KR101775728B1 - Apparatus and method for controlling network timing - Google Patents

Abstract

Disclosed is a network timing control apparatus and method capable of improving synchronization acquisition quality by selectively controlling the variation of a PDV profile in a packet network of an IEEE 1588 system (PTP), thereby controlling timing. According to the present invention, a timing packet is received from a master, a transmission delay variation (PDV) value of a received timing packet is patterned, a timing packet is dynamically filtered according to the PDV pattern information, Adjust. At this time, the valid packet is monitored, and if there is no valid packet, the master may request to transmit the timing packet considering the network characteristics. Then, the transmission delay of the filtered valid packet is estimated to synchronize the time and frequency.

Description

[0001] APPARATUS AND METHOD FOR CONTROLLING NETWORK TIMING [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of IEEE 1588 (PTP) technology, and more particularly, to an apparatus and method for controlling network timing which can control timing in a packet network to synchronize time and frequency between different devices.

By matching the time and frequency in the network, it is possible to induce accurate measurement of the instrument located in the remote place, and it is utilized as a means to secure mobility in the communication equipment. In particular, in a wireless communication system, in order for a mobile station to communicate with other terminals, the time of each base station must match within a predetermined error range in order to have mobility. For example, the time and frequency tolerances of CDMA, WiMAX and LTE in a wireless communication system are shown in Table 1 below.

Technology Time, frequency tolerance CDMA 3us, 50ppb WiMAX 1us, 2ppm LTE 3us, 50ppb

The wireless communication base station is becoming smaller in size and the cell coverage is becoming smaller as the installation environment is moved to the home or the office. Considering the cost of installing and operating a base station with existing macro coverage, it has a competitive advantage in that it can solve the shadow area in a more economical way.

In CDMA system, timing and synchronization are acquired through GPS satellite and GPS satellite receiver to synchronize the time and frequency between base stations. In this case, in order for the base station to receive a signal from the GPS, it is necessary to secure a sufficient line-of-sight of the GPS antenna and affect the quality such as the accuracy of the synchronization time.

In a WCDMA system with an FDD scheme, a backhaul synchronizes the network by recovering a clock in a synchronized network like E1 / T1.

However, when using ethernet as a backhaul in ALL IP, it can not restore the clock in the network because it is not a synchronized network, so that timing such as PTP (Precision Timing Protocol) and NTP (Network Timing Protocol) Protocol. Especially, femtocell for home uses DSL, Etherent, and Cable network for Internet access. Since this type of network is not a synchronized network, a separate timing synchronization scheme such as PTP should be considered.

IEEE 1588 is a time synchronization standard protocol that provides a protocol for devices to utilize the most precise and accurate clocks on the network. This open protocol is abbreviated as Precision Time Protocol (PTP). PTP is to recover the time and frequency from the slave by measuring the delay between the master and the slave while exchanging timing packets between the master and the slave according to a prescribed protocol. And synchronized to have the same time and frequency. In other words, the PTP compensates the transmission delay and the packet delay variation (PDV: Packet Delay Variation) between the master and the slave while the master and the slave exchange timing packets. In this case, the PDV value of the timing packet arriving at the slave is used by using the statistical characteristic value. For example, the delay average of each packet can be used. In this case, when the probability density function of the PDV does not have a normal distribution, there is a problem that the error of the statistic becomes larger when the average is used as the statistic. PDV distributions found in real networks are often not normally distributed and have various profiles. Therefore, if uniform statistics are used uniformly without reflecting the shape of various PDV profiles, uniform acquisition quality can not be obtained.

It is an object of the present invention to provide a network timing control apparatus and method capable of improving synchronization acquisition quality by selectively controlling the variation of a PDV profile in a packet network of an IEEE 1588 system (PTP).

According to one aspect of the present invention, a network timing control apparatus and method capable of improving synchronization acquisition quality by controlling timing corresponding selectively to variation of a PDV profile in a packet network of an IEEE 1588 system (PTP) is disclosed. According to the present invention, a timing packet is received from a master, a transmission delay variation (PDV) value of a received timing packet is patterned, a timing packet is dynamically filtered according to the PDV pattern information, Adjust. At this time, the valid packet is monitored, and if there is no valid packet, the master may request to transmit the timing packet considering the network characteristics. Then, the transmission delay of the filtered valid packet is estimated to synchronize the time and frequency.

According to the present invention, quality such as WCDMA for synchronizing the network using timing packets such as PTP, stable call service for LTE base stations, and high handoff success rate can be achieved.

It also reduces the dependency on network conditions when synchronizing clock frequency and time using PTP. Particularly, when the load of the network increases, the problem that the quality of the synchronized clock is largely deteriorated is solved and the excellent quality can be maintained.

