KR101833894B1 - Time synchronization method for PON Network - Google Patents

Abstract

The present invention relates to a time synchronization method for a passive optical network (PON) which corrects a time by calculating a time difference between an optical line terminal (OLT) and an optical network unit (ONU) forming a PON, thereby effectively performing time synchronization for the PON. Furthermore, the time synchronization method of the present invention can provide dualization of the ONU to the OLT by selecting any one of two ONUs as a best master clock (BMC) so as to perform time synchronization when the OLT receives time difference information from each of the two ONUs.

Description

{Time synchronization method for PON Network}

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

Korean Patent No. 10-0876776 (December 23, 2008) proposes a time synchronization technique using GPS information.

In this technique, a GPS receiver is used to extract 1PPS (1 Pulse Per Second), TOD (Time Of Day), and 10MHz clocks from a GPS receiver, stabilize the extracted signals, And transmits the generated synchronization message to the slave node.

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

Then, the 1PPS and TOD signals are extracted using the modified TOD information in the time synchronization block, and the signals are stabilized by transferring them to the stabilization block of the slave node.

Then, the stabilized signals are transmitted to the time synchronization block again to update the TOD information of the time synchronization block, and a synchronization message for time synchronization of another slave node is generated using the updated TOD information.

The present inventor has been studying a time synchronization technique between a master and a slave of a communication system.

In the time synchronization system of the communication network, the base station synchronizes with the national station through IEEE 802.as. However, in many cases, the GPS reception is better around the base station, and the integrated base station is located in the center of the city, which makes it difficult to receive the GPS. In addition, the integrated operating base station is difficult to access because it is managed by various communication companies. Accordingly, rather than synchronizing the time through an OLT (Optical Lint Terminal) installed inside the national office, an OLT (Optical Lint Terminal), an ONU (Optical Network Unit) connected thereto, an ENB (eNodeB ) Are considered to be synchronized.

Korean Patent No. 10-0876776 (Dec. 23, 2008)

The present invention has been made under the above-mentioned circumstances, and it is an object of the present invention 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 for effectively performing time synchronization between an optical line terminal (OLT) and an optical network unit (ONU), which form a passive optical network (PON).

Furthermore, the proposed technology supports redundancy of an optical network unit (ONU) to support failover of an optical network unit (ONU).

Furthermore, the proposed technique aims to define the protocol between the ONU and the ONT for precise time synchronization of the network devices by connecting the IEEE 1588 grand master device to the ONU in the passive optical network.

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

In an aspect, the OLT may verify the clock quality of the selected BMC for a predetermined time before the time synchronization step, and may further include a BMC lock step of fixing the BMC when the verification result satisfies a predetermined condition .

     In an aspect, the BMC selection step may further include a BMC re-selection step of re-selecting the BMC upon occurrence of the conversion condition.

     In an aspect, if the BMC is selected before the time synchronization step, the OLT further includes a step of notifying the selection of the BMC by transmitting a UTPS role message to the selected ONU.

     In an aspect, after the ONU recognizes the selection of the BMC prior to the time synchronization step, the OLT includes a time difference information receiving step of receiving the time difference information calculated and transmitted by the ONU.

     In another aspect, the OLT further includes a time synchronization information transmission step of transmitting the time synchronization information to another ONU connected to the OLT after the time synchronization step.

In another aspect, the method further includes transmitting the time synchronization information received from the OLT to another slave device connected to the ONU.

In one aspect, the OLT apparatus includes a time synchronization processor for time-synchronizing with the ONU by correcting the time based on the time difference information received from the ONU.

In one aspect, the time synchronization processor includes a BMC selection unit for selecting one of the two or more ONUs as a BMC by comparing the received time information when the OLT receives time information from two or more ONUs.

The proposed technique can efficiently perform time synchronization between master and slave of communication system. In particular, there is an effect of efficiently performing time synchronization between an optical line terminal (OLT) and an optical network unit (ONU), which form a passive optical network (PON).

