JP2012244233A - Onu, time synchronization method and time synchronization program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ONU capable of keeping a link in a PON section without detecting any time stamp drift error when a system changeover of OLT occurs.SOLUTION: An ONU is equipped with a first reception data processing section 211 to detect an input interruption of a signal sent from an OLT1a, a second reception data processing section 212 to detect a time sync information from the signal sent from the OLT1a, a MPCP control section 214 to update a current value of a local timer 215 so as to match with a local timer current value indicated by the time sync information, and a monitoring control section 213 which orders the MPCP control section 214 to start a hold-over processing in which detected time sync information is stored and the time management of the local timer 215 is performed on the basis of the time sync information, when an input interruption is detected. The MPCP control section 214 performs a hold-over processing in accordance with the order from the monitoring control section 213.

Description

  The present invention relates to an ONU that performs communication with an OLT having a redundant configuration, a time synchronization method using the ONU, and a time synchronization program.

  As a conventional access network, a GE-PON (Gigabit Ethernet (registered trademark / hereinafter, omitted) -Passive Optical Network) system is known (see, for example, Non-Patent Document 1). In this GE-PON system, a plurality of subscriber side communication devices (ONU: Optical Network Unit) are connected to a station side communication device (OLT: Optical Line Terminal) via an optical fiber cable via a star coupler. Since a plurality of ONUs share a single OLT, an economical network can be constructed.

  Communication between the ONU and a subscriber line termination function unit (OSU: Optical Subscriber Unit) in the OLT is performed using an MPCP (Multi-Point Control Protocol) message. Examples of the MPCP message include a GATE message for notifying the ONU of transmission permission of the data signal, and a REPORT message for notifying the accumulated amount of the data signal requested to be transmitted to the OLT. Generated based on a local timer in the OLT.

Communication by the PON system is performed by executing an MPCP Discovery sequence between the OLT and the ONU. In this sequence, first, the OLT transmits a GATE message including a data signal transmission start time and transmission amount information set based on a local timer in the OLT to the ONU. Then, after receiving the GATE message, the ONU transmits a REPORT message including the accumulated amount information of the data signal requested to be transmitted to the OLT. Then, when the local timer in the ONU indicates the transmission start time included in the GATE message, the ONU transmits the accumulated data signal to the OLT with the transmission amount included in the GATE message as an upper limit.
Here, each ONU transmits a data signal of a set transmission amount at an individually different transmission start time set by the OLT, so that the data signal is multiplexed when each data signal is multiplexed by the star coupler. It can prevent that each other collides. At this time, in order for each ONU to transmit data correctly at the transmission start time, the local timer in each ONU needs to be synchronized with the local timer in the OLT.

  Therefore, in the PON system, when the MPCP Discovery sequence is executed between the OLT and the ONU, the MPCP Local timer synchronization sequence is executed to perform time synchronization (for example, refer to Non-Patent Document 2). That is, when the OLT transmits a GATE message to the ONU, the current value (time stamp value) of the local timer in the OLT is embedded in the GATE message as time sync information. The ONU performs time synchronization by updating the current value (time stamp value) of the local timer in the ONU in accordance with the time stamp value indicated by the time sync information included in the received GATE message.

  Thereafter, communication is performed between the ONU and the OLT by repeating a GATE message and a REPORT message. At this time, the OLT embeds local timer information (current value of the local timer in the OLT) for causing the ONU to perform time management in the GATE message and transmits it to the ONU. The ONU is based on the local timer information included in the GATE message. To manage the time of the local timer in the ONU. Further, when performing time management, the ONU determines whether the drift amount of the time stamp value of the local timer in the ONU with respect to the time stamp value indicated by the local timer information is within the specified value. Is detected as a time stamp drift error.

IEEE (Institut of Electric and Electronics Engineers) 802.3ah-2005 Section 5 IEEE (Institut of Electric and Electronics Engineers) 802.1AS

  On the other hand, in the case where a system with redundant OLTs is used, when a signal from the active OLT is in an input-disconnected state, the standby OLT is replaced with a new active system in place of the active OLT. The communication with the ONU is continued. When such OLT system switching occurs, a GATE message including local timer information in the new active OLT is transmitted from the new active OLT to the ONU. Then, the ONU performs time management of the local timer in the ONU based on the local timer information in the new active ONU included in the GATE message.

