JP6053172B2 - Optical access system, OLT, OSU, and OSU redundancy method - Google Patents

Description

  The present invention relates to an N: 1 redundant optical access system in which one of a plurality of optical subscriber line termination boards (OSUs) is used for redundancy, and a station side device (OLT; Optical Line Terminal) provided therein. And the OSU and the OSU redundancy method performed by the OSU.

[Description of protection]
In recent years, an optical access network that lays an optical fiber to each user and provides high-speed communication has been spreading. The optical access network connects each user and a communication station via a PON (Passive Optical Network) described later or a media converter.

  The PON is a point-to-point in which an OSU included in one OLT and one or more user-side transmission equipment, an optical network unit (ONU) are connected to an optical fiber via a splitter. It is a multipoint optical access network. The media converter is a point-to-point optical access network in which one ONU is connected to one OSU.

  In this optical access network, the OSU, ONU, optical fiber, or related technology for making a splitter redundant, which is a component of the system, makes an OSU failure, an ONU failure, an optical fiber by making the above-described components redundant. There is an optical access protection technique for avoiding system down when breakage or splitter breakage occurs (see, for example, Non-Patent Document 1, pages 113 to 116). In other words, when optical access protection is applied, when these system configuration factors fail or break, the service is continued by switching the operation from the normal system to the redundant system. The invention according to the present application pays attention to the OSU redundancy method among these optical access protections.

(Description of 1: 1 method)
Normally, one OLT is connected to one to a plurality of OSUs, an exchange switch (connected to the upper side of one to a plurality of OSUs), and an upper network interface (upper side of the exchange switch). ) And the OLT control unit are accommodated together.

  That is, the OLT is a communication node for exchanging the optical access network and the upper network, and there can be many OSUs serving as interfaces on the optical access side. Therefore, for the redundancy of OSU, an optimal configuration must be considered on the premise of such a basic configuration of OLT.

  Hereinafter, description will be made based on an example of PON. As shown in FIG. 1, the first configuration of the related art OSU redundancy technology is a redundant system OSU 12-1 to a redundant system for each of the normal OSU 11-1 to the normal OSU 11-3 in the OLT 10. One OSU 12-3 is prepared (see, for example, Non-Patent Document 1, page 114, Type-B). For convenience, this first configuration will be referred to as “1: 1 redundancy type”. The specific configuration and operation of the “1: 1 redundancy type” are as follows.

  The OLT 10 includes a replacement switch 13 and an interface 14. The exchange switch 13 is a layer 2 switch (L2SW), and when it receives downlink data from a higher level, it reads an identifier (for example, Virtual LAN Identifier (VID)) attached to the data. Since the exchange switch 13 has registered in advance the association between the VID number and the ONU number and the correspondence information of the connection destination OSU number of each ONU 15, the association information is associated with the corresponding VID number from the received VID number. The connection destination OSU number of the received ONU is known, and downlink data is transmitted to the port to which the connection destination OSU is connected. The interface 14 connects the host network 100 and the exchange switch 13.

  The normal system OSU 11-1 and the redundant system OSU 12-1 are connected to the ONU 51-1 to ONU 51-M via an M: 2 splitter 41-1 (N is an integer of 1 or more). Further, another branch may be performed by installing a splitter again beyond the M: 2 splitter 41-1 to M: 2 splitter 41-3. The number of connection destination ONUs is an integer of 0 or more. The ports on the ONU side of the M: 2 splitter 41-1 to M: 2 splitter 41-3 may have empty ports.

  For example, the normal OSU 11-1 transfers user data from the lower ONUs 51-1 to ONU51-M to the exchange switch 13, and transfers user data from the exchange switch 13 to the lower ONUs 51-1 to ONU51-M. ing. Here, when the normal system OSU 11-1 fails during communication, the OLT control unit 15 detecting this switches to the redundant OSU 12-1 in the following order.

(I) Falling of normal OSU 11-1 (light emission stopped from light emission state)
(Ii) Startup of redundant system OSU 12-1 (light emission start from light emission stop state)
(Iii) The setting of the exchange switch 13 is changed.

  The redundant system OSU 12-1 then sends the user data from the lower ONUs 51-1 to ONU51-M to the exchange switch 13 and the user data from the exchange switch 13 to the lower ONUs 51-1 to ONU51, as before the failure. Continue the service by initiating each transfer to -M.

  Normal OSU11-2 and normal OSU11-3, redundant OSU12-2 and redundant OSU12-3 (the number of redundant OSUs may be a natural number greater than or equal to 1) and the operation during protection are also normal. The relationship between the system OSU 11-1 and the normal system OSU 12-1 is the same. In this “1: 1 redundancy type” configuration, the same number of redundant OSUs as normal OSUs must be accommodated in the OLT 10 in advance, which causes problems such as OLT slot consumption and OSU introduction cost increase. Was.

