JP2016163229A - Passive optical network system, subscriber-side termination device, station-side termination device and traffic recovery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent data that are stored in an uplink buffer of a subscriber-side termination device, from being sent up as invalid dust data even if a frame loss is generated by uplink buffer overflow of the subscriber-side termination device in fault switching of a station-side termination device.SOLUTION: A passive optical network system comprises: a subscriber-side termination device including an uplink buffer and a buffer monitor part for monitoring a storage amount of uplink signals in the uplink buffer; a station-side termination device which communicates with the subscriber-side termination device via an optical fiber transmission line; and an auxiliary-station-side termination device. The passive optical network system also comprises a protection function for switching to the auxiliary-station-side termination device if a fault occurs in the station-side termination device. If a fault occurs in the station-side termination device, the auxiliary-station-side termination device transmits a clear frame signal including a signal instructing uplink buffer clear of the uplink buffer to the subscriber-side termination device. If overflow of the uplink buffer is detected and the subscriber-side termination device receives the clear frame signal, the buffer monitor part clears the uplink buffer.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a passive optical network system, a subscriber-side termination device, a station-side termination device, and a traffic recovery method.

  2. Description of the Related Art Conventionally, there is known a communication system including one station side device and a plurality of subscriber side devices connected to the station side device via a distributor. In recent years, as such a communication system, a communication system using an optical signal as a signal medium, such as a passive optical network (hereinafter also referred to as PON: Passive Optical Network) system, has attracted attention.

  The PON system is a part of an optical network, and can use the Internet protocol (IP) to provide various services such as an Internet connection service, an IP phone, and a video distribution service.

  The schematic configuration of the PON system will be described with reference to FIG.

  The PON system 10 includes a station side communication device (OLT) 12 installed in a carrier (communication carrier) station, and N subscriber side terminal devices (ONU: Optical) installed in subscriber homes. (Network Unit) 14-1, 14-2,..., 14-N (hereinafter collectively referred to as “ONU 14”), and one optical fiber to an optical splitter 16 (N: in FIG. 6). The optical fiber transmission line 18 is branched into a plurality of optical fibers via a two-optical splitter).

  One or a plurality of station-side terminal units (OSU: Optical Subscriber Units) 20 are mounted on the OLT 12 (FIG. 6 illustrates the case where one OSU 20 is mounted on the OLT 12). Is connected to the ONU 14 via the working fiber 22 and the optical splitter 16. The OLT 12 includes an OLT controller 24 that performs overall control of the entire OLT 12. The number of ONUs 14 connected to one OSU 20 via the optical splitter 16 is, for example, 32 (N = 32). A configuration including the optical splitter 16, the working fiber 22, and the backup fiber 22R (described later) may be referred to as a PON line.

  Each OSU 20 is connected to a line collecting switch (not shown). When the line concentrator switch receives a downstream frame from a higher level, it reads an identifier (for example, Virtual LAN Identifier (VID)) attached to the frame. Since the link switch has previously registered the association between the VID number and the ONU number and the correspondence information of the connection destination OSU number of each ONU, the association information and the received VID number are linked to the corresponding VID number. The connected OSU number of the attached ONU 14 is known.

  On the other hand, each of the ONUs 14-1, 14-2,..., 14-N is connected to a subscriber terminal (not shown) or the like via a UNI (User Network Interface) port. As shown in FIG. 6, uplink traffic as an uplink transmission signal is transmitted from a subscriber terminal or the like toward OUN 14. In the PON system, the direction from the ONU to the OLT is referred to as “up”, and the direction from the OLT to the ONU is referred to as “down”.

  Among the PON technologies, those using the Ethernet (registered trademark) technology are referred to as Ethernet (registered trademark) -PON, and those using the Gigabit Ethernet (registered trademark) technology are referred to as GE-PON. GE-PON is standardized by IEEE 802.3ah. A device using 10 Gigabit Ethernet (registered trademark) technology is referred to as 10GE-PON. 10GE-PON is standardized by IEEE802.3av. Hereinafter, among the PON systems, a system related to the PON technology using the Ethernet (registered trademark) technology in particular will be simply referred to as a “PON system”, and the above specifications related to the PON technology using the Ethernet (registered trademark) technology will be described. It is simply referred to as “specification”.

  In the PON system 10, a control function called MPCP (Multi Point Control Protocol) is defined for access control between the OLT 12 (OSU 20) and the ONU 14. That is, point-to-multipoint communication by MPCP control is realized by transmitting and receiving a control message called a MAC (Media Access Control) message between the OLT 12 and the ONU 14.

