KR20100048124A - Time synchronization method in bridged local area network - Google Patents

Abstract

PURPOSE: A synchronizing time method in local area network for securing accurate time by reuse of a time stamp is provided to maintain compatibility with a physical layer of a network device. CONSTITUTION: If a local time(308) is more exact than the local time of the other apparatus, a grandmaster decision unit(305) decides as the grandma master. In case a time synchronizing unit(306) operates as a grandmaster, the time synchronization unit records its own time information in multifunctional time sync message. In case the time synchronization part acts as the slave, it is based on in the content of the multifunction time synchronization message from the grandmaster.

Description

Time synchronization method in local area network {TIME SYNCHRONIZATION METHOD IN BRIDGED LOCAL AREA NETWORK}

The present invention relates to a time synchronization method in a local area network, and more particularly, to obtain time stamp information in a time synchronization layer located between a data link layer and a network layer using a multi-function time synchronization message in a local area network. The present invention relates to a time synchronization method in a local area network for maintaining compatibility with a physical layer of a general network device without overloading the network.

In addition, in the present invention, a communication device that provides a reference time between communication devices that should guarantee real-time in a local area network is set as a grandmaster, and time for each operation after calculating an average transmission delay time between the communication devices. The present invention relates to a technology for processing real-time data by synchronizing with the time of the grandmaster.

Currently, time synchronization technology in a local area network is a standardization process in IEEE 802.1 AS, a detailed group of the Institute of Electrical and Electronics Engineers (IEEE) 802.1 AVB, which is a standard for time synchronization in an industrial network environment. It is based on IEEE 1588 Precision Time Protocol (PTP) technology.

Here, IEEE 1588 PTP is a standard for a precision clock synchronization protocol for networked measurement and control systems, and is a protocol for equalizing time information between interconnected devices.

The synchronization process through the introduction of Ethernet in industrial network environments ensures precise time synchronization down to nanoseconds. Industrial network environments that ensure precise time synchronization include technical elements that are not suitable for commonly used local area network environments.

Therefore, the current local area network is based on virtual local area network (VLAN) technology, and it is expected that the IEEE will establish a technology including VLAN as a standard for developing Ethernet.

As a result, a new standard was required as IEEE 1588 PTP was transferred to the IEEE 802.x series of standards, and IEEE 802.1AS is emerging as a standard for this.

IEEE 802.1 AS synchronizes the transmitting side and the receiving side using time stamps in the physical layer of Ethernet in relation to frame synchronization. That is, the IEEE 802.1 AS uses the time stamps synchronized at the physical layer as the reference time, so that the time stamps received at the physical layer can be processed at a higher layer than the transport layer. It is the next generation network synchronization technology that can synchronize devices with more accurate time by applying new time to all devices in consideration of difference and transmission delay time.

Time-synchronization technology in local area networks ensures precisely synchronized time for multimedia data such as video / audio that should be virtually free of jitter. That is, a grandmaster providing a reference time among the devices in the network for time synchronization in the local area network is selected according to the priority of each device, and the reference time is provided to other devices in the same network.

In general, the Ethernet synchronization method provides time synchronization to the entire network based on a single device including a global positioning system (GPS) or a self-time generator. This synchronization method of Ethernet overlooks any delay in the transmission packet because there is no consideration of jitter or wonder affecting the network while the packet is being transmitted.

Here, jitter refers to the amount of change in the pulse signal for a short period of time not accumulated from the ideal time. And wonder is the amount of change over a period longer than jitter. Jitter and wonder increase in magnitude as they pass through each device in transit or when unwanted phase changes in the pulse signal occur on the transmission line.

Since the Ethernet synchronization method generates a delay of 1 second or less, it can be used in a small office network such as a local area network (LAN).

However, this Ethernet synchronization method has a limit to be applied to the Internet environment. The Internet environment is a collection of several LANs. It is not a delay of a second but more delay, and the probability of occurrence of irregular (irregular) delay increases according to network conditions.

For time synchronization in the Internet environment, Network Time Protocol (NTP) version 3, which is defined as a standard in Request For Comments (RFC) 1305 published by the Internet Architecture Board (IAB) STD 12 and the Internet Engineering Task Force (IETF). I use it.