  However, since the local timer in the active OLT and the local timer in the new active OLT are not synchronized in time, the local timer in the ONU is based on the local timer information in the new active OLT. When the time management is performed, there is a case where the drift amount becomes a predetermined value or more, and the ONU detects a time stamp drift error, which causes a link down in the PON section.

  The present invention has been made to solve the above-described problems. When a system with redundant OLT is used, ONU detects a time stamp drift error when OLT system switching occurs. It is an object of the present invention to provide an ONU that can maintain a link in a PON section, a time synchronization method using this ONU, and a time synchronization program.

  The ONU according to the present invention includes a first reception data processing unit that detects a signal input interruption from the active OLT and a time indicating the current value of the local timer in the OLT from the signal from the active OLT. The current value of the local timer in the own device is updated in accordance with the current value of the local timer indicated by the second received data processing unit for detecting the sync information and the time sync information detected by the second received data processing unit. When an input interruption is detected by the MPCP control unit and the first received data processing unit, the MPCP control unit holds the detected time sync information, and based on the time sync information, A monitoring control unit for instructing start of a holdover process for managing the time of the timer. And performs management.

  According to the present invention, since it is configured as described above, when an OLT system switchover occurs, the ONU does not detect a time stamp drift error, and the link in the PON section can be maintained.

It is a figure which shows the structure of the PON system which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of OLT in Embodiment 1 of this invention. It is a figure which shows the structure of ONU in Embodiment 1 of this invention. It is a figure which shows the communication sequence by the PON system which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of ONU in Embodiment 2 of this invention. It is a figure which shows the communication sequence by the PON system which concerns on Embodiment 2 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
As shown in FIG. 1, the PON system includes active and standby OLTs (# 1, 2) 1a, 1b having a redundant configuration, a plurality of ONUs (# 11-1z, 21-2z) 2, a plurality of And the star coupler 3. Further, the OLTs 1a and 1b and the star coupler 3 and the ONUs 2 and the star coupler 3 are connected by optical fiber cables. Further, time synchronization is not performed between the active OLT 1a and the standby OLT 1b.
In a normal state, this PON system communicates between the active OLT 1a and each ONU 2. On the other hand, when the signal from the OLT 1a is in an input-disconnected (LOS: Loss of Signal) state, the standby OLT 1b becomes a new active system instead of the active OLT 1a, and communication with each ONU 2 is continued. To do.

Next, the configuration of each part of the PON system will be described.
As shown in FIG. 2, the OLT 1a includes an L2SW (layer 2 switch) 11, a synchronous clock generation unit 12, a monitoring control unit 13, an MPCP control unit 14, and a plurality of OSUs (# 1 to y) 15. Note that the configuration of the standby OLT 1b is the same as that of the active OLT 1a, and the description thereof is omitted. In FIG. 2, only the signal lines connecting the synchronous clock generation unit 12, the monitoring control unit 13, the MPCP control unit 14, and the OSU # 1 are illustrated, but the other OSUs # 2 to #y are illustrated. Similarly, signal lines are connected.

The L2SW 11 outputs a data signal from a host device (not shown) to the MPCP control unit 14 and transmits a data signal from the MPCP control unit 14 to the host device.
The synchronous clock generation unit 12 generates a reference clock in the OLT 1a. A signal indicating the reference clock generated by the synchronous clock generation unit 12 is output to each functional unit (the monitoring control unit 13 and each OSU 15).

  The monitoring control unit 13 includes a local timer 131, and generates local timer information indicating a current value (time stamp value) of the local timer 131. Note that the local timer 131 operates according to a signal indicating the reference clock from the synchronous clock generator 12. The local timer information generated by the monitoring control unit 13 is output to each OSU 15.

