JP2016143950A - PON system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability, in a PON system where the OLT is redundant configuration.SOLUTION: A PON system 10 includes OLT12 including an active OSU24 and a preliminary OSU26 provided redundantly, an ONU14 performing communication with the OLT12, and a supervisory control section 28. The preliminary OSU26 transmits a test frame to the ONU14, in the discovery window of the active OSU24. Upon receiving the test frame, the ONU14 transmits a response test frame to the preliminary OSU26. The supervisory control section 28 performs normality confirmation of the preliminary OSU26, based on the communication test results between the preliminary OSU26 and ONU14.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a PON (Passive Optical Network) that performs communication between a station side device (hereinafter also referred to as OLT (Optical Line Terminal)) and a plurality of subscriber side devices (hereinafter also referred to as ONU (Optical Network Unit)). In particular, the present invention relates to a PON system in which the OLT has a redundant configuration.

  2. Description of the Related Art Conventionally, a PON system is known as a subscriber optical fiber network system intended for a subscriber house such as a general home. This PON system is a double star type system in which the OLT and the ONU are connected by 1: m (m is an integer of 2 or more). The PON system can construct a low-cost optical communication network because a single optical fiber is shared by a plurality of ONUs as compared to a single star type system in which an OLT and an ONU are connected one-to-one.

  In order to increase the reliability of the communication system, a PON system having a redundant configuration on the OLT side has been proposed. In such a PON system, an active system and a standby optical line unit (hereinafter also referred to as OSU (Optical Subscriber Unit)) are redundantly provided in the OLT, and an OSU that communicates with the ONU using an optical switch is provided as the active system. And a backup system (see, for example, Patent Document 1).

JP 2010-147801 A

  However, sudden use of a standby OSU that is not used at normal times in the event of a failure is not reliable in consideration of the possibility of a failure in the standby OSU.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a technique capable of improving reliability in a PON system in which an OLT has a redundant configuration.

  In order to solve the above-described problems, a PON system according to an aspect of the present invention includes a station side device including redundantly used optical line units and backup optical line units, and a subscriber communicating with the station side device. Side device. In this PON system, a communication test is performed between the standby optical line unit and the subscriber side device within the discovery window of the active optical line unit, and the standby optical line unit is determined based on the result of the communication test. Check for normality.

  It should be noted that any combination of the above-described constituent elements and a representation of the present invention converted between an apparatus, a method, a system, a program, a recording medium storing the program, and the like are also effective as an aspect of the present invention.

  According to the present invention, reliability can be improved in a PON system in which the OLT has a redundant configuration.

It is a figure which shows the PON system which concerns on embodiment of this invention. It is a figure for demonstrating the discovery process performed when registering ONU newly to OLT. It is a figure for demonstrating the normality confirmation process of spare system OSU in the PON system which concerns on this embodiment. It is a flowchart for demonstrating the normality confirmation process of spare system OSU in the PON system which concerns on embodiment of this invention.

  FIG. 1 is a diagram showing a PON system 10 according to an embodiment of the present invention. As shown in FIG. 1, the PON system 10 includes a station side device (OLT) 12, a plurality (n: n is an integer of 2 or more) subscriber side devices (ONU) 14, and an optical splitter 16. . The OLT 12 includes an active optical line unit (active OSU) 24, a standby optical line unit (protective OSU) 26, and a monitoring control unit 28 that controls various components of the OLT 12.

  An active optical fiber 18 is connected to the active OSU 24. A backup optical fiber 20 is connected to the backup OSU 26. The working optical fiber 18 and the standby optical fiber 20 are branched into a plurality (n) of branched optical fibers 22 by the 2: n optical splitter 16. Each branch optical fiber 22 is connected to the ONU 14.

  In order to perform communication between the OLT 12 and each ONU 14, a logical link (Logical Link) needs to be established between the OLT 12 and each ONU 14. In the PON section between the OLT 12 and the ONU 14, the downstream optical signal from the OLT 12 to each ONU 14 is a continuous optical signal multiplexed by time division multiplexing (TDM). The downstream optical signal output from the OLT 12 is transmitted to the ONU 14 connected to the optical splitter 16, but only the ONU 14 with which the logical link is established takes in the optical signal transmitted to itself.

