CN114157381A - Network delay jitter-oriented dynamic delay estimation period adjustment method - Google Patents
Network delay jitter-oriented dynamic delay estimation period adjustment method Download PDFInfo
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- H—ELECTRICITY
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- H04J3/00—Time-division multiplex systems
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- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
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- H—ELECTRICITY
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- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
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- H—ELECTRICITY
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- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
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- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
- H04J3/0658—Clock or time synchronisation among packet nodes
- H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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- H04L7/0016—Arrangements for synchronising receiver with transmitter correction of synchronization errors
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Abstract
The invention relates to a dynamic adjustment method of a delay estimation period facing to network delay jitter, which comprises the following steps: step S1, all nodes in the clock synchronization domain send Announce messages to other nodes and determine the master clock of the nodes in the domain; step S2, the master clock periodically sends synchronous messages to the slave clock nodes in the domain; step S3, the master clock encapsulates the first time stamp into an accompanying message, sends the accompanying message to the slave clock, and the slave clock decapsulates the message; step S4, calculating clock offset from the clock; step S5, judging whether jitter occurs by comparing the deviation with the deviation jitter threshold value, step S6, calculating the credible clock deviation according to the time delay, and when the time delay is larger than the threshold value, calculating the credible clock deviation
When the network environment is normal, the network environment is not jittered and used
And correcting a local clock to finish high-precision clock synchronization. The invention effectively reduces the influence of the time delay error caused by jitter on the clock synchronization precision.
Description
Technical Field
The invention relates to the technical field of clock synchronization, in particular to a dynamic time delay estimation period adjusting method facing network time delay jitter.
Background
The time delay refers to a transmission time of a time stamp data packet from a reference node (master clock) to a terminal node (slave clock), which includes a processing time of the reference point, a transmission time, a processing time of the terminal point, and the like. The time delay estimation error of the clock synchronization technology directly influences the precision of clock synchronization.
In an actual industrial field, the factors forming the delay jitter are many. Congestion caused by frequent forwarding of heterogeneous data streams such as audio and video, control data and the like, uncertainty of packet processing delay and complex and severe electromagnetic environment can cause delay jitter, and how to reduce delay jitter and the influence caused by delay jitter are one of challenges of clock synchronization technology development.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a method for dynamically adjusting a delay estimation period for network delay jitter, which can significantly reduce clock synchronization errors caused by frequent jitter.
In order to achieve the purpose, the invention adopts the following technical scheme:
a time delay estimation period dynamic adjustment method facing network time delay jitter comprises the following steps:
step S1, after the clock synchronization process is started, all nodes in the clock synchronization domain send Announce messages to other nodes, and compare the clock attributes through an optimal master clock algorithm to determine the master clock of the nodes in the domain, wherein the other nodes are slave clocks;
step S2, the master clock periodically transfers the slave clock node to the domainThe point sends the synchronous message, the main clock sets the first time stamp t when the message passes the link layer and the middle layer of the physical layer1And storing as the time of the packet popping. Receiving the synchronous message from the clock, and recording a second time stamp t at the same position2；
Step S3, the master clock sends the first time stamp t1Packaging the packet into an accompanying message, sending the accompanying message to a slave clock, decapsulating the message from the slave clock, and obtaining a first timestamp t from the slave clock1And a second time stamp t2；
Step S4, the slave clock according to t1And t2And the last measured delay data, calculating the clock offset tf；
Step S5 by comparing the deviation tfAnd deviation jitter threshold thetafJudging whether dithering occurs, if tf≤θfIf the network is not jittered normally, the process goes to step S6 to update the clock; if tf＞θfAnd represents the network delay jitter, and directly changes the delay estimation period to be a short period T2And immediately triggering a time delay measurement to obtain time delay data tdThen, the process proceeds to step S6;
step S6, according to the time delay tdCalculating a trusted clock offset tfWhen t isf≤θfWhen the time is longer, the network environment is normal and not jittered, and t is usedfAnd correcting a local clock to finish high-precision clock synchronization.
Further, the Announce packet includes an attribute data set of the clock.
Further, the calculating clock offset tfThe method specifically comprises the following steps:
tf＝t2-(t1+t’d)
wherein, t'dIs the time delay data measured last time.
Further, the delay measurement trigger condition includes that the timer triggers periodically, and the delay jitter is sensed in step S5.