1 is a diagram illustrating a system of a passive optical network according to one embodiment.
2 is a flow chart illustrating a time synchronization method of a passive optical network, according to one embodiment.
3 is a block diagram illustrating a servo algorithm in accordance with one embodiment.
4 is a flowchart illustrating a time synchronization method of a passive optical network according to another embodiment.
5 is a block diagram illustrating a configuration of a passive optical network equipment according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

The terms used throughout the specification of the present invention have been defined in consideration of the functions of the embodiments of the present invention and can be sufficiently modified according to the intentions and customs of the user or operator. It should be based on the contents of.

The invention described below can be applied to the implementation of a network switch for aviation.

The proposed invention is a PON (passive optical network) system composed of an OLT 30 (Optical Line Terminal) and an ONU (Optical Network Unit) A protocol defined between the ONU 20 and the OLT 30 is presented. Specifically, the ONU 20 collects time difference information from the GM 10 and transmits this information to the OLT 30 using an Upstream Time Sync Protocol (UTSP).

UTSP (Upstream Time Sync Protocol) - Transport

According to one embodiment, the transport layer protocol of UTSP uses Ethernet / IP / UDP. When the ONU 20 transmits to the OLT 30, IP multicast or Unicast is used according to the setting. Conversely, when the OLT 30 transmits to the ONU 20, the ONU 20 transmits the unicast. When using IP Multicast, use 224.0.1.124, TTL = 1, and port = 2781.

In one embodiment, when messages transmitted from the ONU 20 to the OLT 30 are used for IP multicast, a monitoring port is added to the VLAN between the ONU 20 and the OLT 30, The ONU 20 can monitor the packet transmitted to the OLT 30 or confirm the transmission / reception packet using the port mirroring function.

UTSP  (Upstream Time Sync Protocol) - Messages

In one embodiment, the ONU 20 and the OLT 30 exchange different messages with each other through the transport layer. For example, the ONU 20 transmits an announcement, a master-slave offset, a slave-master offset, and a Presence to the OLT 30 . For example, the OLT 30 (Optical Line Terminal) transmits Clock information and Grant Role to the ONU 20.

In one embodiment, all the messages transmitted and received between the ONU 20 and the OLT 30 use a common header, and the payload includes different data for each message type. For example, the following are common headers:

MAGIC (2) Version (1) Message Type (1) ID (8)

MAGIC: MAGIC code to identify UTSP

Version: UTSP version

Message Type: Message Type

ID: Message send / receiver ID

In an exemplary embodiment, an Announce message includes a Sender ID sent from the ONU 20 to the OLT 30 with a MAC address of 6 bytes of the ONU 20 and a port number of 2 bytes, and includes a PTP announce message. In one embodiment, the announce message is transmitted to the OLT 30 upon receipt of an announcement message transmitted by the IEEE 1588 GM (Grand Master) connected to the ONU 20. For example, the packets of the announce message are:

MAGIC = 0x2D3F Version = 0x01 Message Type = 0x01 Sender ID = ONU MAC (6) + Port (2) PTP Announce Message (PTP common header + Announce Message)

In one embodiment, the master-slave offset message uses the source port identity of the GM 10 as the Source Port Identity. The ONU 20 timestamp is the time of the ONU 20 that has transmitted the difference information. Master-slave offset is the difference value calculated from Sync or Sync follow up message. It is the cycle of the Sync message. For example, the packet of the master-slave offset message is as follows.

MAGIC = 0x2D3F Version = 0x01 Message Type = 0x02 Sender ID = ONU MAC (6) + Port (2) source Port Identity (10) ONU timestamp (10) Master-slave offset (10) Log sync interval (1)

In one embodiment, the source port identity in the slave-master offset message uses the source port identity of the GM 10. The ONU timestamp is the time of the ONU 20 that has received the difference information. The slave-master offset is the difference value calculated from the delay response message. Delay is the period of the request message. For example, the packet of the slave-master offset message is as follows.

MAGIC = 0x2D3F Version = 0x01 Message Type = 0x03 Sender ID = ONU MAC (6) + Port (2) source Port Identity (10) ONU timestamp (10) Slave-master offset (10) Log delay request interval (1)

In one embodiment, the presence message is a Presence message timeout of the ONU 20, and the unit is 'second'. If the Presence message is not received within this time, it is judged to be an invalid ONU (20). If the ONU 20 is no longer operating before the timeout, it is set to zero. For example, a packet of a presence message is as follows.

