JP5546663B2 - Slave station device, master station device, communication line switching method, communication system and control device - Google Patents

Description

  The present invention relates to a communication system and a communication method connected by redundant notification lines, and includes, for example, an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Unit: user-side terminator). The present invention relates to a configured communication system and the like.

  A communication system is considered in which communication terminals are redundantly connected with a plurality of lines to improve robustness against communication failures. In such a communication system, when a communication failure is detected on a line being used by the communication device, the use of the line on which the failure has occurred is stopped, a link on another communication line is established, and communication is resumed.

Japanese Patent Laid-Open No. 2001-119345 discloses an optical communication system in which an OLT and a star coupler are connected by two redundant optical fibers (Patent Document 1).
International Publication WO2008 / 126162 discloses a protection system that switches a used line from an active optical fiber to a standby optical fiber when the OLT does not receive an upstream signal from the ONU for a certain period of time (Patent Document 2).

  The IEEE (The Institute of Electrical and Electronic Engineers) 802.3av standard defines a communication protocol using an optical line. In the PON system, since a plurality of ONUs communicate with the OLT by time division multiple access using a common line, it is necessary to transmit data at a timing when each ONU is correctly assigned. Therefore, the OLT controls synchronization between a plurality of ONUs using a downlink control message. The OLT inserts a time stamp based on its own clock reference into the downlink control message and notifies each ONU of the reference time. The ONU extracts a time stamp from the received downlink control message, and updates a local timer serving as a transmission / reception timing reference as a PON (Passive Optical Network) counter value.

  Since the OLT frequently transmits a downlink control message including this time stamp, the ONU can check the difference between the time stamp included in the received signal and its own PON counter, and can always monitor the synchronization error and line abnormality. . If the time stamp and the PON counter are more than the threshold, the ONU must detect a time stamp drift error, disconnect the logical link, and return to the initial state. The ONU that has returned to the initial state is able to resume communication by newly setting a logical link by the discovery processing by the OLT and resetting necessary synchronization and control information.

JP 2001-119345 A (FIG. 1) International Publication No. 2008/126162 (Figure 1)

  In a conventional communication system, when a communication failure occurs on the active line, the slave station (ONU) detects the failure and tries to re-establish the communication link, so the communication using the standby line is resumed. There was a problem that it took time.

A slave station device according to the present invention is a slave station device that is connected to a master station device and a splitter that splits an optical signal by a plurality of redundant physical lines and communicates with the master station device via the splitter. A transmission / reception device that transmits / receives a transmission signal using a logical link, and a transmission / reception message instructing a transition to a holdover state in a registration state registered in the parent station device as a communicable slave station device. And a control unit that receives a downlink signal, suppresses transmission of the uplink signal, and shifts to a holdover state that maintains communication link setting information .

The communication line switching method of the present invention is a communication line switching method of an optical communication system in which a master station device and a slave station device are connected via a plurality of redundant physical lines, wherein the master station device A discovery step for registering the slave station device as a communicable slave station device, and when the master station device performs protection switching for switching a transceiver used for communication from a current transceiver to a spare transceiver After transmitting a downlink message to the registered slave station device that receives the downlink signal and suppresses the transmission of the uplink signal and instructs the transition to the holdover state for maintaining the communication link setting information , A switching step of switching from the physical line of the active system to the physical line of the standby system, and when the registered slave station device receives the transition message, The during the period is obtained and a holdover step shifts to holdover state to maintain the configuration information of suppressing vital communication links to transmit the uplink signal performs reception of the downlink signal.

The control device of the slave station device of the present invention is a slave device in which the master station device and the splitter that branches the optical signal are connected by a plurality of redundant physical lines and communicates with the master station device via the splitter. When a transition message instructing transition to a holdover state is received in a registration state registered in the parent station device as a slave station device with which the base station can communicate, the control device of the station device is predetermined. During this period, the downlink signal is received, the transmission of the uplink signal is suppressed , and the state shifts to the holdover state in which the communication link setting information is maintained .

  A control device for a master station device according to the present invention communicates with a plurality of slave station devices via a plurality of redundant physical lines and a splitter for branching signals of these physical lines into a plurality of signal lines. Holdover state for receiving a downlink signal and suppressing the transmission of an uplink signal when performing protection switching for switching a transceiver used for communication from an active transceiver to a spare transceiver The protection switching is performed after transmitting a migration message instructing the migration to the plurality of slave station devices.

  The slave station device, the master station device, the communication line switching method, the communication system, and the control device according to the present invention can start communication resumption after line switching at an early stage.

FIG. 1 is a configuration diagram showing a configuration of a communication system in an embodiment of the present invention. FIG. 2 is a state transition diagram showing the state transition of the communication terminal in the embodiment of the present invention. FIG. 3 is a sequence diagram showing a communication line switching process. FIG. 4 is a sequence diagram showing a communication line switching method according to Embodiment 1 of the present invention. FIG. 5 is a configuration diagram showing an example of a communication system in the embodiment of the present invention. FIG. 6 is a configuration diagram illustrating an example of a control device according to the embodiment of the present invention. FIG. 7 is a flowchart showing the processing of the control device for the communication terminal in the embodiment of the present invention. FIG. 8 is a sequence diagram showing a communication line switching method according to Embodiment 2 of the present invention. FIG. 9 is a flowchart showing processing of the communication terminal control apparatus according to Embodiment 2 of the present invention. FIG. 10 is a sequence diagram showing a communication line switching method according to Embodiment 3 of the present invention. FIG. 11 is a flowchart showing processing of the communication terminal control apparatus according to Embodiment 3 of the present invention. FIG. 12 is a flowchart showing processing of the control device on the station side according to Embodiment 3 of the present invention. FIG. 13 is a configuration diagram showing the configuration of the communication system in the embodiment of the present invention.

Embodiment 1 FIG.
FIG. 1 shows communication devices 10-1 to 10-3 that are a plurality of slave stations in communication device 1 that is a master station (hereinafter referred to as a slave station or a slave station device 10 when one slave station device is not specified). 1 shows a communication system in which The communication device 1 sets a communication line with each slave station device 10 and controls communication with a plurality of slave station devices 10. The communication device 1 and the slave station device 10 are connected by redundant communication lines (lines) 30-1 and 30-2. In the communication system of FIG. 1, the communication device 1 to the splitter 40 are made redundant. Has been. Such a redundant system is called a TYPE-B protection system in a PON (Passive Optical Network) system. The splitter 40 branches the signals of the lines 30-1 and 30-2 and transmits them to the respective lines (subscriber lines) 31, and also transmits the signals of the respective lines 31 to the lines 30-1 and 30-2. The communication device 1 of the master station includes transmitters / receivers 5-1 and 5-2 for each of the lines 30-1 and 30-2, and the lines 30-1 and 2-2 are controlled by the control devices 2-1 and 2-2. Transmit and receive signals using 30-2. The communication lines 30-1 and 30-2 are physical lines such as optical fibers having different physical paths, and this physical line can accommodate a plurality of logical logical links.