Looking at NTP version 3, each individual device first contacts the world time server to synchronize the time of each individual device before sending packets to other devices over the Internet. At this time, the world time server operates on the basis of Greenwich Mean Time (GMT), and the time servers are divided evenly among the countries.

When a reference time is received from a world time server, it first establishes time synchronization on the subnet to which each individual device belongs, then adjusts the local time of the individual device and ensures accurate synchronization up to milliseconds. Since NTP is a time synchronization procedure for the Internet, there is a limit to more precise synchronization required by LAN.

Therefore, SNTP (Simple NTP) procedure, a sub-concept of NTP, is used for more accurate time synchronization in narrow networks such as LAN.

However, the problem of SNTP may be defined as in Equation 1 below.

Here, t means time when the packet is generated by the time client, and T means time when the time server receives the packet from the physical layer by sending the packet from the time client.

A represents the influence of the frequency change on the oscillation element in the time client. This value indicates the influence of fluctuations in the center frequency due to the accuracy of the oscillator itself, temperature, etc., and the characteristic change of the oscillator frequency itself over time.

In addition, B represents the jitter or wonder that occurs on the transmission line and the processing of the intermediate node due to the influence of jitter or wonder that occurs during the transmission between the two devices. That is, in the case of the conventional Ethernet or SNTP, there is no compensation for such a time difference, and thus it cannot be used in an industrial network environment.

The aforementioned IEEE 1588 PTP used 'Sync', 'Follow_Up', 'Pdelay_Req', 'Pdelay_Resp', and 'Pdelay_Follow_Up' messages to solve the SNTP problem. That is, the 'Sync' message and the 'Follow_Up' message deliver time information for synchronizing different operating times, and the 'Pdelay_Req' message, 'Pdelay_Resp' message, and 'Pdelay_Resp_Follow_Up' message transmit the average with neighboring devices. It is delivered to measure the delay time.

Eventually, the 'Sync' and 'Follow_Up' messages are sent periodically, so that the ratio of elapsed time between previously transmitted 'Sync' and 'Follow_Up' messages and currently transmitted 'Sync' and 'Follow_Up' messages We solved the problem of SNPT by using, and solved B by calculating average propagation delay time between two devices using 'Pdelay_Req', 'Pelay_Resp' and 'Pdelay_Resp_Follow_Up'.

Meanwhile, a time synchronization procedure in a local area network based on IEEE 1588 PTP technology is being developed in IEEE 802.1 AS. Hereinafter, a time synchronization process in a conventional IEEE 802.1 AS will be described with reference to FIG. 1.

As shown in FIG. 1, a local area network to which the technology of IEEE 802.1 AS is applied may include, for example, a first terminal device 11, a first intermediate bridge 12, a second intermediate bridge 13, and a second terminal. Device 14.

First, when a network supporting IEEE 802.1 AS is first established, each device (terminal device and intermediate bridge) records its time information in the corresponding field of the Announcement message 101 and transmits it to the neighboring device.

That is, the first terminal device 11 records its time information in the notification message and transmits it to the first intermediate bridge 12, and the first intermediate bridge records its time information in the notification message and then the first terminal device. (11) and the second intermediate bridge 13, and the second intermediate bridge records its time information in the notification message and transmits it to the first intermediate bridge 12 and the second terminal device 14, and The second terminal device 14 records its time information in the notification message and transmits the time information to the second intermediate bridge 13.

Of course, each device delivers the received notification message to other devices so that each device can obtain time information of all neighboring devices.

Thereafter, each terminal device and each intermediate bridge compare their own time information with the time information recorded in the received notification message 101, and update their time information with more accurate time information. In this case, the compared time information includes a priority of time information, a category of time information, accuracy of time category, stability of time information, and a MAC address of a device corresponding to time information.

Here, a device having more accurate time information than a neighboring device (terminal device or intermediate bridge) is called a grandmaster. In the exemplary embodiment of FIG. 1, the first intermediate bridge 12 is determined as the grandmaster. Also, devices other than the grandmaster are determined to be slaves.

Then, when the grandmaster is determined, a delay request (Pdelay_Req) message 102 is delivered to calculate the average propagation delay time between the neighboring devices.

