JP6326468B2 - Time synchronization method for passive optical network - Google Patents

Description

  The present invention relates to a time synchronization technique, and more particularly, to a time synchronization method for a passive optical network.

  Patent Document 1 proposes a time synchronization technique using GPS information.

  This technology extracts 1 PPS (1 Pulse Per Second), TOD (Time Of Day), and 10 MHz clock using a GPS signal at a grand master node equipped with a GPS receiver, stabilizes the extracted signal, and A synchronization message for time synchronization is generated using the converted signal and transmitted to the slave node.

  Then, the slave node receives the synchronization message, and the time synchronization block of the slave node performs time synchronization calculation using OFCC (Offset & Frequency Compensation Clock) synchronization technology that supports time offset and frequency separation compensation. Modify the TOD information of the block.

  Then, using the TOD information corrected in the time synchronization block, the 1PPS and TOD signals are extracted and transmitted to the stabilization block of the slave node to stabilize the signal.

  Next, the stabilized signal is transmitted again to the time synchronization block, and the TOD information of the time synchronization block is updated. Using the updated TOD information, the time synchronization of another slave node is further updated. Generate a synchronization message for

  The inventor has conducted research on a time synchronization technique between a master and a slave of a communication system.

  In the communication network time synchronization system, IEEE802. The base station synchronizes the time with the station through as. However, the GPS reception around the base station is often better, and in the case of an integrated operation base station, the GPS reception is sometimes difficult because it is located in the city center. In addition, in the case of an integrated operation base station, since it is managed by various communication companies, there is an aspect in which access is difficult. Thus, rather than synchronizing the time through an OLT (Optical Line Terminal) provided inside the station, the OLT through the base station ONU (Optical Network Unit) and the ONU and ENB (eNodeB) connected thereto A method to synchronize the time is considered.

Korean Registered Patent No. 10-087776 (2008.12.23)

  The present invention has been invented to solve the above-described problems, and an object thereof is to provide a time synchronization technique between a master and a slave of a communication system.

  In particular, it is an object of the present invention to provide a time synchronization method that can efficiently perform time synchronization between an OLT and an ONU that form a passive optical network (PON).

  Furthermore, the present technology aims to support duplication of ONUs and to support failover for the ONUs.

  Furthermore, the present technology aims to define a protocol between the ONU and the ONT in order to accurately synchronize the time of the network equipment by connecting the IEEE 1588 grand master device to the ONU in the passive optical network. .

  In one aspect, the time synchronization method of the passive optical network includes a time information reception stage in which the OLT receives time information received by the ONU from the GM, and a case in which the OLT receives time information from two or more ONUs. , Comparing the received time information, selecting one of the two or more ONUs as a BMC (Best Master Clock), and the time difference information received from the selected BMC by the OLT. A time synchronization step of correcting the time based on the selected BMC and synchronizing the time with the selected BMC.

  In one aspect, before the time synchronization step, the clock quality of the BMC for which the OLT is selected for a certain time is verified, and if the result of the verification satisfies a certain condition, the BMC lock (Lock) step for fixing the BMC May be included.

  In one aspect, if a BMC is selected before the time synchronization step, the method further includes transmitting a UTPS role message to the ONU for which the OLT has been selected to inform the selection of the BMC.

  In one aspect, after the ONU knows the selection of the BMC before the time synchronization stage, the OLT includes a time difference information receiving stage for receiving time difference information calculated and transmitted by the ONU.

  In yet another aspect, after the time synchronization step, the OLT further includes a time synchronization information transmission step in which the time synchronization information is transmitted to other lower ONUs connected to the OLT.

  In yet another aspect, the method further includes a step of transmitting time synchronization information received from the OLT by another ONU in the lower part to a slave device connected to the time synchronization information.

  In one aspect, the OLT device includes a time synchronization processor that corrects the time based on the time difference information received from the ONU and synchronizes the time with the ONU.

  In one aspect, when the OLT receives time information from each of two or more ONUs, the time synchronization processor compares the received time information and selects one of the two or more ONUs as a BMC. A BMC selection unit.

  The present technology can efficiently perform time synchronization between a master and a slave of a communication system. In particular, time synchronization between the OLT and the ONU forming the passive optical network (PON) can be efficiently performed.