In addition, the quality of the recovery clock can be maintained by selectively responding to fluctuations of the PDV due to network characteristics such as a queuing delay of a switch or a router.

In addition, a small number of timing packets per unit time can be maintained without degrading the synchronization quality. The timing packet is operated in a burst mode only when the load on the network is large, and a timing packet of a high rate is not required in a normal load condition

1 shows a configuration of an IEEE 1588 system to which the present invention can be applied;
2 shows an IEEE 1588 timing message.
Figures 3A-3C illustrate various examples of PDV profiles observed in a PTP slave;
4 is a diagram illustrating a process of periodically transmitting a timing packet from a PTP master to a PTP slave;
5 is a diagram showing a configuration of a network timing control apparatus according to an embodiment of the present invention.
6 illustrates a detailed configuration for measuring a PDV profile in a PDV shaper in accordance with an embodiment of the present invention.
7 illustrates a process of delivering a timing packet to burst from a PTP master to a PTP slave according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

FIG. 1 is a diagram illustrating a configuration of an IEEE 1588 system to which the present invention can be applied. FIG. 2 is a view showing an IEEE 1588 timing message, and FIGS. 3A to 3C are diagrams showing various examples of PDV profiles observed in a PTP slave. 4 shows a process of periodically transmitting a timing packet from the PTP master to the PTP slave.

The IEEE 1588 system, which is a method for time synchronization on a packet network, is composed of several nodes, all represented by clocks and the clocks are connected to each other through a network.

The IEEE 1588 system consists of a PTP master that can transmit packets containing time information to all nodes of the network and a PTP master that synchronizes the clock of the master using a timing packet transmitted by the master And a PTP slave.

The PTP master receives time information from GPS (Global Positioning System) or an accurate clock source and uses it as a base clock of the internal IEEE 1588 algorithm. The PTP slave extracts the time information contained in the time packet received from the master, local clock) to the master's clock.

In the IEEE 1588 system, the master and the slave are synchronized through the offset correction process and the transmission delay measurement process as shown in FIG.

The offset correction process corrects a time difference between the PTP master 10 and the PTP slave 20. To this end, the PTP master 10 periodically transmits a synchronization message, sync message to the PTP slave 20 (e.g., transmitted every 2 seconds). At this time, the PTP master 10 measures the exact time of transmitting the sync message using hardware or software, and the measured transmission time is transmitted to the PTP slave 20 again using a follow-up message . The PTP slave 20 measures the reception time of the sink message using hardware or software and calculates the difference between the transmission time of the sink message of the PTP master 10 included in the poll up message and the reception time of the measured sink message The offset to the PTP master 10 is corrected. That is, since the deviation between the master clock and the slave clock can be calculated using the accurate transmission time included in the poll-up message and the measured reception time, the time of the PTP slave 20 is matched. However, the determined deviation still includes network transmission delays. For this, the following transmission delay measurement procedure is performed.

The transmission delay measurement process measures a delay between the PTP master 10 and the PTP slave 20. To this end, the PTP slave 20 transmits a delay request message to the PTP master 10 The PTP master 10 measures the reception time of the delay request message using hardware or software and transmits the delay request message of the PTP slave 20 to the mobile station 10 using a delay response message And informs the PTP slave 20. Therefore, the PTP slave 20 receiving the delay response message measures the transmission delay of the network using the difference between the transmission time of the delay request message and the reception time transmitted by the PTP master 10 through the delay response message .

A process of adjusting time synchronization between the PTP master 10 and the PTP slave 20 using a sync message, a poll up message, a delay request message, and a delay response message will be described. a time t _0, PTP the slave 20 is a time after receiving the sync message t _1, PTP slave 20 receives the time to transfer the delay request message t _2, the delay response message PTP master 10 When one time is t ₃ , the offset time and the transmission delay time are expressed by the following Equation (1).

A router and a switch may be placed between the PTP master 10 and the PTP slave 20 according to the configuration of the packet network and the packet network is not transmitted along a fixed path The path can change instantaneously depending on the state of the network. Therefore, the transmission delay between the PTP master 10 and the PTP slave 20, which changes with time, can be expressed by the following equation (2).

Of course, if the transmission delay time between the PTP master 10 and the PTP slave 20 is constant, the time synchronization between the PTP master 10 and the PTP slave 20 can be performed simply by an arithmetic calculation according to Equation (1). However, due to the transmission delay variation (PDV), the transmission delay time exhibits stochastic or random characteristics. Therefore, it is necessary to accurately reflect the PDV in order to accurately estimate the transmission delay time and to adjust the time synchronization. If uniform statistical quantities are used uniformly without reflecting the shape of various PDV profiles, a uniform synchronous acquisition quality can not be obtained.

