Abstract:
According to an aspect of this invention, dynamic bandwidth assignment (DBA) can be performed without interrupting communication of a regular cell and interfering with communication between child stations. In a passive optical network including a parent station and a plurality of child stations, a maintenance signal for a mini slot signal is provided. Each of the child stations sends a corresponding maintenance signal if necessary, and the parent station controls state transition by using the maintenance signal concerning on the mini slot signal for each of the child stations. By controlling the state transition, the dynamic bandwidth assignment can be performed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a maintenance signal corresponding to a mini slot signal in a slot according to international standard ITU-T G.983.1 regulating a physical interface in a PON (Passive Optical Network) and a method for controlling a state in dynamic bandwidth assignment (DBA) for upstream by using the mini slot signal.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIG. 3 illustrates an example of a configuration of a system in the PON including a DBA function, in which an OLT (optical line terminator—parent station)  101  and a plurality of ONU&#39;s (optical network terminating units—child stations)  102 - 104  are coupled to by a star coupler  105 . FIG. 4 illustrates a downstream frame format  151  and an upstream frame format  152  in the PON according to international standard ITU-T G.983.1 regulating a physical interface in the PON according to the related art. FIG. 5 shows a state transition table for managing a state of an individual ONU dealing unit in the OLT according to international standard ITU-T G.983.1 regulating an operation by the OLT for controlling starting and halting of an individual ONU. FIG. 6 illustrates an example of a condition of detecting and resetting according to international standard ITU-T G.983.1 related to a maintenance signal provided for each of the ONU&#39;s indicating a state of receiving an ATM (asynchronous transfer mode) cell and PLOAM (Physical Layer Operation Administration and Maintenance) cell in an upstream frame in the OLT. Further, FIG. 7 illustrates a format of a mini slot in a slot according to international standard ITU-T G.983.1 related to the upstream frame.  
           [0005]    In FIG. 3, the OLT  101  includes an individual ONU dealing unit  106 B, a generator  107  for downstream frame, a controller  108  for upstream band, a DBA controller  109 B, a terminator  110  of upstream frame, and a terminator  111  of mini slot. The ONU  103  includes a terminator  112  of downstream frame, a detector  113  for upstream band, a cell buffer  114  for upstream, a monitor  115  for buffer state, and a cell generator  116  for upstream.  
           [0006]    With reference to FIG. 3, an operation in the PON is explained.  
           [0007]    The OLT  101  receives a main signal  122  of downstream including an ATM cell, and generates a frame signal  124  of downstream by the generator  107  for downstream frame. Particularly, the generator  107  for downstream frame receives control information  126  on the ONU from the individual ONU dealing unit  106 B and information  125  on an upstream band from the controller  108  for upstream band, generates a PLOAM cell of downstream, and inserts the generated PLOAM cell into the frame signal  124  of downstream. The individual ONU dealing unit  106 B exchanges information on each of the ONU&#39;s as a control signal  121  with an external operation system.  
           [0008]    A frame signal  129  of upstream sent from each of the ONU&#39;s is terminated. A regular cell is terminated by the terminator  110  of upstream frame, and a mini slot is terminated by the terminator  111  of mini slot. The terminator  110  of upstream frame detects a PLOAM cell of upstream when the regular cell is terminated, and notifies the individual ONU dealing unit  106 B of control information  130  on the ONU corresponding to the PLOAM cell. At the same time, the terminator  110  of upstream frame outputs a main signal  123  of upstream when the ATM cell besides the PLOAM cell is detected. State information  131  on a cell buffer for upstream of an ONU corresponding to the mini slot terminated by the terminator  111  of mini slot is sent to the DBA (Dynamic Bandwidth Assignment) controller  109 B. Further, state information  127  corresponding to the individual ONU and information  132  on the upstream band is sent to the DBA controller  109 B and the controller  108  for upstream band, and an operation of dynamic bandwidth assignment (DBA) for upstream is performed.  
