JP5120097B2 - Time synchronization system and time synchronization apparatus - Google Patents

Description

  The present invention relates to a network system and a time synchronization device that synchronize time and clock between devices using PTP (Precision Time Protocol).

  PTP (Precision Time Protocol) is a time transmission protocol that realizes high-precision synchronization in a network such as Ethernet (registered trademark) defined in IEEE 1588-2002.

  FIG. 7 is a diagram illustrating a configuration example of a network using PTP. The node PM1, which is a PTP master device, transmits the reference timing from the reference clock source T as a PTP packet. The nodes PS2 to PS6 that are PTP slave devices synchronize with the timing of the node PM1 that is the PTP master device, using the timing information of the PTP packet from the PTP master device. The node PS4 is a PTP repeater that operates as a PTP master device for the nodes PS5 and PS6 which are PTP slave devices.

  In FIG. 7, all the devices of the node PM1 and the nodes PS2 to PS6 are synchronized with the reference clock source PT1 as a reference.

By using such a PTP, for example, an inexpensive and lightweight base station that cannot mount a GPS receiver such as a femtocell base station acquires a high-accuracy clock by exchanging packets over the IP network. be able to.
JP 2007-267421 A "IEEE 1588 Standard" (USA), IEEE, 2002

  However, the network using PTP described above has the following problems.

  In FIG. 7, when the timing information (time, clock, etc.) from the PTP master device becomes abnormal due to a failure of the node PM1 which is the PTP master device, the nodes PS2 to PS6 which are PTP slave devices are The failure of the node PM1, which is a device, cannot be detected. The nodes PS2 to PS6, which are PTP slave devices, synchronize with the abnormal timing information without detecting the failure of the PTP master device. As a result, there is a possibility that all PTP devices in the network using PTP will malfunction.

  Even if the PTP slave device can detect the failure of the PTP master device, there is only one PTP master device, and correct timing information cannot be acquired, so normal operation cannot be continued.

  An object of the disclosed time synchronization system is to provide a technique for continuing normal operation of a network even when a failure or the like of a device that executes a protocol for performing time synchronization (for example, PTP) occurs.

The disclosed time synchronization system is a time synchronization system that operates a protocol for performing time synchronization,
Comprising a first device for executing the protocol and a plurality of second devices;
The first device includes:
A time source,
A receiver for receiving time information from the second device;
A determination unit for determining a failure of the own device and a failure of the second device based on time information from the time information source and time information from the second device;
When the determination unit determines that there is a failure of the own device, the time information from the second device is transmitted, and when the determination unit determines that the failure is the second device, the time information source A transmission unit that transmits time information from

  The disclosed time synchronization system includes a first device that executes a time synchronization protocol (eg, PTP) and a plurality of second devices, and the first device includes time information of the device itself and a plurality of second devices. From this time information, it is determined whether it is a failure of the own device or the failure of the second device, and if it is a failure of the own device, the time information from the second device is transmitted, In the case of a failure, the time information from the time information source is transmitted. Even when the failure of the own device is determined, by transmitting the time information of the second device, other devices in the network (for example, subordinate devices) can acquire the correct time information and continue normal operation. Can do.

In addition, the determination unit
If the time information from the time information source is different from the time information from the second device, it is determined as a failure of the own device,
If the time information of the third device in the second device is different from the time information from the time information source and the time information from the other second device, it is determined that the third device is faulty. You may do it. In this way, the first device can identify which device in the network has a failure.

  The disclosed time synchronization system can also be specified as a time synchronization apparatus, a time synchronization method, a program, and a program recording medium having similar functions.

  According to the disclosed time synchronization system, normal operation of a network can be continued even when a failure or the like of a device that executes a protocol for performing time synchronization occurs.

<First Embodiment>
Hereinafter, an embodiment of a time synchronization system will be described based on the drawings. The configuration of the following embodiment is an exemplification, and the time synchronization system is not limited to the configuration of the embodiment.