(N: Explanation of 1 method)
On the other hand, as shown in FIG. 2, the second configuration of the related art OSU redundancy technique includes a plurality of normal OSU 11-1 to normal OSU 11-i and normal OSU 11-N in the OLT 10. One redundant OSU 12 is prepared for (i = 1, 2, 3,..., N: N is an integer of 1 or more). This suppresses the problem of OLT slot consumption and the problem of cost increase (see FIG. 8 of Patent Document 1). For convenience, this second configuration is referred to as “N: 1 redundancy type”. The specific configuration and operation of “N: 1 redundant type” are as follows.

  In FIG. 2, the OLT 10 accommodates a normal OSU 11-i (i = 1, 2, 3,..., N: N is an integer equal to or greater than 1) and one redundant OSU 12. The redundant OSU 12 is connected to an optical switch 35 of N × 1 type (number of ONU side ports N, number of OLT side ports 1). The optical switch 35 has one OLT side port (port x) and N ONU side ports (ports 1, 2, 3,..., I,..., N).

  The M: 2 splitter 41 has M ports on the ONU side, and is connected to M or less ONUs 51 respectively. There may be empty ports in the M ports on the ONU side of the M: 2 splitter 41. Furthermore, a splitter may be installed again between the M: 2 splitter 41 and the ONU group 50 to perform further branching. The M: 2 splitter 41 has two ports on the OLT side, one of which is connected to the OSU 11 and the other is connected to the optical switch 35. Specifically, the M: 2 splitter 41-i connects one OLT side port and the normal system OSU 11-i, and connects the other OLT side port and the port i of the optical switch 35.

  The normal system OSU 11-1 to the normal system OSU 11 -N respectively send user data from the subordinate ONUs 51-1 to 54 -M to the exchange switch 13, and user data from the exchange switch 13 to the subordinate ONUs 51-1 to 1 to OSU 51. -1 to M, respectively. For example, when the normal OSU 11-1 fails during communication, the OLT control unit 15 that has detected the failure switches to the redundant OSU 12 in the following order.

(I) Connection between port x and port 1 in the optical switch 35 (ii) Setting change of the exchange switch 13 (iii) Falling down of the normal OSU 11-1 (light emission is stopped from the light emission state)
(Iv) Startup of redundant system OSU 12 (light emission starts from light emission stop state)

  The redundant OSU 12 then sends the user data from the subordinate ONUs 51-1-1 to 51-1 -M to the exchange switch 13 and the user data from the exchange switch 13 to the subordinate ONU 51-1 in the same manner as before the failure occurred. The service is continued by starting the transfer to each of -1 to 51-1-M.

  Other normal system OSUs 11-i (i = 2, 3,...) Are also operated at the time of failure, normal system OSU 11-2 to normal system OSU 11-N, M: 2 splitter 41-2 to M: 2 splitter, respectively. 41-N is the same as the above description except that the port of the optical switch 35 is switched.

  In this “N: 1 redundant type” configuration, since only one redundant OSU 12 can be accommodated in the OLT 10 at the same time for N normal OSU 11-1 to normal OSU 11 -N, OLT slot consumption is reduced. The problem and the problem of the OSU introduction cost increase are solved.

  Further, under the condition that the probability that a plurality of normal OSUs 11-1 to 11-N simultaneously fail is sufficiently low, it is easy to ensure reliability by redundancy in this configuration and operation.

  In the OLT, the exchange switch, the upper network interface, and the OLT control unit may be made redundant, but the description is omitted here because they are not directly related.

  Also, in the case of an optical access system using a media converter instead of a PON, the protection method can be realized with an equivalent configuration. In this case, the M: 2 optical splitter 41-1 to M: 2 splitter 41-N shown in FIG. 2 become the 1: 2 optical splitter 42-1 to 1: 2 optical splitter 42-N shown in FIG. Here, except that each OSU 11 is connected to a maximum of one ONU 51-1 to ONU 51-N, the configuration and operation are the same as in the case of the PON.

International publication WO2013 / 058179 brochure

ITU-T G. 983.1

  As described above, for redundancy of OSU, N: 1 redundant optical access system that prepares one redundant OSU for N normal OSUs is routed by an optical switch when a failure of normal OSU occurs. Are switched, the path between the ONU under the failed OSU and the redundant OSU is established, and the redundant OSU is operated, so that the ONU communication under the failed normal OSU can be restored.