  In the MPCP control, in a state where a logical link is established, the OLT 12 transmits a Gate frame describing the transmission start time of the uplink packet to each ONU 14, and each ONU 14 is designated by the Gate frame. At this time, a data packet and a report (report) frame are transmitted to the OLT 12 to perform normal communication.

  On the other hand, the PON system 10 stipulates that a discovery process is performed in order to register an unregistered ONU 14 in the OLT 12. In this discovery process, the unregistered ONU 14 waits until the OLT 12 can receive a Discovery Gate frame that is transmitted as a frame at regular time intervals, and after receiving the Discovery Gate frame, transmits a Register Request frame to the OLT 12 in response thereto. Thus, the registration process is started.

  In the discovery process, the OLT 12 measures RTT (Round Trip Time) with the ONU 14 to be registered, and the OUN 14 performs time synchronization with the OLT 12. RTT measurement and time synchronization are periodically performed thereafter, and when a deviation occurs due to a change in the condition of the optical fiber transmission line, it is corrected as needed.

  The PON system 10 employs a method using a time stamp embedded in a Gate frame as a method for maintaining the time synchronization state. That is, the OLT 12 transmits the current time of the local station master counter to the ONU 14 as time stamp information, and the ONU 14 updates the master counter value of the local station according to the received time stamp value.

  Even when the logical link of the PON system 10 is interrupted for some reason and the registration of a specific ONU 14 is canceled, the OLT 12 transmits a Discovery Gate frame to the ONU 14 and performs a process of attempting to re-register.

  Incidentally, a protection system may be provided in the optical transmission apparatus in order to cope with a line failure or a line maintenance application. The protection system is a system in which, for example, a redundant backup communication line that is not normally used is provided for the current communication line, and the line is switched to the backup communication line at the time of line failure or line maintenance.

  As an example of a PON system protection system (PON protection system), Patent Document 1 discloses a PON having a mechanism capable of avoiding a link break due to a time stamp drift error that occurs between an ONU and a switching destination OSU when switching OSUs. A system ONU switching method is disclosed. In the PON protection system disclosed in Patent Document 1, link breakage due to a time stamp drift error is avoided by completing time adjustment between the ONU and the switching destination OSU during OSU switching. Note that the time stamp drift error means that a time synchronization between the OLT 12 and the ONU 14 is out of order.

  A protection system is also adopted in the PON system 10 shown in FIG. 6, and a protection line 32 including a protection fiber 22R and a protection OSU 20R is provided for a work line 30 including the work fiber 22 and the OSU 20. In general, when a line failure occurs, the working line 30 is automatically switched to the protection line 32. Further, at the time of line maintenance such as firmware change of the optical transmission apparatus, it is common to switch to the protection line 32 and change the firmware of the working line 30 and then switch to the working line 30 and switch back. Switching that automatically switches in the event of a line failure or the like is generally referred to as “failure switching”, and switching that is switched manually during line maintenance or the like is generally referred to as “command switching”.

  An example of the OSU switching sequence at the time of failure switching will be described with reference to FIG. FIG. 7 shows time on the horizontal axis, a line collecting switch, an OLT controller 24 (indicated as “OLT controller” in FIG. 7), a spare OSU 20R (indicated as “switching destination OSU” in FIG. 7), an ONU 14 (in FIG. 7). In FIG. 7, operations in the OSU switching sequence of each configuration of “ONU” and OSU 20 (indicated as “switching source OSU” in FIG. 7) are shown. In FIG. 7, points on the time axis indicated by numerals E (E1 etc.) indicate the occurrence and end of events (light emission stop, etc.), and between the components indicated by numerals F (F1 etc.) The arrows that connect the messages indicate the exchange of messages and information. Also, the double-ended arrows represent the ONU state at that time (S1 etc.).

  As shown in FIG. 7, when a failure occurs in the switching source OSU (E1), the OLT controller detects this failure by frame loss, for example (E2). The OLT controller that has detected the failure of the ONU instructs the concentration switch to change the VID accommodation destination (F1). The line concentrator switch that has received the VID accommodation destination change notification changes the correspondence information of its own VID number-connection destination OSU number in accordance with the contents. The OLT controller further transmits an instruction to stop the light emission of the optical interface connected to the PON line to the switching source OSU (F2), and the switching source OSU stops the light emission (E3).