  The MPCP control unit 14 transmits and receives data signals and MPCP messages to / from each OSU 15 and performs MPCP processing. The MPCP control unit 14 outputs a data signal from the L2SW 11 to each OSU 15 and outputs a data signal from each OSU 15 to the L2SW 11. In addition, the MPCP message processed by the MPCP control unit 14 notifies the GATE message for notifying the ONU 2 of transmission permission of the data signal from the OLT 1a and the accumulation amount of the data signal requested to be transmitted from the ONU 2 to the OLT 1a. For example, there is a REPORT message (report frame information).

  The OSU 15 is connected to each ONU 2 via the star coupler 3. The OSU 15 includes a first reception data processing unit 151, a second reception data processing unit 152, a PON-MAC unit 153, and a transmission data processing unit 154.

The first reception data processing unit 151 outputs the data signal from the MPCP control unit 14 to the transmission data processing unit 154 as a transmission data signal.
The second reception data processing unit 152 outputs the reception data signal (data signal or MPCP message) from the transmission data processing unit 154 to the MPCP control unit 14.

  The PON-MAC unit 153 has an MPCP function, and includes a local timer 155 and a report message information monitoring unit 156, and sets a transmission start time of a data signal to the ONU 2 based on the local timer 155. . Note that the local timer 155 operates in accordance with a signal indicating the reference clock from the synchronous clock generation unit 12 and the local timer information from the monitoring control unit 13. Further, the report message information monitoring unit 156 monitors the REPORT message acquired from each ONU 2 via the transmission data processing unit 154.

The transmission data processing unit 154 transmits the transmission data signal from the first reception data processing unit 151 to each ONU 2 through the star coupler 3, and receives the data signal and MPCP message acquired from the ONU 2 through the star coupler 3. The data signal is transmitted to the second received data processing unit 152. The REPORT message from the ONU 2 is also transmitted to the PON-MAC report message information monitoring unit 156.
In addition, the transmission data processing unit 154 adds an LLID (Logical Link. ID) corresponding to the transmission destination ONU 2 or the ONU 2 to the GATE message acquired from the MPCP control unit 14 via the first reception data processing unit 151. The data signal transmission start time and transmission amount information set for the data signal are embedded. The transmission start time is set by the PON-MAC unit 153. Further, when the MPCP Local timer synchronization sequence is executed, the local timer information from the monitoring controller 13 is embedded in the GATE message as time sync information in order to cause the ONU 2 to perform time synchronization. Further, after this sequence, the local timer information from the monitoring control unit 13 is embedded in the GATE message in order to cause the ONU 2 to perform time management.

  On the other hand, the ONU 2 includes a PON-MAC unit 21. The PON-MAC unit 21 includes a first reception data processing unit 211, a second reception data processing unit 212, a monitoring control unit 213, and an MPCP control unit 214.

  The first received data processing unit 211 operates according to the MPCP protocol, and analyzes a data signal from the OLT 1a to detect an input interruption (LOS) of the signal from the OLT 1a. Here, when the first received data processing unit 211 detects the LOS, the first received data processing unit 211 notifies the monitoring control unit 213 to that effect. In addition, the first received data processing unit 211 analyzes the MPCP message from the OLT 1a and detects local timer information. Here, when detecting the local timer information, the first received data processing unit 211 notifies the monitoring control unit 213 together with the local timer information.

  The second received data processing unit 212 operates according to the TimeSync protocol, and analyzes the MPCP message from the OLT 1a to detect time sync information. Here, if the second received data processing unit 212 detects the time sync information, the second received data processing unit 212 notifies the monitoring control unit 213 together with the time sync information.

  The monitoring control unit 213 starts hold over state processing (hold over processing) for the hold over state processing unit 216 of the MPCP control unit 214 when LOS detection is notified from the first reception data processing unit 211. Is instructed. The hold over state processing is detected by the second received data processing unit 212, holds the time sync information notified to the MPCP control unit 214 until the processing stop is instructed, and the time sync information is stored in the time sync information. A process for managing the time of the local timer 215 in the ONU 2 based on this is shown. Further, when the time sync information is notified from the second received data processing unit 212, the monitoring control unit 213 instructs the hold over state processing unit 216 to stop the hold over state processing, and the time sync information is received. Notify information. Further, when the local timer information is notified from the first reception data processing unit 211, the monitoring control unit 213 notifies the MPCP control unit 214 of this local timer information.