  However, the OLT control unit may not be able to confirm the path to which the optical switch is switched, that is, the connection destination due to some failure during the redundant OSU operation. In such a case, the OLT control unit cannot detect the connection destination of the optical switch, and cannot output the downstream optical signal to the redundant system OSU even if an abnormality occurs in the connection destination of the optical switch. As a result, there is a problem that the downstream optical signal of the normal OSU and the downstream signal of the redundant OSU may collide and hinder communication between the normal OSU and the ONU.

  Therefore, in order to solve the above-described problem, the present invention provides a normal OSU− when the connection destination of an optical switch becomes unknown due to a failure during operation of a redundant OSU in N: 1 protection with an optical switch. It is an object of the present invention to provide an optical access system, an OLT, an OSU, and an OSU redundancy method that can prevent communication between ONUs from being affected.

  In order to achieve the above object, the optical access system of the present invention stops the light emission of the redundant OSU when the connection destination information of the optical switch cannot be acquired.

Specifically, an optical access system according to the present invention includes an optical subscriber line termination board (OSU) installed in a station side apparatus (OLT; Optical Line Terminal) and at least one subscriber side transmission. An optical access system for connecting a device (ONU; Optical Network Unit),
Among the OSUs, N (N ≧ 1) normal OSUs used at normal times,
One redundant OSU used as a substitute for any one of the N normal OSUs among the OSUs;
N optical splitters having a C (1 ≦ C) branch side and a two branch side, the ONU being connected to the C branch side, and the N normal system OSU being connected to one of the two branch sides;
An optical switch having one OSU side port to which the redundant OSU is connected and N ONU side port to which the other of the two branch sides of the optical splitter is connected;
An OLT control unit for controlling start / stop of light emission for an optical signal for the OSU, and for controlling any one of the one OSU side port and the N ONU side port for the optical switch;
With
When the connection destination that is one of the N ONU side ports coupled to the one OSU side port in the optical switch becomes unknown during the operation of the redundant OSU, the OLT control unit The light emission of the redundant system OSU is stopped.

  The OLT according to the present invention includes the OLT control unit included in the optical access system.

  Furthermore, the OSU redundancy method according to the present invention is an OSU redundancy method in the optical access system, wherein the OLT control unit is configured to operate the one OSU side in the optical switch during the operation of the redundant OSU. When the connection destination, which is one of the N ONU ports coupled to the port, becomes unknown, the redundant OSU stops emitting light.

  When the connection information of the optical switch can no longer be acquired, the output of the downstream optical signal from the redundant OSU is stopped by stopping the light emission of the redundant system OSU. Collision between the downstream optical signal of the OSU and the downstream signal of the redundant OSU can be prevented. Therefore, the present invention has an effect on the communication between the normal OSU and the ONU when the connection destination of the optical switch becomes unknown due to a failure during the operation of the redundant OSU in the N: 1 system protection including the optical switch. It is possible to provide an optical access system, an OLT, and an OSU redundancy method that can prevent such an effect.

For example, the OLT control unit includes an optical switch control link monitoring unit that periodically transmits a predetermined signal to the optical switch and detects a control link that recognizes the connection destination in response to the optical switch. And
The connection destination is unknown when the optical switch control link monitoring unit detects a control link disconnection without a response from the optical switch when the control link detection is performed.

  The OLT control unit periodically acquires connection destination information from the optical switch. Then, the OLT control unit stops the light emission of the redundant OSU when the failure occurs in the optical switch when the connection destination information cannot be obtained and the connection destination becomes unknown. Light emission of the redundant OSU can be stopped without delay due to the failure of the optical switch, and the influence on communication between the normal OSU and ONU can be minimized.

For example, an ONU link monitoring unit that monitors a link state with the ONU under the OSU is further provided.
The OLT control unit includes an optical switch control link monitoring unit that periodically transmits a predetermined signal to the optical switch and performs control link detection for recognizing the connection destination in response to the optical switch.
When the optical switch control link monitoring unit detects a control link disconnection without a response from the optical switch when the control link detection is performed, and the ONU link monitoring unit detects all of the redundant OSU subordinates. When the link disconnection of the ONU is detected, the connection destination is unknown.

  At this time, the OSU according to the present invention includes the ONU link monitoring unit.

  The OLT control unit not only periodically acquires connection destination information from the optical switch but also acquires ONU link information from the redundant OSU. Then, the OLT control unit confirms the ONU link when the connection destination information cannot be obtained. If the ONU link is normal, the OLT control unit determines that only the control system between the optical switch and the OLT control unit is abnormal and does not stop the redundant OSU from emitting light. Even when the control link between the optical switch and the OLT is disconnected, if at least one ONU link is established, the redundant OSU can continue to emit light, so that the downstream optical signal of the redundant OSU is transmitted between the normal OSU and the ONU. While ensuring that communication is not affected, the possibility that communication between redundant OSUs and ONUs cannot be reduced can be reduced.