  The switch 8 is a device that switches the connection between the control devices 2-1 and 2-2 and an external device or a network in accordance with a switch signal from the control devices 2-1 and 2-2. Note that when the communication device 1 does not relay a signal to an external device and communication is completed by the communication device 1, the switch 8 is not necessary.

  Next, the operation of this communication system will be described. The communication device 1 designates one (part) of the redundant lines 30-1 and 30-2, for example, the line 30-1, as a working communication line, and performs communication with the communication apparatus 10. . The remaining communication lines are set as standby communication lines, for example, the line 30-2, in a standby state or a dormant state in preparation for the occurrence of a failure. The communication device 1 monitors the failure of the line 30 from the state of the received signal, and switches the line used for transmission / reception from the active communication line 30-1 to the standby communication line 30-2 when a failure occurs. . After switching, the line 30-2 is used as a new working communication line.

  FIG. 2 shows the state transition of the slave station device 10. The state transition shown on the left is a state transition when switching of the communication line 30 is not considered, and the state transition shown on the right is initialized so that communication can be resumed quickly when the communication line 30 is switched. Is a state transition provided with a grace state (holdover state).

  Based on the state transition shown on the left side of FIG. 2, the initial setting of the communication device 10 and the return from the line abnormality will be described. When the unconnected communication device 10 is newly connected to the line 31, or when the communication device 10 that has been turned off is turned on, the communication device 10 communicates with the communication device 1 on the master station side. For this reason, communication is not possible (state St1). This state is referred to as an unregistered state. The unregistered communication device 10 only receives data until it is registered in the communication device 1 and is in a standby state until communication is permitted from the communication device 1 on the master station side.

  When receiving a control message (discovery gate) for accepting new registration from the master station, the communication device 10 shifts to a state St2 (discovery state) for initial setting. In this state, the communication device 10 transmits its own identification information, if necessary, capability information to the parent station and is registered as a communication partner in the parent station based on this information. When the master station registers the communication device 10, the master station transmits a control message notifying the registration to the communication device 10. This control message includes communication link setting information, and the communication device 10 that has received this control message stores the setting information and enters the communicable state St3 by performing necessary communication settings in its own device. This state is called a registered state. The communication device 10 that has shifted to the registered state subsequently transmits / receives data to / from the master station using the setting information.

  The registered communication device 10 constantly / intermittently monitors the state of the received signal. For example, if the signal is not received for a predetermined period, it is determined that a line abnormality has occurred, and alarm information is displayed. Generate. The communication device 10 that has detected the line abnormality discards the setting information, disconnects the communication link, returns to unregistered St1, and waits again until the communication link is set from the master station.

  When the communication device 10 that executes this process is connected to a protection system in which the communication line 30 is made redundant as shown in FIG. 1, communication is performed as shown in the sequence diagram of FIG. It takes longer to recover. When the master station transceiver 5-1 operates as the active system and the transceiver 5-2 is in the standby state as the standby system, the communication status of the active system becomes unstable, and the downlink signal reaches the communication device 10 normally. Suppose you didn't. At this time, the master station switches the communication line used for communication (protection switching), and starts communication using the standby communication path 30-2 as a new active communication line. On the other hand, the communication device 10 on the slave station side disconnects the communication link and returns to the unregistered state even when the protection switching is performed at the master station when there is a line abnormality such as the downlink signal does not reach. . Then, the communication device 10 returns to the registered state after restarting the link by the initial process (discovery process), and resumes communication. As a result, the time during which communication is interrupted becomes longer.

  Therefore, as shown in the state transition shown on the right side of FIG. 2, when a line abnormality occurs, a suspend state St4 (holdover state) for suspending the initial setting is provided so that the communication interruption time at the protection switching time Can be shortened. When the communication device 10 in the registered state St3 detects a line error, the communication device 10 does not directly move to the unregistered state St1, and maintains the setting information without disconnecting the communication link during the grace period. Reception continues until a normal signal arrives. If the communication line is switched normally within the grace period (holdover period), the communication device 10 returns to the registered state St3 without disconnecting the communication link, so the unregistered state St1, the initial setting state St2 (discovery state) Communication interruption time can be shortened compared with the case where communication is resumed via.

  With reference to FIG. 4, the communication sequence when the postponement state St4 is used will be described. By using the communication sequence of FIG. 4, it can be seen that when communication path switching occurs, the registered state can be restored to an early stage without going through the non-registered state and the initial state as compared with the communication sequence of FIG. 3.

  The master transmitter / receiver 5-1 that is the active transmitter / receiver specifies the transmission band that each communication device 10 can use for uplink communication by using band allocation information, and repeatedly notifies it regularly or irregularly using control messages. (P1, P11, P15). The communication device 10 performs uplink transmission using the notified transmission band. When this control message is received, the communication device 10 checks this to detect whether there is an abnormality in downlink communication (P2). There are two types of error detection: (a) detection to check whether abnormal data is included in the received signal, and (b) detection to check for an error when judging that communication has been interrupted when a downlink signal has not been received for a predetermined period of time. is there.

An example of detection (a) is detection of synchronization loss (time stamp drift error). The master station transmits time information (time stamp) serving as a reference for transmission timing to each communication device 10 and performs control to synchronize the reference time of each communication device 10. Each communication device 10 adjusts the time of its own device to the received time information, but the difference between the received time information and the time (local time) information measured by its own device exceeds a predetermined threshold Then, it is determined that an abnormality has occurred in the downstream signal, and a synchronization error is detected.
An example of detection (b) is LOS (Loss of Signal) detection. When the communication device 10 does not receive a downlink signal for a predetermined period TLoS, it detects LOS. The communication device 10 has a timer or a counter, resets this timer each time a message is received, and detects a LOS when a value of the timer or the like elapses for a predetermined time TLoS.