In the structure as shown in FIG. 3A, it is possible to secure a stable statistic by using a timing packet having a minimum transmission delay and filtering the rest. Therefore, it is possible to more accurately obtain the time and frequency acquisition to be restored in the PTP slave 20 by filtering some valid packets (hereinafter referred to as "meaningful packet") without determining that all packets reaching the PTP slave 20 are valid .

However, it should be considered that PDV fluctuates according to load conditions. As shown in FIGS. 3A to 3C, it can be seen that the PDV type greatly differs under 20% network load (FIG. 3A), 40% network load (FIG. 3B), and 60% network load When a packet with a minimum transmission delay is filtered and a packet with a minimum transmission delay is used as a meaningful packet, the probability is low and the frequency of the slave and the time of the slave are determined by using the measured transmission delay between the master and the slave as a reference The probability that a reference does not exist increases and becomes a holdover condition in some cases.

Another consideration is that PDV types are different depending on the type of network. Asymmetric networks such as DSL and symmetric networks such as Ethernet are different. This is due to the structure of the network. When considering the various types of networks and traffic conditions, assuming that the PDV type is simplified, the clock disciplining becomes unstable or inconsistent in some cases. In a mobile communication system such as a base station, This causes a defect.

Another consideration is that the probability that a meaningful packet is present in the PTP slave 20 is significantly reduced due to the manner in which the PTP master 10 delivers a timing packet to the PTP slave 20, This is the case with a large increase. Generally, a timing packet is periodically transmitted between the PTP master 10 and the PTP slave 20 by defining the number of timing packets per second. Referring to FIG. 4, when the timing packet reaches the PTP slave 20 by the traffic of the network It can be seen that the timing packet is not reached at the expected time due to the large transmission delay. This is the case when meaningful packets can not be found in the PTP slave 20. In the case of having the profile as shown in FIG. 3A, high traffic can be temporarily generated. If a packet having a minimum transmission delay is filtered with a meaningful packet, a meaningful packet will not exist for a certain period of time.

5 is a diagram illustrating a configuration of a network timing control apparatus according to an embodiment of the present invention.

As described above, the PTP master 10 and the PTP slave 20 exchange timing packets with a predetermined protocol. The PTP slave 20 estimates a transmission delay between the master and the slave (time stamping) and uses the estimated transmission delay value as a reference for clock discipling. The PTP slave 20 generates the time and frequency synchronized with the PTP master 10 through clock discipling. The operation of the PTP slave 20 can be achieved by a known technique, and thus a detailed description thereof will be omitted.

Under ideal conditions, the transmission delay between the PTP master 10 and the PTP slave 20 will have a constant value, but in real life it will have a variation (PDV) due to various factors, The queuing delay that occurs in the network becomes one of the biggest factors.

Therefore, when a transmission delay value is obtained through a time stamp included in a timing packet arriving at the PTP slave 20, a packet having a large transmission delay may arrive, May arrive. In the case of the transmission delay variation, the stability is degraded when the clock is recovered. Therefore, it is necessary to perform a filtering operation to invalidate a packet having a large jitter and to selectively use a packet having a small jitter for stable clock recovery. The jitter is a variation amount of the pulse signal for a short period which is not accumulated from the ideal time. The jitter increases when a phase change of an undesired pulse signal occurs on each transmission device during transmission or on a transmission line.

To this end, the network timing control apparatus of the PTP slave 20 includes a PDV shaper 21 for patterning a transmission delay variation (PDV) value of a timing packet received from the PTP master 10, a PDV shaper 21 And a timing packet filter 22 for dynamically filtering the timing packet according to the PDV pattern information of the transmission timing estimation unit 21 and adjusting the valid packet to be used for the transmission delay estimation. The packet monitoring unit 23 further monitors the valid packet to request the PTP master 10 to transmit the timing packet in consideration of the network characteristic when the valid packet does not exist.

Here, the PDV shaper 21 transmits PDV pattern information characterizing the PDV as a histogram to a timing packet filter using a slide window accumulation scheme, and the timing packet filter 22 transmits a timing packet For example, by filtering a minimum delay packet as a valid packet, filtering a maximum delay packet as an effective packet, filtering an average delay packet as an effective packet, do.

According to the filtering algorithm, the timing packet filter 22 selectively applies a method of filtering the minimum transmission delay packet, a method of filtering the maximum transmission delay packet, and a method of filtering the average transmission delay packet, the effect of varying the quality of the recovery clock can be minimized. Therefore, the timing packet filter 22 must be dynamically filtered according to the PDV type, and a PDV shaper 21 is required for this purpose.