The OLT control unit of the optical access system according to the present invention periodically transmits a predetermined signal to the optical switch, and performs an optical switch control link for detecting a control link that recognizes the connection destination by a response from the optical switch. Has a monitoring unit,
The OLT control unit causes the optical switch control link monitoring unit to perform the control link detection when light emission of the redundant OSU is stopped, and detects the establishment of a control link with a response from the optical switch The redundant system OSU is caused to start light emission.

  After the redundant OSU starts emitting light, the communication between the redundant OSU-ONU can be resumed without affecting the communication between the normal OSU and the subordinate ONU by establishing a link with the subordinate ONU. it can.

  The present invention affects the communication between normal OSU and ONU when the connection destination of the optical switch becomes unknown due to a failure during operation of the redundant OSU in N: 1 protection with an optical switch. Optical access system, OLT, OSU, and OSU redundancy method can be provided.

It is a figure explaining 1: 1 system protection. It is a figure explaining N: 1 system protection. It is a figure explaining N: 1 system protection. It is a figure explaining the structure of OLT which concerns on this invention. It is a figure explaining the structure of OLT which concerns on this invention. It is a table | surface explaining the state transition of the optical access system which concerns on this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 4 is a diagram illustrating the OLT 10-1 of the present embodiment. The OLT 10-1 is used as an OLT of an N: 1 redundant optical access system as shown in FIG. Such an optical access system is an optical access system that connects an OSU mounted on an OLT and at least one ONU,
Among the OSUs, N (N ≧ 1) normal OSUs 11 used at normal time,
One redundant OSU 12 used as a substitute for any one of the N normal OSUs 11 among the OSUs;
An N optical splitter 41 having a C (1 ≦ C) branch side and a two branch side, the ONU is connected to the C branch side, and the N normal system OSU 11 is connected to one of the two branch sides;
An optical switch 35 having one OSU side port to which the redundant OSU 12 is connected and N ONU side port to which the other of the two branches of the optical splitter 41 is connected;
An OLT control unit 15 that controls the start / stop of light emission for the optical signal to the OSU, and the control to couple any one of the one OSU side port and the N ONU side port to the optical switch 35;
Is provided.

  The OLT control unit 15 includes an optical switch control link monitoring unit 61 that periodically transmits a predetermined signal to the optical switch 35 and performs “control link detection” for recognizing the connection destination in response to the optical switch 35.

  OSUs # 1 to #N are normal OSUs 11, OSU # N + 1 is a redundant OSU 12, and each OSU includes a PON interface (PON-IF) 62 and an OSU processing control unit 63, respectively. Note that descriptions of other components that are not necessary for the description of the present embodiment are omitted.

  The OLT composed of functional blocks of the above operation is applied to an optical access system that employs N: 1 redundant protection shown in FIG. In this optical access system, even when the OLT control unit 15 cannot confirm the connection destination of the optical switch while the redundant OSU 12 is in operation, the communication between the normal OSU and the ONU is affected by the downstream signal from the redundant OSU 12. Prevent giving.

  First, each part of OLT10-1 of FIG. 4 is demonstrated.

  The PON-IF 62 receives the upstream frame of the optical signal transmitted from the ONU 51 toward the OSU (11, 12), converts it into an electrical signal, and outputs it to the OSU processing control unit 63. The PON-IF 62 receives the downstream frame of the electrical signal from the OSU processing control unit 63, converts it into an optical signal, and outputs it to the optical transmission line. Further, the PON-IF 62 receives a light emission start / light emission stop instruction for transmitting an optical signal from the OSU processing control unit 63, and stops light emission from the light emission state and starts light emission from the light emission stop state according to the instruction.

  The OSU processing control unit 63 receives the upstream frame of the signal from the PON-IF 62, and when it is user data, outputs it to the upper exchange switch. Further, it receives a light emission start / light emission stop instruction from the OLT control unit 15 to be described later, and transfers it to the PON-IF 62.

  The OLT control unit 15 transmits a light emission start / stop instruction to the OSU (11, 12), and instructs the optical switch 35 to change the connection destination when OSU switching is necessary due to a failure of the OSU. Manage connection destinations. Further, the optical switch control link monitoring unit 61 of the OLT control unit 15 checks whether a control link between the optical switch and the OLT has been established by the following method.