1 illustrates a passive optical network system according to one embodiment. FIG. 3 is a flowchart illustrating a method for synchronizing time of a passive optical network according to an embodiment. It is a block diagram which shows the servo algorithm by one Embodiment. 7 is a flowchart illustrating a time synchronization method of a passive optical network according to another embodiment. It is a block diagram which shows the structure of the passive optical network equipment by one Embodiment.

  Hereinafter, the present invention will be described in detail so that those skilled in the art can easily understand and reproduce the present invention through preferred embodiments described with reference to the accompanying drawings.

  In describing the present invention, if it is determined that a specific description of a related known function or configuration may obscure the gist of the embodiment of the present invention, a detailed description thereof will be given. Is omitted.

  The terms used throughout the specification of the present invention are defined in consideration of the functions in the embodiments of the present invention, and can be sufficiently modified according to the intention or custom of the user or operator. As such, the definition of the term must be made based on the overall content of the specification.

  Hereinafter, the present invention can be applied to implementation of an aerial network switch.

  In the PON (Passive Optical Network) system composed of the OLT 30 (hereinafter referred to as OLT) and the ONU 20 (hereinafter referred to as ONU), the present invention provides the ONU 20 and the OLT 30 for accurate time synchronization of equipment. Presents the protocol defined between Specifically, the ONU 20 collects time difference information from the GM 10 and transmits the information to the OLT 30 using UTSP (Upstream Time Sync Protocol, hereinafter referred to as UTSP).

UTSP-Transport
According to one embodiment, the transmission layer protocol of UTSP uses Ethernet / IP / UDP. When the ONU 20 transmits to the OLT 30, IP multicast or Unicast is used depending on the setting. Conversely, when the OLT 30 transmits to the ONU 20, it transmits to the ONU 20 by Unicast. When using IP Multicast, 224.0.124 is used, TTL is 1, and 2781 can be used as a port.

  In one embodiment, when a message transmitted from the ONU 20 to the OLT 30 is used as an IP multicast, a monitoring port is added to the VLAN between the ONU 20 and the OLT 30, and the packet transmitted from the ONU 20 to the OLT 30 by participating in the multicast group. Can be monitored or the transmitted / received packet can be confirmed using the port mirroring function.

UTSP-Messages
In one embodiment, the ONU 20 and the OLT 30 send and receive different messages through the transmission layer. For example, the ONU 20 transmits an announcement, a master-slave offset, a slave master offset, and a presence to the OLT 30. Further, for example, the OLT 30 transmits the clock information and the grant role to the ONU 20.

  In one embodiment, every message sent and received between the ONU 20 and the OLT 30 uses a common header and includes different data for each message type in the Payload. For example, the common header is as follows.

MAGIC: MAGIC code for confirming UTSP Version: UTSP version Message Type: Message type ID: Message sending / recipient category ID
In one embodiment, the announcement message includes a sender ID sent from the ONU 20 to the OLT 30 and includes the ONU 20 MAC address 6 bytes and the Port number 2 bytes, and includes a PTP announcement message. In one embodiment, the announcement message is transmitted to the OLT 30 every time an announcement message transmitted by an IEEE 1588 GM (Grand Master) connected to the ONU 20 is received. For example, the packet of the announcement message is as follows.

  In one embodiment, the master-slave offset message uses the source port identity of GM10 as the source port identity. The ONU20 timestamp is the time of the ONU 20 that transmitted the difference information. Master-slave offset is a difference value calculated from the Sync or Sync follow up message. This is the cycle of the Sync message. For example, the packet of the master slave offset message is as follows.

  In one embodiment, the Source Port Identity in the slave master offset message uses GM10's source port identity. The ONU timestamp is the time of the ONU 20 that received the difference information. Master-slave offset is a difference value calculated from the Delay response message. This is the cycle of the Delay request message. For example, the packet of the slave master offset message is as follows.

  In one embodiment, the presence message is the ONU 20 presence message timeout and the unit is 'seconds'. If the Presence message cannot be received within that time, it is determined that the ONU 20 is no longer valid. Even before the timeout, when no further operation is performed by the ONU 20, it is set to 0. For example, the presence message packet is as follows.

  In one embodiment, the clock information is composed of ONU MAC address 6 bytes and Port number 2 bytes as the source ID of the ONU 20 to which the GM 10 is connected. The PTP announcement message of Clock selected as the BMC is included. The announcement message is transmitted to the ONU 20 every time the OLT 30 receives the announcement message from the ONU 20. For example, the packet of the packet information is as follows.