           [0009]    The ONU  103  extracts a main signal  141  of downstream including an ATM cell directed to the ONU  103  as the terminator  112  of downstream frame terminates a downstream frame signal  143 . Particularly, a PLOAM cell  144  of downstream is extracted, and control information  145  on outputting the upstream cell is output to the cell generator  116  for upstream by the detector  113  for upstream band.  
           [0010]    Further, a main signal  142  of upstream including the ATM cell is maintained in the cell buffer  114  for upstream once, and read out as information  146  on the cell based on an instruction from the cell generator  116  for upstream. A header is attached to the information  146  on the cell by the cell generator  116  for upstream, and the information  146  on the cell is output as a frame signal  149  of upstream. Information  147  on the cell buffer  114  for upstream is always monitored by the monitor  115  for buffer state, and output to the cell generator  116  for upstream as information  148  on a buffer state for mapping in the mini slot.  
           [0011]    In the following, with reference to FIG. 4, a frame format of upstream and a downstream frame used in the PON system is explained.  
           [0012]    In FIG. 4, the frame format  151  of downstream includes 56 ATM cells in a fixed length of 53 bytes located consecutively. Among the cells, the first cell and the 29th cell are PLOAM cells for monitoring and controlling between the OLT and the ONU.  
           [0013]    The upstream frame format  152  includes 53 cells of 56 bytes. 56 bytes include 3 bytes of overhead and 53 bytes of ATM cells. It is also possible that the PLOAM cell is provided in an ATM cell at an arbitrary position. According to international standard ITU-T G. 983 . 1 , in a system configuration illustrated in FIG. 3, the OLT  101  manages a state of each of the ONU&#39;s  102 - 104  connected to the PON individually based on a state transition table of the individual ONU dealing unit in the OLT illustrated in FIG. 5.  
           [0014]    In the following, a state transition operation of the individual ONU dealing unit in the OLT illustrated in FIG. 5 is explained.  
           [0015]    In FIG. 5, columns arranged horizontally illustrate an initial state (OLT-IDV 1 ), a state of measuring delay (OLT-IDV 2 ), and an operation state (OLT-IDV 3 ). The initial state (OLT-IDV 1 ) illustrates a state of initializing a start operation temporally as a corresponding ONU is not started or there is a certain failure. The state of measuring delay (OLT-IDV 2 ) illustrates a state of measuring a delay in transmission of a cell due to a transmission distance between the OLT and the ONU. The operation state (OLT-IDV 3 ) illustrates a state of transmitting an upstream cell in timing in which the ONU compensated the delay in upstream by measuring the delay in the transmission of the cell due to the transmission distance and informing the ONU of information on the measured delay by the OLT.  
           [0016]    Rows arranged from a top to a bottom regulate a horizontal direction, and illustrate four state transition events: instructing to start measuring delay (n), completing measuring delay (n), detecting abnormality of measuring delay (n), and detecting each of maintenance signals (LOSi, CPEi, LCDi, OAMLi, LOAi, R-INHi). In this description, n means the number of ONU. Instructing to start measuring delay (n) is an instruction issued in the initial state when the ONU is started. Completing measuring delay (n) is issued to the ONU which is measured the delay in the state of measuring delay when the delay is measured normally. Detecting abnormality of measuring delay (n) is issued to the ONU which is measured the delay in the state of measuring delay when the delay is not measured normally. Each of the maintenance signals is a signal detected and reset in the operation state in each of conditions illustrated in FIG. 6.  
           [0017]    With reference to FIG. 5, an operation of a third ONU (n=3) is explained as an example. The third ONU which is in the initial state (OLT-IDV 1 ) receives a state transition event of instructing to start measuring delay (n), and a state transits to the state of measuring delay (OLT-IDV 2 ). When measuring of the delay is completed, a state transition event of completing measuring delay (n) is received, and the state transits to the operation state (OLT-IDV 3 ). However, when measuring of the delay is failed due to a certain reason, a state transition event of detecting abnormality of measuring delay (n) is received, and the state transits to the initial state (OLT-IDV 1 ). The individual ONU dealing unit in the OLT corresponding to the third ONU which is in the operation state (OLT-IDV 3 ) begins to monitor each of the maintenance signals (LOSi, CPEi, LCDi, OAMLi, LOAi, R-INHi) corresponding to the third ONU. When at least one of the maintenance signals is detected, the state transits to the initial state (OLT-IDV 1 ). After then, the individual ONU dealing unit in the OLT corresponding to the third ONU which is not in the operation state is started to go back to the operation state by a state transition event of instructing to start measuring delay (n) which occurs regularly.  