  In FIG. 2, in a state where no failure or the like has occurred in the normal system OSU 11 and only the normal system OSU 11 is operated, the redundant system OSU 12 is in a light emission stop state. Here, it is assumed that a failure has occurred in the normal system OSU 11-1. The OLT control unit 15 operates the redundant OSU 12 according to the light emission start instruction, and switches the connection destination of the optical switch 35 to the port 1 for the M: 2 optical splitter 41-1 according to the connection destination change instruction. Then, the OLT control unit 15 places the normal OSU 11-1 in a light emission stop state in response to the light emission stop instruction. By such a switching operation, communication can be continued between the redundant OSU 12 and the ONUs 51-1-1-1 to ONU51-1-M.

  At this time, the OLT control unit 15 periodically transmits a predetermined signal (for example, a keep alive message) to the optical switch 35. The OLT control unit 15 confirms the failure of the optical switch 35 based on whether there is a response from the optical switch 35 to the keep-alive message. That is, the OLT control unit 15 confirms whether or not the control link between the optical switch and the OLT is established based on the presence or absence of a response to the keep alive message (control link detection).

  Here, the optical switch 35 notifies the OLT control unit 15 of “connection destination” indicating which port x and which port i (i = 1, 2,..., N) are connected. Specifically, the optical switch 35 includes the connection destination in the response, or transmits the connection destination to the OLT control unit 15 separately from the response. That is, the OLT control unit 15 can acquire the connection destination of the optical switch 35 by confirming whether the control link between the optical switch and the OLT is established.

  When the redundant system OSU 12 is in operation, the OLT control unit 15 determines whether the connection destination that is one of the N ONU side ports to be coupled to the one OSU side port in the optical switch 35 becomes unknown. The light emission of the OSU 12 is stopped. Specifically, the connection destination is unknown when the optical switch control link monitoring unit 61 detects a control link disconnection without a response from the optical switch 35 when performing the control link detection.

  Here, it is assumed that there is no response from the optical switch 35 with respect to the keep-alive message transmitted by the OLT control unit 15 (control link disconnection), and the OLT control unit 15 cannot acquire the connection destination of the optical switch. For example, even if the optical switch 35 changes the connection of the port x from the port 1 for the M: 2 optical splitter 41-1 to the port 2 for the M: 2 optical splitter 41-2 for some reason, the OLT control unit 15 does not change the optical switch. 35 connection destinations cannot be acquired.

  Thus, when the connection destination of the optical switch 35 is different from the setting of the OLT control unit 15, the downstream optical signal from the normal OSU 11-2 collides with the downstream optical signal from the redundant OSU 12, and the normal OSU 11- 2 and ONUs 51-2-1 to ONUs 51-2 to M cannot be communicated.

  In order to solve this problem, when there is no response from the optical switch 35 to the keep alive message transmitted by the OLT control unit 15, the OLT control unit 15 instructs the redundant OSU 12 to stop the light emission, and receives the instruction to perform redundancy. The PON-IF 62 # N + 1 of the system OSU 12 stops emitting light. With this operation, the downstream optical signal of the redundant OSU 12 is prevented from affecting communication between the normal OSU 12 and the subordinate ONU 50. In addition, when the notification of the connection destination other than the connection destination set by the OLT control unit 15 is received from the optical switch 35, the connection destination of the optical switch 35 is not in the set state, and therefore the OLT control unit 15 emits light to the redundant OSU 12. A stop instruction may be given.

  On the other hand, the OLT control unit 15 causes the optical switch control link monitoring unit 61 to perform control link detection when the light emission of the redundant OSU 12 is stopped, and detects the establishment of a control link with a response from the optical switch 35 The redundant system OSU 12 starts light emission.

  When the redundant system OSU detects the control link while the light emission is stopped, and the optical switch control link monitoring unit 61 confirms the return of the control link between the OLT and the optical switch, the OLT control unit 15 starts the light emission to the redundant system OSU 12. Instruct. With this operation, after the redundant OSU 12 starts emitting light, a link is established with the subordinate ONU 51, and communication between the redundant OSU and the ONU is resumed without affecting the communication between the normal OSU and the subordinate ONU. can do.

  Although the case of the PON has been described in the present embodiment, the present embodiment can also be applied to a media converter by changing the N: 2 splitter 41 to a 1: 2 splitter 42 as shown in FIG.

(Embodiment 2)
In the first embodiment, the OLT control unit confirms the connection destination of the optical switch from the state of the control link between the OLT and the optical switch, and instructs the redundant OSU to start / stop the light emission. As another method for confirming the connection destination of another optical switch, there is a method using the ONU link state under the redundant OSU together with the control link state.

  FIG. 5 is a diagram illustrating the OLT 10-2 according to the present embodiment. The OLT 10-2 has a configuration in which an ONU link monitoring unit 64 that monitors an ONU link state under the OSU is added to the OSU processing control unit 63 of the OLT 10-1 described in FIG.