That is, after transmitting the delay request message 102 to the first intermediate bridge 12, the first terminal device 11 records and stores the time stamp t ₁ at that time in the physical layer. Then, the first intermediate bridge 12 records the time stamp t ₂ at the time when the delay request message 102 is received from the first terminal device 11 in the delay request response (Pdelay_Resp) message 103. Transmit to the first terminal device (11).

At this time, the first intermediate bridge 12 records and stores the time stamp t ₃ at the time when the delay request response message 102 is transmitted to the first terminal device 11 in the physical layer. Here, t ₃ means the time in consideration of the processing delay time in the first intermediate bridge 12.

Thereafter, the first intermediate bridge 12 records the time stamp t ₃ in the Pdelay_Resp_Follow_Up message 104 and transmits the time stamp t ₃ to the first terminal device 11.

Through this process, the first terminal device 11 can obtain all the time stamps t ₁ , t ₂ , t ₃ , t ₄ , and the average transfer delay between the two devices through Equation 2 below. You can calculate the time.

Here, r is the same as the following [Equation 3].

All devices in the local area network know the time of the grandmaster by using the time information of the grandmaster in the Pdelay_Resp message 103, and receive the Pdelay_Resp message 103 twice in succession. The time difference received can be calculated.

Therefore, the r value used to calculate the average propagation delay time can be calculated, and this r value represents the ratio of the time difference between each device from the grandmaster.

When all the devices go through the above process, the average propagation delay time between each neighboring device can be calculated.

The grandmaster then forwards a sync message 105, 107 and a follow_up message 106, 108 for time synchronization with the slave device.

That is, the second intermediate bridge 13 records the value (OldrxTime) obtained by subtracting the average propagation delay time from the value of the timestamp t ₅ at the time when the synchronization message 105 arrives from the first intermediate bridge 12.

In addition, the second intermediate bridge 13 records a value rxTime obtained by subtracting the average propagation delay time from the value of the timestamp t ₆ at the time when the synchronization message 107 arrives from the first intermediate bridge 12.

After recording the time information of the previous grandmaster recorded in the notification message 106 and the time information of the current grandmaster recorded in the notification message 108, the first intermediate being the grandmaster is represented by Equation 4 below. The rate of time change between the bridge 12 and the second intermediate bridge 13 is obtained.

Thereafter, the second intermediate bridge 13 synchronizes time by multiplying its time information by a time change rate.

Meanwhile, when the synchronization message 105, 107 and the notification message 106, 108 are delivered to the second terminal device 11 via the second intermediate bridge 13, the second intermediate bridge 13 sends a message in the middle. Since time occurs during processing, this time must be corrected.

The first intermediate bridge 12 transmits a synchronization message 105 to the second intermediate bridge 13, and the second intermediate bridge 13 timestamps t ₅ at the time when the synchronization message 105 is received. Record it.

The second intermediate bridge 13 waits without transmitting the synchronization message 105 to the second terminal device 11 until the notification message 106 arrives from the first intermediate bridge 12.

Thereafter, when the second intermediate bridge 13 receives the notification message 106 from the first intermediate bridge 12, it transmits the synchronization message 105 to the second terminal device 11 and timestamps t ₇ at that time. Save). At this time, the first intermediate bridge 12 transmits the notification message 106 to the second intermediate bridge 13 continuously following the synchronization message 105.

Thereafter, the second intermediate bridge 13 may calculate the intermediate processing time using Equation 5 below using time recording information t ₅ and t ₇ .

After that, the value obtained by adding the intermediate processing time is recorded and transmitted to the grandmaster time value of the notification message 106 transmitted through the second intermediate bridge 13.

The conventional IEEE 802.1 AS uses a plurality of control messages to determine the grandmaster, calculate the average propagation delay time, and synchronize the time, thereby causing an overload of the entire network.

In addition, the conventional IEEE 802.1 AS guarantees the correct time stamps obtained from the physical layer of the network layer while the time stamps used in each synchronization procedure guarantee the accurate time. Since the time accuracy required in the environment is not required, there is a problem that causes unnecessary complexity.