  Here, when the downlink signal from the transmitter / receiver 5-1 of the master station does not normally reach the communication device 10 (P3) and the communication device 10 detects a line abnormality (P4), the communication device 10 Suppress the output of time stamp drift error (P5). That is, control is performed so as not to detect a synchronization error or not to shift to the unregistered state St1 even if it is detected. At this time, the communication device 10 shifts to the grace state and starts measuring the grace period using a timer or a counter in order to measure the grace period. While the slave station in the suspended state continues to receive the downlink signal, it stops the transmission of the uplink signal in order to avoid signal loss at the time of line switching and duplication of transmission with other slave stations. Further, by stopping the transmission of the uplink signal, the slave station can notify the master station that an abnormality has occurred and can prompt line switching.

  This implicit notification of the slave station is effective as an abnormality notification when there is a possibility of a line failure. This is because when the line 30 is disconnected, an explicit abnormality notification by transmitting an abnormality signal can be notified only to the standby communication apparatus.

  Also, the output suppression of the synchronization error by the slave station in the suspended state brings about the effect of early communication restart. As will be described later, since the communication distance may change when the communication line is switched, an error in synchronization is likely to occur. Further, when the time information does not match between the plurality of control devices 2-1 and 2-2 on the master station side, this mismatch causes a synchronization error on the slave station side. When a synchronization loss error occurs, the slave station reestablishes the communication link and returns to the unregistered state St1, so that the communication interruption period after switching the communication line becomes long. Suppression of synchronization loss errors suppresses such a prolonged interruption period and realizes early communication restart.

  On the other hand, the master station observes the state of the communication line 30-1 such that the signal from the slave station does not reach normally, and detects a line abnormality (P6). The control device 2-1 of the master station that has detected the abnormality performs a communication line switching process (P7). The control device 2-1 transmits a line switching signal to the standby control device 2-2 and the switch 8, and further passes the setting information of each slave station to the standby control device 2-2. Then, the control device 2-1 stops transmission using the line 30-1, and thereafter operates as a standby system. The standby control device 2-2 that has received the line switching signal starts operation as the active system. First, in order to synchronize each slave station, a synchronization signal having time information (time stamp) is transmitted to each slave station in the suspended state. This synchronization signal may be a unicast message or a multicast message.

  Upon receiving the synchronization signal, the slave station synchronizes its own timer or counter with the time information included in the synchronization signal (P9), and shifts from the postponement state St4 to the registration state St3. At this time, the output suppression of the synchronization error (timestamp drift error) is canceled, and normal error detection is resumed (P10). Grace period measurement is suspended upon termination of the grace state.

  The master station transmits a control message (GATE) including band allocation information to each slave station (P11). The slave station receives this message, performs error checking including a synchronization error, and transmits a message (REPORT) including band request information using the allocated band (P13), as described above (P2).

  Next, when the master station receives the bandwidth request, it updates the RTT (Round Trip Time) for each slave station (P14, P18). The RTT can be measured by the transmission time of the bandwidth allocation control message (P11) and the reception time of the response message (band request: P13) to this message. Since the communication distance between each slave station and the master station is not necessarily the same, the transmission time of the uplink signal reaching the master station is different. Therefore, the master station determines the bandwidth to be assigned to each slave station in consideration of the RTT and the bandwidth request so that the signals transmitted from each slave station do not overlap when received by the master station, The allocation information is transmitted (P15). The slave station makes a new bandwidth request and data transmission based on the allocated bandwidth (P17, 19).

  In addition, after detecting a line abnormality (P4), if the slave station in the grace state St4 does not normally receive the downlink signal after switching the line during the grace period, that is, the grace period is set by the timer or counter that measures the grace period. When the elapse of the period is detected, the slave station ends the grace state St4 and shifts to the non-registration state St1 in order to reset the communication link. When the communication link is reset, the setting information before line switching is discarded and rewritten with new setting information.

  As described above, according to the communication system of this embodiment, it is possible to maintain a communication link by providing a grace state at the time of line switching, so that communication after line switching can be resumed early. In addition, since the slave station suppresses the synchronization error during the grace period, the slave station is less likely to return to the unregistered state after the line is switched, and early restart of communication can be effectively realized.

・ Example of application to IEEE802.3 communication system

  Next, an example in which the first embodiment is applied to an optical communication system using the IEEE 802.3 communication protocol will be described. FIG. 5 is a diagram showing a PON system of this application example. 5, the same reference numerals as those in FIG. 1 represent the same or corresponding configurations. The master station is composed of a working wOLT (Working Optical Line Terminal) and a standby bOLT (Backup Optical Line Terminal). Each wOLT1-1 and bOLT1-2 (hereinafter referred to as OLT1 when not distinguished from each other) and the ONUs 10-1 to 10-3 are connected to each other by subscriber lines 30-1 and 30-2 via a splitter 40. The splitter 40 is a passive element that branches the subscriber lines (communication lines) 30-1 and 30-2 connected to the OLT 1 into the number of ONUs 10-1 to 10-3. The ONU 10-1 which is a communication device of the slave station is connected to the terminals 20-1 and 20-2. Although an example in which three ONUs are used is shown here, the number of ONUs is not limited to this, and any number may be used.

  Each OLT 1 receives PON control units 2-1 and 2-2 (hereinafter referred to as PON control unit 2) that perform processing on the OLT side based on the PON protocol, and uplink data received from the ONUs 10-1 to 10-3. A reception buffer 3 that is a buffer for storing, a transmission buffer 4 that is a buffer for storing downlink data to be transmitted to the ONUs 10-1 to 10-3, and an optical transceiver 5-1 that performs transmission / reception processing of optical signals 5-2, WDM (Wavelength Division Multiplexing) coupler (WDM) 6 that wavelength-multiplexes upstream data and downstream data, and a physical layer processing unit that realizes a physical interface function of NNI (Network Node Interface) (PHY) 7. Each of the optical transceivers 5-1 and 5-2 includes an optical receiver (Rx: Receiver) 51 that performs reception processing, and an optical transmitter (Tx: Transmitter) 52 that performs transmission processing.

  The ONU 10-1 includes a PON control unit 11 that performs processing on the ONU side based on the PON protocol, a transmission buffer (upstream buffer) 12 that is a buffer for storing transmission data (upstream data) to the OLT 1, and an OLT 1 Receive buffer (downlink buffer) 13 which is a buffer for storing received data (downlink data) from the optical receiver 14, an optical transceiver 14, a WDM 15 for wavelength multiplexing uplink and downlink data, and terminals 20-1, 20- 2, physical layer processing units (PHYs) 16-1 and 16-2 for realizing a physical interface function of UNI (User Network Interface).