The present embodiment further includes an ONU link monitoring unit 64 that monitors the link state with ONUs under the OSU,
When the optical switch control link monitoring unit 61 detects a control link disconnection without a response from the optical switch 35 when performing the control link detection, and the ONU link monitoring unit 64 detects all of the redundant OSU subordinates. When the ONU link disconnection is detected, the connection destination is unknown.

  Other functional blocks and message operations described in FIG. 5 are the same as those in FIG. The OSU processing control unit 63 receives the upstream frame of the signal from the PON-IF 62, and when it is user data, outputs it to the upper exchange switch. On the other hand, when the upstream frame is PON control data other than user data, the OSU processing control unit 63 uses the information about the subordinate ONU link state in the PON control data, and the ONU link state monitoring unit 64 Management is performed and the state is notified to the OLT control unit 15. That is, even if the control link between the optical switch and the OLT is not established (even when the control link is disconnected), the OLT control unit 15 manages the ONU link state as a result of the ONU link state management. If the link is established, the connection destination of the optical switch can be estimated from the ONU link state.

FIG. 6 is a table summarizing operations according to the state of the connection destination of the optical switch during operation of the redundant OSU 12 in the optical access system of this embodiment.
(A) Since the current state is the ONU link and control link established, the redundant OSU is emitting light, and the next state is the ONU link and control link established, there is no state change, so the OLT control unit Continues the emission of the redundant OSU.
(B) Although the current state is the control link disconnection, the ONU link is established, and the OLT control unit can identify the connection destination of the optical switch, so that the redundant OSU emits light, and the next state is the control link. Is recovered and the ONU link and the control link are established, the OLT control unit continues the light emission of the redundant OSU.
(C) The current state is that all ONU links are disconnected, but the control link is established, and the OLT control unit can identify the connection destination of the optical switch, so that the redundant OSU emits light. The next state is the ONU Since the link is recovered and the ONU link and the control link are established, the OLT control unit continues the light emission of the redundant OSU.
(D) The current state is a state where all the ONU links are disconnected and the control link is disconnected, and the OLT control unit cannot identify the connection destination of the optical switch, and therefore stops the light emission of the redundant OSU. Since the control link and the ONU link are not recovered simultaneously from this state, they are shaded.
(E) The current state is the ONU link and the control link is established, the redundant OSU is emitting light, the next state is the control link disconnection but the ONU link is established, and the OLT control unit Since the connection destination of the optical switch can be identified, the redundant OSU continues to emit light.
(F) Although the current state is the control link disconnection, the ONU link is established, and the OLT control unit can identify the connection destination of the optical switch, so that the redundant OSU emits light, and the next state is the control link. Since there is no state change when the ONU link is disconnected and the ONU link is established, the OLT control unit continues the light emission of the redundant OSU.
(G) The current state is that all ONU links are disconnected, but the control link is established, and the OLT control unit can identify the connection destination of the optical switch, so that the redundant OSU emits light. Since there is no direct transition from this state to a state in which the control link is broken and the ONU link is restored, it is shaded.
(H) The current state is that all the ONU links are disconnected and the control link is disconnected, and the OLT control unit cannot identify the connection destination of the optical switch, and therefore the light emission of the redundant OSU is stopped. Since the ONU link does not recover from this state while the control link is disconnected, it is shaded.
(I) The current state is an ONU link and control link is established, the redundant OSU is emitting light, the next state is a state in which all ONU links are disconnected but the control link is established, and the OLT control unit Since the connection destination of the optical switch can be identified, the redundant system OSU continues to emit light.
(J) The current state is that the control link is disconnected, but the ONU link is established, and the OLT control unit can identify the connection destination of the optical switch, so that the redundant OSU is emitting light. Since there is no direct transition from this state to a state in which all ONU links are disconnected and the control link is restored, it is shaded.
(K) Although the current state is that all ONU links are disconnected, the control link is established, and the OLT control unit can identify the connection destination of the optical switch, so that the redundant OSU emits light. Since there is no state change when the ONU link is disconnected and the control link is established, the OLT control unit continues to emit light from the redundant OSU.
(L) The current state is a state where all ONU links are disconnected and the control link is disconnected, and the OLT control unit cannot identify the connection destination of the optical switch. In this state, the control link is established, and the OLT control unit can identify the connection destination of the optical switch, and thus starts the redundant OSU to emit light.
(M) The current state is a state where the ONU link and the control link are established, and the redundant OSU is emitting light. Since there is no direct transition from this state to a state in which all ONU links are disconnected and the control link is disconnected, it is shaded.
(N) Although the current state is the control link disconnection, the ONU link is established, and the OLT control unit can identify the connection destination of the optical switch, so that the redundant OSU emits light. The next state is the all ONU Since the OLT control unit cannot identify the connection destination of the optical switch in a state where the link is disconnected and the control link is disconnected, the redundant OSU stops light emission.
(O) The current state is that all ONU links are disconnected, but the control link is established, and the OLT control unit can identify the connection destination of the optical switch, so that the redundant OSU emits light. Since the OLT control unit cannot identify the connection destination of the optical switch when the ONU link is disconnected and the control link is disconnected, the redundant OSU stops light emission.
(P) The current state is a state where all ONU links are disconnected and the control link is disconnected, and the OLT control unit cannot identify the connection destination of the optical switch. Since there is no state change in the disconnected and control link disconnected state, the OLT control unit continues to stop the light emission of the redundant OSU.