  Thereafter, the OLT controller instructs the switching destination OSU to emit light (F3), and the switching destination OSU starts emitting light (E4). The switching destination OSU transmits a Discovery Gate frame for time adjustment to the ONU (F4), and the ONU performs time (Local time) adjustment according to the time stamp described in the frame (E5). . As a result, the time between the switching destination OSU and the ONU is synchronized.

  When the time synchronization with the ONU is completed, the switching destination OSU notifies the OLT controller of the completion of the time synchronization (F5). The OLT controller knows that the switching has been completed upon receipt of the time synchronization completion notification from the switching destination OSU. Thereafter, the switching destination OSU transmits a normal Gate frame (indicated as “Normal Gate” in FIG. 7) that gives upstream transmission permission to the ONU (F6). The ONU that has received the normal gate frame starts transmission of the uplink frame by the report frame according to the uplink transmission permission time described in the frame (F7). With the above procedure, the OSU switching sequence is completed, and data communication is resumed (F8, F9).

  The ONU state in the above sequence is the state S1 during the data communication before the light emission stop of the switching source OSU in E3, and the light from the light emission stop of the switching source OSU in E3 to the light emission start of the switching destination OSU in E4. The state S3 during the time synchronization procedure from the start of light emission of the switching destination OSU in the disconnected states S2 and E4 to the transmission of the Normal Gate frame of F6 is the state S4 during the data communication after the transmission of the Normal Gate frame of F6.

  In FIG. 6, the upstream traffic is accumulated in the upstream buffer of the ONU 14 and, as described above, in the upstream direction from the ONU 14 toward the working line 30 according to the upstream transmission permission timing given by the OSU 20 in the Gate frame (Normal Gate frame). Sent out.

Here, the upstream buffer of the ONU 14 is generally configured as follows according to the specifications of the PON system at the time of normal operation in a link establishment state and at the time of re-establishing a link after a link disconnection.
<Configuration A> At the time of normal operation in the ONU link establishment state, a sufficient buffer size is prepared so that the upstream buffer does not overflow, and the upstream buffer allocation control by the OLT does not cause upstream buffer overflow Sufficient uplink bandwidth is allocated.
<Configuration B> When the link is established again after the link disconnection of the ONU, the link is established in a state where no frame is accumulated in the uplink buffer, and the data in which the residual data in the uplink buffer does not make sense after the link is established (hereinafter, It is not sent in the upstream direction as “garbage data”.

JP 2014-121038 A

By the way, when a failure occurs in the OSU 20, there is generally a high possibility that a frame loss will occur in the traffic. In the PON protection system shown in FIG. 6, when considering the uplink traffic at the time of switching due to the failure of the OSU 20, the occurrence of frame loss due to the following factors can be considered, and as a result, the uplink traffic may not be guaranteed.
<Factor 1> Frame loss due to OSU failure occurrence <Factor 2> Frame loss due to overflow of ONU buffer after OSU failure switching until recovery by spare OSU

  Upstream traffic during the switching process of the OSU 20 is accumulated in the upstream buffer of the ONU 14. Data accumulated in the upstream buffer of the ONU 14 during the switching process of the OSU 20 is transmitted as upstream traffic after the switching of the OSU 20 is completed. Although the amount of data stored in the upstream buffer depends on the switching processing time of the OSU 20, FIG. 7 shows the upstream buffer storage period corresponding to this switching processing time. That is, the uplink buffer accumulation period is a period from the occurrence of a failure (E1) in the switching source OSU to the uplink data transmission (F9) using the Report frame.

  Depending on the relationship between the upstream inflow traffic to the ONU 14, the size of the upstream buffer of the ONU 14, and the OSU switching processing time, the upstream buffer of the ONU 14 may overflow during the OSU switching processing. If an overflow occurs in the upstream buffer of the ONU 14 during the OSU switching process, the data stored in the upstream buffer of the ONU 14 that is sent after the completion of the OSU switching becomes meaningless data. Further, the recovery timing of the upstream traffic is after the transmission of the data stored in the upstream buffer of the ONU 14 is completed.

  That is, the data stored in the upstream buffer after the frame loss due to the failure of the OSU 20 (above <factor 1>) and the frame loss due to the overflow of the upstream buffer (above <factor 2>) has occurred There is a concern that there is a possibility that after the OSU 20 failure is switched, it may be transmitted as garbage data that does not make sense.

Unlike command switching, command switching does not correspond to the case where frame loss occurs due to an OSU failure (above <Factor 1>). >). That is, command switching is different from failure switching in the following respects regarding the occurrence of frame loss of upstream traffic.
(1) The OSU can be switched under the control that the upstream buffer does not overflow.
(2) Even if an overflow of the upstream buffer occurs during OSU switching, only the overflow of the upstream buffer is a frame loss, and the data stored in the upstream buffer is valid data.

