CN104993900B - A kind of synchronization correction method based on IEEE1588 clock models - Google Patents
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Abstract
The invention discloses the synchronization correction method based on IEEE1588 clock models, belong to communication technical field.This method performs following steps：1）IEEE1588 clock models at the time of points are obtained, and each timestamp is obtained with this；2）The relation between the time of server and the time of client is obtained by IEEE1588 clock models, and the relation in the transmission of Sync messages and receive process between each timestamp is obtained with reference to PTP protocol；3）Calculus of differences is carried out based on the relation between a stamp；4）By step 3）Given first-order difference value, obtains the asymmetric skew of n-th exchange process, then levels off to zero by exponentially weighted moving average (EWMA) wave filter come θ values, the correction between completion server and client.This method jumps out conventional thinking, is compensated again on the basis of IEEE1588 clock models, solves the problems, such as time irreversibility end to end so that interaction time is symmetrical end to end.
Description
Technical Field
The invention relates to a clock synchronization correction method, and belongs to the technical field of communication.
Background
The adoption of IEEE1588v2 and a specially designed clock recovery mechanism can provide clock synchronization precision of microsecond or even sub-microsecond level. This is based on the important assumption that the transmission delay of the data packet from the master clock to the slave clock and the transmission delay from the slave clock to the master clock are equal. In reality, however, the communication paths are not completely symmetrical, mainly due to the delays and queuing delays of the different forward and reverse links. The differences in packet delays are mainly due to different queuing engineering of packets for elements in the communication network, such as switches and routers. This is particularly useful where the timing transport is in an end-to-end fashion, and there is no timing assistance in any form from the network to mitigate the effects of queuing delay.
The asymmetry of propagation delay has become a significant challenge to solve the clock synchronization problem. Boundary Clock (BC) and Transparent Clock (TC) in a network timing mechanism may eliminate delay asymmetry in the following two cases. The first scenario, forward and reverse paths of variable queuing delay; the second scenario is by timing the asymmetry that the packet makes in different paths in each direction. It is noted that the time support mechanisms (BC and TC) do not correct the delay asymmetry due to the different physical links between the network elements.
In order to solve the problem of asymmetry of delay in the prior art, a lot of work is being carried out to pay attention to and solve the problem of symmetry of troops of a physical link, and there is little research on the problem of transmission of QIA in an end-to-end mode.
Disclosure of Invention
The invention aims to solve the technical problem that aiming at the defects of the prior art, the invention provides a synchronous correction method with a secondary calibration process based on an IEEE1588 clock model so as to solve the problem of time asymmetry between a master clock and a slave clock.
The technical scheme provided by the invention for solving the technical problems is as follows: a synchronous correction method based on an IEEE1588 clock model executes the following steps:
1) Acquiring a time point of the IEEE1588 clock model;
master clock at T 1 [n]Time point transmission with T 1 [n]The Sync message of the timestamp reaches the slave clock, and the time point when the slave clock receives the Sync message is T 2 [n]And stamping a time stamp T for the Sync message 2 [n]；
At T from the clock 3 [n]Time point transmission with T 3 [n]A DelayReq message of a timestamp reaches a master clock, and the time point when the master clock receives the DelayReq message is T 4 [n]And stamping a time stamp T for the DelayReq message 4 [n]；
The master clock sends a time stamp T 4 [n]Embedding the message into the nth DelayResp message and transmitting the message to a slave clock to finish the nth exchange process;
when all the n exchange processes are finished, the whole PTP message exchange is finished;
wherein n is a positive integer;
2) Obtaining the relation between the time S (t) of the server and the time C (t) of the client by the IEEE1588 clock model, wherein S (t) = (1 + alpha) C (t) + theta (1)
The relation of each timestamp in the sending and receiving process of the Sync message is obtained by combining the PTP protocol and the formula (1),
T 1 [n]+d f +q f [n]＝(1+α[n])T 2 [n]+θ[n] (2)
the relation of each timestamp in the sending and receiving processes of the DelayReq message,
T 4 [n]-d r -q r [n]＝(1+α[n])T 3 [n]+θ[n] (3)
the time offset of the nth switching process of the slave clock in the equations (2) and (3) is θ [ n ],
