CN114070448B - Main clock selection method based on multi-attribute decision - Google Patents
Main clock selection method based on multi-attribute decision Download PDFInfo
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Abstract
The invention relates to the technical field of clock synchronous communication of an industrial time sensitive network, in particular to a master clock selection method based on multi-attribute decision, which comprises the steps of adding a synchronous centralized control node in a clock synchronous domain, wherein the node is responsible for synchronous configuration of all time sensitive nodes in the network and issuing of master clock node information; the synchronous centralized control node receives state information messages reported by each time-sensitive node in the clock synchronous domain, and calculates the state information of the nodes according to the state information messages; the synchronous centralized control node calculates the weight value of each state information through a multi-attribute decision algorithm, calculates the clock attribute value of the node, and selects the clock corresponding to the node with the largest clock attribute value as a global clock reference; according to the invention, on the premise of ensuring the clock source precision, the master clock node with the minimum hop count from any node of the whole network can be selected, so that the accumulated error caused by the hop count is reduced, and the effect of improving the synchronous precision is achieved.
Description
Technical Field
The invention relates to the technical field of clock synchronous communication of an industrial time sensitive network, in particular to a master clock selection method based on multi-attribute decision.
Background
With the continuous development of industrial internet of things technology, emerging services, particularly time-sensitive services, are also emerging, which presents a strict challenge for the real-time and reliability of conventional industrial networks. To address this problem, the IEEE802.1 working group proposed a time-sensitive network (TSN) protocol. The Time Sensitive Network (TSN) technology has the functions of periodic traffic shaping and scheduling, data seamless redundant transmission, path reservation, network configuration and the like based on time synchronization, so that the requirements of time sensitive services on related indexes such as data transmission delay, packet loss and the like can be met. The global clock synchronization is used as a premise of TSN standard to ensure correct matching of transmission time slots of data frames in each device, and meets the end-to-end deterministic time delay and queuing-free transmission requirements of communication flows. In order to meet the requirement of clock synchronization precision, the TSN adopts an IEEE802.1AS protocol for time synchronization. The IEEE802.1AS protocol has simple structure, strong expansibility, easy deployment and accurate synchronization precision to nanosecond level, and provides high-precision clock synchronization service for various fields such AS automatic factories, automobile control, audio and video transmission and the like.
IEEE802.1AS operates AS a clock synchronization protocol in a time sensitive network (TSN, time Sensitive Networking) at the data link layer of a full duplex ethernet network, and achieves high-precision clock synchronization by means of time stamp transfer. The protocol can be divided into three parts of master clock selection, link delay measurement and master-slave synchronization error measurement and correction. In the main clock selection stage, each node selects an optimal main clock node through BMCA and generates a corresponding clock tree. And the nodes perform path delay measurement through the interactive delay measurement message, meanwhile, the master node sends a sync message and a follow message to the slave node in the two-step mode, and after the slave node receives the message, the slave node performs synchronous error calculation by combining the path delay measurement value, so as to correct the local time.
One of the main factors affecting the ieee802.1as protocol is link asymmetry. The data transmission delay, the data processing delay and the synchronization parameter configuration of each node in the synchronous domain may be different, corresponding errors may be caused by adopting a delay peer-to-peer mechanism, and such errors are accumulated continuously along with the increase of the hop count of the master node and the slave node. When the network scale is enlarged, the network topology structure and the influence of the congestion degree of the link are not considered by adopting a mode of fixing the master clock, and the problem that the synchronization requirement of the time-sensitive node cannot be met due to the fact that the path asymmetry error is accumulated due to the fact that the hop count of the master clock node from other nodes is too large may exist. Therefore, a flexible master clock selection scheme is necessary. The master clock selection algorithm considering the information such as link congestion, network topology structure, source parameters and the like can effectively reduce accumulated errors caused by path asymmetry by selecting the master clock node with the minimum hop count from any node of the whole network.