FIG. 1 is a diagram illustrating an example of the entire time synchronization system. In the time synchronization system of FIG. 1, nodes M1 to M3, which are PTP master devices, are connected by a network (for example, an IP network). Nodes S4 to S8 which are PTP slave devices are connected to the nodes M1 to M3 which are the respective PTP master devices. The nodes M1 to M3, which are PTP master devices, are each provided with a GPS receiver, and acquire the time and clock from the GPST1 to T3. Based on the acquired time, clock, etc., each PTP master device generates timing information as a synchronization timing, and transmits it to the subordinate PTP slave devices. For example, the node M1 that is the PTP master device generates timing information from the time acquired from the GPST1, and distributes the timing information to the nodes S4 and S5 that are subordinate PTP slave devices. At this time, the node M1 also receives timing information from the nodes M2 and M3 which are other PTP master devices. When normal, the timing information transmitted by each of the nodes M1 to M3, which are PTP master devices, is synchronized.

  FIG. 2 is a diagram illustrating an example of the entire time synchronization system when it is determined that a failure has occurred in the node M1. FIG. 2 shows a case where the operation of GPST1, which is the reference clock of the node M1, becomes abnormal, and abnormality also occurs in the timing information generated by the node M1. Timing information from each PTP master device is synchronized when normal. However, for example, when the operation of GPST1, which is the reference clock source of the node M1, is abnormal, the time and clock received by the node M1 also become abnormal, and only the timing information generated by the node M1 is received from other PTP master devices. Deviation from timing information. The node M1 compares the timing information generated by itself with the timing information received from another PTP master device, and detects that the timing information transmitted by itself is abnormal. When the node M1 detects that there is a cause of abnormality, the node M1 stops functioning as a PTP master and operates as a PTP slave. That is, the node M1 stops distributing the timing information generated by itself to the subordinate nodes S4 and S5, and the timing information received from the nodes M2 and M3 to the subordinate PTP slave devices, the nodes S4 and S5. Send.

  When an abnormality occurs in its own device, as described above, the function as the PTP master is stopped and the PTP slave device under its control causes a failure in the master device under its control. Even when it occurs, correct timing information can be acquired.

  FIG. 3 is a diagram illustrating a configuration example of the node M1 in FIG. 1 and FIG. The node M1 (corresponding to a PTP device) includes a reference clock source 1, an own device timing information generation unit 2, a timing information comparison / determination unit 3, an other device timing information generation unit 4, a timing information selection unit 5, and a pair. A slave transmission interface unit 6, a master transmission interface unit 7, a slave reception interface unit 8, and a switch unit 9 are provided. Node M1 is connected to nodes M2 and M3, which are PTP master devices, and nodes S4 and S5, which are PTP slave devices, via switch W1.

  The reference clock source 1 (corresponding to a time information source) is, for example, a GPS receiver that receives radio waves from the GPS and acquires time, clock, and the like. Alternatively, the reference clock source 1 may be a reception function unit that acquires the time and clock received by the device from the GPS from another GPS receiver. Further, the reference clock source 1 may be a high precision oscillator or the like.

  The own device timing generation unit 2 generates timing information (corresponding to time information) based on information such as time received from the reference clock source 1. This timing information may indicate time, for example, or clock. The timing information generated by the own apparatus timing information generation unit 2 is referred to as own timing information.

  The master reception interface units (corresponding to reception units) 8a and 8b receive PTP packets including information such as time and clock transmitted from the nodes M2 and M3 which are PTP master devices.

  The other device timing information generation unit 4 generates timing information used in the device from the PTP packet received from the master reception interface unit 8. For example, the other timing information A is generated from the PTP packet received from the node M2, and the other timing information B is generated from the PTP packet received from the node M3. The other timing information A and B indicates the same type of information (time, clock, etc.) as the own timing information.