The PDV shaper 21 determines whether the peak value is normal distribution or peak value by characterizing the peak value using the transmission delay value of the timing packet, and transmits the parameterized PDV pattern information to the timing packet filter 22. The timing packet filter 22 passes a meaningful packet in a manner of dynamically filtering according to the PDV pattern information recognized by the PDV shaper 21, and uses the meaningful packet as a reference clock for clock recovery.

Referring to FIG. 6, the PDV shaper 21 comprises a plurality of stages of accumulators having a slide window. The total transmission delay range to be monitored is divided by a constant interval, and the number of timing packets measured within each interval is counted. A histogram can be obtained by plotting the number of timing packets corresponding to each transmission delay period on a two-dimensional graph. The PDV profile can be characterized by envolope the number of packets delayed each transmission including the position of the vertex.

Referring again to FIG. 5, the timing packet filter 22 dynamically filters according to the PDV pattern information recognized by the PDV shaper 21. If the PDV profile shown in FIG. 3A is the minimum transmission delay packet, If the PDV profile has the PDV profile as shown in FIG. 3C, the average transmission delay packet is filtered as a meaningful packet. If the vertex is located in the opposite direction of FIG. 3A, the maximum delay packet is filtered as a meaningful packet, .

The packet monitoring unit 23 monitors a meaningful packet and notifies the PTP master 10 of a meanningful packet when there is no meanningful packet for a predetermined period. In this case, the packet monitoring unit 23 performs a periodic transmission, a burst transmission, a random transmission To the PTP master 10 so as to transmit the timing packet in accordance with the network characteristics of the network.

That is, the packet monitoring unit 23 may request the PTP master 10 to send a burst packet when it is monitored that there is no meaningful packet expected under the PDV pattern obtained from the PDV shaper 21. The PTP master 10 pseudo-repetitively transmits a repetitive timing packet for a short time in the burst region to the PTP slave 20 in the PTP slave 20 as shown in FIG. 7, The probability that a meaningful packet exists can be increased.

Although the method has been described through particular embodiments, the method may also be implemented as computer readable code on a computer readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission over the Internet) . In addition, the computer-readable recording medium may be distributed over network-connected computer systems so that computer readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the above embodiments can be easily deduced by programmers of the present invention.

Although the present invention has been described in connection with some embodiments thereof, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention as understood by those skilled in the art. something to do. It is also contemplated that such variations and modifications are within the scope of the claims appended hereto.

10: PTP master 20: PTP slave
21: PDV Shaper 22: Timing Packet Filter
23: Packet monitoring section

Claims (10)

A slave network timing controller for synchronizing the clock frequency and time using a Precision Timing Protocol (PTP)
A PDV shaper for patterning a transmission delay variation (PDV) value of a timing packet received from the master;
A timing packet filter for dynamically filtering the timing packet according to the PDV pattern information to adjust an effective packet to be used for transmission delay estimation; And
Monitors the valid packet, and when the valid packet does not exist, requests the master to transmit a timing packet in consideration of network characteristics. The method according to claim 1,
Wherein the PDV varies in shape depending on a load and a network type. delete 3. The method according to claim 1 or 2,
Wherein the PDV shaper delivers the PDV pattern information, which is characterized by a histogram of a PDV using a slide window accumulation scheme, to the timing packet filter. 5. The method of claim 4,
The timing packet filter may filter the minimum delay packet as an effective packet according to the PDV pattern information, filter the maximum delay packet as an effective packet, To the valid packet. The method according to claim 1,
Wherein the master bursts the timing packet when the load of the network increases. delete A network timing control method of a slave synchronizing a clock frequency and a time using a Precision Timing Protocol (PTP)
Receiving a timing packet from a master;
Patterning a transmission delay variation (PDV) value of the received timing packet;
Dynamically filtering the timing packet according to the PDV pattern information to adjust an effective packet to be used for transmission delay estimation;
Estimating a transmission delay of the filtered effective packet to synchronize time and frequency; And
Monitoring the valid packet and requesting the master to transmit a timing packet in consideration of network characteristics if the valid packet does not exist. 9. The method of claim 8,
Wherein the PDV pattern information is information obtained by characterizing the PDV as a histogram using a slide window accumulation scheme. 10. The method of claim 9,
The dynamically filtering may include filtering a minimum delay packet as a valid packet according to the PDV pattern information, filtering a maximum delay packet as a valid packet, or performing an average dekay ) ≪ / RTI > packets into valid packets.

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