In summary, it is necessary to introduce TSN technology to guarantee deterministic delay transmission of time-sensitive services in multi-hop industrial ethernet. Meanwhile, in order to achieve deterministic time delay transmission of time-sensitive service, the synchronous error of less than 1us within 7 hops is ensured as a basic requirement, so that the IEEE802.1AS protocol adopting ns-level synchronous precision is a good choice. However, the BMCA adopted by the protocol in the stage of selecting the master clock does not consider network information, so that the hop count of master-slave nodes of a clock tree generated by the selected optimal master clock may be too large, the accumulated error increase caused by link asymmetry can reduce the synchronization precision in the network, and how to minimize the hop count of the selected master clock node from any node of the whole network becomes a research key on the premise of ensuring the clock source precision.
Disclosure of Invention
Based on the problems of the existing protocols, the invention provides a master clock selection method based on multi-attribute decision, which comprises the following steps:
adding a synchronous centralized control node in a clock synchronous domain, wherein the node is responsible for synchronous configuration of all time-sensitive nodes in a network and issuing of master clock node information;
the synchronous centralized control node receives state information messages reported by each time-sensitive node in the clock synchronous domain, and calculates the clock source quality coefficient, the link congestion coefficient and the node topology attribute of the node according to the state information messages;
the synchronous centralized control node calculates the weight values of the clock source quality coefficient, the link congestion coefficient and the node topology attribute through a multi-attribute decision algorithm, calculates the clock attribute value of the node, and selects the clock corresponding to the node with the largest clock attribute value as the global clock reference.
Further, the clock attribute value of the node is expressed as:
H B ＝ω a U a +ω b U b +ω c U c ；
wherein H is B The clock attribute value of the node; u (U) a 、U b 、U c The method is characterized in that the method comprises the steps that the number of the link congestion coefficients, the topological structure attribute values and the self clock source parameters of local nodes are superior to the proportion of the number of neighbor nodes to the total neighbor nodes; omega a 、ω b 、ω c The weight of the number of the link congestion coefficients, the topological structure attribute values and the self clock source parameters, which are superior to those of the neighbor nodes, in the proportion of the total neighbor nodes is respectively represented.
Further, the calculating of the link congestion coefficient of the local node includes:
the node estimates the congestion condition of the link by sending a link detection packet based on a synchronous request-response mechanism defined in the IEEE802.1AS protocol, and calculates the departure interval time and arrival interval time of the data packet according to the recorded time stamp;
setting a link delay threshold, comparing whether the difference between the departure interval time and the arrival interval time of the data packet exceeds the threshold, if so, judging that the link congestion occurs, and if not, judging that the link congestion is a surviving message;
calculating the link congestion coefficient U by calculating the ratio of the number of surviving messages to the total number of messages a Expressed as:
wherein n is save Representing the number of surviving messages, N p Representing the total number of detection messages.
Further, the calculation of the ratio of the number of the local node's own clock source parameters to the number of the neighbor nodes to the total neighbor nodes includes:
U b ＝α 1 N 1 +α 2 N 2 +α 3 N 3 +...+α n N n ；
α 1 +α 2 +α 3 +...+α n ＝1；
N 1 +N 2 +N 3 +...+N n ＝1；
wherein N is 1 ,N 2 ,N 3 ,...,N n For 1 hop, 2 hops until n hops of nodes are in proportion to total nodes in the topological structure, alpha 1 ,α 2 ,α 3 ,...,α n For its corresponding weight value.
Further toSequentially comparing the clock information of each node by adopting a data set comparison algorithm to obtain a time clock source quality coefficient U c Expressed as:
wherein alpha is the optimal proportion, N all N for the number of received nodes good Is the number of nodes that is superior to itself.
Further, the process of selecting the link congestion coefficient, the topology attribute value and the weight of the number of the self clock source parameters superior to the neighbor nodes in proportion to the total neighbor nodes comprises the following steps:
101. candidate set C i (i=1, 2,., n), each clock node has an attribute a j (j=1, 2, 3), U a 、U b 、U c Respectively used as attribute values of three attributes to establish a decision matrix
102. The weight vector of each decision attribute isUnder the action of the weight vector, a weight normalization decision matrix is constructed>
103. Computing clock node C i The total attribute evaluation value is
104. For attribute A j According to the clock node C i Clock node C for calculating total attribute evaluation value i With other nodes C k And the total dispersion of all clock nodes in the candidate set;
105. build to maximize clock node C i Total dispersion of all propertiesSolving the target by adopting a Lagrangian function to obtain a weight corresponding to the attribute;
wherein,,representing candidate scheme C i Corresponding decision attribute A j Weight vector, mu ij Representing candidate scheme C i Corresponding decision attribute A j Is a property value of (a).