Further, the time delay measurement specifically includes:
the slave clock node sends a time delay measurement request message to the master clock, and the slave clock records the sending time to form a third timestamp t3The master clock records the arrival time of the message to form a fourth timestamp t4(ii) a The master clock will timestamp t4Encapsulating a Delay measurement reply message (Delay _ resp) and sending the message to the slave clock; decapsulating the packet from the clock to obtain all the four required timestamps t1、t2、t3、t4；
The slave clock will t1、t2、t3、t4Substituting the following formula to obtain the observed value t of the time delay at the current momentdI.e. tdIs the average value of the two-way time delay
Comparing the time delays tdAnd a delay threshold thetad(ii) a When t isd≤θdWhen the network is in the normal period T, the time delay measurement period is adjusted to the normal period T, which represents that the current network does not shake or the shaking is over1(ii) a When t isd＞θdIndicating that the delay jitter occurs or continues, adjusting the delay measurement period to a short period T2。
Compared with the prior art, the invention has the following beneficial effects:
1. for the network with time delay jitter, the invention can reduce the influence of time delay error caused by jitter on clock synchronization precision;
2. the invention can automatically adjust the time delay estimation period, thereby enhancing the accurate estimation of the time delay jitter, enhancing the robustness of a network system and ensuring the precision requirement of clock synchronization.
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FIG. 1 is a schematic diagram illustrating error variation in a clock synchronization process according to an embodiment of the present invention;
FIG. 2 is a flow chart of the method of the present invention.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
In this embodiment, an IEEE1588 precision time synchronization protocol (PTP) is operated in a network, a synchronization period is set to 1s, a delay measurement period is set to 8s, and delay data and clock skew of a master clock and a slave clock of the network are collected. Most of the time delay is stable around 2800us, the time delay jitters for many times, the time delay during jittering reaches 3100us, the clock deviation of the jittering has great influence, and when the jittering occurs, the clock deviation is large and reaches 750us at most. It can be seen from the above that the delay of the network is unstable, the jitter frequency is high, and the amplitude is large, which becomes the main factor affecting the clock synchronization.
In this embodiment, the offset threshold and the delay threshold are determined according to a statistical method. From the offset data collected above, a mean value of the clock offset of 33.27us and a standard deviation of 66.69us were obtained. If 95% of the offset value is required to be within the threshold interval, the threshold θ of the offset isfμ +2 σ, i.e. threshold θf166.65us were taken.
Similarly, the mean value of the obtained time delay is 2807.64us, and the standard deviation is 45.49 us. If 95% of the offset value is required to be within the threshold interval, the threshold θ of the time delaydμ +2 σ, i.e. delay threshold θd2898.62us were taken.
Substituting the threshold parameter into the method of the invention, defaulting the time delay measurement period to 8s, when the time delay exceeds the threshold, judging that the jitter occurs, changing the period to 1s, and keeping the synchronization period unchanged. And starting a clock synchronization process to acquire time delay data and clock offset.
Referring to fig. 2, the present invention provides a method for dynamically adjusting a delay estimation period for network delay jitter, which includes the following steps:
step S1, after the clock synchronization process is started, all nodes in the clock synchronization domain send an Announce message to other nodes, including the attribute data set of the clock, after the other nodes receive the Announce message, the other nodes compare the clock attributes through the Best Master Clock Algorithm (BMCA) to determine the master clock of the nodes in the domain, and the other nodes are slave clocks;
step S2 is that the master clock periodically sends a synchronization message to the intradomain slave clock node,when a message passes through the intermediate layers of the link layer and the physical layer, the master clock marks a first time stamp t1And storing as the time of the packet popping. Receiving the synchronous message from the clock, and recording a second time stamp t at the same position2；
Step S3, the master clock sends the first time stamp t1Packaging the packet into an accompanying message, sending the accompanying message to a slave clock, decapsulating the message from the slave clock, and obtaining a first timestamp t from the slave clock1And a second time stamp t2；
Step S4, the slave clock according to t1And t2And the time delay data measured last time, calculating the clock offset t by formula (1)f
tf＝t2-(t1+td)
(1)；
Step S5 by comparing the deviation tfAnd deviation jitter threshold thetafJudging whether dithering occurs, if tf≤θfIf the network is not jittered normally, the process goes to step S6 to update the clock; if tf＞θfAnd represents the network delay jitter, and directly changes the delay estimation period to be a short period T2And immediately triggering a time delay measurement to obtain time delay data tdThen, the process proceeds to step S6;