           [0018]    An operation of the mini slot signal illustrated in FIG. 7 is explained.  
           [0019]    The ONU which is in the operation state communicates by using the downstream frame format  151  and the upstream frame format  152  as illustrated in FIG. 4. In a certain phase of a cell, there is a case in which a certain cell is used in a slot  162  of an upstream frame  161  illustrated in FIG. 7 and the ONU sends a mini slot signal  163 . In this case, when the OLT sets a phase of an upstream cell in the slot  162 , a plurality of ONU&#39;s send the mini slot signals  163  in the slot  162 . In this case, the mini slot signals  163  sent from the plurality of ONU&#39;s are controlled by the OLT for preventing collision. For preventing the collision, the OLT sets a phase (offset) from a beginning of the slot  162  and information on length of the mini slot signal  163  corresponding to the ONU in the ONU&#39;s individually.  
           [0020]    In the following, as an example of operating a system using the mini slot signal illustrated in FIG. 8, control in dynamic bandwidth assignment (DBA) for upstream is explained.  
           [0021]    The dynamic bandwidth assignment (DBA) for upstream is performed by using a mini slot signal including a function equivalent to an individual communication channel besides a regular cell from the plurality of ONU&#39;s to the OLT. By using the mini slot signal, each of the ONU&#39;s informs the OLT of a buffer state of upstream in the ONU. Then, the OLT extracts a content of the mini slot signal, and detects a buffer state in each of ONU&#39;s. It is a control method for reallocating the upstream bandwidth dynamically to each of the ONU&#39;s based on the information in the mini slot signal. For applying this control method, it is necessary that the OLT detects if the ONU can deal with the mini slot signal before controlling the bandwidth by using the mini slot.  
           [0022]    In FIG. 8, arrangement  171  of cells in the upstream frame when the OLT provides an arbitrary band of upstream for each of the ONU&#39;s is illustrated. In the arrangement  171  of cells for upstream, ONU# 1  shows a cell sent from a first ONU in a band allocated for the first ONU. ONU# 2  and ONU# 3  also show cells. In this state, all of the ONU&#39;s informs the OLT of a cell buffer state for upstream by using the mini slot signal constantly. For example, when it is judged that the cell buffer state for upstream in the first ONU exceeds a threshold value of the buffer determined by the OLT, the OLT temporally allocates a bandwidth wider than a present bandwidth of the upstream band. Therefore, the arrangement  171  of the cells is changed to an arrangement  172  of the cells in the upstream frame. The arrangement  172  indicates that an utilized upstream band is allocated to the first ONU.  
           [0023]    A control method using the mini slot signal in the slot according to international standard ITU-T G. 983 . 1  regulating the physical interface in the PON according to the related art only describes a configuration of a format of the slot. There isn&#39;t any definition about maintenance signal by the mini slot. There isn&#39;t also any definition of using the mini slot for DBA request, and of controlling method for the mini slot. Therefore, it is impossible to monitor and control a receiving state of the regular cell and the mini slot signal individually. For example, when the maintenance signal of the regular cell illustrated in FIG. 6 is used for the mini slot signal, even if only the mini slot signal operates in failure, it is judged as a state transition of the regular cell of the ONU by the individual ONU dealing unit  106 B in the OLT illustrated in FIG. 5, and whole communication is suspended.  
           [0024]    Further, FIG. 9 illustrate a state of failure of the mini slot signal in the slot  181 . As illustrated, when the ONU misjudges a phase of transmission of the mini slot signal, there is a possibility of the collision with another cell or mini slot signal sent from another ONU, located before and after the mini slot signal. In such a case, there is no method of individually controlling the mini slot signal in failure by misjudging the phase of transmission, a state of the collision is maintained, and transmission of the cell or mini slot from another ONU is prevented continuously. Particularly, when the assignment of the upstream band to the ONU is controlled dynamically by using the mini slot signal, communication by all of the other ONU&#39;s is prevented by the failure of the mini slot signal of one ONU as in this case.  