A specific example will be described.
(Example 1) During operation of the redundant OSU 12, there is an ONU link under the redundant OSU, and the optical switch control link monitoring unit 61 disconnects the optical switch control link from the normal state of the optical switch control link between the OLT and the optical switch. Will be described (example after (b) in FIG. 6). When the ONU link monitoring unit 64 confirms that all the ONU links are disconnected after the optical switch control link disconnection is detected, it is considered that an optical switch connection destination error has occurred, so the OLT control unit 15 emits light to the redundant OSU 12. The stop is instructed ((n) in FIG. 6). On the other hand, when the ONU link monitoring unit 64 detects the ONU link under the redundant OSU even after detecting the optical switch control link disconnection, the OLT control unit does not instruct the redundant OSU to stop the light emission ((f in FIG. 6 )). In this state, the connection destination of the optical switch is not abnormal as set by the OLT control unit, and only the control link between the OLT and the optical switch is disconnected due to the control port connected to the OLT of the optical switch or the power switch of the optical switch etc. It is thought that. Therefore, the OLT control unit 15 instructs the redundant OSU 12 to continue light emission and continues communication with the subordinate ONU.

(Example 2) During operation of the redundant OSU 12, there is an ONU link under the redundant OSU, and the ONU link monitoring unit 64 detects that all ONU links are disconnected from the normal state of the optical switch control link between the OLT and the optical switch. A case will be described (an example after (i) in FIG. 6). When the optical switch control link monitoring unit 61 detects an optical switch control link disconnection after detecting all ONU link disconnections, there is no ONU link under the redundant OSU, and the OLT control unit 15 confirms the connection destination of the optical switch. Can not. Therefore, the OLT control unit 15 instructs the redundant system OSU 12 to stop the light emission so that the light emission of the redundant system OSU 12 does not affect the communication between the normal system OSU and the subordinate ONU ((( o)).

(Example 3) A return from the redundant OSU light emission stop state to the light emission start will be described. In the redundant system OSU light emission stop state, when the optical switch control link monitoring unit 61 confirms the return of the control link between the OLT and the optical switch, the OLT control unit 15 instructs the redundant system OSU to restart the light emission (FIG. 6). (L)). After the light emission of the redundant OSU 12 is started, a link with the subordinate ONU is established ((c) in FIG. 6), so that the redundant OSU-ONU is not affected between the normal OSU and the subordinate ONU. Communication between them can be resumed.

  Compared with the OLT 10-1 of the first embodiment, the OLT 10-2 can continue the emission of the redundant OSU 12 as long as one ONU link is established even when the control link between the optical switch and the OLT is disconnected. . For this reason, the OLT 10-2 may prevent communication between the redundant OSU and the ONU while ensuring that the downstream optical signal of the redundant OSU does not affect the communication between the normal OSU and the ONU. Can be reduced.

  In the present embodiment, the case of PON has been described. However, the present embodiment can also be used for a media converter as in the first embodiment.

[Appendix]
The following describes the optical access system of this embodiment.
[Task]
In an N: 1 OSU redundant system (N × 1 optical switch type), when an abnormality occurs in the connection destination of the switch due to some failure during the operation of the redundant OSU, the normal OSU-ONU is detected by the downstream optical signal of the standby OSU. There is a risk of interfering with communication.

[Solution]
(1)
To an optical access system that connects one OSU mounted in an OLT that is a station side device and at least one ONU that is a subscriber side transmission device,
N (N ≧ 1) OSUs used as normal (hereinafter referred to as normal OSUs),
One redundant OSU used as a substitute for any one of the N normal OSUs;
N optical splitters having a C (1 ≦ C) branch side and a two branch side, the ONU being connected to the C branch side, and the N normal system OSU being connected to one of the two branch sides;
An optical switch having one OSU side port to which the redundant OSU board is connected, and N ONU side ports to which the other of the two branches of the optical splitter is connected;
An OLT control unit for controlling the OLT to start / stop light emission for the OSU and to couple any one of the one OSU side port and the N ONU side port to the optical switch;
An optical access system comprising:
An optical access system, wherein when the redundant OSU is operating as a substitute for a normal OSU, the redundant OSU stops light emission when the OLT control unit cannot confirm the connection destination of the optical switch in the previous period.