  In this regard, the OSU switching specifically disclosed in Patent Document 1 relates to command switching. Therefore, Patent Document 1 does not specifically disclose the above problem in OSU failure switching.

  The present invention has been made in order to solve the above-described problems. Even when a frame loss occurs due to overflow of the upstream buffer of the subscriber-side termination device in the failure switching of the station-side termination device, the uplink of the subscriber-side termination device is achieved. An object of the present invention is to provide a passive optical network system, a subscriber-side termination device, a station-side termination device, and a traffic recovery method capable of suppressing data accumulated in a buffer from being transmitted as invalid garbage data. And

  In order to achieve the above object, a passive optical network system according to the present invention includes an uplink buffer that stores an uplink signal, and a buffer monitoring unit that monitors an accumulation amount of the uplink signal in the uplink buffer. A terminal-side terminal device, a station-side terminal device that communicates with the subscriber-side terminal device through a multi-point control protocol via an optical fiber transmission line, and a backup station-side terminal device, and the station-side terminal device fails. And a protection function for switching to the backup station side termination device when the failure occurs, and the backup station side termination device includes a signal that instructs to clear the uplink buffer when a failure occurs in the station side termination device A frame signal is transmitted to the subscriber-side terminating device, the buffer monitoring unit detects an overflow of the upstream buffer, and the subscription The clearing up buffer when the side terminating device receives the clear frame signal.

  In order to achieve the above object, a subscriber-side termination device according to the present invention is a subscriber-side termination device provided in the above passive optical network system.

  In order to achieve the above object, a station-side terminating device according to the present invention is a station-side terminating device provided in the above passive optical network system.

  In order to achieve the above object, a traffic recovery method according to the present invention comprises a subscriber-side termination comprising: an uplink buffer for storing an uplink signal; and a buffer monitoring unit for monitoring an accumulation amount of the uplink signal in the uplink buffer. Device, a station-side termination device that communicates with the subscriber-side termination device through a multi-point control protocol via an optical fiber transmission line, and a backup station-side termination device, and a failure occurs in the station-side termination device A traffic recovery method using a passive optical network system having a protection function for switching to the standby station side termination device in the case where a failure occurs in the station side termination device, and instructing to clear the upstream buffer The backup station side terminating device transmits a clear frame signal including a signal to be transmitted to the subscriber side terminating device, and § monitoring unit detects the overflow of the uplink buffer, and if the subscriber side terminating device receives the clear frame signal, the buffer monitoring unit clears the uplink buffer.

  According to the present invention, even when a frame loss occurs due to the overflow of the uplink buffer of the subscriber-side terminating device in the failure switching of the station-side terminating device, the data stored in the uplink buffer of the subscriber-side terminating device is invalid garbage. It is possible to provide a passive optical network system, a subscriber-side terminal device, a station-side terminal device, and a traffic recovery method that can suppress upstream transmission as data.

It is a block diagram which shows an example of a structure of ONU which concerns on embodiment. It is a figure explaining the structure of the buffer clear instruction | indication Gate frame which concerns on embodiment. It is a figure explaining the precondition in the OSU switching sequence which concerns on embodiment. It is a figure explaining the OSU switching sequence at the time of the threshold excess generation | occurrence | production of the ONU upstream buffer concerning embodiment. It is a figure explaining the OSU switching sequence at the time of the threshold value excess non-occurrence | production of the ONU upstream buffer concerning embodiment. It is a block diagram which shows an example of a structure of the PON system which concerns on a prior art. It is a figure explaining the OSU switching sequence of the PON protection system which concerns on a prior art.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. Note that the overall configuration of the PON system according to the present embodiment is the same as that of the PON system 10 according to the prior art shown in FIG. 6, and therefore, when referring to the overall configuration of the PON system, refer to FIG. I will explain.

  First, an example of the configuration of the ONU 14 in the PON system 10 according to the present embodiment will be described with reference to FIG. The ONU 14 according to the present embodiment includes an upstream buffer 50, an ONU controller 52, an MPCP layer control unit 54, a UNI 56, and a PON IF (PON Interface) 58.

  As described above, the upstream buffer 50 is a buffer memory that temporarily accumulates (stores) upstream traffic data. The stored upstream traffic data is sequentially read out and sent to the PON line as PON line data. The upstream buffer 50 may be configured by, for example, a RAM (Random Access Memory).