         SUMMARY OF THE INVENTION  
         [0025]    It is one of objects of this invention to solve the above-stated problems in the related art. By controlling an apparatus in a method besides a control method using the regular cell, the dynamic bandwidth assignment (DBA) can be performed without interrupting the communication of the regular cell and interrupting the communication between child stations.  
           [0026]    According to an aspect of this invention, a control system uses a mini slot signal in a passive optical network. The passive optical network includes a parent station (OLT: optical line terminal) and a plurality of child stations (ONU: optical network terminating unit) for transmitting an upstream frame and a downstream frame each other. The parent station includes an individual ONU dealing unit for providing a maintenance signal corresponding to each of the plurality of child stations concerning on a mini slot and controlling state transition in dynamic bandwidth assignment (DBA) for each of the plurality of child stations by using the maintenance signal concerning on the mini slot.  
           [0027]    The parent station instructs a corresponding child station to transit to a state beside an operation state when one of failures of receiving an effective mini slot signal from the child station and receiving a mini slot in a correct phase is detected as a maintenance signal concerning on the mini slot signal.  
           [0028]    According to another aspect of this invention, a control method uses a mini slot signal in a passive optical network. The passive optical network includes a parent station (OLT: optical line terminal) and a plurality of child stations (ONU: optical network terminating unit) for transmitting an upstream frame and a downstream frame each other. The control method provides a maintenance signal corresponding to each of the plurality of child stations concerning on a mini slot and controls state transition in dynamic bandwidth assignment (DBA) for each of the plurality of child stations by using the maintenance signal concerning on the mini slot by an individual ONU dealing unit in the parent station.  
           [0029]    The control method instructs a corresponding child station to transit to a state beside an operation state by the parent station when one of failures of receiving an effective mini slot signal from the child station and receives a mini slot in a correct phase is detected as a maintenance signal concerning on the mini slot signal.  
           [0030]    According to this invention, it is possible to monitor the mini slot signal in each of the ONU&#39;s individually besides the regular cell by providing a maintenance signal for the mini slot signal besides the regular cell when the OLT receives the mini slot signal.  
           [0031]    Further features and applications of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
       [0032]    Other objects features, and advantages of the invention will be apparent from the following description when taken in conjunction with the accompany drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]    [0033]FIG. 1 illustrates an example of a maintenance signal for a mini slot signal provided in Embodiment  1  of this invention;  
         [0034]    [0034]FIG. 2 shows a state transition table corresponding to the dynamic bandwidth assignment (DBA) for upstream by using the mini slot signal in Embodiment 1 of this invention;  
         [0035]    [0035]FIG. 3 shows a configuration chart for explaining the PON system and the function of the OLT and the ONU;  
         [0036]    [0036]FIG. 4 illustrates a frame format of downstream and an upstream frame according to international standard ITU-T G.983.1 regulating the physical interface in the PON;  
         [0037]    [0037]FIG. 5 shows a state transition table of the individual ONU dealing unit (n) in the OLT according to international standard ITU-T G.983.1 regulating the physical interface in the PON;  
         [0038]    [0038]FIG. 6 illustrates an example of the maintenance signal for monitoring each of the ONU&#39;s by the OLT according to international standard ITU-T G.983.1 regulating the physical interface in the PON;  
         [0039]    [0039]FIG. 7 shows a configuration chart of an upstream frame, a slot and a mini slot according to international standard ITU-T G.983.1 regulating the physical interface in the PON;  
         [0040]    [0040]FIG. 8 shows an explanatory chart of an operation of dynamic bandwidth assignment (DBA) for upstream by using the mini slot signal; and  
         [0041]    [0041]FIG. 9 shows a chart for explaining that a mini slot signal in a slot misjudges a phase of transmission and that prevents transmission of another regular cell or mini slot signal. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     EMBODIMENT 1  
       [0042]    Embodiments of this invention are explained.  