  The timing information comparison / determination unit (corresponding to the determination unit) 3 compares the own timing information received from the own device timing information generating unit 2 with the other timing information A and B received from the other device timing information generating unit 4. The timing information comparison / determination unit 3 has a threshold value for deviation between the allowable timing information by setting in advance. When the timing information is compared, it is determined that a failure has occurred in the PTP master device that is the transmission source of the timing information that has shifted from the other timing information beyond the threshold. For example, when the difference between the own timing information and the other timing information A and B is equal to or less than the threshold value, it is determined that no failure has occurred in any PTP master device and is in a normal state. In this case, timing information is compared based on PTP packets from a plurality of PTP master devices, and a PTP master device in which a failure has occurred is determined by majority vote.

  For example, when only the own timing information is shifted from the other timing information A and B by a threshold value or more, it is determined that a failure has occurred in the own device. For example, when only the other timing information A is shifted from the own timing information and the other timing information B by a threshold or more, it is determined that a failure has occurred in the node M2 that is the transmission source of the other timing information. . The timing information comparison / determination unit 3 transmits the determination result to the timing information selection unit 5 and the master transmission interface unit 7. In particular, when it is determined that a failure has occurred in another PTP master device, a failure notification may be transmitted to the node that is the PTP master device together with the determination result.

  The timing information selection unit 5 selects which timing information is transmitted from the slave transmission interface unit 6. When the determination result from the timing information comparison / determination unit 3 indicates that any PTP device is normal or a failure of another PTP device, the own timing information is selected as timing information to be transmitted from the slave transmission interface unit 6. When the determination result from the timing information comparison / determination unit 3 indicates a failure of the own device, the other timing information A and B are selected as timing information to be transmitted from the slave transmission interface unit 6. At this time, since the other timing information A and B are synchronized, either information may be selected.

  The slave transmission interface unit 6 generates a PTP packet from the timing information selected by the timing information selection unit 5 and transmits it to the subordinate PTP slave devices (node S4 and node S5).

  The master-to-master transmission interface unit 7 receives the determination result from the timing determination comparison unit 3, and when the determination result indicates normality or indicates a failure of another PTP master device, continues the operation as the PTP master, Information is transmitted to other PTP master devices (node M2 and node M3). When the determination result from the timing information comparison / determination unit 3 indicates a failure of the own apparatus, the operation is stopped.

  The slave transmission interface unit 6 and the master transmission interface unit 7 correspond to a transmission unit.

  The switch unit 9 performs switching of PTP packets among a physical interface (not shown), the slave transmission interface unit 6, the master transmission interface unit 7, and the master reception interface unit 8.

  FIG. 4 is a diagram illustrating an example of an operation flow when the timing information comparison / determination unit 3 compares timing information and determines a failure.

When the node M1 is activated (OP1), it is determined whether or not a failure occurrence notification indicating the failure occurrence of the own device is received from another PTP master device (OP2).

  If no failure notification has been received from any of the other PTP master devices (OP2: Yes), whether the difference between the timing information from the node M2 (other timing information A) and the own timing information is smaller than the threshold value. (OP3).

  When the deviation between the timing information from the node M2 (other timing information A) and the own timing information is smaller than the threshold (OP3: Yes), the deviation between the timing information from the node M3 (other timing information B) and the own timing information. Is less than the threshold value (OP4).

  When the deviation between the timing information from the node M3 (other timing information A) and the own timing information is smaller than the threshold (OP4: Yes), the deviation between the own timing information and the other timing information A and B is smaller than the threshold and the synchronization is performed. You can consider that it is removed. Therefore, since it can be determined that the network is operating normally, the node M1 continues to operate as a PTP master (OP6). Specifically, the PTP packet generated from the own timing information is transmitted from the slave transmission interface unit 6 and the master transmission interface unit 7.

  When the difference between the timing information from the node M3 (other timing information B) and the own timing information is equal to or greater than the threshold (OP4: No), only the timing information (other timing information B) of the node M3 is not synchronized. It is considered. Since the local apparatus (node M1) and the node M2 are considered to be synchronized, the abnormality of the node M3 can be determined by majority vote. Therefore, it is determined that a failure has occurred in the node M3, and a failure occurrence notification is sent to the node M3 (OP7). Specifically, the PTP packet generated from the own timing information is transmitted from the slave transmission interface unit 6 and the master transmission interface unit 7, and a failure occurrence notification is transmitted from the master transmission interface unit 7 to the node M3. .