In addition, the conventional IEEE 802.1 AS records a timestamp at the physical layer and transmits the timestamp to the time synchronization layer, thereby losing compatibility with the physical layer of a general network device.

It is a problem of the present invention to solve the problems of the prior art as described above.

Accordingly, the present invention obtains the time stamp information in the time synchronization layer located between the data link layer and the network layer by using the multi-function time synchronization message in the local area network, so as not to overload the local area network with the physical layer of the general network device. The purpose is to provide a time synchronization method in a local area network to maintain compatibility.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided a method of synchronizing time, comprising: a first propagation delay time obtaining step of acquiring a first propagation delay time with a neighboring device by transmitting and receiving a first multifunction time synchronization message; Determining a grandmaster using local time information of the first multi-function time synchronization message; Obtaining a second propagation delay time with the neighboring device by transmitting and receiving a second multifunction time synchronization message; And a time synchronization step of synchronizing time by using the first and second multifunction time synchronization messages and the first and second transfer delay times.

In addition, the present invention defines a multi-function time synchronization message that can be used for grandmaster determination, average propagation delay time calculation, and time synchronization, and synchronizes the times of devices connected in the local area network using the multi-function time synchronization message. Determining a grandmaster that provides a reference time; Determining a grandmaster and calculating an average transmission delay time between two neighboring devices by using the generated time stamp and the time stamp of the multi-function time synchronization message in response to the message; And synchronizing the time using the generated time stamp while determining the grand master and calculating the average transmission delay time.

In addition, the present invention succinctly processes the time synchronization procedure between devices using a multi-function time synchronization message in a local area network, thereby providing the grandmaster's determination and average transfer delay time calculation and time synchronization between devices.

In addition, the present invention replaces a plurality of messages used in IEEE 1588 PTP and IEEE 802.1 AS using a multi-function time synchronization message.

In addition, the present invention is useful for ensuring accurate time in an industrial network environment, although the timestamp obtained at the physical layer is difficult to apply the technology as it is in a local area network, so that the time synchronization layer (between the datalink layer and the network layer) Location stamp) to obtain the timestamp information and maintain compatibility with the physical layer applied to general network equipment.

In addition, the present invention has the advantage that it is possible to ensure accurate time by a simple processing procedure by the reuse of the time stamp used in the grandmaster determination, the average transfer delay time calculation and time synchronization process.

The present invention as described above, by using the multi-function time synchronization message in the local area network to obtain the time stamp information in the time synchronization layer located between the data link layer and the network layer, without overloading the local area network of the general network device It is effective to maintain compatibility with the physical layer.

In addition, the present invention, by performing a simple device-to-device time synchronization procedure using a multi-function time synchronization message in a local area network, it is possible to replace a large number of messages and complex time synchronization method used in IEEE 1588 PTP and IEEE 802.1AS There is.

In addition, while the conventional technique uses a time stamp obtained at the physical layer to ensure proper time accuracy in an industrial network environment, the present invention obtains a time stamp at the IEEE 802.1 AVB layer (between the data link layer and the network layer). It is possible to ensure the accuracy of time synchronization suitable for the application of the local area network, to simplify the processing procedure, and to eliminate the need to modify the conventional data link layer.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, It can be easily carried out. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram of an embodiment of a local area network to which the present invention is applied.

As shown in FIG. 2, a local area network to which the present invention is applied is a terminal device for generating real-time data and a multi-function time synchronization message or processing real-time data and a multi-function time synchronization message received from another terminal device. (21) (25 terminal devices in the embodiment of the present invention), the intermediate bridge 22 for receiving the real-time data and the multi-function time synchronization message from each terminal device to transfer to other terminal devices and other intermediate bridge (the present invention) 11 intermediate bridges), an Ethernet communication medium 23 for connecting each terminal device and an intermediate bridge and connecting an intermediate bridge and an intermediate bridge (in the embodiment of the present invention, the transmission speed of the medium is 100 Mbps, 1 Gbps). And a terminal device 24 for transmitting background traffic to the entire local area network, and providing a reference synchronization time to the entire local area network. Includes grandmaster 25 (in the embodiment of the present invention the intermediate bridge is grandmaster).

Here, the multi-function time synchronization message includes time information for grandmaster determination, average propagation delay time calculation, and time synchronization in a local area network.