         [0043]    A maintenance signal for a mini slot signal and an operation of this invention are explained by FIG. 1 and FIG. 2.  
         [0044]    In FIG. 1, as types of the maintenance signal, failure of receiving a mini slot signal (LOS-Di) I 51 , out-of-synchronization of the mini slot signal (LCD-Di) I 52 , error in a phase of receiving the mini slot signal (CPE-Di) I 53 , error in a block of the mini slot signal (ERR-Di) I 54  are provided besides the maintenance signal of the regular cell.  
         [0045]    [0045]FIG. 2 shows a state transition table for corresponding the maintenance signals for the mini slot signal described in FIG. 1 to a state of controlling the ONU individually by the OLT. An operation of this invention is explained by FIG. 1 and FIG. 2. As illustrated in FIG. 2, an individual ONU dealing unit  106  and a DBA controller  109 , which are provided additionally, manage and control by performing the dynamic bandwidth assignment (DBA) for upstream corresponding to each of the ONU&#39;s individually. In this embodiment, the individual ONU dealing unit  106  and the DBA controller  109  provide three states, i.e., halt state of DBA (DBA-ST 1 ) S 1 , wait state of DBA operation (DBA-ST 2 ) S 2  and DBA operation state (DBA-ST 3 ) S 3  arranged horizontally in FIG. 2 as states of controlling the DBA by using the mini slot signal. Further, as state transition events for changing the states, the state transition events are regulated sequentially from the top to the bottom in FIG. 2. Event I 1  of detecting the instruction for halting the DBA function for instructing if a function of the DBA is operated, and event I 2  of detecting a state in which the OLT controls the ONU individually and one of maintenance signals IDV 1 , IDV 2 , LOSi, LCDi, CPEi, OAMLI, LOAi, and R-INHi are provided. Further, event I 3  of detecting IDV 3  without detecting the instruction of halting the DBA function, and event I 4  of recognizing an ONT-DBA type are provided. Finally, an event I 5  of detecting CPE-Di which is a maintenance signal of the mini slot signal is provided. A number of a child station of 1−n is shown as i.  
         [0046]    The maintenance signal for the mini slot signal described in FIG. 1 is explained.  
         [0047]    When an O/E receiver for dealing ONUi in the OLT does not receive an effective optical signal in an expected period for receiving an upstream mini slot signal n times consecutively, it is judged that interruption of receiving a mini slot signal (LOS-Di) is detected. When the OLT receives an optical signal matched with its slot GRANT in the DBA operation state (DBA-ST 3 ), it is judged that the interruption of receiving the mini slot signal (LOS-Di) is reset.  
         [0048]    When the receiver for dealing ONUi in the OLT receives an ineffective delimiter n times consecutively, it is judged that out-of-synchronization of the mini slot signal (LCD-Di) is detected. When a mini slot signal in a correct phase is received in the DBA operation state (DBA-ST 3 ), it is judged that the out-of-synchronization of the mini slot signal (LCD-Di) is reset.  
         [0049]    When a phase of a received mini slot signal exceeds a limit causing the OLT uncontrollable in a period when the OLT can receive a correct delimiter, it is judged that error in a phase of receiving the mini slot signal (CPE-Di) is detected. When a mini slot signal in a correct phase is received, it is judged that the error in the phase of receiving the mini slot signal (CPE-Di) is reset.  
         [0050]    When a result of CRC (cyclic redundancy check) attached to the mini slot signal and a result of CRC by the OLT are not matched, it is judged that error in a block of the mini slot signal (ERR-Di) is detected. When a next mini slot signal is received, it is judged that error in the block of the mini slot signal (ERR-Di) is reset.  
         [0051]    In the PON system using the maintenance signal corresponding to the mini slot signal as explained with reference to FIG. 1, the individual ONU dealing unit  106  in the OLT relates a state of controlling the ONU individually with a maintenance signal for the mini slot signal. Further, the DBA controller  109  controls dynamic bandwidth assignment (DBA) for upstream corresponding to each of ONU&#39;s individually. The OLT performs the dynamic bandwidth assignment (DBA) for upstream based on the state transition table illustrated in FIG. 2.  