The MPCP control unit 214 performs MPCP processing by transmitting and receiving data signals and MPCP messages to and from the OLT 1a based on the held local timer 215. The MPCP control unit 214 outputs a data signal from a lower-level device (not shown) to the OLT 1a via the star coupler 3, and transmits a data signal acquired from the OLT 1a via the star coupler 3 to the lower-level device. The MPCP control unit 214 also includes a hold over state processing unit 216.
The hold over state processing unit 216 performs hold over state processing in accordance with an instruction from the monitoring control unit 213. Here, when the local timer information is notified from the monitoring control unit 213, the hold over state processing unit 216 sets the local timer information to avoid detection of a time stamp drift error if the hold over state processing is in progress. If it is not stored and the holdover process is not in progress, the local timer information is stored, and the time of the local timer 215 in the ONU 2 is managed based on the local timer information.

Next, communication operation by the PON system configured as described above will be described.
In the communication operation by the PON system, as shown in FIG. 4, first, the MPCP Discovery sequence is executed between the active OLT 1a (OLT “A” in FIG. 4) and the ONU 2 (step ST1).

  In this MPCP Discovery sequence, first, the OLT 1a generates and transmits a GATE message for notifying the ONU 2 of permission to transmit a data signal. That is, first, the MPCP control unit 14 generates a GATE message and transmits it to a predetermined OSU 15. On the other hand, the PON-MAC unit 153 in the OSU 15 sets a data signal transmission start time for the ONU 2 based on the local timer 155. Then, the transmission data processing unit 154 embeds the LLID corresponding to the ONU 2, the transmission start time and transmission amount information of the data signal, and time sync information for synchronizing the time (local timer information of the monitoring control unit 13) in the GATE message. And transmitted to all ONUs 2 via the star coupler 3.

  Next, the ONU 2 that is the transmission destination of the GATE message confirms that it is a GATE message addressed to itself by referring to the LLID, and then transmits a REPORT message to the OLT 1a in response to this GATE message. That is, the MPCP control unit 214 generates a REPORT message indicating the accumulated amount information of the data signal requested to be transmitted. This REPORT message is transmitted to the OLT 1a via the star coupler 3, and is notified to the report message information monitoring unit 156 and the MPCP control unit 14.

  Next, the ONU 2 transmits a data signal. That is, when the local timer 215 held by the MPCP control unit 214 indicates the transmission start time included in the GATE message, the MPCP control unit 214 sends the data signal to the OLT 1a via the star coupler 3 with the transmission amount included in the GATE message as an upper limit. Send. This data signal is transmitted to the host device via the MPCP control unit 14 of the OLT 1a.

  Next, the MPCP Local timer synchronization sequence is executed between the OLT 1a and the ONU 2 to perform time synchronization (steps ST2 and 3, time sync information detection step, time synchronization step). That is, in the OLT 1a, when transmitting the GATE message to the ONU 2, the local timer information of the monitoring control unit 13 is embedded in the GATE message as time sync information. Then, the ONU 2 performs time synchronization by updating the current value (time stamp value) of the local timer 215 of the MPCP control unit 214 in accordance with the time stamp value indicated by the time sync information included in the GATE message.

Time synchronization between the OLT 1a and the ONU 2 is established by the sequence in steps ST2 and ST3 (step ST4). Thereby, when the data signal transmitted from each ONU 2 is multiplexed by the star coupler 3, the collision of the data signals can be prevented and transmitted to the OLT 1a.
Thereafter, communication is performed by repeatedly exchanging the GATE message and the REPORT message between the ONU 2 and the OLT 1a. At this time, the OLT 1a embeds the local timer information of the monitoring control unit 13 in the GATE message transmitted to the ONU 2 in order to cause the ONU 2 to perform time management. Then, the MPCP control unit 214 of the ONU 2 performs time management by updating the time stamp value of the local timer 215 in the ONU 2 in accordance with the time stamp value of the local timer information included in the received GATE message. Further, when performing time management, the MPCP control unit 214 determines whether or not the drift amount of the time stamp value of the local timer 215 with respect to the time stamp value of the local timer information is within the specified value. Is detected as a time stamp drift error.