Further, to maximize the clock node C i The objective function of the total dispersion of all attributes is expressed as:
constraint 1:
constraint 2:
wherein e j (w) represents the total dispersion for all clock nodes in the candidate set for attribute j.
Further, for attribute j, the total dispersion e of all clock nodes in the candidate set j (w) is expressed as:
wherein,,for clock node C i With other nodes C k Is the dispersion of (2); />Is the number of Shi Min nodes in the clock synchronization domain.
Further, candidate C i Corresponding decision attribute A j The calculation of the attribute value of (1) includes:
defining clock nodes in a network topology as candidate optimal master clock schemes and denoted as C i (i=1, 2,., n), where n is the number of nodes in the network topology;
defining the degrees of neighboring nodes and the local clock data set as multi-attribute decision attributes and denoted as A j (j=1, 2, 3), wherein j=1 represents a link congestion coefficient, j=2 represents a topology attribute, and j=3 represents a ratio of the number of self-clock source parameters better than that of neighbor nodes to the total neighbor nodes;
candidate scheme C i Corresponding decision attribute A j Attribute value of mu ij Due to U a 、U b 、U c The values are all between 0,1]The decision matrix is:
further, after clock attribute values of nodes of all nodes are obtained, a node with the largest clock attribute value is used as a root node to generate a whole network clock tree, and the tree is packaged and then issued to other nodes; the ports of the nodes are divided into Master, slave, disable types, all ports of the node with the largest clock attribute value are set as masters, one port of the other nodes close to the node with the largest clock attribute value is set as a Master, and the other ports are set as Slave; if the port of the node is in the Master state, the port sends out a synchronous message; if the port of the node is in a Slave state, waiting for a synchronous message sent by the master clock, and calculating and correcting a local clock error after receiving the synchronous message; if the port of the node is in an Disable state, the port does not participate in the master clock selection.
According to the invention, the role of the synchronous centralized control node is designed, so that the original distributed selection is changed into centralized reporting, and the optimal master clock is selected by calculating the optimal attribute value of the clock through the synchronous centralized control node, so that the master clock selection time can be reduced; by adopting the multi-attribute decision master clock selection method, network information such as link congestion and node topology attribute values and clock source quality factors are comprehensively considered, and the master clock node with the minimum hop count from any node of the whole network can be selected on the premise of ensuring clock source accuracy, so that the accumulated error caused by the hop count is reduced, and the effect of improving the synchronization accuracy is achieved.
Drawings
FIG. 1 is a diagram of an industrial TSN network scenario in accordance with the present invention;
FIG. 2 is a flow chart of a method for selecting a master clock for multi-attribute decision in the present invention;
fig. 3 is a flow chart of link propagation delay measurement in the present invention;
FIG. 4 is a node status message format in accordance with the present invention;
FIG. 5 is a flow chart of the calculation of the clock optimal attribute value by the synchronous centralized control node in the invention;
FIG. 6 is a table of clock tree information employed in the present invention;
fig. 7 is a flow chart of the synchronization of nodes by clock tree information in the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a master clock selection method based on multi-attribute decision, which comprises the following steps:
adding a synchronous centralized control node in a clock synchronous domain, wherein the node is responsible for synchronous configuration of all time-sensitive nodes in a network and issuing of master clock node information;
the synchronous centralized control node receives state information messages reported by each time-sensitive node in the clock synchronous domain, and calculates the clock source quality coefficient, the link congestion coefficient and the node topology attribute of the node according to the state information messages;
the synchronous centralized control node calculates the weight values of the clock source quality coefficient, the link congestion coefficient and the node topology attribute through a multi-attribute decision algorithm, calculates the clock attribute value of the node, and selects the clock corresponding to the node with the largest clock attribute value as the global clock reference.