  The optical transceiver 14 includes an optical transmitter (Tx: Transmitter) 141 that performs transmission processing and an optical receiver (Rx: Receiver) 142 that performs reception processing. The PHY 16-1 includes a reception unit (Rx: Receiver) 161-1 that performs reception processing and a transmission unit (Tx: Transmitter) 162-1 that performs transmission processing. The PHY 16-2 performs reception processing. It has a receiving unit (Rx: Receiver) 161-2 and a transmitting unit (Tx: Transmitter) 162-2 that performs transmission processing.

  Although two terminals are connected to the ONU 10-1, the number of terminals is not limited to this, and any number of terminals may be provided, and a physical layer processing unit (PHY) corresponding to the number of terminals is provided. In addition, FIG. 5 shows the configuration example of the ONU 10-1 as a representative, but the ONUs 10-2 and 10-3 have the same configuration as the ONU 10-1.

  As specified in IEEE 802.3, the PON control unit 2 of the OLT 1 performs upstream data bandwidth allocation so that transmission time zones do not overlap with the ONUs 10-1 to 10-3, and the ONUs 10-1 to 10-10 -3 transmission data collision is prevented. Any method may be used for this bandwidth allocation. For example, “Su-il Choi and Jae-doo”, “HuhDynamic Bandwidth Allocation Algorithm for Multimedia Services over Ethernet (registered trademark) PONs”, ETRI Journal, Volume 24, Number 6, December 2002, p. 465 to p. 466 ”can be used.

  Next, the overall operation of the OLT 1 and the ONUs 10-1 to 10-3 will be described. The PON control units 2-1 and 2-2 (hereinafter referred to as the PON control unit 2 when the PON control units 2-1 and 2-2 are not distinguished from each other) receive the downlink data (downlink communication data) received from the network via the PHY 7. Store in transmit buffer 4. When transmitting data from each OLT 1, the PON control unit 2 reads the downlink data stored in the transmission buffer 4 and outputs it to the optical transceiver 5, and the Tx 52 of the optical transceiver 5 transmits the transmission data to the optical signal. Output to the WDM 6, the WDM 6 performs wavelength multiplexing on the optical signal output from the optical transceiver 5, and outputs as a downstream signal to the ONUs 10-1 to 10-3 via the subscriber lines 30-1 and 30-2 To do. When the PON control unit 2 transmits a control message such as transmission band allocation for transmitting a transmission permission instruction, the PON control unit 2 outputs the control message generated by the PON control unit 2 to the optical transmitter / receiver 5. Like the data, it is transmitted to the ONUs 10-1 to 10-3. In the PON system of FIG. 1, the WDMs 6 and 15 are used for wavelength multiplexing, but the WDMs 6 and 15 are not essential when communicating at a single wavelength.

  In ONUs 10-1 to 10-3, when a downstream signal is received from wOLT, WDM 15 separates the downstream signal and outputs it to optical transceiver 14, and Rx142 of optical transceiver 14 converts the downstream signal into downstream data of an electrical signal. And output to the PON control unit 11. The PON control unit 11 stores the downlink data output from the Rx 142 of the optical transceiver 14 in the reception buffer 13. The PON control unit 11 reads the downlink data stored in the reception buffer 13 and outputs it to both or one of the PHYs 16-1 and 16-2 according to the destination of the data. The PHYs 16-1 and 16-2 that have received the downlink data perform predetermined processing on the downlink data and transmit the downlink data to the terminals 20-1 and 20-2 to which they are connected.

  On the other hand, when transmitting upstream data from the ONUs 10-1 to 10-3, the PON control unit 11 transmits upstream data acquired from the terminals 20-1 and 20-2 via the PHYs 16-1 and 16-2. Store in 12. Then, the uplink data stored in the transmission buffer is read out based on the transmission band given from wOLT and output to the optical transceiver 14. The Tx 141 of the optical transceiver 14 converts the upstream data into an optical signal (upstream signal) and transmits it to the OLT 1 via the WDM 15 and the subscriber line 30.

  The PON control unit 2 of the wOLT stores the uplink data received from the ONUs 10-1 to 10-3 via the subscriber line 30, the WDM 6, and the Rx 51 of the optical transceiver 5 in the reception buffer 3. The PON control unit 2 reads the uplink data stored in the reception buffer 3 and outputs it to the network via the PHY 7.

  The ONUs 10-1 to 10-3 receive the control message transmitted from the wOLT by the PON control unit 11 via the WDM 15 and the Rx 142 of the optical transceiver 14, and execute and control the operation based on the instruction of the control message. Generate a response to the message.

  The operation of the communication system shown in FIG. 5 is as described above with reference to FIGS. In IEEE803.2 (IEEE803.2-2008, IEEE803.2av), the state St2 in which the initial setting in FIG. 2 is performed is a discovery state, and in this state, a discovery process is performed using discovery GATE or the like.

  In FIG. 4, GATE is used as the control message for bandwidth allocation, and REPORT is used as the bandwidth request message. In the error check, Optical LoS and / or MAC LoS are detected as LOS. Optical LoS is an error detected when the transmitter / receiver does not receive the optical signal TLoS_optical for a certain period. The default for TLoS_optical is 2 ms, but TLOS_optical can be changed to a different value by using a control message between OLT 1 and ONU 10. MAC (Media Access Control) LOS is an error detected when the transceiver does not receive TLoS_MAC and GATE for a predetermined period, and the default value of TLoS_MAC is set to 50 ms. Similarly to TLoS_optical, the value of TLoS_MAC can be changed by a control message.

  Both Optical LoS and MAC LoS are alarms indicating an optical line abnormality, and are monitored and detected not only in the ONU 10 but also in the OLT 1 using an alarm timer. In addition, this communication system detects a time stamp drift error as a synchronization error. This error is detected in each of the OLT 1 and the ONU 10 and is detected when the difference between the OLT 1 clock and the ONU 10 clock exceeds a predetermined threshold (guardThresholdONU, guardThresholdOLT). The detection with OLT1 also takes into account RTT. The clock to be compared is acquired from a time stamp included in a received MPCPDU (Multi-Point Control Protocol Data Unit) signal.

  FIG. 6 is a diagram showing an example of the PON control unit 11 of the ONU. The controller 11a reads an instruction of the program stored in the memory 11f, inputs / outputs a signal according to the instruction, and controls each component. The timer 11b measures the local time while following the time stamp included in the received signal, and supplies time information for determining the transmission / reception timing to the controller 11a. The synchronization error alarm unit (first alarm means) 11c compares the local time with the time stamp of the received signal, monitors the presence or absence of a synchronization error, and notifies the controller 11a of the alarm.