  The ONU controller 52 performs overall control of the entire ONU 14. The ONU controller 52 may be configured by, for example, a CPU (Central Processing Unit). The MPCP layer control unit 54 executes access control and the like between the OLT 12 and the ONU 14 using MPCP.

  The UNI 56 is a specification of an interface for connecting communication equipment on the telecommunications carrier side (PON system 10 in the present embodiment) and equipment on the user side (such as a subscriber terminal). The PON IF 58 is an interface specification for connecting the ONU 14 to the PON line, and includes specifications of an optical transmission unit and an optical reception unit.

  The ONU 14 according to the present embodiment is configured such that a predetermined threshold can be set for the size (storage capacity) of the upstream buffer 50. That is, in the ONU 14 according to the present embodiment, an upper limit is set for the capacity of upstream traffic stored in the upstream buffer 50, and upstream traffic exceeding this upper limit is not stored, that is, overflowed. In the present embodiment, the ONU controller 52 sets the threshold value for the upstream buffer 50.

  The threshold value may be set according to the uplink traffic characteristics of the provided service. That is, when the provided service has a low burst property such as a voice service and has a small occupied band, the threshold is set to be relatively large. You may make it set small.

  The MPCP layer control unit 54 constantly monitors whether or not the accumulation amount of the upstream buffer 50 exceeds a preset threshold value, and always grasps the accumulation state. The MPCP layer control unit 54 has a function of clearing all data (frames) stored in the upstream buffer 50. In the present embodiment, the clearing of the upstream buffer 50 by the MPCP layer control unit 54 is executed by a “buffer clear instruction Gate” frame that is a frame for instructing the clearing of the upstream buffer 50 from the OLT 12.

  The buffer clear instruction Gate frame will be described with reference to FIG. In this embodiment, a buffer clear instruction information area is defined in the reserved area of the Normal Gate frame, and it is possible to instruct clearing of the upstream buffer from the OLT 12 to the ONU 14.

  FIG. 2A shows an MPC PDU (Multipoint Control Protocol Data Unit) of a Normal Gate frame in the MAC frame format defined in the specification. An MPCPDU is a protocol data unit that carries information necessary to establish a logical link between an OLT and an ONU.

  A Pad / Reserved area is provided as one of the MPC PDU areas of the Normal Gate frame. In the present embodiment, as shown in FIG. 2B, the LSB 1 bit is allocated as a buffer clear instruction bit in one byte of this Pad / Reserved area. Note that other areas of the MPCPDU are not directly related to the present embodiment, and thus the description thereof is omitted (for example, see the above specification).

  In this embodiment, when the buffer clear is instructed, the value of the buffer clear instruction bit is set to “1”. However, the logic may of course be reversed. That is, when the buffer clear is instructed, the value of the buffer clear instruction bit may be set to “0”. Note that the buffer clear instruction Gate frame can also give the ONU upstream transmission permission timing in the same manner as a normal normal gate frame without buffer clear instruction information (the buffer clear instruction bit is not set to “1”). It is.

  The MPCP layer control unit 54 of the ONU 14 that has received the Gate frame transmitted from the OSU 20 recognizes that the buffer clear instruction is issued from the OLT 12 when the buffer clear instruction information (bit) is set to “1”. To do. When the ONU 14 receives the buffer clear instruction, the MPCP layer control unit 54 clears the upstream buffer 50 when the upstream buffer 50 has exceeded the threshold.

  That is, in the present embodiment, the MPCP layer control unit 54 clears the upstream buffer 50 when the buffer clear instruction Gate frame is received and the upstream buffer 50 has exceeded the threshold value. In other words, even if the buffer clear instruction Gate frame is received, the MPCP layer control unit 54 does not clear the upstream buffer 50 if the upstream buffer 50 does not exceed the threshold value. Even in this case, the ONU 14 may transmit uplink data to the OSU 20 using the Report frame in accordance with the uplink transmission permission timing given by the buffer clear instruction Gate frame.

  Here, in the present embodiment, it is assumed that the PON system 10 maintains the link establishment state in OSU failure switching. That is, when a link break occurs in OSU failure switching, it is not assumed in the present embodiment because it results in <Configuration B>.

  In order to maintain the link establishment state in OSU failure switching, it is necessary to perform switching processing so that timeout does not occur in mpcp_timer even during OSU failure switching processing.

  In the PON system 10, the state of the communication link by MPCP control is determined by monitoring the reception interval of the Gate frame or the Report frame with the monitoring timer mpcp_timer. The monitoring time by this mpcp_timer is defined as 1 second by the specification.