wherein the content of the first and second substances,
alpha is a skew coefficient, and the type k of the transmission medium is in direct proportion to the length l of the propagation path;
alpha [ n ] is the skew coefficient of the nth exchange process;
θ is the time offset from the clock;
θ q [n]variable queuing delay skew;
d f a physical link delay from a master clock to a slave clock;
q f variable queuing delay, q, for the master clock f [n]Variable queuing delay for the nth switching process of the master clock;
d r is the physical link delay from the slave clock to the master clock;
q r for variable queuing delay of slave clocks, q r [n]Variable queuing delay for the nth switching process of the slave clock;
3) Based on the time stamp T in step 1) 1 [n]、T 2 [n]、T 3 [n]、T 4 [n]The difference operation is carried out to obtain the difference,
ε[n]＝q f [n]-q f [n-1]＝(1+α[n])dT 2 [n]-dT 1 [n]
γ[n]＝q r [n]-q r [n-1]＝dT 4 [n]-(1+α[n])dT 3 [n]
ε[n]variable queuing delay q of the nth switching process of a master clock f [n]The first-order difference of (a) is,
γ[n]variable queuing delay q of the nth switching process of the slave clock r [n]A first order difference of;
4) Obtaining the asymmetry of the nth switching process from the first order difference value given in step 3)Offset ofThen obtaining the result through an exponential weighted moving average filterAverage amount of (2)To average variable queuing delay offset
Wherein β is a filter factor, 0< β <1, and the synchronization correction between the server and the client is completed by adjusting β so that θ approaches zero.
The improvement of the technical scheme is as follows: q after step 3) f [n]And q is r [n]Performing normalization processing and minimizing variable queuing delay of the master clock mentioned in step 3)And minimum amount of variable queuing delay from clockAs reference value for normalization, and obtaining q f And q is r Corresponding normalized quantityAnd
wherein, the first and the second end of the pipe are connected with each other,
ε s [n]＝ε s [n-1]+ε[n]
＝ε s [n-1]+q f [n]-q f [n-1]
＝ε s [0]+q f [n]-q f [0]
γ s [n]＝γ s [0]+q r [n]-q r [0]
ε s [0]＝γ s [0]＝0。
the improvement of the technical scheme is as follows: instantaneous asymmetric offset of nth switching processNormalized by the corresponding nth switching processAndto determine
The improvement of the technical scheme is as follows: respectively determining the forward direction and the reverse direction of the PTP message according to the sequence of the variable queuing time delay of the master clock and the sequence of the variable queuing time delay of the slave clock, and determining the instantaneous asymmetric offset by using the forward variable queuing time delay and the reverse variable queuing time delay
The improvement of the technical scheme is as follows: the forward and reverse data flows of the PTP message are independent.
The invention adopts the technical scheme that the method has the beneficial effects that: the invention is based on the basis of an IEEE1588 clock model, a conventional method is skipped on the basis, and the condition that the time asynchronism between a server and a client caused by the time error between a master clock and a slave clock is eliminated by a compensation method is considered; the method mainly considers the time offset brought by the master clock and the slave clock, calculates by obtaining the time stamp on each point in the message transmission process, determines the compensation amount of the system, and corrects (or corrects) the time offset so as to synchronize the server and the client. And the operation is simplified through normalization, so that the operation time is shortened, multiple operations and the selection of sample capacity are performed more quickly, the implementation of a compensation algorithm is facilitated, and the synchronization between the terminals can be realized more quickly.
Drawings
The invention will be further explained with reference to the drawings.
Fig. 1 is a schematic diagram of a master-slave clock transmission flow of an embodiment of a synchronization correction method based on an IEEE1588 clock model in the present invention.
Fig. 2 is a compensation algorithm flow of an embodiment of a synchronization correction method based on an IEEE1588 clock model according to the present invention.
Fig. 3 is a branch diagram of a distribution network topology established based on OPNET in the embodiment of the present invention.
FIG. 4 is a comparison graph A of the results in the example of the present invention.
FIG. 5 is a comparison of the results in the example of the present invention with FIG. B.
Fig. 6 shows end-to-end time offsets for packet transmission at different β values according to an embodiment of the present invention.
Fig. 7 shows end-to-end delay of packet transmission under different β values according to the embodiment of the present invention.
Detailed Description
Examples
For convenience of description, the compensation method mentioned in the present invention is referred to as a QIA compensation algorithm in this embodiment.