On the other hand, when a failure occurs in the OLT 1a (symbol A in FIG. 4), the first received data processing unit 211 detects the LOS and notifies the monitoring control unit 213 (step ST5, input disconnection detection). Step).
Next, the monitoring control unit 213 instructs the hold over state processing unit 216 to start the hold over state processing (step ST6, hold over processing instruction step).

Next, the hold over state processing unit 216 performs hold over state processing in accordance with the instruction from the monitoring control unit 213 (step ST7, hold over processing step). That is, when the signal from the active OLT 1a is cut off, the standby OLT 1b (OLT “B” in FIG. 4) is switched to the new active system, and the new active OLT 1b is connected to the OLT 1b. Until time synchronization is performed, time synchronization information from the active OLT 1a that has been detected is held, and time management of the local timer 215 in the ONU 2 is performed based on this time synchronization information.
When a GATE message including local timer information is transmitted from the new active OLT 1b during the hold over state process (reference numeral B in FIG. 4), in order to avoid detection of a time stamp drift error, this local Timer information is not stored.

  As a result, even when the local timer information is transmitted to the ONU 2 from the new active OLT 1b that is not time-synchronized with the active OLT 1a, the ONU 2 stores the ONU 2 in the ONU 2 based on the local timer information. The time management of the local timer 215 is not performed, and detection of a time stamp drift error can be avoided.

After that, when a GATE message including time sync information for time synchronization is transmitted from the new active OLT 1b (step ST8), the second received data processing unit 212 detects this time sync information, and to that effect. Is sent to the monitoring control unit 213 together with the time sync information (step ST9).
Next, the monitoring control unit 213 instructs the hold over state processing unit 216 to stop the hold over state processing and notifies the time sync information (step ST10).

Next, the hold over state processing unit 216 stops the hold over state processing in accordance with the instruction from the monitoring control unit 213, and updates the time stamp value of the local timer 215 in the ONU 2 in accordance with the time stamp value of the time sync information. Thus, time synchronization is performed (steps ST11 and ST12). As a result, time synchronization can be performed between the new active OLT 1b and the ONU 2.
Thereafter, when a GATE message including local timer information is transmitted from the new active OLT 1b and notified to the MPCP control unit 214 via the first reception data processing unit 211 and the monitoring control unit 213, the MPCP control unit 214 The local timer information is stored, and time management of the local timer 215 in the ONU 2 is performed based on the local timer information.

  As described above, according to the first embodiment, when the ONU 2 detects an LOS with the active OLT 1a, the ONU 2 detects new time sync information from the LOS detection to the new active OLT 1b. Since the time synchronization information that has been detected is held and the time management of the local timer 215 in the ONU 2 is performed based on this time synchronization information, the system switching between the OLTs 1a and 1b occurs. The link of the PON section can be maintained without the ONU 2 detecting a time stamp drift error.

Embodiment 2. FIG.
In the first embodiment, when the ONU 2 detects the LOS, the case where the detected time sync information is retained from the detection of the LOS until the new time sync information is detected has been described. A case will be described in which detection of a time stamp drift error is avoided by holding detected time sync information for a predetermined period from the detection of LOS.
FIG. 5 is a diagram showing the configuration of the ONU 2 according to the second embodiment of the present invention. The ONU 2 in the second embodiment shown in FIG. 5 is obtained by changing the hold over state processing unit 216 of the ONU 2 in the first embodiment shown in FIG. 3 into a hold over timer processing unit 217. Other configurations are the same, and the same reference numerals are given and description thereof is omitted.