In addition, the intermediate bridge 22 is composed of a plurality of ports to calculate the average propagation delay time for each port and delivers a multi-function time synchronization message.

Also, in a state where devices in a local area network are transmitting and receiving non-real-time data, one device becomes a grandmaster and all other devices become slaves by transmitting time-sink frames to each other, and the slave devices set their own time synchronization values. Match the master.

The configuration diagram applied to the present invention is up to seven hops. Therefore, a local area network is formed within the range of the maximum hop specified by IEEE 802.1 AVB. However, it is extensible.

3 is an exemplary view illustrating a structure for each communication layer of a device in a local area network according to the present invention.

As shown in FIG. 3, all devices in the local area network according to the present invention are the grandmaster determiner 305, the time synchronizer 306, and the average propagation delay time measurer 307 in the time synchronization layer 304. It includes.

Here, the grandmaster determination unit 305 compares the local time of the other devices using the time information of its local time 308. As a result of the comparison, if its local time 308 has more accurate time information, it determines itself as the grandmaster, otherwise it updates its data set at its local time 308 with the grandmaster's data set.

In addition, when operating as a grandmaster, the time synchronizer 306 records its time information in a multi-function time synchronization message and transmits the time information to neighboring devices. In this case, when operating as a slave, the timing is synchronized by adjusting its local time 308 based on the contents of the multi-function time synchronization message received from the grandmaster.

In addition, the average propagation delay time measuring unit 307 uses a multi-function time synchronization message to measure the average propagation delay time with a neighboring device. When the average propagation delay time with the neighboring device is measured, this information is used by the time synchronization unit 306 to synchronize the time.

In addition, the time synchronization layer 304 receives a multi-function time synchronization message delivered to the datalink layer 309 through the physical layer 310.

Unlike the IEEE 802.1 AS, the present invention records the time stamp when the multi-function time synchronization message arrives at the time synchronization layer 304 without recording the time stamp at the physical layer. At this time, when message and data packets other than the multi-function time synchronous message arrive, the message and packets are delivered to the network layer 303 and then to the transport layer 302.

4 is a diagram illustrating an embodiment of a multi-function time synchronization message according to the present invention.

As shown in FIG. 4, the multi-function time synchronization message according to the present invention includes an 'Announce' message, a 'Sync' message, a 'Follow_Up' message, a 'Pdelay_Req' message, a 'Pdelay_Resp' message, and a 'Pdelay_Resp_Follow_Up' of the IEEE 802.1 AS. Following the format of the message, it is designed for the application of concise processing procedures.

That is, since the multi-function time synchronization message has a total size of 94 bytes and is stacked in a general Ethernet frame, the forward and backward Ethernet headers of the destination address 401, the source address 402, and the FCS (frame check) 428 Is located.

In addition, the ether type 403 following the source address 402 follows the ether type of the IEEE 802.1 AVB, and the message type 404 is a unique value of the multi-function time synchronization message type other than the message type of the IEEE 802.1 AS. Have In particular, in the case of the multi-function time synchronization message that performs the 'Announce' message function of the IEEE 802.1 AS, the message type 404 is the same as the 'Announce' message. At this time, if the message type is not the same as the 'Announce' message, the reservation bit 417 field to the grandmaster priority 2 field 425 are not reflected.

In addition, the reserved bits (405, 409, 412, 417, 419) are placed to follow the message format of the IEEE 802.1 AS.

In addition, the version 406 field of the current multi-function time synchronization message is set so that when the multi-function time synchronization message is updated, the version is known to allow compatibility between versions.

In addition, the message length 407 field indicates the total length of the multifunction time synchronization message, and the domain number 408 records the unique domain number of the local area network supporting IEEE 802.1 AVB.

In addition, the local time attribute 410 field records local time information of each device. At this time, information such as 'twoStepFlag', 'leap61', 'leap59', 'currentUtcOffsetValid', 'ptpTimescale', 'timeTraceable', and 'frequencyTraceable' are set as flag values, and time information that local time can be used in a local area network Record information such as recognition or compliance with time information as defined by world standards. In addition, each flag value is graded for use in determining the grandmaster.