  The timer 11e is a timer that measures the reception interval of the received signal, and measures reception time information of each signal in order to detect, for example, Optical LoS and MAC LoS. The line abnormality alarm unit (second alarm means) 11d monitors the line abnormality based on the reception time information of the timer 11e, and outputs an alarm to the controller 11a when an abnormality is detected. The optical LoS may be detected by the optical transceiver 14 and an alarm signal may be notified from the optical transceiver 14 when an abnormality occurs. Also, the functions of the synchronization loss alarm unit 11c and the line abnormality alarm unit 11d can be incorporated in the controller 11a.

  Next, the operation of the PON control unit 11 will be described as an example of the control device with reference to FIG. The PON control unit 11 is a control device incorporated in the PON interface, and is a processor formed as an IC chip (the same applies to the PON control unit 2). The processing described in FIG. 7 is stored in a memory that is internally or externally connected to the processor as a computer-executable program.

  The PON control unit 11 of the unregistered ONU 10 first performs a discovery process (step S1). The PON control unit 11 refrains from transmission until the transmission permission is given by the discovery GATE transmitted from the OLT 1 and continues the reception process. When receiving the discovery GATE, the PON control unit 11 shifts to a discovery state, and establishes a logical link with the OLT 1 by transmitting and receiving a control message. When the setting information is obtained from the OLT 1 by the discovery process, the PON control unit 11 stores this information, and thereafter, the logical link transmission / reception process based on the setting information becomes possible, and the state shifts to the registration state.

  The PON control unit 11 that has shifted to the registration state performs a reception process of receiving a control message from the OLT 1 and other downlink data based on the setting information (step S2). Next, the PON control unit 11 performs LOS detection using an alarm timer and checks whether there is an abnormality in the optical line (for example, whether a line disconnection or the like has occurred) (steps S3 and S4). If there is an abnormality, the state shifts to a holdover state (step S11).

If there is no abnormality, the PON control unit 11 extracts a time stamp included in the received signal, and calculates whether a time stamp drift error has occurred by calculating a difference from the time information indicated by the clock of the own device. Inspect (steps S5 and S6). If an error has occurred, the PON control unit 11 shifts to a non-registered state in order to reset the line (step S17). If there is no error, the PON control unit 11 synchronizes its own clock with the extracted time stamp (step S7), and transmits the uplink data using the band allocated from the OLT 1 by the GATE. The GATE describes the start time and the length of transmission permission as band allocation information as defined in the GATE description of IEEE802.3. Furthermore, the GATE has a plurality of band allocation information and one ONU 10 It is possible to assign a plurality of transmission bands to. Data transmission from the ONU 10 is performed according to these band allocation information and setting information.
And when continuing communication, it returns to step S2 and continues communication in a registration state (step S10).

The setting information includes, for example, the following logical link information.
(1) LLID (Logical Link Identification) or Assigned Port
The LLID or Assigned Port is an identifier assigned to identify a plurality of logical links from each other, and is added to a frame (data) transmitted using the logical link.
(2) Sync Time
Sync Time indicates the time required for the receiver to synchronize signals when the OLT transceivers 5-1 and 5-2 perform reception.
(3) Target Laser On Time
(4) Target Laser Off Time
Target Laser On Time and Target Laser Off Time are the time required for the ONU10 transmitter laser to turn on or off, and the OLT takes into account the transmitter characteristics reported by the ONU10 in the discovery process. It is the specified value.

  When the LOS is detected in step S4, the PON control unit 11 shifts to the holdover state, and starts to suppress the output of the synchronization error alarm (time drift error) and the LOS detection by the alarm timer. At the same time, the PON control unit 11 starts measuring a holdover period that is a grace period (step S11). It should be noted that the suppression of time drift error output can also be realized simply by not performing the synchronization deviation inspection process that should be originally performed as in step S5 after the reception process. Further, the PON control unit 11 does not discard the stored setting information during the holdover period, and delays the disconnection of the logical link.

  Next, the PON control unit 11 performs reception processing (step S12). The information received here is a GATE including a time stamp. Note that, since data transmission is not performed in the holdover state, the PON control unit 11 does not return REPORT to GATE. Since this GATE is transmitted for the purpose of synchronizing the clock of the ONU 10, a control message other than GATE can be substituted if it includes a time stamp.

  The PON control unit 11 synchronizes the clock with the time stamp extracted from the GATE (step S13), and determines whether or not the line used is switched from the active system to the standby system (step S15). Here, the PON control unit 11 considers that the switching has been completed when a valid GATE is received from the OLT 1, cancels the output suppression of the synchronization error alarm (time drift error) (step S18), and sets the setting information. It shifts to the registration state while maintaining (step S2). At this time, the PON control unit 11 also stops measuring the elapsed time of the holdover period. In addition, the PON control unit 11 resets the alarm timer when the holdover state ends, and resets the time so that an unnecessary LOS alarm is not generated immediately after returning to the registered state.

  The PON control unit 11 that has returned to the registered state performs communication using the logical link using the setting information carried over from the state before switching. For example, when receiving, the PON control unit 11 extracts Assigned Port (LLID) information of the received message, compares this information with the setting information, and identifies the logical link addressed to the own device. Further, the PON control unit 11 can insert the carried-over Assigned Port information into the transmission message and use the logical link without resetting the logical link.

  Also, Sync Time and Target Laser On / Off Time are used to determine a band in which data can actually be transmitted among the allocated bands received from OLT 1. That is, the PON control unit 11 transmits actual data using a band obtained by subtracting Sync Time and Target Laser On / Off Time from the allocated band. It takes a short time until the light is completely extinguished after the laser is turned off. If the transmitter of the ONU 10 continues to output residual light beyond the Target Laser Off Time, the transmission signal of other ONUs 10 will be disturbed. Therefore, the OLT checks the characteristics of each ONU 10 in the discovery process, and notifies the ONU 10 of setting information related to the laser so that stable communication can be maintained without affecting other ONUs 10. The PON control unit 11 that has succeeded in preventing the discard of the setting information due to the holdover state determines the transmission band using the maintained Target Laser On / Off Time and transmits data.

  Also, if the Sync Time is not appropriate, there is a problem with bit synchronization when OLT1 is received, and data cannot be reproduced normally. Therefore, the PON control unit 11 of the ONU secures a signal necessary for synchronization in consideration of the Sync Time and transmits it. Output a signal.

  Such discovery processing including setting information negotiation takes time because messages are exchanged many times between the ONU 10 and the OLT 1. In this application example, the PON control unit 11 can adjust the synchronization problem after the physical line switching according to the holdover state, and can omit the resetting of the setting information.