The embodiment is a co-correction method based on IEEE1588 clock model, wherein the principle of IEEE1588 clock model is shown in fig. 1, and the correction work for realizing master-slave clock synchronization between the server and the client based on the principle of the model can be performed through the following steps,
1) Acquiring a time point of an IEEE1588 clock model;
master clock at T 1 [n]Time point transmission with T 1 [n]The time from the Sync message of the timestamp to the slave clock, and the time point when the slave clock receives the Sync message is T 2 [n]And stamping a time stamp T for the Sync message 2 [n]；
The slave clock is at T 3 [n]Time point transmission with T 3 [n]The delayReq message of the timestamp reaches the master clock, and the time point when the master clock receives the delayReq message is T 4 [n]And stamping a time stamp T for the DelayReq message 4 [n]；
The master clock sends a time stamp T 4 [n]Embedding the message into the nth DelayResp message and transmitting the message to a slave clock to finish the nth exchange process;
when all the n exchange processes are finished, the whole PTP message exchange is finished;
wherein n is a positive integer.
After the timestamps of the points are obtained, the difference between the master clock and the slave clock is compensated, and the compensation algorithm is applied to the QIA compensation algorithm shown in FIG. 2;
2) Obtaining the relation between the time S (t) of the server and the time C (t) of the client from an IEEE1588 clock model, wherein S (t) = (1 + alpha) C (t) + theta (1)
The relation of each timestamp in the sending and receiving process of the Sync message is obtained by combining a PTP protocol (the PTP protocol is short for IEEE1588 protocol, the IEEE1588 protocol is called as 'precision clock synchronization protocol standard of a network measurement and control system') and a formula (1),
T 1 [n]+d f +q f [n]＝(1+α[n])T 2 [n]+θ[n] (2)
the relational expression of each timestamp in the sending and receiving processes of the DelayReq message,
T 4 [n]-d r -q r [n]＝(1+α[n])T 3 [n]+θ[n] (3)
the time offset of the n-th switching process of the slave clock in the equations (2) and (3) is θ n,
wherein the content of the first and second substances,
alpha is a skew coefficient, and the type k of the transmission medium is in direct proportion to the length l of the propagation path;
alpha [ n ] is the skew coefficient of the nth exchange process;
θ is the time offset from the clock;
θ q [n]variable queuing delay skew;
d f a physical link delay from a master clock to a slave clock;
q f variable queuing delay, q, for the master clock f [n]Variable queuing delay for the nth switching process of the master clock;
d r is the physical link delay from clock to master clock;
q r for variable queuing delay of slave clocks, q r [n]Variable queuing delay for the nth switching process of the slave clock;
3) Based on the time stamp T in step 1) 1 [n]、T 2 [n]、T 3 [n]、T 4 [n]The difference operation is carried out to obtain the difference,
ε[n]＝q f [n]-q f [n-1]＝(1+α[n])dT 2 [n]-dT 1 [n]
γ[n]＝q r [n]-q r [n-1]＝dT 4 [n]-(1+α[n])dT 3 [n]
ε[n]variable queuing delay q of the nth switching process being the master clock f [n]The first-order difference of (a) is,
γ[n]is the nth switching process of the slave clockVariable queuing delay q r [n]A first order difference of;
4) Obtaining the asymmetric offset of the nth switching process by the first-order difference value given in the step 3)Then obtaining the Average value through an exponential Weighted Moving Average Filter (exponential Weighted Moving Average Filter)Average amount of (2)To average variable queuing delay offset
Wherein β is a filter factor, 0< β <1, and the synchronization correction between the server and the client is completed by adjusting β so that θ approaches zero.
This example pairs q after step 3) f [n]And q is r [n]Performing normalization processing and minimizing variable queuing delay of the master clock mentioned in step 3)And minimum amount of variable queuing delay from clockAs a reference value for normalization processing, and q is obtained f And q is r Corresponding normalized quantityAnd
wherein the content of the first and second substances,
ε s [n]＝ε s [n-1]+ε[n]
＝ε s [n-1]+q f [n]-q f [n-1]
＝ε s [0]+q f [n]-q f [0]
γ s [n]＝γ s [0]+q r [n]-q r [0]
ε s [0]＝γ s [0]＝0。
the nth switching process of this embodiment is instantaneously asymmetric offsetNormalized by the corresponding nth switching processAndto determine that the position of the target is within the predetermined range,
in this embodiment, the forward direction and the reverse direction of a PTP message are respectively determined according to the sequence of variable queuing delays of a master clock and a slave clock, and the instantaneous asymmetric offset is determined by the forward variable queuing delay and the reverse variable queuing delay
The forward and reverse data flows of the PTP message in this embodiment are independent of each other.