In addition, the nanosecond 411 of the grandmaster records the time in seconds or less in the grandmaster time information. The grandmaster's nanoseconds 411 are used to calculate time differences and calculate transmission delay times in the local area network.

In addition, the transmission destination port ID 413 has a value in the case of a terminal device, but in the case of an intermediate bridge device, several ports may exist, and each port may have a different average propagation delay time, thus making the port unique. It serves to distinguish.

In addition, the message sequence number 414 indicates the sequential sequence of the multi-function time synchronization message. According to the message sequence number 414, a message pair can be found when calculating the average propagation delay time.

In addition, the message management 415 is a field required for integrating and managing messages defined by the IEEE as a standard.

In addition, the message delivery period 416 represents a delivery period of the multi-function time synchronization message, which is, for example, 10 ms in the present invention. However, the period may be set by the network administrator according to the application of the local area network.

In addition, the current UTC difference value 418 field indicates a difference between Temp Atomique International (TAI) and Universal Time Coordinated (UTC). Since the current time difference is 33 seconds, the multi-function time synchronization message is also set to 33 seconds. At this time, according to the version of the multi-function time synchronization message, the value should be adjusted to the world standard.

In addition, the clock source source 420 indicates where the clock of each local time is obtained. At this time, the clock source source 420 may be an atomic clock, a global positioning system (GPS), a RADIO reception, a clock of an IEEE 1588 PTP, an NTP, or a user setting value.

In addition, the hop count 421 is used to use a hop count smaller message when receiving a duplicate message in the intermediate bridge.

In addition, the grandmaster ID 422 records the MAC address of the device currently designated as the grandmaster, so that the grandmaster can be uniquely distinguished.

In addition, the grandmaster time attribute 423 is used to indicate the attribute of which device has a more accurate time when determining the grandmaster between devices. At this time, the attribute can be expressed as 'clockClass', 'clockAccuracy', where 'clockClass' is divided into several classes depending on whether or not it has been synchronized at a predetermined time from the world standard, and 'clockAccuracy' has an accuracy within a few seconds. There are several stages that can be used to determine the Grandmaster.

Grandmaster priority 1 424 is also used when the network administrator determines the grandmaster by prioritizing the top of other time attribute conditions.

In addition, Grandmaster Priority 2 425 is used to give priority to the final decision when the Grandmaster cannot be determined even under conditions of other temporal attributes.

Also, the seconds 426 of the grandmaster are recorded in units of seconds of the grandmaster. Therefore, adding the grandmaster's seconds (426) and the grandmaster's nanoseconds (411) field can represent both the grandmaster's time.

In addition, the previous message timestamp 427 and the current message timestamp 428 are used to calculate the average propagation delay time. That is, the previous message time stamp 427 records the time stamp when the previous multi-function time synchronization message is received, and the current message time stamp 428 records the time stamp when the current multi-function time synchronization message is delivered. The two timestamps 427 and 428 are received from the device sending the multifunction time synchronization message to the neighboring device to calculate the average propagation delay time.

5 is a flowchart illustrating a time synchronization method in a local area network using a multi-function time synchronization message according to the present invention.

As shown in FIG. 5, the local area network using the multi-function time synchronization message according to the present invention includes, for example, a first terminal device 51, a first intermediate bridge 52, a second intermediate bridge 53, and a first communication device. 2, the terminal device 54.

First, when the network is first set up, each device (terminal device and intermediate bridge) receives a timestamp S1t1, B1t1, B2t1, S2t1 for the time of transmission of the first multifunction time synchronization message 501. Record in timestamp 428 field of message 501 and send to neighboring devices.

That is, the first terminal device 51 records the time stamp S1t1 in the time stamp field of the first multifunction time synchronization message 501 and transmits the time stamp S1t1 to the first intermediate bridge 52.

In addition, the first intermediate bridge 52 records the time stamp B1t1 in the timestamp field of the first multifunction time synchronization message 501 and transmits it to the first terminal device 51 and the second intermediate bridge 53. do.

In addition, the second intermediate bridge 53 records the time stamp B2t1 in the time stamp field of the first multifunction time synchronization message 501 and transmits the time stamp B2t1 to the first intermediate bridge 52 and the second terminal device 54. .