  When the OLT 12 receives the Report frame, the OLT 12 activates the mcp_timer in which the monitoring time is set. If the OLT 12 receives the next Report frame within the monitoring time, the OLT 12 determines that the link is UP and resets the mcpp_timer. Further, if the Report frame is not received even when the monitoring time of mpcp_timer has elapsed (in the case of mpcp_timer timeout), it is determined that the link is in the DOWN state.

  Similarly, when the ONU 14 receives a Gate frame, the ONU 14 activates the mcp_timer in which the monitoring time is set. If the ONU 14 receives the next Gate frame within the monitoring time, the ONU 14 determines that the link is UP and resets the mcp_timer. In addition, when the Gate frame is not received even when the monitoring time of mpcp_timer has elapsed (in the case of mpcp_timer timeout), it is determined that the link is in the DOWN state.

  Therefore, in order to prevent the OSU 20 from causing the mcpp_timer timeout during the OSU failure switching process, the monitoring of the mcp_timer is stopped in the OSU switching sequence, and the occurrence of the mcpp_timer timeout is suppressed by the OSU 20 itself. It is only necessary to maintain the link establishment state.

  With reference to FIG. 3, conditions for the ONU 14 not to disconnect the link due to a timeout of mpcp_timer during the OSU failure switching process will be described. FIG. 3 shows the OSU switching sequence shown in FIG. 7 again.

In order for the ONU 14 not to disconnect the link due to a timeout of the mcpp_timer during the OSU failure switching process, it is necessary to control the OSU failure switching process so that the following time conditions are satisfied from the monitoring conditions by the mpcp_timer. is there.
(1) The time from the occurrence of a failure in the switching source OSU (E1), that is, the transmission stop of the Gate frame to the transmission of the Discovery Gate frame by the switching destination OSU (F4) is less than one second.
(2) The time from transmission of the Discovery Gate frame by the switching destination OSU (F4) to transmission of the Normal Gate frame (F6) is less than 1 second.

  The control for satisfying the above time condition may be executed by the OLT controller 24, for example. In the present embodiment, it is assumed that the above time condition is satisfied.

  Next, with reference to FIG. 4, an example of an OSU switching sequence in the case where an overthreshold value occurs in the upstream buffer 50 of the ONU 14 during the OSU failure switching process will be described.

  As shown in FIG. 4, when a failure occurs in the switching source OSU (E1), the OLT controller detects this failure by frame loss, for example (E2). The OLT controller that has detected the failure of the ONU instructs the concentration switch to change the VID accommodation destination (F1). The line concentrator switch that has received the VID accommodation destination change notification changes the correspondence information of its own VID number-connection destination OSU number in accordance with the contents. The OLT controller further transmits an instruction to stop the emission of the optical interface connected to the PON line to the switching source OSU (F2), and stops the switching source OSU emission (E3).

  Thereafter, the OLT controller instructs the switching destination OSU to emit light (F3), and the switching destination OSU starts emitting light (E4). The switching destination OSU transmits a Discovery Gate frame for time adjustment to the ONU (F4), and the ONU performs time (Local time) adjustment according to the time stamp described in the frame (E5). . As a result, the time between the switching destination OSU and the ONU is synchronized. In this embodiment, thereafter, the threshold is exceeded in the upstream buffer 50 (E6).

  When the time synchronization with the ONU is completed, the switching destination OSU notifies the OLT controller of the completion of the time synchronization (F5). The OLT controller knows that the switching has been completed upon receipt of the time synchronization completion notification from the switching destination OSU. The switching destination OSU that has recognized that a failure has occurred in the switching source OSU via the OLT controller may cause an overthreshold value in the upstream buffer 50 of the ONU. A Gate frame is transmitted (F6). The ONU (MPCP layer control unit 54) that has received the buffer clear instruction Gate frame clears the upstream buffer 50 (E7).

  Thereafter, the ONU transmits a Report frame corresponding to the buffer clear instruction Gate frame (F7). However, since the upstream buffer 50 is cleared, the requested bandwidth of the report frame is set to zero. Note that the time relationship between the clearing of the upstream buffer in E7 and the transmission of the Report frame in F7 may be reversed. That is, the upstream buffer may be cleared after the Report frame is transmitted.

  In F7, the switching-destination OSU that has recognized that the upstream buffer has been cleared by transmitting the Report frame with the requested bandwidth = 0 from the ONU, then transmits a Normal Gate frame to the ONU (F8). ). In accordance with the uplink transmission permission time described in the frame, the ONU starts transmission of the uplink frame (F9) using the Report frame. With the above procedure, the OSU switching sequence is completed, and the uplink traffic is restored by exchanging the Normal Gate frame and the Report frame.