  On the other hand, if the switching has not been completed, the PON control unit 11 checks whether the holdover period has expired, and if it has not expired, returns to step S12 and continues the reception process. In steps S12 and S13, when there is no received data, the above-described processing is not executed, and the PON control unit 11 proceeds to the next step S15 to receive a signal or the holdover period expires. Repeat the same process.

  When the holdover period has expired, the PON control unit 11 determines that the switching has not been performed normally or a failure due to another cause, and shifts to a non-registered state (step S17). When transitioning to the unregistered state, the logical link is disconnected and the setting information is discarded and invalidated.

  The application example to the embodiment of the communication system using the communication protocol defined in IEEE 803.2 has been described above. In IEEE 803.2, although discovery is performed at a predetermined interval, it is not performed every cycle. Therefore, if the ONU 10 becomes unregistered when the communication line 30 is switched, the ONU 10 resumes the interrupted communication until the discovery process is completed. Can not do it. On the other hand, according to this application example, early restart of communication can be realized effectively as described above.

Embodiment 2

  Next, an embodiment capable of improving tolerance to instability at the time of line switching and realizing early restart of communication more reliably will be described using an application example to IEEE 803.2.

  FIG. 8 shows a communication sequence of the communication system according to this embodiment. 8, the same reference numerals as those in FIG. 4 denote the same or corresponding parts. If a communication failure occurs on the active communication line, the communication becomes unstable, and the downstream signal reaches or does not reach the ONU 10. In addition, since the failure detection timing of the ONU 10 and the failure detection timing of the OLT 1 do not necessarily match, there is a possibility that the GATE from the wOLT before switching is reached in the ONU 10 in the holdover state.

  In the communication sequence shown in FIG. 4, when the ONU 10 in the holdover state receives GATE (P9), it shifts from the holdover state to the registration state (P10). However, if the GATE sent by the wOLT before switching reaches the ONU 10 in the holdover state as described above (see FIG. 8, P20), the ONU 10 returns to the registered state in the communication sequence of FIG. When receiving a GATE transmitted by a later OLT, the ONU 10 detects a time stamp drift error.

  Therefore, in the communication sequence of FIG. 8, even if the GATE from the wOLT before switching is received during the holdover period, the ONU 10 maintains the holdover state until the holdover completion message (P21) is received (P10). .

  When ONU 10 detects a line abnormality (P4), it shifts to a holdover state (P5). At this time, if wOLT does not detect a line abnormality, GATE is transmitted (P20). When the ONU 10 receives this GATE, it identifies the type of control message and maintains the holdover state. On the other hand, the wOLT detects the line abnormality such as LOS when the upstream signal from the ONU 10 is interrupted (P6), and switches the communication line (P7). When the switching is completed, the bOLT starts communication control as a new wOLT, and transmits a GATE including a time stamp (P8). Subsequently, the bOLT transceiver 5-2 transmits a control message to instruct the ONU 10 to complete the holdover state (P21). The transmission of the control message (instruction message) may be multicast transmission using an extended MPCP (Multi-Point Control Protocol) message addressed to a plurality of ONUs 10 or an extended OAM (Operation Administration and Address) addressed to each ONU 10. Maintenance) message may be used for unicast transmission.

  The ONU 10 performs a synchronization process based on the GATE (P9), and upon receiving a holdover completion (Holdover_complete) control message, identifies the message type and ends the holdover state. Based on this sequence, even if the GATE is received from the OLT immediately after switching as the second GATE, the time stamp drift error is effectively suppressed, so the ONU 10 maintains the logical link, Communication can be resumed.

  FIG. 9 shows the control executed by the PON control unit 11, and the same reference numerals as those in FIG. 7 indicate the same or corresponding processes. In the holdover state, the PON control unit 11 extracts the type information of the control message from the control message in step S14 and identifies the type. If the type is holdover completion, the process proceeds to step S18 to return to the registered state (step S15a). On the other hand, if the type is not a holdover completion, the process proceeds to step S16 and the holdover state is continued.

Embodiment 3

  Next, an embodiment in which the time required for line switching can be shortened by shifting to the grace state (holdover state) at an early stage will be described using an application example to IEEE 803.2.

  FIG. 10 shows a communication sequence of this embodiment, and the same reference numerals as those in FIG. 8 indicate the same or corresponding parts. In a redundant protection system, there is a case where it is desired to perform line switching processing quickly for maintenance of an active device. For example, it is necessary to replace the PON interface board on which the transceivers 5-1 and 5-2 and the PON control units 2-1 and 2-2 are mounted. Even in the above-described communication system, the ONU 10 detects a line abnormality by shutting down the active PON interface, so the ONU 10 can resume communication using the holdover state. The ONU 10 does not shift to the holdover state until TLOS elapses for a certain period from the detection to LOS detection. Therefore, a certain time is required until the switching is completed.

  Therefore, when the PON control unit 2-1 of the wOLT receives the instruction signal input by the user, the control message instructing the holdover start (Holdover_start) is transmitted to each ONU 10 in order to forcibly shift the ONU 10 to the holdover state. (P22). The transmission of the control message (migration message) may be multicast transmission using an extended Multi-Point Control Protocol (MPCP) message addressed to a plurality of ONUs 10, or an extended OAM (Operation Administration and Address) addressed to each ONU 10. Maintenance) message may be used for unicast transmission. When the ONU 10 receives this control message, it shifts to the holdover state even if no line abnormality is detected (P5). 8 is compared with FIG. 10, in FIG. 8, the ONU 10 shifts to the holdover state after a certain period of time TLoS, whereas in FIG. You can see that it is made.

  Also, bOLT does not wait for detection of line abnormality, and can receive the notification from wOLT or the instruction signal input by the user, so that the operation as the active system can be started at an early stage, so that the switching process is completed in a short time. Can do. The instruction signal is transmitted by the working transceiver 5-1. This notification method has an effect of preventing the ONU 10 from generating a time stamp drift error and extending the interruption time.

  FIG. 11 is a flowchart showing the processing of the PON control unit 11 of the ONU 10, and the same reference numerals as those in FIG. 9 indicate the same or equivalent processing. In the registered state, the PON control unit 11 extracts type information from the received control message and identifies the type of this message (step S8). When the identified type is the start of holdover (step S9), the PON control unit 11 starts the process of step S11 and shifts to the holdover state. On the other hand, if the type is not a holdover start, the PON control unit 11 maintains the registration state and continues processing such as transmission.

  FIG. 12 is a flowchart showing processing executed by the PON control unit 2 of the OLT. When activated, the PON control unit 2 determines whether the operation of the own device is the active system or the standby system (step S21). If the mode is not the active system, the process proceeds to step S36 and waits as the standby PON control unit 2 until the mode is switched.