  On the other hand, the upstream optical signal from each ONU 14 to the OLT 12 is multiplexed by a TDMA (Time Division Multiple Access) method. In TDMA, in order to prevent the optical signals from the ONUs 14 from colliding, a non-signal period called a guard time is inserted between the optical signals. Therefore, unlike the downstream optical signal from the OLT 12 to each ONU 14 is a continuous optical signal, the upstream optical signal from the ONU 14 to the OLT 12 is a burst-like optical signal in which signal transmission is performed intermittently. In the PON system, generally, the transmission order of the upstream optical signal of each ONU 14 and the signal band allocated to each ONU 14 are controlled by the dynamic bandwidth allocation function (DBA) of the OLT 12.

  During normal operation, the OLT 12 communicates with the ONU 14 using the active OSU 24. When an abnormality occurs in the active OSU 24, the monitoring control unit 28 switches the OSU that performs communication with the ONU from the active OSU 24 to the standby OSU 26. Specifically, the monitoring control unit 28 stops the output of the downstream optical signal from the active OSU 24 and causes the standby OSU 26 to output the downstream optical signal. In addition, the supervisory control unit 28 causes the active OSU 24 to stop the upstream optical signal reception process and causes the standby OSU 26 to perform the upstream optical signal reception process. By performing such redundancy switching processing, it is possible to maintain a communication line with the ONU 14 connected under the optical splitter 16.

  The active OSU 24 includes an active optical transmitter / receiver 30, an active signal processor 32, an active PON controller 34, an active ONU management table 36, and an active frame normality determination unit 38.

  The working optical transceiver 30 includes a light receiving element such as a photodiode and a light emitting element such as a laser diode. The active optical transmission / reception unit 30 is configured such that the start and stop of light emission can be controlled by the monitoring control unit 28. The working signal processing unit 32 performs predetermined signal processing on the upstream signal from the working optical transceiver 30 and the downstream signal to the working optical transceiver 30.

  The active PON control unit 34 controls various components of the active OSU 24. The working PON control unit 34 includes a working MPCP function unit 35. The working MPCP function unit 35 controls the transmission start time and the transmission amount of the upstream optical signal for each ONU 14 using a Multi-Point Control Protocol (MPCP) frame. The working MPCP function unit 35 performs dynamic bandwidth allocation by exchanging the GATE frame and the REPORT frame with the ONU 14. The GATE frame is a frame for notifying the ONU 14 of the transmission start time and the transmission amount of the upstream optical signal from the OLT 12. The REPORT frame is a frame that notifies the ONU 14 to the OLT 12 of the transmission waiting data amount accumulated in the ONU 14. The active MPCP function unit 35 repeats the exchange of the GATE frame and the REPORT frame between the OLT 12 and each ONU 14 so as to grasp the state of the upstream traffic in each ONU 14 so that the upstream optical signal from each ONU 14 does not collide. The transmission start time and transmission amount of each ONU 14 are appropriately controlled.

  The active ONU management table 36 stores information (LLID (Logical Link Identifier), RTT (Round Trip Time)) and the like of the ONU 14 with which a logical link is established with the active OSU 24.

  The working frame normality determination unit 38 determines the normality of the frames transmitted and received by the working optical transmission / reception unit 30. If the frame is normal, the working frame normality determination unit 38 informs the working PON control unit 34 that the frame is normal. When there is an abnormality such as when the frame is broken or when the frame does not reach from the ONU 14, the active frame normality determination unit 38 notifies the active PON control unit 34 that the frame is abnormal. The active PON control unit 34 reports information related to the normality of the frame to the monitoring control unit 28.

  The standby OSU 26 includes a standby optical transceiver 40, a standby signal processor 42, a standby PON controller 44, a standby ONU management table 46, and a standby frame normality determination unit 48. The backup PON control unit 44 includes a backup MPCP function unit 45. Since the functions of the functional units of the standby OSU 26 are the same as the functions of the corresponding functional units of the active OSU 24, the description thereof is omitted here.