In this embodiment, each node estimates the link congestion condition by sending a link probing packet based on the synchronization request-response mechanism defined in the ieee802.1as protocol. The link detection message is sent together with the delay measurement message, and the departure interval time and the arrival interval time of the data packet are calculated according to the recorded time stamp and are used for estimating the queuing of the data packet and the congestion condition of the link. Setting a link delay threshold, comparing whether the difference between the departure interval time and the arrival interval time of the data packet exceeds the threshold, if so, judging that the link congestion occurs, and if not, judging that the link congestion is a surviving message.
In the invention, each node reports a state information message composed of network information such as a neighbor node clock identification number, an adjacent link congestion coefficient and the like, and local node clock source information such as a local clock source level, a clock source jitter error, a local clock identification number and the like, and uploads the state information message to a synchronous centralized control node, wherein the synchronous centralized control node comprises the following functions:
the synchronous centralized control node generates a global network topology structure according to the collected network information and calculates node topology attribute values corresponding to the nodes;
the synchronous centralized control node compares and calculates the quality coefficient of the clock source corresponding to each node according to the collected clock source parameter information;
the synchronous centralized control node calculates an optimal weight value corresponding to each factor according to a multi-attribute decision algorithm; substituting weight values corresponding to the factors, calculating and comparing optimal attribute values of the nodes until an optimal master clock node is selected, packaging clock tree information generated by the optimal master clock node into a configuration message, and transmitting the configuration message to each node in a clock domain, wherein each node extracts the clock tree information to determine each port role and perform clock synchronization.
Fig. 1 is a schematic view of an industrial lan scenario used in an embodiment of the present invention, as shown in fig. 1, which may be divided into plant-level and field-level applications according to the network architecture and the location of the switches in the network. The workshop level is mainly oriented to user levels such as engineers, operators and the like and comprises a man-machine interface and data acquisition and monitoring equipment. The field level is mainly a plurality of terminal devices such as a PLC, an engine, a camera, a mechanical arm, a numerical control airport and the like. The workshop-level application communicates with the lower field-level terminal equipment through the middle industrial TSN local area network, the upper-level application sends configuration instructions and operation instructions to the lower-level application, and simultaneously, the audio and video streams and the state information isochronous service streams fed back by the lower-level application are collected and monitored. To meet the synchronization requirement that the synchronization error of master-slave nodes is less than 1us within 7 hops, the IEEE802.1AS protocol is adopted for clock synchronization, wherein the protocol prescribes that each network node should support the protocol.
Fig. 2 is a flowchart of a multi-attribute decision-based master clock selection method according to the present invention, where the multi-attribute decision-based master clock selection method specifically includes:
s1, each node estimates the congestion condition of a link by sending a link detection packet based on a synchronous request-response mechanism defined in an IEEE802.1AS protocol;
the link detection message is sent together with the delay measurement message, and the departure interval time and the arrival interval time of the data packet are calculated according to the recorded time stamp so as to be used for estimating the queuing of the data packet and the congestion condition of the link. Setting a link delay threshold, comparing whether the difference between the departure interval time and the arrival interval time of the data packet exceeds the threshold, if so, judging that the link congestion occurs, and if not, judging that the link congestion is a surviving message. Calculating the link congestion coefficient U by calculating the ratio of the number of surviving messages to the total number of messages a 。
Wherein n is save Representing the number of surviving messages, N p Representing the total number of detection messages.
S2, each node constructs a state information message and reports the state information message to the synchronous centralized control node
Each time-sensitive node in the network collects network information such as a neighbor node clock identification number, an adjacent link congestion coefficient and the like, and constructs a state information message by combining local node clock source information of a local clock source grade, a clock source jitter error and a local clock identification number and reports the state information message to the synchronous centralized control node; fig. 4 is a node status message format in the present invention, as shown in fig. 4, each report message includes a node's own clock source parameter, its own clock identification number and a neighbor node identification number. In the main clock selection stage, each node needs to report own network information and clock source parameter information like a synchronous centralized control node.