  In one embodiment, the Grant Role is the ID of the ONU 20 whose Receiver ID receives the message. Source Port Identity is the ID of the target Clock. If Role is Master, it plays the role of BMC, and if it is Slave, it relinquishes the role of BMC. For example, the Grant Role packet is as follows.

UTSP-Operation
FIG. 1 illustrates a communication network time synchronization system according to one embodiment.

  As shown, the IEEE 1588 GM 10 is connected to the ONU 20, and the ONU 20 can be set as the BC or TC of the IEEE 1588. The IEEE 1588 GM 10 periodically transmits an Announce message for notifying its own clock information and a Sync / Follow-Up message including Timestamp information to the ONU 20.

  FIG. 2 is a flowchart illustrating a configuration of an embodiment of a time synchronization method for a passive optical network according to an embodiment.

  As shown, the time synchronization method according to the present invention includes a time information reception stage, a BMC selection stage, and a time synchronization stage.

  In one aspect, in the time information reception stage, the OLT 30 receives the time information received by the ONU 20 from the GM 10. In one embodiment, the ONU 20 stores the announcement message received from the GM 10 in the UTSP announcement message and transmits it to the OLT 30. The OLT 30 knows what ONU 20 is connected to what clock from the received message.

  In one aspect, in the BMC selection stage, when the OLT 30 receives time information from two or more ONUs 20, respectively, the received time information is compared and one of the two or more ONUs 20 is selected as a BMC. .

  In one embodiment, the OLT 30 can select one BMC by comparing the SFs included in the UTSP announcement message. In one embodiment, the announcement message transmitted from the ONU 20 to the OLT 30 includes priority1, clockClass, clockAccuracy, offsetScaledLogVariance, priority2, Source Port Id, Grand Master Id, Step Sd in order of priority. The OLT 30 selects the BMC by comparing the SFs of the announcement messages having such priorities.

  In still another embodiment, the OLT 30 selects the BMC by comparing the MAC address of the ONU 20 with the received port number when the same configuration of the messages received from the two ONUs 20 is the same.

  In one aspect, in the time synchronization stage, the OLT 30 corrects the time based on the time difference information received from the selected BMC, and synchronizes with the selected BMC. A specific time correction method will be described later.

  In one aspect, the method for time synchronization of the passive optical network may further include a BMC rack stage before the time synchronization stage. At the BMC rack stage, the OLT 30 verifies the clock quality of the BMC selected for a certain period of time, and fixes the BMC if the result of the verification satisfies a certain condition.

  In one embodiment, the fixed conditions under which the BMC is fixed include 1) the quality condition of the announcement message and 2) the quality condition of the differential message. For example, 1) The announcement message quality condition determines the time for receiving the announcement message as a multiple of the announcement interval (basic 3, range: 2 to 8 times). Also, for example, 2) The quality condition of the differential message determines whether or not the differential message is stably received within a specified time as a multiple of the Sync interval (basic 5, range: 3 to 128 times).

  When the above two conditions 1) and 2) are satisfied, the BMC is fixed, and the fixed BMC is not changed as long as the switching condition described later does not occur.

  In yet another aspect, the OLT 30 may further include a BMC reselection step of reselecting a BMC when a switching condition occurs.

  In one embodiment, when the link is broken with the ONU 20 with the OLT 30 selected as the master, the switching condition is a forced switching of the user through the CLI, a timeout of receiving the announcement message and the difference information (for example, basic 5 times, range: 3 to 16), and a case where a value larger than the designated difference value is held for a certain time or more. When such a switching condition occurs, the OLT 30 compares the SF of the announcement message received again and reselects the BMC.

  In one aspect, if the BMC is selected before the time synchronization stage, the OLT 30 further includes a step of transmitting a UTPS role message to the ONU 20 for which the OLT 30 is selected to inform the selection of the BMC. In one embodiment, a specific reason may occur when the ONU 20 is unable to receive a role message. For example, when the ONU 20 has not received the master role, the ONU 20 does not play a role as a BMC, so the quality verification fails and the BMC selection process is performed again. As another example, when the ONU 20 has not received the slave roll, the ONU 20 continuously transmits the difference information to the OLT 30, and the OLT 30 ignores the difference information and transmits the slave role message again. To do.