  In this embodiment, the active MPCP function unit 35 and the standby MPCP function unit 45 are synchronized so that information can be shared. Similarly, the active ONU management table 36 and the standby ONU management table 46 are also synchronized and share information.

  FIG. 2 is a diagram for explaining a discovery process performed when the ONU 14 is newly registered in the OLT 12. In the PON system, when a new ONU 14 is connected, the OLT 12 automatically discovers the ONU 14 and assigns an LLID to the ONU 14 to automatically establish a logical link. This process is called a discovery process. The discovery process is performed during main signal communication. Here, a case where the active OSU 24 performs discovery processing will be described.

  In the discovery process, first, the active OSU 24 broadcasts a Discovery Gate frame and notifies the unregistered ONU 14 of the transmission timing. Further, the active OSU 24 sets a discovery window that is a period for accepting a registration request from the unregistered ONU 14. The unregistered ONU 14 that has received the Discovery Gate frame transmits a Register Req frame to the active OSU 24 as a registration request frame. When the active OSU 24 receives the Register Req frame in the discovery window, the active OSU 24 transmits the Register frame to the ONU 14 that has transmitted the Register Req frame, and notifies the LLID. Further, the active OSU 24 transmits a Gate frame to the ONU 14 to notify the transmission band and the transmission timing. On the other hand, when the ONU 14 transmits a Register_Ack frame and makes a registration reception response, the discovery process is completed, and a logical link is established between the active OSU 24 and the ONU 14 to enable communication. Such discovery processing is repeated every predetermined discovery cycle. That is, a Discovery Gate frame is transmitted from the active OSU 24 at every discovery cycle.

  FIG. 3 is a diagram for explaining normality confirmation processing of the standby OSU 26 in the PON system 10 according to the present embodiment. In the PON system 10, a communication test is performed between the standby OSU 26 and the ONU 14 within the discovery window of the active OSU 24, and the normality of the standby OSU 26 is confirmed based on the result of the communication test. While the active OSU 24 is in the discovery window, no downstream optical signal is transmitted from the active OSU 24 to the ONU 14. Therefore, the downstream optical signal from the active OSU 24 and the downstream signal from the standby OSU 26 do not collide during the discovery window, and the communication test of the standby OSU 26 can be suitably performed.

  As shown in FIG. 3, in the normality confirmation process of the standby OSU 26, the standby OSU 26 transmits a test frame to the ONU 14 within the discovery window of the active OSU 24. When the ONU 14 receives the test frame, the ONU 14 transmits a response test frame to the standby OSU 26. The standby frame normality determination unit 48 of the standby OSU 26 determines the normality of the response test frame. This normality determination result is reported to the monitoring control unit 28 by the active PON control unit 34.

  The supervisory control unit 28 determines that the standby OSU 26 is normal when the standby OSU 26 has successfully received the response test frame from the ONU 14. On the other hand, the supervisory control unit 28 determines that the standby OSU 26 is abnormal when the standby OSU 26 cannot normally receive the response test frame from the ONU 14, such as when the response test frame is broken or when the response test frame does not arrive. judge.

  FIG. 4 is a flowchart for explaining normality confirmation processing of the standby OSU 26 in the PON system 10 according to the embodiment of the present invention. As a premise, a logical link is established between the active OSU 24 and the ONU 14.

  First, the ONU management table information and the MPCP information of the active OSU 24 and the standby OSU 26 are synchronized so that the frame can be transmitted from the active OSU 24 to the ONU 14 (S10).

  Next, a Discovery Gate frame is transmitted from the active OSU 24 every discovery cycle (S12).

  Next, the monitoring control unit 28 determines whether or not the Discovery Gate frame has been transmitted a predetermined number of times (S14). When the Discovery Gate frame has not been transmitted a predetermined number of times (N in S14), the process returns to S12. On the other hand, when the Discovery Gate frame has been transmitted a predetermined number of times (Y in S14), the process proceeds to S16. Here, the condition is whether or not the Discovery Gate frame has been transmitted a predetermined number of times. If normality is confirmed in all discovery processes, it will hinder the registration of unregistered ONUs, which is the original purpose of the discovery process. This is because there is a fear. The predetermined number of times may be about 100 to 1000, for example.