Based on the method, a distribution network topology structure based on the OPNET is established in the embodiment, as shown in fig. 3 (the OPNET is common software for communication simulation, and has a better simulation effect on the comparative analysis of the path delay and the time deviation), and a typical branch is adopted to compare the time synchronization effects between different time synchronization modes. The system comprises a server node (namely a master node), 8 client nodes (namely terminal nodes), a plurality of routers, switch nodes and related links. In the whole network topology, the server node is used as a main battle site and is a client node needing time synchronization, corresponding time synchronization messages are sent according to protocol convention, the client node is used as a terminal node, and the client node periodically interacts with the server node in the time synchronization messages, so that the consistency of a local clock and a server node clock is ensured.
It is clear that the number of network elements and the network transmission load situation have a significant impact on each part of the QIA compensation algorithm (QIACA). The method mainly aims at the topological structure of a typical power distribution network and the load condition of the power distribution network, and corresponding compensation algorithms are adopted for research. The present disclosure mainly analyzes the sensitivity of the QIACA parameter, and tries to perform a comparative analysis and obtain the best delay compensation effect when selecting different skew coefficients α, filter factors β and sample volumes N. Since the skew coefficient α is approximately a constant and the sample size N is preferably larger, we will use α to be 0.1 and N to be 20min for comparison.
In the node model of the server node and the client node in the power distribution network, the nodes comprise a standard five-layer framework of an OSI communication protocol, and the node comprises a physical layer, an access layer, a network layer, a transmission layer and an application layer. The PTP is used as a protocol stack in an application layer and is positioned above a UDP protocol layer, and the transmitted time synchronization messages are encapsulated into UDP/IP packets and then transmitted in a network. In addition, for the IEEE1588 time synchronization protocol, the model also needs to be configured with corresponding parameters.
The end-to-end time deviation and time delay of IEEE1588 protocol message transmission without QIA compensation algorithm are analyzed, the result comparison graphs A and B shown in FIGS. 4 and 5 are respectively based on the end-to-end deviation of message transmission and the end-to-end time delay QIA compensation algorithm of message transmission in the model of the embodiment,
as can be seen from the results shown in fig. 4 and 5, after the QIA compensation algorithm mentioned in the embodiment of the present invention is adopted, the time offset and the time delay are far smaller than those of data without the QIA compensation algorithm, and experiments prove that the compensation effect of the QIA algorithm for the forward and reverse time delays is relatively effective.
When the filter factors β are 0.0008,0.0009,0.0010,0.0011, and 0.0012, the end-to-end time offset and the time delay of the global packet transmission are respectively shown in fig. 6 and fig. 7.
Experiments prove that under the environment of the embodiment with the α =0.1 and the N =20min, when β =0.0010, both the time offset and the time delay tend to be minimum values, wherein the time offset is 0.000013s, and the time delay value is 0.0000222s, both of which are kept within a relatively good precision range.
The QIA compensation algorithm mentioned in the embodiment greatly improves the time synchronization precision through the IEEE1588 protocol. The QIA compensation algorithm can be used for fine tuning by changing the corresponding sample capacity, the skew coefficient alpha and the filter factor beta to obtain the most accurate time delay and time deviation value.
The present invention is not limited to the above-described embodiments. All technical solutions formed by equivalent substitutions fall within the protection scope of the claims of the present invention.