MAGIC = 0x2D3F Version = 0x01 Message Type = 0x04 Sender ID = ONU MAC (6) + 0x0000 Presence timeout (1) Mode (Available = 0x01, No more valid = 0x0)

In one embodiment, the clock information is configured such that the source ID of the ONU 20 to which the GM 10 is connected is 6 bytes of the ONU MAC address and 2 bytes of the port number. The PTP announce message of Clock selected by 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 clock information is as follows.

MAGIC = 0x2D3F Version = 0x01 Message Type = 0x010 Source ID = ONU MAC (6) + Port (2) PTP Announce Message (PTP common header + Announce Message)

In one embodiment, the Grant Role is the ID of the ONU 20 where the receiver ID is to receive the message. The source Port Identity is the Id of the target clock. Role acts as a BMC when it is Master, and relinquishes BMC role when it is Slave. For example, the Grant Role's packet looks like this:

MAGIC = 0x2D3F Version = 0x01 Message Type = 0x11 Receiver ID = ONU MAC (6) + Port (2) source Port Identity (10) Role (Master = 0x1, Slave = 0x0)

UTSP (Upstream Time Sync Protocol) - Operation

1 illustrates a time synchronization system of a communication network according to one embodiment.

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

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

As shown in the figure, the time synchronization method according to the present invention includes a time information receiving step, a BMC selecting step, and a time synchronization step.

In an aspect, in the time information reception step, the OLT 30 receives the time information received by the ONU 20 from the GM 10. In one embodiment, the ONU 20 stores an announcement message received from the GM 10 in a UTSP announce message, and transmits the announce message to the OLT 30. The OLT 30 can know which clock is connected to which ONU 20 from the received message.

In one aspect, in the BMC selection step, when the OLT 30 receives the time information from two or more ONUs 20, it compares the received time information and transmits one of the two or more ONUs 20 to the BMC Best Master Clock).

In one embodiment, the OLT 30 may compare one or more SFs included in the UTSP announce message to select one BMC. In one embodiment, the announcement message transmitted by the ONU 20 to the OLT 30 includes an SF (Selection) having priority in order of priority 1, clockClass, clockAccuracy, offsetScaledLogVariance, priority 2, Source Port Id, Grandmaster Id, Factor. The OLT 30 compares SFs of the incoming messages having such a priority order to select the BMC.

In another embodiment, when the same configuration of the messages received from the two ONUs 20 is identical, the OLT 30 compares the MAC address of the ONU 20 with the received port number to select the BMC.

In one aspect, in the time synchronization step, 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 an aspect, the passive optical network time synchronization method may further include a BMC lock step prior to the time synchronization step. In the BMC lock phase, the OLT 30 verifies the clock quality of the selected BMC for a predetermined time, and fixes the BMC if the verification result satisfies a certain condition.

In one embodiment, certain conditions under which the BMC is fixed include 1) the quality condition of the incoming message and 2) the quality condition of the differential message. For example, 1) an incoming message quality condition determines the time to receive the incoming message as a multiple of the incoming interval. (Default 3, range: 2 to 8). For example, 2) The quality condition of the differential message determines whether the difference message is stably received within a specified time, in multiples of the Sync interval. 3 to 128 times)

The BMC is fixed at a time point when both of the conditions 1) and 2) are satisfied, and the fixed BMC is not changed unless the conversion condition described later occurs.

      In another aspect, the OLT 30 may further include a BMC re-selection step of re-selecting the BMC upon occurrence of the switching condition.

In one embodiment, the switching condition is such that when the link with the ONU 20 selected by the OLT 30 as the master is disconnected, the user is forced to switch through the CLI, time out of the incoming message and receipt of the differential information , Basic 5 times, range: 3 to 16), a value larger than the specified difference value may be maintained for a certain time or the like. The OLT 30 resets the BMC by comparing the SF of the received message again when such a switching condition occurs.