  In S <b> 16, the monitoring controller 28 stops the light emission of the active optical transceiver 30 using the discovery window timing of the active OSU 24. Normally, the optical transmission unit of the PON system always transmits an idle signal at the time of ACTIVE other than the time of frame transmission. Therefore, when the test frame is transmitted from the standby OSU 26, it is necessary to stop the light emission of the active optical transmitter / receiver 30 in order to prevent frame collision.

  Next, a test frame is transmitted from the standby OSU 26 to the ONU 14. After transmitting the test frame, the standby OSU 26 continues to transmit an idle signal (S18).

  When receiving the test frame from the standby OSU 26, the ONU 14 transmits a response test frame (S20). Here, the monitoring control unit 28 stops the light emission of the standby optical transmission / reception unit 40 by the end of the discovery window, and starts the light emission of the active optical transmission / reception unit 30 (S22).

  Next, the monitoring control unit 28 determines whether or not the standby OSU 26 has successfully received the response test frame from the ONU 14 (S24). When the standby OSU 26 has successfully received the response test frame from the ONU 14 (Y in S24), the monitoring controller 28 determines that the standby OSU 26 is normal (S26). On the other hand, if the standby OSU 26 cannot normally receive the response test frame from the ONU 14 (N in S24), the monitoring controller 28 determines that the standby OSU 26 is abnormal (S28).

  As described above, in the PON system 10 according to the present embodiment, the communication test is performed between the standby OSU 26 and the ONU 14 using the test frame during the discovery window of the active OSU 24, so that the redundant OS The normality of the standby OSU 26 can be confirmed in an actual environment. When it is determined that the spare OSU 26 is abnormal, the maintenance person can inspect and repair the spare OSU 26. As a result, when a failure occurs in the active OSU 24 and the operation is switched to the standby OSU 26, it is possible to prevent a situation in which the standby OSU 26 is unable to communicate due to an abnormality, thereby improving the reliability of the PON system 10. be able to.

  In the PON system 10 according to the present embodiment, since the test frame is transmitted from the standby OSU 26 during the discovery window, the test frame does not collide with the downstream optical signal from the active OSU 24. However, if a Register Req frame is transmitted from an unregistered ONU 14 at the same timing as when a response test frame is transmitted from a registered ONU 14, these may collide and the response test frame may be broken. If the response test frame is broken, the standby OSU 26 may be erroneously determined to be abnormal.

  Therefore, in the PON system 10, when the standby OSU 26 cannot normally receive the response test frame continuously a plurality of times (for example, 2 to 10 times), it may be determined that the standby OSU 26 is abnormal. In this case, the possibility that the backup OSU 26 is erroneously determined to be abnormal can be reduced. For unregistered ONUs 14, a logical link may be established in the next and subsequent discovery processes.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  10 PON system, 12 OLT, 14 ONU, 16 optical splitter, 24 active OSU, 26 standby OSU, 28 monitoring control unit.

Claims (4)

A station-side apparatus comprising a redundant working optical line unit and a standby optical line unit;
A subscriber side device communicating with the station side device;
A PON system comprising:
In the discovery window of the working optical line unit, a communication test is performed between the standby optical line unit and the subscriber side device, and the normality of the standby optical line unit is determined based on the result of the communication test. A PON system characterized by performing confirmation. The standby optical line unit transmits a test frame to the subscriber side device within the discovery window of the active optical line unit,
2. The PON system according to claim 1, wherein the subscriber-side device transmits a response test frame to the protection optical line unit when the test frame is received. 3.   3. The PON system according to claim 2, wherein when the backup optical line unit cannot normally receive the response test frame from the subscriber side device, the backup optical line unit is determined to be abnormal. .   4. The PON system according to claim 3, wherein when the backup optical line unit cannot normally receive the response test frame a plurality of times, the backup optical line unit is determined to be abnormal.

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