S3, the synchronous centralized control node extracts state information and calculates topology attribute values of all nodes;
the synchronous centralized control node extracts the neighbor node information of each node contained in the received state message, generates the topological structure of the clock tree generated by taking each node as the root node by comparing and expanding the topological structure of the nodes, and selects the network topology layer with the smallest hop count as the network topology layer of the node if a certain node simultaneously generates the results of different hop counts during the query and comparison. The topology attribute values of each node are calculated as follows:
node topology attribute value U b Expressed as:
U b ＝α 1 N 1 +α 2 N 2 +α 3 N 3 +...+α n N n ；
n of which is 1 ,N 2 ,N 3 ,...,N n For 1 hop, 2 hops until n hops of nodes are in proportion to total nodes in the topological structure, alpha 1 ,α 2 ,α 3 ,...,α n For its corresponding weight value, there are:
α 1 +α 2 +α 3 +...+α n ＝1；
N 1 +N 2 +N 3 +...+N n ＝1；
s4, the synchronous centralized control node extracts state information and calculates the master clock coefficient value of each node;
after receiving the status messages reported by the nodes, the synchronous centralized control node compares the clock source parameters of the nodes one by adopting a data set comparison algorithm to obtain a master clock coefficient value.
Clock source quality coefficient U c Expressed as:
alpha is the optimal proportion, N all N for the number of received nodes good Is the number of nodes that is superior to itself.
S5, the synchronous centralized control node calculates an optimal weight based on a multi-attribute decision algorithm;
by analysis of the optimal master clock selection problem for multiple clock nodes, the multi-attribute decision base elements are defined herein as follows:
candidate set of schemes: defining clock nodes in a network topology as candidate optimal master clock schemes and expressed as
C i (i=1, 2,) n, where n is the number of nodes in the network topology.
Decision attributes: by analyzing the optimality of clock nodes in the network topology, the degrees of neighboring nodes and the local clock data set are defined as multi-attribute decision attributes and expressed as A j (j＝1,2,3)。
Decision matrix: candidate scheme C i Corresponding decision attribute A j Attribute value of mu ij Due to U a 、U b 、U c The values are all between 0,1]Mu, then ij ∈[0,1]And the decision matrix is:
attribute weight: definition omega a 、ω b 、ω c Respectively represent candidate scheme C i Corresponding decision attribute neighbor node degrees and weights of a local clock data set and meetingω a +ω b +ω c ＝1；
Based on a maximum method of dispersion, the self-adaptive maximum method of dispersion in the topological scene is designed, and the weight is calculated, wherein the specific steps are as follows:
step 1: scene initialization, candidate scheme set C i (i=1, 2,., n), each clock node has an attribute a j (j=1, 2, 3), and according to U a 、U b 、U c The attribute value corresponding to the clock node can be obtained, and a decision matrix is established
Step 2: assume that the weight vector of each decision attribute isUnder the action of the weight vector, a weight normalization decision matrix is constructed>
Step 3: computing clock node C i The total attribute evaluation value is
Step 4: for attribute A j Calculation clock node C i With other nodes C k The dispersion of (2) is
Step 5: for attribute A j Calculating the total dispersion of all clock nodes in the candidate scheme set as
Step 6: calculating the total dispersion of all attributes in all candidate clock node sets as
Step 7: according to constraintsAnd->Constructing a dispersion maximization objective function as
Step 8: construction of Lagrangian function
Step 9: respectively solving partial derivatives of Lagrangian functionsAnd->
Step 10: obtaining two optimal solutions omega of the optimal weights a 、ω b 、ω c 。
S6, the synchronous centralized control node obtains the optimal weight omega according to the obtained optimal weight omega a 、ω b 、ω c Calculating clock optimum attribute value
Consider the optimal master clock weight coefficient H by three factors, such as a time clock source quality coefficient, a link congestion coefficient and a node topology attribute value B Modeling is carried out, and the synchronous centralized control node selects the optimal master clock by comparing the clock optimality attribute values:
H B ＝ω a U a +ω b U b +ω c U c ；
wherein U is a 、U b 、U c The method is characterized in that the method is that the number of the link congestion coefficients, the topological structure attribute values and the self clock source parameters of the local nodes are superior to the proportion of the number of the neighboring nodes to the total neighboring nodes, omega a 、ω b 、ω c The weights of link congestion coefficients, topology attribute values, and local clock dataset optimality are represented, respectively.