In an aspect, when the BMC is selected before the time synchronizing step, the OLT 30 further includes a step in which the OLT 30 transmits a UTPS role message to the selected ONU 20 to inform the selection of the BMC. In one embodiment, the ONU 20 may not receive a role message for a specific reason. For example, if the ONU 20 fails to receive the master role, the ONU 20 fails to perform the role as a BMC, so the quality verification fails and the BMC selection process is performed again. For example, if the ONU 20 does not receive the slave role, the ONU 20 continuously transmits the difference information to the OLT 30, the OLT 30 ignores the corresponding difference information, Lt; / RTI >

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

In one embodiment, the ONU 20 calculates Master-Slave difference information from the Sync / Sync Follow-up message periodically received from the GM 10. [ In 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.

3 is a flowchart showing a clock servo algorithm.

In a specific aspect, the time synchronization step synchronizes the time using the master-slave difference information and the slave-master difference information. In one embodiment, the OLT 30 performs time synchronization using two difference information and a servo algorithm.

The servo algorithm can calculate Offset and Delay using two difference information. The servo algorithm compensates the frequency by the offset difference according to the unit time according to PI (proportional-integral) control, so that the time of the OLT 30 converges along the Master Clock. Here, the delay and offset to be used are a stable value through a low-pass filter from the received difference information.

In one embodiment, the Clock servo algorithm utilizes the open source project PTPd.

In an aspect, the OLT 30 includes a time synchronization information transmission step for transmitting time synchronization information to another ONU 20 connected to the OLT 30 after the time synchronization step. For example, time synchronization information can be transmitted to another ONU 20 at the bottom using the 802.1as precision time protocol.

In another aspect, the other ONUs 20 on the lower side can transmit the time synchronization information received from the OLT 30 to the slave device connected thereto. For example, time synchronization information may be transmitted to the slave device through a 1588 PTP packet.

The present invention efficiently performs time synchronization between the optical line terminal (OLT) 30 and the optical network unit (ONU) 20, which form a passive optical network (PON).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. .

10: Grand Master
20: ONU
30: OLT

Claims (9)

A method for time synchronization of an OLT through an optical network unit (ONU) connected to a grand master,
A time information receiving step of the OLT receiving the time information received by the ONU from the GM;
A BMC selecting step of selecting one of the two or more ONUs as a BMC (Best Master Clock) by comparing received time information when the OLT receives time information from two or more ONUs;
A BMC lock step in which the OLT verifies the clock quality of the selected BMC for a predetermined time and fixes the BMC when the verification result satisfies a certain condition including an incoming message quality condition and a differential message quality condition;
A time synchronization step of time synchronization with the selected BMC by correcting the time based on the time difference information received from the selected BMC by the OLT;
The time synchronization method comprising:
delete The method of claim 1, wherein the BMC selection step
A BMC re-selection step of re-selecting the BMC when the switching condition occurs;
Further comprising the steps of:
2. The method of claim 1, wherein before the time synchronization step
When the BMC is selected, the OLT transmits a UTPS role message to the selected ONU to inform the selection of the BMC;
Further comprising the steps of:
2. The method of claim 1, wherein before the time synchronization step
After the ONU knows the selection of the BMC, the OLT receives the time difference information that the ONU calculates and transmits;
The time synchronization method comprising:
2. The method of claim 1, wherein after the time synchronization step
A time synchronization information transmission step in which the OLT transmits time synchronization information to another ONU connected to the OLT;
Further comprising the steps of:
The method according to claim 6,
Transmitting time synchronization information received from the OLT to another slave device connected to the OLT;
Further comprising the steps of:
1. An OLT apparatus for time synchronization through an ONU connected to a grand master,
A time synchronization processor for correcting the time based on the time difference information received from the ONU and synchronizing the time with the ONU;
, ≪ / RTI &
Wherein the time synchronization processor includes a BMC selection unit for selecting one of the two or more ONUs as a BMC by comparing the received time information when the OLT receives time information from two or more ONUs, An OLT device in a passive optical network that verifies the clock quality of a BMC and fixes the BMC if the verification result meets certain conditions, including an incoming message quality condition and a differential message quality condition.

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