In addition, the second terminal device 54 records the time stamp S2t1 in the time stamp field of the first multifunction time synchronization message 501 and transmits the time stamp S2t1 to the second intermediate bridge 53.

Subsequently, each neighboring device receiving the first multifunction time synchronization message 501 records the time stamps S1t2, B1t2, B2t2, and S2t2 when the first multifunction time synchronization message 501 arrives.

That is, the first terminal device 51 records the time stamp S1t2 at the time when the first multifunction time synchronization message 501 arrives from the first intermediate bridge 52.

In addition, the first intermediate bridge 52 records the time stamp B1t2 at the time when the first multifunction time synchronization message 501 arrives from the first terminal device 51 and the second intermediate bridge 53.

The second intermediate bridge 53 also records a timestamp B2t2 at the time when the first multifunction time synchronization message 501 arrives from the first intermediate bridge 52 and the second terminal device 54.

In addition, the second terminal device 54 records the time stamp S2t2 at the time when the first multifunction time synchronization message 501 arrives from the second intermediate bridge 53.

At this time, each device (terminal device and intermediate bridge) is compared to the local time information of the local time information in the first multi-function time synchronization message 501 received by their own time, more accurate than their own local time information High) local time information, the received first multifunction time synchronization message 501 is transmitted to another device (502), otherwise it may not be delivered.

For example, as a result of comparing the local time information in the first multifunction time synchronization message 501 received from the second terminal device 54 with its own local time information, the second intermediate bridge 53 compares its own local time information. If is more accurate local time information may not transmit the first multi-function time synchronization message 501 received from the second terminal device 54 to the first intermediate bridge (52).

As another example, as a result of comparing the local time information in the first multifunction time synchronization message 501 received from the first intermediate bridge 52 with its local time information, the second intermediate bridge 53 compares its local time information with itself. If is more accurate local time information may not transmit the first multi-function time synchronization message 501 received from the first intermediate bridge 52 to the second terminal device (54).

Thereafter, the grandmaster is determined using the local time information in the first multi-function time synchronization message 501.

5 illustrates an example in which the first intermediate bridge 52 is determined to be a grandmaster. At this time, when the grandmaster is determined, the remaining terminal device and the intermediate bridge operate as slaves.

Then, after determining the grandmaster uniquely in the LAN environment, each device sends a second multifunction time synchronization message 503 to the neighboring devices to calculate the average propagation delay time between the devices.

Subsequently, each device transmits the first multi-function time synchronization message 501 to the grandmaster's local time information, timestamps (S1t1, B1t1, B2t1, S2t1, S1t2, B1t2, B2t2, S2t2) and the second multi-function time synchronization. Using the time stamps (S1t3, B1t3, B2t3, S2t3, S1t4, B1t4, B2t4, S2t4) obtained when the message 503 is transmitted and received, the average propagation delay time between neighboring devices is expressed by Equation 6 below. Calculate

In this case, Equation 6 below is an example of calculating an average propagation delay time between the neighboring first terminal device 51 and the first intermediate bridge 52, which is the grandmaster. The average propagation delay time can be found.

In this case, S1t4 is a timestamp of when the second multifunction time synchronization message is received from the grandmaster, S1t1 is a timestamp of when the first multifunction time synchronization message is transmitted to the grandmaster, and B1t3 is a timestamp of the grandmaster. A timestamp at the time when the second multifunction time synchronization message is transmitted, B1t2 means a timestamp at the time when the grandmaster receives the first multifunction time synchronization message.

Here, r is as shown in Equation 7 below.

In this case, S1t2 means a timestamp of when the first multifunction time synchronization message is received from the grandmaster.

In addition, the 'current grandmaster time' may be obtained through the second multi-function time synchronization message 503, and the 'previous grandmaster time' may be obtained through the first multi-function time synchronization message 501.

The present invention does not need to generate a separate message to calculate the average propagation delay time as in the IEEE 802.1 AS, and can calculate the average propagation delay time using a previously stored timestamp.

This not only simplifies the processing of each device, but also reduces the number of control messages.

