregoing description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the following claims. For example, the capabilities of the invention can be performed fully and/or partially by one or more of the blocks, modules, processors or memories. Also, these capabilities may be performed in the current manner or in a distributed manner and on, or via, any device able to provide and/or receive information. Further, although depicted in a particular manner, various modules or blocks may be repositioned without departing from the scope of the current invention. Still further, although depicted in a particular manner, a greater or lesser number of modules and connections can be utilized with the present invention in order to accomplish the present invention, to provide additional known features to the present invention, and/or to make the present invention more efficient.