・ Operation in active system (normal)
When the operation mode is the active system, the discovery process is started (step S22). When the logical link establishment by the discovery process and the registration of the ONU 10 are completed, the PON control unit 2 determines whether a forced switching reason for the communication circuit has occurred (step S23). The forced switching reason is, for example, the above-mentioned forced switching by the user's intention, and when the instruction signal is received from the external input device connected to the PON control unit 2 or via the network, the PON control unit 2 Determines that forced switching is required. If there is no reason for forced switching, the PON control unit 2 detects a line abnormality (step S24).

  If there is no line abnormality, the PON control unit 2 notifies the bandwidth allocation information to each ONU 10 using GATE (step S25), and receives REPORT from each ONU 10 (step S26). Next, the PON control unit 2 calculates the RTT of each ONU based on the time stamp included in the REPORT (step S27), and determines the transmission band allocated to each ONU 10 based on the requested bandwidth information of the REPORT and the RTT (step S27). S28). In parallel with these processes, the PON control unit 2 transmits / receives data in the current bandwidth update cycle (step S29). Next, the PON control unit 2 determines whether a discovery process is necessary (step S30), and if not necessary, returns to step S23, and if necessary, returns to step S21. In order to discover newly connected ONUs 10 and activated ONUs 10, discovery processing is periodically executed. When the OLT needs to be shut down, the process is terminated here.

・ Operation in active system (during switching operation)
If it is determined in step S23 that forced switching is necessary, the PON control unit 2 transmits a grace state start notification (holdover start notification) (step S31), and the process proceeds to step S33. When a line abnormality is detected in step S24, the PON control unit 2 performs an alarm output process in step S32. Next, the PON control unit 2 transmits the setting information of each ONU 10 to the bOLT (step S33). When the setting information is already shared with bOLT, the PON control unit 2 does not need to transmit this information again.

  Subsequently, the PON control unit 2 executes line switching processing (protection switching processing) (step S34). When switching the line, the PON control unit 2 transmits a switching instruction signal to the bOLT and stops transmitting the control message to the ONU 10 (step S35). When the line switching process is completed, the PON control unit 2 thereafter rewrites the operation mode information to “standby”, returns to step S21, and starts the operation as the standby PON control unit 2. If the line abnormality is an irrecoverable abnormality or the own apparatus needs to be shut down, such as during forced switching, the apparatus is shut down and the process is terminated without shifting to the operation as a standby system.

Operation in the standby system Next, the operation of the PON control unit 2 when the operation mode is the standby system will be described. In step S36, the PON control unit 2 monitors whether line switching is necessary and waits until line switching is necessary. The PON control unit 2 executes line switching when a switching instruction signal is received from the wOLT or when it is determined that there is an abnormality by monitoring the operation of the wOLT. When switching is performed, the PON control unit 2 of the bOLT transmits a signal notifying that switching is to be performed to the wOLT and the switch 8. The switch 8 that has received this switching instruction signal switches the connection with the network to the bOLT side thereafter.

  Subsequently, the PON control unit 2 acquires setting information from the wOLT (step S37), and transmits a GATE including a time stamp to each ONU 10 using the setting information (step S38). In the PON protection system, the splitter 40 relays the upstream signal from the ONU 10 to both the working and protection lines 30-1 and 30-2. Therefore, the bOLT PON control unit 2 can receive a signal from the ONU 10 even when operating as a standby system. For this reason, the setting information included in the upstream signal may be constantly monitored to obtain the setting information in advance in the standby state in step S36.

  Since the ONU 10 during the holdover period does not transmit an uplink signal, a REPORT for GATE is not transmitted. Therefore, the PON control unit 2 can transmit a control message instructing completion of holdover without waiting for reception of REPORT (step S39). It is also possible to notify GATE and holdover completion with one control message. Further, a control message other than GATE can be used as a control message for synchronization.

  The PON control unit 2 that has transmitted the holdover completion notification rewrites the operation mode information to the working system, and thereafter operates as the working PON control unit 2 (step S40). When the operation as the active system is started after line switching, the PON control unit 2 restarts communication using the setting information inherited from wOLT, so that the discovery process (step S22) can be omitted. Therefore, the communication interruption time is shortened.

  In this embodiment, the holdover state may be terminated without using the holdover completion control message as in the first embodiment.

  According to the third embodiment, since the transition to the grace period is possible without waiting for the error detection period to expire, the line can be switched instantaneously, and the interruption of communication gives the user a sense of incongruity Can be suppressed. In communications that require real-time performance, such as when voice communication is being performed, instantaneous line disconnection and signal arrival delay are problems. In this embodiment, this problem can be improved.

  Also, when a line switch is required, if the master station suddenly sends a signal to the slave station using a line with a different communication path, the slave station will detect a synchronization error alarm and will need to reset the communication. End up. As a result, the interruption time becomes longer, but in this embodiment, a synchronization delay detection grace time is provided, and at the time of switching, the slave station quickly shifts to this detection grace period and synchronizes before communication. In order to resume, communication can be resumed early.

  The embodiment of the present invention has been described above. The present invention is not limited to these embodiments, and any modifications may be made as long as they are included in the gist of the present invention. For example, the communication system to which this communication method is applied need not be a PON system. The present invention can also be applied to an optical communication system using an active element. Further, the present invention is not limited to optical communication, and can also be applied to a communication system that communicates between terminals using electrical signals.

  The processing of the PON control unit 2 of the OLT shown in FIG. 12 can be applied to the first or second embodiment. In the case of the second embodiment, since it is not necessary to carry out the holdover start notification, step S31 can be omitted. In the case of the first embodiment, since the holdover completion notification need not be performed in addition to the holdover start notification, steps S31 and S39 can be omitted. Further, since the PON control unit 2 (PON processor) of the OLT can execute processing using a program executable by a computer, the processing of FIG. 12 can be described using a computer program.

  In the first to third embodiments, a plurality of master station control devices 2-1 and 2-2 are provided corresponding to the transceivers 5-1 and 5-2 as shown in FIG. However, the control device 2 may be a single device as shown in FIG. In this case, the transfer of setting information between the control devices 2-1 and 2-2 and the switch 8 are not required.

In the embodiment, not only a general-purpose communication system but also an application example to IEEE 802.3 has been described. However, the present invention is not limited to this, and can be implemented in a communication system using another protocol. It is.
It is also possible to connect the line between the slave station 10 and the branching means (splitter) 40 with a redundant line.