  In one aspect, after the ONU 20 knows the selection of the BMC, it includes a time difference information receiving stage in which the OLT 30 receives the time difference information calculated and transmitted by the ONU 20.

  In one embodiment, the ONU 20 calculates Master-Slave difference information from the Sync / Sync Follow-up message that is periodically received from the GM 10. In yet another embodiment, the ONU 20 transmits a Delay request message to the GM 10, receives a Delay response message from the GM 10, and calculates Slave-Master difference information from the received Delay response. The ONU 20 transmits the calculated two difference information to the OLT 30, and the OLT 30 receives it.

  FIG. 3 is a flowchart showing the Clock server algorithm.

  In a specific aspect, in the time synchronization step, time synchronization is performed using the above-described Master-Slave difference information and Slave-Master difference information. In one embodiment, the OLT 30 synchronizes time using two pieces of difference information and a servo algorithm.

  The servo algorithm can calculate Offset and Delay through two pieces of difference information. The servo algorithm corrects the frequency by an offset difference due to unit time under the control of PI (Proportional-Integral), and the time of the OLT 30 converges according to the Master Clock. Here, Delay and offset used are set to stable values through the low-pass filter from the received two pieces of difference information.

  In one embodiment, the Clock server algorithm uses the open source project PTPd.

  In one aspect, the OLT 30 includes a time synchronization information transmission step of transmitting the time synchronization information to another ONU 20 connected to the OLT 30 after the time synchronization step. For example, the time synchronization information can be transmitted to the other ONU 20 below using the 802.1as precise time protocol.

  In still another aspect, the other ONU 20 at the lower part can transmit the time synchronization information received from the OLT 30 to the slave device connected to itself. For example, the time synchronization information can be transmitted to the slave device through a 1588 PTP packet.

  By implementing in this way, this invention can perform efficiently time synchronization with OLT30 and ONU20 which comprise a passive optical network (PON).

  The present invention has been described with reference to the preferred embodiments referred to by the accompanying drawings. However, various modifications can be made without departing from the scope of the present invention within the scope of the following claims. Obviously, variations are possible.

  The present invention is applicable to a technical field related to a time synchronization method of a passive optical network.

Claims (7)

In a method in which an OLT synchronizes time through an ONU connected to a grand master,
A time information receiving stage in which the OLT receives time information received by the ONU from the GM;
When the OLT receives time information from each of two or more ONUs, a BMC selection step of comparing the received time information and selecting one of the two or more ONUs as a BMC;
A BMC lock stage for fixing the BMC if the clock quality of the BMC for which the OLT is selected for a certain period of time is verified, and the result of the verification satisfies a certain condition including the quality condition of the announcement message and the difference message quality condition;
A time synchronization stage in which the OLT corrects the time based on the time difference information received from the selected BMC and synchronizes the time with the selected BMC;
A method of time synchronization of a passive optical network including: The BMC selection step includes:
The time synchronization method of the passive optical network according to claim 1, further comprising a BMC reselection step of reselecting a BMC when a switching condition occurs. Before the time synchronization step,
The method of claim 1, further comprising transmitting a UTPS role message to the ONU for which the OLT has been selected if the BMC is selected to inform the selection of the BMC. Before the time synchronization step,
The method of claim 1, wherein the OLT includes a time difference information reception step of receiving time difference information calculated and transmitted by the ONU after the ONU knows the selection of the BMC. After the time synchronization step,
The method of claim 1, further comprising a time synchronization information transmission step in which the OLT transmits time synchronization information to another ONU below the OLT. The method of claim 5 , further comprising transmitting the time synchronization information received from the OLT by the other ONUs at the lower part to a slave device connected to the ONT. In an OLT device that synchronizes time through an ONU connected to a grand master,
Time to correct the on the basis of the time difference information received from the ONU, see including time synchronization processor to ONU and time synchronization,
When the OLT receives time information from each of two or more ONUs, the time synchronization processor compares the received time information and selects one of the two or more ONUs as a BMC selection. Part
The OLT device of the passive optical network that fixes the BMC when the clock quality of the BMC for which the OLT is selected for a certain period of time is verified and the verification result satisfies a certain condition including the quality condition of the announcement message and the difference message quality condition .

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