  The ONU state in the above sequence is the state S1 during the data communication before the light emission stop of the switching source OSU in E3, and the light from the light emission stop of the switching source OSU in E3 to the light emission start of the switching destination OSU in E4. From the start of light emission of the switching destination OSU in the interrupted state S2, E4 to the transmission of the buffer clear instruction Gate frame in F6 to the transmission of the buffer clear instruction Gate frame in the state S3, F6 during the time synchronization procedure to the transmission of the Normal Gate frame in F8 Between the state S4 in which the upstream buffer clear is being executed, the state after transmission of the normal gate frame in F8 is the state S5 in which data communication is in progress.

  In the sequence shown in FIG. 4, the ONU upstream buffer 50 accumulation period is a period from the occurrence of a failure in E1 to the transmission of a buffer clear instruction Gate frame by F6. That is, whether or not the threshold value excess (overflow) has occurred in the upstream buffer 50 is determined by the amount of upstream data stored during this storage time.

  Next, an OSU switching sequence in the case where the OSU failure switching process is completed without the threshold being exceeded in the upstream buffer 50 will be described with reference to FIG. The process from the failure occurrence at E1 in the sequence shown in FIG. 5 to the matching of the local time at E5 is the same as the sequence shown in FIG.

  In the sequence shown in FIG. 5, after the local time is adjusted in E5, the threshold of the uplink buffer has not been exceeded. The switching destination OSU that recognizes that a failure has occurred in the switching source OSU via the OLT controller 24, transmits a Discovery Gate frame and performs time synchronization between the switching destination OSU and the ONU. The completion of time synchronization is notified to the OLT controller (F5), and a buffer clear instruction Gate frame is transmitted to the ONU (F6).

  In the present embodiment, the switching destination OSU cannot recognize that the threshold is not exceeded in the ONU. On the other hand, since it is recognized through the OLT controller that a failure has occurred in the switching source OSU, the ONU upstream buffer 50 recognizes that there is a possibility that a threshold has been exceeded, and the buffer clear instruction Gate to the ONU is recognized. A frame will be transmitted. Naturally, the buffer clear instruction information of the buffer clear instruction Gate frame in this case is set to “1”.

  The ONU that has received the buffer clear instruction Gate frame requests an upstream band in the Report frame based on the amount stored in the upstream buffer 50 because the upstream buffer 50 does not exceed the threshold (F7). As a result, the data stored in the upstream buffer 50 during the OSU switching process is upstream transmitted (F9) corresponding to the normal gate frame transmission (F8) after the switching is completed, and the upstream traffic is restored.

  The OSU switching sequence according to the present embodiment shown in FIG. 5 is basically the same sequence as the OSU switching sequence according to the prior art shown in FIG. 7, and the frame at F6 is the normal gate in the OSU switching sequence according to the prior art. The only difference is that the frame is a buffer clear instruction Gate frame in the OSU switching sequence according to the present embodiment.

  However, also in this embodiment, when the uplink buffer threshold has not been exceeded, the ONU (MPCP layer control unit 54) does not clear the uplink buffer, so the OSU switching sequence according to this embodiment The OSU switching sequence according to the prior art is substantially the same sequence. In other words, in this embodiment, when the threshold is not exceeded in the upstream buffer, the action of the buffer clear instruction Gate frame is the same as the action of the Normal Gate frame.

  As described in detail above, according to the passive optical network system, subscriber-side termination device, station-side termination device, and traffic recovery method according to the present embodiment, the ONU upstream buffer is set in advance during the OSU failure switching process. When the specified threshold is exceeded, the ONU (MPCP layer control unit) clears the upstream buffer at the reception timing of the buffer clear instruction Gate frame. As a result, it is possible to prevent the data stored in the upstream buffer from being upstream transmitted as invalid garbage data after the completion of OSU failure switching.

  Also, according to the passive optical network system, subscriber-side termination device, station-side termination device, and traffic recovery method according to the present embodiment, the ONU (MPCP layer control unit) receives the buffer clear instruction Gate frame. However, when the threshold value is not exceeded in the upstream buffer, the upstream buffer is not cleared. Therefore, if the threshold value of the uplink buffer is not exceeded during the switching process, the upstream traffic is transmitted earlier than the case where the uplink buffer is always cleared by sending the data accumulated in the uplink buffer after switching to the upstream after switching. It can be recovered.