         [0052]    With reference to FIG. 2, controlling state transition of the mini slot signal for performing the dynamic bandwidth assignment (DBA) for upstream is explained. How the individual ONU dealing unit  106  in the OLT relates a state of controlling the ONU individually with the maintenance signal for the mini slot signal is explained.  
         [0053]    After the individual ONU dealing unit  106  in the halt state of DBA (DBA-ST 1 ), i.e., a state before detecting an instruction of stopping DBA function, detects that a state of the individual ONU dealing unit (n) in the OLT is IDV 3  (operation state), the individual ONU dealing unit  106  instructs the ONU to be in the state transits to the wait state of DBA operation (DBA-ST 2 ). Then, when a certain maintenance signal (LOSi, LCDi, CPEi, OAMLi, LOAi, R-INHi) for the regular cell is detected or IDV 1  (initial state) or IDV 2  (state of measuring delay) is detected as a state of the individual ONU dealing unit in the OLT, it is judged that the concerning ONU is not in the operation state. Then, the slot GRANT is reset, and the state transits to the halt state of DBA (DBA-ST 1 ) again.  
         [0054]    Further, when the individual ONU dealing unit in the wait state of DBA operation (DBA-ST 2 ) recognizes an ONT-DBA type by ITU-TG.983.2, the slot GRANT is set, and the state transits to the DBA operation state (DBA-ST 3 ). When a certain maintenance signal (LOSi, LCDi, CPEi, OAMLi, LOAi, R-INHi) is detected, or the state of the individual ONU dealing unit (n) in the OLT is either IDV 1  or IDV 2 , the individual ONU dealing unit (n) in the OLT which is the DBA operation state (DBA-ST 3 ) judges that the concerning ONU is not in the operation state. Then, setting of the slot GRANT is reset, and the state transits to the halt state of DBA (DBA-ST 1 ). Further, when error in the phase of receiving the mini slot signal (CPE-Di (n)) which is a maintenance signal concerning on the mini slot signal is detected, setting of the slot GRANT is reset, and the state transits to the wait state of DBA operation (DBA-ST 2 ).  
         [0055]    Further, when the DBA controller  109  which controls the dynamic bandwidth assignment (DBA) function individually detects the instruction of halting DBA function for a purpose of halting the dynamic bandwidth assignment (DBA) function, the state transits to the halt state of DBA (DBA-ST 1 ).  
         [0056]    In this embodiment, only the error in the phase of receiving the mini slot signal (CPE-Di) is set as an event. However, in addition to the error in the phase of receiving the mini slot signal (CPE-Di), it is possible to set events of out-of-synchronization of the mini slot signal (LCD-Di) and interruption of receiving the mini slot signal (LOS-Di) as OR condition.  
         [0057]    In this embodiment, when a state as illustrated in FIG. 9 occurs, since phases of mini slot signal  1  and mini slot signal  2  are not correct, CPE-Di is detected. Therefore, this child station is controlled to become the state of DBA-ST 2 . Further, an instruction on the phase is sent to this child station in a downstream frame. The child station corrects the phase based on the instruction. As stated, an influence on another child station is temporary.  
         [0058]    According to this invention, it is possible to monitor the mini slot signal in each of the ONU&#39;s individually besides the regular cell by providing a maintenance signal for the mini slot signal besides the regular cell when the OLT receives the mini slot signal. Further, by providing the state transition table corresponding to the dynamic bandwidth assignment (DBA) for upstream by using the mini slot signal, when a failure, e.g., the error in the phase of sending the mini slot signal, etc. occurs in an ONU, only the mini slot signal in failure can be separated from the regular cell and other mini slot signals of which communication is interfered with. Accordingly, it is possible to reduce an interference with the communication of other ONU&#39;s by the mini slot signal in failure.  
         [0059]    Having thus described several particular embodiments of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is limited only as defined in the following claims and the equivalents thereto.