S7, the synchronous centralized control node compares the optimal attribute values of the clocks to select an optimal master clock
Fig. 5 is a flowchart of the calculation of the clock optimal attribute value by the synchronous centralized control node in the present invention. As shown in the figure, the synchronous centralized control node compares the optimal attribute values corresponding to the nodes obtained through calculation, so that the optimal master clock is selected as a global clock reference, and meanwhile, a clock tree generated by taking the node as a root node and generated before is adopted as a full-network clock tree.
S8, the synchronous centralized control node generates clock tree information and transmits the clock tree information to other nodes
The synchronous centralized control node generates a network topology structure according to the information contained in the configuration message, and outputs a corresponding clock tree after the optimal master clock is selected. FIG. 6 is a table of clock tree information used in the present invention, where the table entry includes the corresponding clock roles for each port in each node, as shown. The clock roles fall into three categories: master, slave, disable all ports of the Master clock node are in a Master state and send synchronous messages outwards, the role of the other nodes close to the ports on the Master clock side is Slave, and the other ports are masters.
S9, each node performs clock synchronization through clock tree information
Fig. 7 is a flow chart of synchronization of each node through clock tree information, and as shown in the drawing, after the node receives the clock tree information, the node queries the corresponding constant roles of each port of the node according to the self clock source identification number. If each port of the node is a Master, the node is the optimal Master clock node, and all ports send synchronous messages outwards. If the node is not the optimal Master clock node, traversing the state of each port, if the port is in a Master state, sending out a synchronous message, if the port is in a Slave state, waiting for the synchronous message sent by the Master clock, and calculating and correcting the local clock error after receiving the synchronous message.
The invention is mainly based on the multi-attribute decision master clock selection algorithm; the invention centrally selects the master clock by adding the synchronous centralized control node, thereby reducing the time for selecting the master clock. By comprehensively considering the network topology structure and the clock source quality, calculating the optimal weight corresponding to each factor based on multi-attribute decision and substituting the optimal attribute value of the clock of each node, comparing the generated optimal attribute value of the clock to select the optimal master clock, the hop count from the selected master clock node to any node in the network is minimized on the premise of guaranteeing the clock source precision, and further the clock synchronization error accumulated due to asymmetric link delay is reduced.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (9)
1. A master clock selection method based on multi-attribute decision is characterized by comprising the following steps:
adding a synchronous centralized control node in a clock synchronous domain, wherein the node is responsible for synchronous configuration of all time-sensitive nodes in a network and issuing of master clock node information;
the synchronous centralized control node receives state information messages reported by each time-sensitive node in the clock synchronous domain, and calculates the clock source quality coefficient, the link congestion coefficient and the node topology attribute of the node according to the state information messages;
the synchronous centralized control node calculates the weight values of the clock source quality coefficient, the link congestion coefficient and the node topology attribute through a multi-attribute decision algorithm, calculates the clock attribute value of the node, and selects the clock corresponding to the node with the largest clock attribute value as a global clock reference; the clock attribute value of a node is expressed as:
H B ＝ω a U a +ω b U b +ω c U c ；
wherein H is B The clock attribute value of the node; u (U) a 、U b 、U c As a local nodeThe number of the link congestion coefficients, the topological structure attribute values and the self clock source parameters which are superior to those of the neighbor nodes is the proportion of the total neighbor nodes; omega a 、ω b 、ω c The weight of the number of the link congestion coefficients, the topological structure attribute values and the self clock source parameters, which are superior to those of the neighbor nodes, in the proportion of the total neighbor nodes is respectively represented.
2. The method for master clock selection based on multi-attribute decision according to claim 1, wherein the calculation of the link congestion coefficient of the local node comprises:
the node estimates the congestion condition of the link by sending a link detection packet based on a synchronous request-response mechanism defined in the IEEE802.1AS protocol, and calculates the departure interval time and arrival interval time of the data packet according to the recorded time stamp;
setting a link delay threshold, comparing whether the difference between the departure interval time and the arrival interval time of the data packet exceeds the threshold, if so, judging that the link congestion occurs, and if not, judging that the link congestion is a surviving message;
calculating the link congestion coefficient U by calculating the ratio of the number of surviving messages to the total number of messages a Expressed as:
wherein n is save Representing the number of surviving messages, N p Representing the total number of detection messages.