  When the difference between the timing information from the node M2 (other timing information A) and the own timing information is equal to or greater than the threshold (OP3: No), the timing information from the node M3 (other timing information B) and the own timing information It is determined whether or not the deviation is smaller than the threshold (OP5). When the difference between the timing information from the node M3 (other timing information B) and the own timing information is smaller than the threshold (OP5: Yes), only the timing information from the node M2 (other timing information A) must be synchronized. I reckon. Since the local apparatus (node M1) and the node M3 are considered to be synchronized, the abnormality of the node M2 can be determined by majority vote. Therefore, it is determined that a failure has occurred in the node M2, and a failure occurrence notification is sent to the node M2 (OP8). Specifically, the PTP packet generated from the self-timing information is transmitted from the slave transmission interface unit 6 and the master transmission interface unit 7, and the failure notification from the master transmission interface unit 7 to the node M2 is transmitted. .

  When a failure notification is received from another PTP master device (OP2: No), and when the difference between the timing information from the node M3 (other timing information B) and the own timing information is equal to or greater than a threshold value ( OP5: No), it is determined that a failure has occurred in the device itself. In this case, the node M1 stops operating as a PTP master, and operates as a PTP slave device (or PTP repeater device) (OP9). Specifically, the operation of the master transmission interface unit 7 is stopped, and the other timing information A or B is transmitted from the slave transmission interface unit 6.

FIG. 5 is a diagram illustrating an example of comparing timing information. The timing information comparison / determination unit 3 handles a clock as timing information, for example. FIG. 5 shows a clock that is timing information (own timing information) of the node M1 on the upper side and a clock that is timing information (other timing information A) on the node M2 on the lower side. In the process of OP3 in FIG. 4, the timing information comparison / determination unit 3 monitors the number of clock edges between the own timing information and the other timing information A in a certain time. The timing information comparison / determination unit 3 determines whether or not synchronization is made based on the difference in the number of edges of the clock. In FIG. 5, the number of clock edges within a certain period of time is 11 for the node M1, whereas it is 15 for the node M2. At this time, if the threshold is set to 3 times, it is considered that the node M1 and the node M2 are not synchronized, and the process proceeds to OP5 (FIG. 4).

<When there are multiple PTP master devices>
In the first embodiment, there are a plurality of PTP master devices in the network. However, the PTP has an algorithm that always has only one PTP master in the PTP domain that is the range in which the PTP operates. Therefore, some countermeasure is required to overcome this algorithm.

  Examples of the case where a plurality of PTP masters are present include the following.

  FIG. 6 is a diagram illustrating a configuration example of a PTP domain. In FIG. 6, there is a PTP domain 1 having the node M1 as a PTP master, a PTP domain 2 having the node M2 as a PTP master, and a PTP domain 3 having the node M3 as a PTP master. In the PTP domain 2 and the PTP domain 3, the node M1 operates as a PTP slave. Similarly, the node M2 and the node M3 operate as PTP slaves in a PTP domain other than the PTP domain as a master. The PTP slaves subordinate to each of the nodes M1 to M3 belong only to the PTP domain in which the subordinate node operates as a PTP master. For example, the node S4 and the node S5 belong only to the PTP domain 1 in which the node M1 operates as a PTP master.

  When the PTP domain is configured as shown in FIG. 6, the master reception interface unit 8 receives PTP packets from the node 2 that is the PTP master of the PTP domain 2 and the node 3 that is the PTP master of the PTP domain 3. The other timing information generation unit 4 generates other timing information A and B from the PTP packets received from each.

  The slave transmission interface unit 6 transmits the PTP packet to the PTP slave devices (nodes S4 and S5) belonging to the PTP domain 1 whose own device is the PTP master. At this time, a PTP packet is generated from the timing information corresponding to the selection of the timing selection unit 5 and transmitted.