  Note that, when the LOS detection is notified from the first reception data processing unit 211, the monitoring control unit 213 performs a holdover timer process (holdover process) to the holdover timer processing unit 217 of the MPCP control unit 214. (Step ST13 in FIG. 6, holdover processing instruction step). This holdover timer process is detected by the second received data processing unit 212, holds the time sync information notified to the MPCP control unit 214 for a predetermined period, and based on this time sync information, The process which performs the time management of the local timer 215 is shown.

  The holdover timer processing unit 217 performs holdover timer processing in accordance with an instruction from the monitoring control unit 213 (step ST14 in FIG. 6, holdover processing step). Here, when the local timer information is notified from the monitoring control unit 213, the holdover timer processing unit 217 avoids the detection of the time stamp drift error if the holdover timer processing is in progress. If the holdover timer process has expired, the local timer information is stored, and the time of the local timer 215 in the ONU 2 is managed based on this local timer information. The holdover timer processing period by the holdover timer processing unit 217 is set to be longer than the period required to detect new sync time information from the LOS detection.

  As described above, according to the second embodiment, when the ONU 2 detects the LOS with the active OLT 1a, the ONU 2 holds the detected time sync information for a predetermined period from the LOS detection. Since the time management of the local timer 215 in the ONU 2 is performed based on this time sync information, the same effect as in the first embodiment can be obtained.

The processing in the PON system may be realized on a computer by one or a plurality of programs, or at least a part thereof may be realized by hardware.
Further, within the scope of the present invention, the invention of the present application can be freely combined with each embodiment, modified with any component in each embodiment, or omitted with any component in each embodiment. .

  1a, 1b OLT (# 1, 2), 2 ONU (# 11-1z, # 21-2z), 3 star coupler, 11 L2SW (layer 2 switch), 12 synchronous clock generation unit, 13 monitoring control unit, 14 MPCP Control unit, 15 OSU (# 1 to y), 21 PON-MAC unit, 131 local timer, 151 first reception data processing unit, 152 second reception data processing unit, 153 PON-MAC unit, 154 transmission data processing Unit, 155 local timer, 156 report message information monitoring unit, 211 first received data processing unit, 212 second received data processing unit, 213 monitoring control unit, 214 MPCP control unit, 215 local timer, 216 hold over state processing Part, 217 Holdover timer processing part.

Claims (5)

In an ONU that communicates with an OLT having a redundant configuration,
A first received data processing unit for detecting a disconnection of a signal from the active OLT;
A second received data processing unit for detecting time sync information indicating a current value of a local timer in the OLT from a signal from the active OLT;
An MPCP control unit that updates the current value of the local timer in the own device in accordance with the current value of the local timer indicated by the time sync information detected by the second received data processing unit;
When an input interruption is detected by the first received data processing unit, the MPCP control unit holds the detected time sync information, and based on the time sync information, A monitoring control unit for instructing start of holdover processing for performing time management,
The MPCP control unit performs the holdover process according to an instruction from the monitoring control unit. The monitoring control unit instructs the MPCP control unit to start the holdover processing when the first reception data processing unit detects an input interruption, and the second reception data processing unit 2. The ONU according to claim 1, wherein when new time sync information is detected, the MPCP control unit is instructed to stop the holdover process. The monitoring control unit instructs the MPCP control unit to perform the holdover processing for a predetermined period when an input interruption is detected by the first reception data processing unit. 1. ONU according to 1. In the time synchronization method by the ONU that communicates with the OLT having a redundant configuration,
A time sync information detecting step of detecting time sync information for time synchronization indicating a current value of a local timer in the OLT from a signal from the active OLT;
A time synchronization step of updating the current value of the local timer in the own device in accordance with the current value of the local timer indicated by the time sync information detected in the time sync information detection step by the MPCP control unit;
An input disconnection detecting step of detecting an input disconnection of a signal from the active OLT;
When an input disconnection is detected in the input disconnection detection step, the MPCP control unit holds the detected time sync information and performs time management of the local timer in the own device based on the time sync information. A holdover processing instruction step for instructing start of holdover processing;
A time synchronization method comprising: a holdover process step in which the MPCP control unit performs the holdover process according to an instruction in the holdover state instruction step. A time synchronization program for causing a computer to function as the ONU according to any one of claims 1 to 3.

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