preferably, the time delay measurement specifically includes:
the slave clock node sends a time delay measurement request message to the master clock, and the slave clock records the sending time to form a third timestamp t3The master clock records the arrival time of the message to form a fourth timestamp t4(ii) a The master clock will timestamp t4Encapsulating a Delay measurement reply message (Delay _ resp) and sending the message to the slave clock; decapsulating the packet from the clock to obtain all the four required timestamps t1、t2、t3、t4；
The slave clock will t1、t2、t3、t4Substituting the following formula to obtain the observed value t of the time delay at the current momentdI.e. tdIs the average value of the two-way time delay
Comparing the time delays tdAnd a delay threshold thetad(ii) a When t isd≤θdWhen the network is in the normal period T, the time delay measurement period is adjusted to the normal period T, which represents that the current network does not shake or the shaking is over1(ii) a When t isd＞θdIndicating that the delay jitter occurs or continues, adjusting the delay measurement period to a short period T2。
Step S6, delaying tdSubstituting equation (1) into, calculate the trusted clock offset tfWhen t isf≤θfWhen the time is longer, the network environment is normal and not jittered, and t is usedfAnd correcting a local clock to finish high-precision clock synchronization.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (5)
1. A time delay estimation period dynamic adjustment method facing network time delay jitter is characterized by comprising the following steps:
step S1: after a clock synchronization process is started, all nodes in a clock synchronization domain send Announce messages to other nodes, and through an optimal master clock algorithm, the attributes of each clock are compared to determine a master clock of the nodes in the domain, and the other nodes are slave clocks;
step S2: a master clock periodically sends a synchronous message to an intra-domain slave clock node, and the master clock marks a first timestamp t when the message passes through the intermediate layers of a link layer and a physical layer1And storing as the time of the packet popping. Receiving the synchronous message from the clock, and recording a second time stamp t at the same position2；
Step S3: the master clock sends a first time stamp t1Packaging the packet into an accompanying message, sending the accompanying message to a slave clock, decapsulating the message from the slave clock, and obtaining a first timestamp t from the slave clock1And a second time stamp t2；
Step S4:the slave clock is according to t1And t2And the last measured delay data, calculating the clock offset tf；
Step S5: by comparing the deviations tfAnd deviation jitter threshold thetafJudging whether dithering occurs, if tf≤θfIf the network is not jittered normally, the process goes to step S6 to update the clock; if tf＞θfAnd represents the network delay jitter, and directly changes the delay estimation period to be a short period T2And immediately triggering a time delay measurement to obtain time delay data tdThen, the process proceeds to step S6;
step S6: according to time delay tdCalculating a trusted clock offset tfWhen t isf≤θfWhen the time is longer, the network environment is normal and not jittered, and t is usedfAnd correcting a local clock to finish high-precision clock synchronization.
2. The method according to claim 1, wherein the Announce packet includes an attribute data set of the local clock.
3. The method according to claim 1, wherein the computing clock offset t is calculated by a time delay estimation period dynamic adjustment method for network time delay jitterfThe method specifically comprises the following steps:
tf＝t2-(t1+t′d)
wherein, t'dIs the time delay data measured last time.
4. The method according to claim 1, wherein the delay measurement trigger condition includes: the timer is triggered periodically, and a time delay jitter is sensed in step S5.
5. The method for dynamically adjusting a delay estimation period for network delay variation according to claim 1, wherein the delay measurement specifically includes:
the slave clock node sends a time delay measurement request message to the master clock, and the slave clock records the sending time to form a third timestamp t3The master clock records the arrival time of the message to form a fourth timestamp t4(ii) a The master clock will timestamp t4Encapsulating a Delay measurement reply message (Delay _ resp) and sending the message to the slave clock; decapsulating the packet from the clock to obtain all the four required timestamps t1、t2、t3、t4；
The slave clock will t1、t2、t3、t4Substituting the following formula to obtain the observed value t of the time delay at the current momentdI.e. tdIs the average value of the two-way time delay
Comparing the time delays tdAnd a delay threshold thetad(ii) a When t isd≤θdWhen the network is in the normal period T, the time delay measurement period is adjusted to the normal period T, which represents that the current network does not shake or the shaking is over1(ii) a When t isd>θdIndicating that the delay jitter occurs or continues, adjusting the delay measurement period to a short period T2。
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