  The present invention is suitable for a communication system having a redundant communication line and a method for switching the communication line.

  1 communication device, 2-1, 2-2 control device (PON control unit), 3,13 reception buffer, 4,12 transmission buffer, 5-1, 5-2, 14 optical transceiver (transceiver), 6, 15 WDM, 7, 16-1, 16-2 PHY, 10-1 to 10-3 communication device, 11 PON control unit, 11a controller, 11b, 11e timer, 11c synchronization loss alarm unit, 11d line abnormality alarm unit, 11f Memory, 20-1, 20-2 Terminal, 30-1, 30-2 Communication line, 31 Subscriber line, 40 Splitter, 51, 142, 161-1, 161-2 Rx, 52, 141, 162-1 162-2 Tx.

Claims (18)

A plurality of redundant physical lines are connected between the master station device and the splitter that branches the optical signal, and the slave station device communicates with the master station device via the splitter,
A transceiver for transmitting and receiving transmission signals using a logical link;
When a transition message instructing transition to a holdover state is received via the transceiver in the registration state registered in the master station device as a communicable slave station device, the downlink signal is received and the upstream signal A control unit that shifts to a holdover state that suppresses transmission and maintains communication link setting information ;
A slave station device comprising: In the holdover state, when the transceiver receives time information,
2. The slave station device according to claim 1, wherein the control unit synchronizes a local time measured by the own device with the received time information, and shifts from the holdover state to the registered state. . In the holdover state, when the transceiver receives an end message instructing the end of the holdover state,
The slave station apparatus according to claim 1, wherein the control unit shifts from the holdover state to the registration state. The migration message is an extended MPCP (Multi-Point Control Protocol) message addressed to the plurality of slave station devices or a plurality of extended OAM (Operation Administration and Maintenance) messages addressed to each of the slave station devices. The slave station apparatus according to claim 1, wherein the slave station apparatus is characterized in that: The end message is an extended MPCP (Multi-Point Control Protocol) message addressed to the plurality of slave station devices or a plurality of extended OAM (Operation Administration and Maintenance) messages addressed to each of the slave station devices. The slave station apparatus according to claim 3, wherein 6. The control unit according to claim 1, wherein when the predetermined period in the holdover state ends, the control unit shifts to a non-registration state and performs an initial setting for returning to the registration state. The slave station device according to any one of the above. It has a timer that measures local time,
The controller is
When the synchronization error is detected based on the difference between the time information of the transmission signal received by the transceiver and the local time, the state shifts to the non-registered state, while the non-registration due to the synchronization error occurs in the holdover state. The slave station apparatus according to any one of claims 1 to 6, wherein transition to a state is suppressed. It has a timer that measures local time,
The controller is
When the synchronization error is detected based on the difference between the time information of the transmission signal received by the transceiver and the local time, the state shifts to the non-registered state, while the detection of the synchronization error is suppressed in the holdover state. The slave station device according to claim 1, wherein the slave station device is a slave station device. A master station device that communicates with a plurality of slave station devices via a plurality of redundant physical lines and a splitter that branches the signals of these physical lines into a plurality of signal lines,
A plurality of transceivers connected to each of the plurality of physical lines;
Among the plurality of transceivers, when performing protection switching for switching the transceiver to be used for communication from the active transceiver to a spare transceiver inhibit vital communication transmitting uplink signals performs reception of the downlink signal the transition message indicating transition to the holdover state to maintain the configuration information of the link after sending the plurality of slave stations via said transceiver, a control unit for performing the protection switching,
A master station device. The master station device according to claim 9, wherein the control unit transmits an end message instructing the end of the holdover state to the slave station device via the transceiver after the protection switching. . A communication line switching method for an optical communication system in which a master station device and a slave station device are connected via a plurality of redundant physical lines,
A discovery step in which the master station device registers the slave station device as a slave station device capable of communication;
When the master station apparatus performs protection switching to switch the transceiver used for communication from the current transceiver to the spare transceiver, the master station apparatus receives the downlink signal, suppresses the transmission of the uplink signal, and controls the communication link. A switching step of switching from the physical line of the active system to the physical line of the standby system after transmitting a transition message instructing transition to the holdover state for maintaining the setting information to the registered slave station device;
When the registered slave station apparatus receives the transition message, the slave station apparatus receives a downlink signal during a predetermined period, suppresses transmission of the uplink signal, and maintains a communication link setting information. Holdover step to transition,
A communication line switching method comprising: The master station device, after the switching step, transmitting a termination message instructing termination of the holdover state to the slave station device;
When the slave station device receives the end message in the holdover state, the slave station device transitions from the holdover state to the registration state;
The communication line switching method according to claim 11, further comprising: A communication system that uses media access control according to the IEEE 802.3 standard, and in which a master station device and a slave station device communicate with each other through a plurality of redundant physical lines and splitters,
In the case of performing protection switching in which the transceiver used for communication is switched from the current transceiver to the spare transceiver, the master station device receives the downlink signal and suppresses the transmission of the uplink signal and the communication link. After transmitting a transition message instructing transition to a holdover state for maintaining setting information to the slave station device, the protection switching is performed.
When the slave station device receives the transition message, the slave station device transitions to a holdover state in which a downlink signal is received and an uplink signal transmission is suppressed during a predetermined period. The master station device transmits an end message instructing the end of the holdover state to the slave station device after the protection switching,
14. The communication system according to claim 13, wherein the slave station device shifts from the holdover state to the registration state when receiving the end message in the holdover state. A control device for a slave station device that is connected with a plurality of redundant physical lines between a master station device and a splitter that branches an optical signal, and communicates with the master station device via the splitter,
When a transition message instructing transition to the holdover state is received in the registration state registered in the master station device as a slave station device with which the base station can communicate, the downlink signal is received during a predetermined period. And a control apparatus that shifts to a holdover state that suppresses transmission of an uplink signal and maintains communication link setting information . 16. The control device according to claim 15, wherein when the end message instructing the end of the holdover state is received in the holdover state, the control unit shifts from the holdover state to the registration state. A control device of a master station device that communicates with a plurality of slave station devices via a plurality of redundant physical lines and a splitter that branches signals of these physical lines into a plurality of signal lines,
When protection switching is performed to switch the transceiver used for communication from the current transceiver to the spare transceiver, a hold that receives downlink signals, suppresses uplink signal transmission, and maintains communication link setting information. A control apparatus that performs the protection switching after transmitting a transition message instructing transition to an over state to the plurality of slave station apparatuses. The control device according to claim 17, wherein after the protection switching, an end message instructing the end of the holdover state is transmitted to the slave station device.

Images