In addition, the process of synchronizing the time after calculating the average propagation delay time between the devices can also synchronize the time without operating a separate message by using the local time information and timestamp of the previously recorded grandmaster.

That is, since the first intermediate bridge 52 is the grandmaster, the 'previous grandmaster time' of the first terminal device 51 at time S1t4 is the grandmaster time at the time when the first multi-function time synchronization message 501 is received. The current grand master time is the grandmaster time at which the second multi-function time synchronization message 503 is received.

In addition, since the first terminal device 51 has calculated the average propagation delay time when the second multi-function time synchronization message 503 has already been received, the time when the second multi-function time synchronization message 503 is delivered to this value. 'RxTime' is obtained by subtracting stamps S1t4, B1t4, B2t4, and S2t4.

In addition, when receiving the first multi-function time synchronization message 501, 'rxTimeOld' is obtained by subtracting the time stamps S1t2, B1t2, B2t2, and S2t2 by the average propagation delay time.

Therefore, the time change rate in time synchronization is calculated as in Equation 8 below.

After obtaining the time change rate through Equation 8, the first terminal device 51 synchronizes time by multiplying the time change rate by its own time information.

In addition, the second intermediate bridge 53 and the other terminal devices also synchronize time in the same manner.

On the other hand, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. The recording medium may include any type of computer readable recording medium.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

The present invention can be used in a local area network or the like.

1 is a flowchart illustrating an embodiment of a time synchronization method in a conventional IEEE 802.1 AS;

2 is a configuration diagram of an embodiment of a local area network to which the present invention is applied;

3 is an example of a structure for each communication layer of a device in a local area network according to the present invention;

4 is a structural diagram of an embodiment of a multi-function time synchronization message according to the present invention;

5 is a flowchart illustrating a time synchronization method in a local area network using a multi-function time synchronization message according to the present invention.

* Explanation of symbols for the main parts of the drawings

51: first terminal device 52: first intermediate bridge

53: second intermediate bridge 54: second terminal device

Claims (6)

In the time synchronization method, A first propagation delay time obtaining step of acquiring a first propagation delay time with a neighboring device by transmitting and receiving a first multifunction time synchronization message; Determining a grandmaster using local time information of the first multi-function time synchronization message; Obtaining a second propagation delay time with the neighboring device by transmitting and receiving a second multifunction time synchronization message; And Synchronizing time by using the first and second multi-function time synchronization messages and the first and second transfer delay times; Time synchronization method comprising a. The method of claim 1, The first and second delivery delay time is, And calculating time stamps using time stamps when the first and second multi-function time synchronization messages arrive at a time synchronization layer. The method according to claim 1 or 2, The first propagation delay time obtaining step, By comparing the local time information of the first multi-function time synchronization message received from the neighboring device with its own local time information, the local time information of the first multi-function time synchronization message is more accurate than its local time information. Otherwise, the first multi-function time synchronization message is not transmitted to another neighboring device. The method of claim 3, wherein The time synchronization step, Calculating an average propagation delay time using the obtained first propagation delay time and the second propagation delay time; Calculating a time change rate using the calculated average transfer delay time; And Synchronizing time by multiplying the calculated time change rate by its time information; Time synchronization method comprising a. The method of claim 4, wherein The average transfer delay time calculating step, A time synchronization method calculated through Equation A below. Equation A

(S1t4 is a timestamp of when the second multi-function time synchronization message is received from the grandmaster, S1t1 is a timestamp of when the first multifunction time synchronization message is transmitted to the grandmaster, and B1t3 is a second timestamp of the grandmaster. A timestamp at the time of transmitting the multifunction time synchronization message, B1t2 means a timestamp at the time when the grandmaster receives the first multifunction time synchronization message, and r is

Satisfying. In this case, S1t2 means a timestamp at the time when the first multi-function time synchronization message is received from the grand master, 'current grand master time' is obtained through the second multi-function time synchronization message, and 'previous grand master time' Is obtained through the first multi-function time synchronization message.) The method of claim 5, The time change rate calculating step, Time synchronization method calculated through the following [Equation B]. Equation B

Here, 'rxTime' is obtained by subtracting S1t4 from the average propagation delay time, and 'rxTimeOld' means subtracting S1t2 from the average propagation delay time.

Images