3. The method for master clock selection based on multi-attribute decision according to claim 1, wherein the calculation of the number of local nodes with self clock source parameters better than the number of neighbor nodes in proportion to the total neighbor nodes comprises:
U b ＝α 1 N 1 +α 2 N 2 +α 3 N 3 +...+α n N n
α 1 +α 2 +α 3 +...+α n ＝1
N 1 +N 2 +N 3 +...+N n ＝1
wherein N is 1 ,N 2 ,N 3 ,...,N n For 1 hop, 2 hops until n hops of nodes are in proportion to total nodes in the topological structure, alpha 1 ,α 2 ,α 3 ,...,α n For its corresponding weight value.
4. The method for selecting a master clock based on multi-attribute decision as recited in claim 1, wherein the data set comparison algorithm is adopted to sequentially compare the clock information of each node to obtain the time clock source quality coefficient U c Expressed as:
wherein alpha is the optimal proportion, N all N for the number of received nodes good Is the number of nodes that is superior to itself.
5. The method for master clock selection based on multi-attribute decision according to claim 1, wherein the process of selecting the link congestion coefficient, the topology attribute value, and the weight of the number of self clock source parameters better than the number of neighbor nodes in proportion to the total neighbor nodes comprises:
101. candidate set C i (i=1, 2,., n), each clock node has an attribute a j (j=1, 2, 3), U a 、U b 、U c Respectively used as attribute values of three attributes to establish a decision matrix
102. The weight vector of each decision attribute isUnder the action of the weight vector, constructingWeight normalized decision matrix
103. Computing clock node C i The total attribute evaluation value is
104. For attribute A j According to the clock node C i Clock node C for calculating total attribute evaluation value i With other nodes C k And the total dispersion of all clock nodes in the candidate set;
105. build to maximize clock node C i Solving the target by adopting a Lagrangian function to obtain a weight corresponding to the attribute;
wherein,,representing candidate scheme C i Corresponding decision attribute A j Weight vector, mu ij Representing candidate scheme C i Corresponding decision attribute A j Is a property value of (a).
6. The method of claim 5, wherein the clock node C is maximized i The objective function of the total dispersion of all attributes is expressed as:
constraint 1:
constraint 2:
wherein e j (w) represents the total dispersion for all clock nodes in the candidate set for attribute j.
7. A method of master clock selection based on multi-attribute decision according to claim 5 or 6, characterized in that for attribute j, the total dispersion e of all clock nodes in the candidate set j (w) is expressed as:
wherein,,for clock node C i With other nodes C k Is the dispersion of (2); />Is the number of Shi Min nodes in the clock synchronization domain.
8. The method of claim 5, wherein candidate scheme C i Corresponding decision attribute A j The calculation of the attribute value of (1) includes:
defining clock nodes in a network topology as candidate optimal master clock schemes and denoted as C i I= {1,2, …, n }, where n is the number of nodes in the network topology;
defining the degrees of neighboring nodes and the local clock data set as multi-attribute decision attributes and denoted as A j Wherein j=1 represents a link congestion coefficient, j=2 represents a topology attribute, and j=3 represents a proportion of the number of self clock source parameters superior to that of neighbor nodes to the total neighbor nodes;
candidate scheme C i Corresponding decision attribute A j Attribute value of mu ij The decision matrix is:
9. the master clock selection method based on multi-attribute decision according to claim 1, wherein after clock attribute values of nodes of all nodes are obtained, a node with the largest clock attribute value is used as a root node to generate a full-network clock tree, and the tree is packaged and then issued to other nodes; the ports of the nodes are divided into Master, slave, disable types, all ports of the node with the largest clock attribute value are set as masters, one port of the other nodes close to the node with the largest clock attribute value is set as a Master, and the other ports are set as Slave; if the port of the node is in the Master state, the port sends out a synchronous message; if the port of the node is in a Slave state, waiting for a synchronous message sent by the master clock, and calculating and correcting a local clock error after receiving the synchronous message; if the port of the node is in an Disable state, the port does not participate in the master clock selection.
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