  The master transmission interface unit 7 transmits the PTP packet to the PTP slave devices (nodes M2 and M3) belonging to the PTP domain 1 whose own device is the PTP master. However, when the determination result of the timing information comparison / determination unit 3 indicates normality and a failure of another PTP master device, the PTP packet generated from the own timing information is transmitted. When the determination result of the timing information comparison / determination unit 3 indicates a failure of the own device, the operation is stopped. However, in the case of the failure of the own device, the PTP packet having the timing of the PTP domain 2 or 3 is transmitted from the slave transmission interface unit 6, so that the PTP packet is transmitted to the nodes S 4 and S 5 which are PTP slaves. . Since the node M1 itself also receives the PTP packet from the node M2 or the node M3, it can maintain synchronization. Therefore, even if a failure occurs in the own device, network synchronization is maintained.

<Operational effects of the first embodiment>
In the timing information comparison / determination unit 3, by comparing the own timing information with the other timing information A and B, if all the PTP master devices are operating normally or a failure has occurred, which PTP master It is possible to determine whether a failure has occurred in the device. When a failure occurs in the own device, the to-slave transmission interface unit 6 transmits timing information from another PTP device and stops the operation of the to-master transmission interface unit 7. That is, when a failure of the own device is detected, the function as the PTP master is stopped and the PTP slave operates. As a result, a PTP packet including correct timing information can be transmitted to a slave device under its control, and normal operation can be continued.

  Further, in a synchronous network such as SDH (Synchronous Digital Hierarchy), when a configuration is adopted in which master devices are monitored from each other, as many physical interfaces as necessary are connected as shown in FIG. However, since the time synchronization system of the first embodiment is configured on the IP network, it is sufficient to have one interface for mutual monitoring of the master devices. Therefore, the time synchronization system of the first embodiment can be realized without adding an interface between devices.

It is a figure which shows the example of the whole time synchronization system. It is a figure which shows the example of the whole time synchronization system at the time of a failure generation. It is a figure which shows the structural example of the PTP apparatus of 1st Embodiment. It is a figure which shows the flow of the operation example of a timing information comparison determination part. It is a figure which shows the comparative example of timing information. It is a figure which shows the structural example of a PTP domain. It is a figure which shows the network structural example which uses PTP. It is a figure which shows the structural example in the case of implementing mutual monitoring of a master apparatus in a SDH network.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reference clock source 2 Own apparatus timing information generation part 3 Timing information comparison determination part 4 Other apparatus timing information generation part 5 Timing information selection part 6 To slave transmission interface part 7 To master transmission interface part 8 To master reception interface part 9 Switch part PM1 to PM3 nodes (PTP master device)
PS4 to PS8 node (PTP slave device)
M1 to M3 nodes (PTP master device)
S4 ~ S8 node (PTP slave device)
T1-T3 GPS
PT1 reference clock source W1 switch

Claims (3)

A time synchronization system that operates a protocol for performing time synchronization,
Comprising a first device for executing the protocol and a plurality of second devices;
The first device includes:
A time source,
A receiver for receiving time information from the second device;
A determination unit for determining a failure of the own device and a failure of the second device based on time information from the time information source and time information from the second device;
When the determination unit determines that there is a failure of the own device, the time information from the second device is transmitted, and when the determination unit determines that the failure is the second device, the time information source A transmission unit for transmitting time information from
With a time synchronization system. The determination unit
If the time information from the time information source is different from the time information from the second device, it is determined as a failure of the own device,
If the time information of the third device in the second device is different from the time information from the time information source and the time information from the other second device, it is determined that the third device is faulty. The time synchronization system according to claim 1. A time synchronization apparatus that executes a protocol for performing time synchronization,
A time source,
A receiver for receiving time information from a plurality of opposing time synchronization devices;
A determination unit for determining a failure of the own device and a failure of the opposite time synchronization device based on time information from the time information source and time information from the opposite time synchronization device;
When the determination unit determines that there is a failure in its own device, it transmits time information from the opposite time synchronization device, and when the determination unit determines that there is a failure in the opposite time synchronization device, the time A time synchronization apparatus comprising: a transmission unit that transmits time information from an information source.

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