Claims (5)
1. A synchronous correction method based on an IEEE1588 clock model is characterized by comprising the following steps:
1) Acquiring a time point of the IEEE1588 clock model;
master clock at T 1 [n]Time point transmission with T 1 [n]The Sync message of the timestamp reaches the slave clock, and the time point when the slave clock receives the Sync message is T 2 [n]And stamping a time stamp T for the Sync message 2 [n]；
At T from the clock 3 [n]Time point transmission with T 3 [n]A DelayReq message of a timestamp reaches a master clock, and the time point when the master clock receives the DelayReq message is T 4 [n]And stamping a time stamp T for the DelayReq message 4 [n]；
The master clock sends a time stamp T 4 [n]Embedding the message into the nth DelayResp message and transmitting the message to a slave clock to finish the nth exchange process;
when all the n exchange processes are finished, the whole PTP message exchange is finished;
wherein n is a positive integer;
2) Obtaining the relation between the time S (t) of the server and the time C (t) of the client from the IEEE1588 clock model, wherein S (t) = (1 + alpha) C (t) + theta (1)
The relation of each timestamp in the sending and receiving process of the Sync message is obtained by combining the PTP protocol and the formula (1),
T 1 [n]+d f +q f [n]＝(1+α[n])T 2 [n]+θ[n] (2)
the relationship of each timestamp in the sending and receiving processes of the DelayReq message,
T 4 [n]-d r -q r [n]＝(1+α[n])T 3 [n]+θ[n] (3)
the time offset of the n-th switching process of the slave clock in the equations (2) and (3) is θ n,
wherein the content of the first and second substances,
alpha is a skew coefficient, and the type k of the transmission medium is in direct proportion to the length l of the propagation path;
alpha [ n ] is the skewness coefficient of the nth exchange process;
θ is the time offset from the clock;
θ q [n]variable queuing delay skew;
d f a physical link delay from a master clock to a slave clock;
q f variable queuing delay, q, for the master clock f [n]Variable queuing delay for the nth switching process of the master clock;
d r is the physical link delay from clock to master clock;
q r for variable queuing delay of slave clocks, q r [n]Variable queuing delay for the nth switching process of the slave clock;
3) Based on the time stamp T in step 1) 1 [n]、T 2 [n]、T 3 [n]、T 4 [n]The difference is calculated to obtain the result,
ε[n]＝q f [n]-q f [n-1]＝(1+α[n])dT 2 [n]-dT 1 [n]
γ[n]＝q r [n]-q r [n-1]＝dT 4 [n]-(1+α[n])dT 3 [n]
ε[n]variable queuing delay q of the nth switching process being the master clock f [n]First order difference of (1), gamma n]Variable queuing delay q of the nth switching process of slave clock r [n]First order difference of (dT) 1 [n]、dT 2 [n]、dT 3 [n]、dT 4 [n]Presentation to time stamp T 1 [n]、T 2 [n]、T 3 [n]、T 4 [n]Differential operation processing of (4);
4) Obtaining the asymmetric offset of the nth switching process by the first-order difference value given by the step 3)Then obtaining the result through an exponential weighted moving average filterAverage amount of (2) To average variable queuing delay offset
Wherein β is a filter factor, 0< β <1, and the synchronization between the server and the client is completed by adjusting β so that θ approaches zero.
2. The synchronization correction method based on IEEE1588 clock model of claim 1, characterized in that: after step 3) to q f [n]And q is r [n]Performing normalization processing and minimizing variable queuing delay of the master clock mentioned in step 3)And minimum amount of variable queuing delay from clockAs a reference value for normalization processing, and q is obtained f And q is r Corresponding normalized quantityAnd
wherein, the first and the second end of the pipe are connected with each other,
ε[n]＝ε[n-1]+ε[n]
＝ε[n-1]+q f [n]-q f [n-1]
＝ε[0]+q f [n]-q f [0]
γ[n]＝γ[0]+q r [n]-q r [0]
ε[0]＝γ[0]＝0。
3. the synchronization correction method based on IEEE1588 clock model of claim 2, characterized in that: instantaneous asymmetric offset of nth switching processNormalized by the corresponding nth switching processAndto determine
4. The synchronization correction method based on IEEE1588 clock model of claim 1, characterized in that: respectively determining the forward direction and the reverse direction of the PTP message according to the sequence of the variable queuing time delay of the master clock and the sequence of the variable queuing time delay of the slave clock, and determining the instantaneous asymmetric offset by using the forward variable queuing time delay and the reverse variable queuing time delay
5. The synchronization correction method based on IEEE1588 clock model as claimed in claim 4, characterized in that: the forward and reverse data flows of the PTP message are independent.
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| CN108418235A (en) * | 2018-01-30 | 2018-08-17 | 国网电力科学研究院武汉南瑞有限责任公司 | The compensation method that signal transmission clock applied to four fracture series trip devices synchronizes |
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| CN113014344B (en) * | 2019-12-19 | 2022-04-15 | 中国科学院沈阳自动化研究所 | Time synchronization method of redundant network |
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| CN115334008B (en) * | 2022-10-18 | 2023-03-21 | 中国电子科技集团公司第三十研究所 | Method, system, equipment and medium for processing 1588 message jitter of PTN network |
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