(2)
The OLT control unit includes an optical switch control link monitoring unit that monitors a control link state between the OLT control unit and the optical switch,
The optical access system according to (1), wherein the redundant OSU stops light emission when the optical switch control link monitoring unit detects the control link disconnection between the OLT control unit and the optical switch. .

(3):
An optical switch control link monitoring unit that monitors a control link state between the OLT control unit and the optical switch;
The OSU includes an ONU link monitoring unit that monitors the link state of the subordinate ONU,
When the optical switch control link monitoring unit detects the control link disconnection between the OLT control unit and the optical switch, and the ONU link monitoring unit detects a link disconnection of all ONUs, the redundant OSU emits light. The optical access system according to (1), wherein the optical access system is stopped.

(4):
When the redundant system OSU is in a light emission stop state and the optical switch control link monitoring unit detects establishment of a control link between the OLT control unit and the optical switch, the redundant system OSU starts light emission. The optical access system according to any one of (1) to (3) above.

(5):
An OLT and an OSU included in the optical access system according to any one of (1) to (4) above.

[effect]
In an N: 1 redundant optical access system using an N × 1 type optical switch, even when the connection destination of the optical switch cannot be confirmed from the OLT control unit during operation of the redundant OSU, the downstream signal of the redundant OSU Therefore, it is possible to avoid hindering communication between the normal OSU and the ONU.

11: Normal OSU
12: Redundant OSU
13: Exchange switch 14: Interface 15: OLT control unit 35: Optical switch 41: M: 2 splitter 42: 1: 2 splitter 50: ONU group 51: ONU
61: Optical switch control link monitoring unit 62: PON-IF
63: OSU processing control unit 64: ONU link monitoring unit

Claims (7)

Optical connection between an optical subscriber line termination board (OSU; Optical Subscriber Unit) mounted on a station side equipment (OLT; Optical Line Terminal) and at least one subscriber side transmission equipment (ONU; Optical Network Unit) An access system,
Among the OSUs, N (N ≧ 1) normal OSUs used at normal times,
One redundant OSU used as a substitute for any one of the N normal OSUs among the OSUs;
N optical splitters having a C (1 ≦ C) branch side and a two branch side, the ONU being connected to the C branch side, and the N normal system OSU being connected to one of the two branch sides;
An optical switch having one OSU side port to which the redundant OSU is connected and N ONU side port to which the other of the two branch sides of the optical splitter is connected;
An OLT control unit for controlling start / stop of light emission for an optical signal for the OSU, and for controlling any one of the one OSU side port and the N ONU side port for the optical switch;
With
When the connection destination that is one of the N ONU side ports coupled to the one OSU side port in the optical switch becomes unknown during the operation of the redundant OSU, the OLT control unit An optical access system characterized by stopping light emission of a redundant OSU. The OLT control unit includes an optical switch control link monitoring unit that periodically transmits a predetermined signal to the optical switch and performs control link detection for recognizing the connection destination in response to the optical switch.
2. The connection destination is unknown when the optical switch control link monitoring unit detects a control link disconnection without a response from the optical switch when the control link detection is performed. Optical access system. An ONU link monitoring unit for monitoring a link state with the ONU under the OSU;
The OLT control unit includes an optical switch control link monitoring unit that periodically transmits a predetermined signal to the optical switch and performs control link detection for recognizing the connection destination in response to the optical switch.
When the optical switch control link monitoring unit detects a control link disconnection without a response from the optical switch when the control link detection is performed, and the ONU link monitoring unit detects all of the redundant OSU subordinates. 2. The optical access system according to claim 1, wherein when the link disconnection of the ONU is detected, the connection destination is unknown. The OLT control unit includes an optical switch control link monitoring unit that periodically transmits a predetermined signal to the optical switch and performs control link detection for recognizing the connection destination in response to the optical switch.
The OLT control unit causes the optical switch control link monitoring unit to perform the control link detection when light emission of the redundant OSU is stopped, and detects the establishment of a control link with a response from the optical switch The optical access system according to claim 1, wherein the redundant system OSU starts light emission.   An OLT having the OLT control unit provided in the optical access system according to claim 1.   An OSU having the ONU link monitoring unit provided in the optical access system according to claim 3. An OSU redundancy method in an optical access system according to any one of claims 1 to 4,
When the connection destination which is one of the N ONU side ports coupled to the one OSU side port in the optical switch becomes unknown during operation of the redundant OSU, the OLT control unit An OSU redundancy method characterized by stopping light emission of a redundant OSU.

Images