  In the above-described embodiment, an example has been described in which the upstream buffer is cleared when a preset threshold value is exceeded in the upstream buffer. However, the upstream buffer is cleared without providing a threshold value. Also good. Even in this case, it is possible to prevent the data accumulated in the upstream buffer from being transmitted as invalid garbage data after completion of the OSU failure switching.

  In the above embodiment, a mode in which the buffer clear instruction bit is assigned to the LSB1 bit of the Pad / Reserved area of the MPCPDU of the Normal Gate frame has been described as an example. However, the present invention is not limited to this. For example, the buffer clear instruction bit may be assigned to another area of the MPCPDU, or the buffer clear instruction bit may be assigned to another bit of one byte, for example, the MSB.

10 PON system 12 OLT (communication equipment on the station side)
14 ONU (Terminal equipment on the subscriber side)
16 Optical splitter 18 Optical fiber transmission line 20 OSU (Station side termination device)
20R Spare OSU
22 working fiber 22R protection fiber 24 OLT controller 30 working line 32 protection line 50 uplink buffer 52 ONU controller 54 MPCP layer control unit 56 UNI
58 PON IF

Claims (11)

A subscriber-side terminating device comprising an upstream buffer for storing upstream signals and a buffer monitoring unit for monitoring an accumulated amount of upstream signals in the upstream buffer; A station-side termination device that performs communication according to a point control protocol, and a protection station-side termination device, and a protection function for switching to the backup station-side termination device when a failure occurs in the station-side termination device,
The standby station side terminal device transmits a clear frame signal including a signal instructing to clear the uplink buffer when a failure occurs in the station side terminal device to the subscriber side terminal device;
The passive monitoring optical network system, wherein the buffer monitoring unit detects overflow of the upstream buffer and clears the upstream buffer when the subscriber-side terminating device receives the clear frame signal. A station side communication device for controlling a protection operation in the protection function;
2. The passive device according to claim 1, wherein the station side communication device stops the optical output of the station side termination device and activates the optical output of the backup station side termination device when detecting a failure of the station side termination device. 3. Type optical network system. The standby station side termination device transmits the clear frame signal to the subscriber side after time synchronization with the subscriber side termination device is completed by a Discovery Gate frame transmitted to the subscriber side termination device after activation of optical output. The passive optical network system according to claim 2, wherein the passive optical network system is transmitted to a termination device. The upstream buffer is configured such that a threshold that is an upper limit of the amount of upstream signal accumulation can be set;
4. The passive optical network according to claim 1, wherein the buffer monitoring unit detects an overflow of the uplink buffer when an accumulated amount of the uplink signal of the uplink buffer exceeds the threshold value. 5. system. The passive optical network system according to claim 4, wherein the threshold value is set according to an uplink signal service format. The passive light according to any one of claims 1 to 5, wherein the clear frame signal is a Gate frame in which a signal instructing clearing of the uplink buffer can be set in a predetermined area of a data unit. Network system. When the buffer monitoring unit clears the uplink buffer, the subscriber-side terminating device transmits a Report frame with a required bandwidth of zero corresponding to the received Gate frame to the backup station-side terminating device. The passive optical network system according to claim 6. When the buffer monitoring unit does not detect overflow of the upstream buffer and the subscriber-side terminal device receives the clear frame signal,
The buffer monitoring unit does not clear the upstream buffer, and the subscriber-side terminating device uses a report frame corresponding to the Gate frame and having a requested bandwidth as the accumulated amount of upstream signals accumulated in the upstream buffer so far. The passive optical network system according to claim 6, wherein: A subscriber-side termination device provided in the passive optical network system according to any one of claims 1 to 8. The station side termination | terminus apparatus with which the passive optical network system of any one of Claims 1-8 is provided. A subscriber-side terminating device comprising an upstream buffer for storing upstream signals and a buffer monitoring unit for monitoring an accumulated amount of upstream signals in the upstream buffer; A station-side terminal device that performs communication by a point control protocol, and a backup station-side terminal device, and a protection function for switching to the backup station-side terminal device when a failure occurs in the station-side terminal device, A traffic recovery method using a passive optical network system,
When a failure occurs in the station-side terminal device, the backup station-side terminal device transmits a clear frame signal including a signal instructing clearing of the uplink buffer to the subscriber-side terminal device,
A traffic recovery method in which the buffer monitoring unit clears the upstream buffer when the buffer monitoring unit detects overflow of the upstream buffer and the subscriber-side terminating device receives the clear frame signal.