CN118337694B - Route optimization method and system based on service function chain - Google Patents
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Abstract
The invention relates to the technical field of electric power communication, and discloses a route optimization method and a system based on a service function chain, wherein the method comprises the steps of calculating the importance of the function chain of the service function chain according to the information physical sensitivity of an electric power system and the cascading failure indication coefficient of a transmission line; calculating a link risk value of the physical link according to the importance of the functional link and the availability of the physical link, and calculating a risk route weight value of the physical link according to the link risk value and the link length; and establishing a service function link route optimization model according to the importance degree of the function link and the risk route weight value, and solving to obtain an optimal route strategy of the power system. The routing strategy of the invention preferentially distributes the high-importance SFC to the network path with low risk value, avoids the concentration of the high-importance information in the local topology of the network, and improves the robustness of the routing mechanism and realizes the self-adaption in the fault scene by searching the solution in the most serious fault scene.
Description
Technical Field
The invention relates to the technical field of power communication, in particular to a route optimization method and system based on a service function chain.
Background
Along with the accelerated evolution of the digital process of the power grid, the national power grid lays a digital foundation for the transformation from the traditional power grid to the energy internet cross-domain upgrade and the power grid enterprise to the energy internet enterprise through the novel digital infrastructure, so that the multi-dimensional deep coupling of the power system and the power communication system from the functions to the topology level is further promoted. Currently, emerging network technologies such as a more typical network slicing technology, a software defined network technology, a network function virtualization technology, and the like have been implemented in a power communication system in a landing manner.
The safety production and emerging business of the power grid continuously evolve to IP and broadband, so that the flexibility and the control capability of the power communication system are greatly improved, and a new solution idea is provided for coping with the cascade fault problem in the information physical fusion scene. As a typical information physical coupling system, a novel power system is capable of improving efficiency due to informatization energization, and meanwhile, the inside of the novel power system is also subjected to cascade fault risks caused by deep coupling of the power system and a power communication system. For example, the power grid is subjected to hacking to cause partial link failure (the control server is shut down) of the power communication system, so that the operation of the physical power grid is affected, and the serious consequence of regional blackout is caused. The service which is most influenced by the communication system in actual operation is an emergency control service carried on a transmission layer, and the loss of related service information directly influences the operation adjustment and the topological structure of the power system after the fault, and in extreme cases, the fault range is enlarged and even the system is unstable.
Regarding the regulation and control of the novel power system, the accurate regulation and control of the energy distribution on the power network line is far more difficult than the optimal regulation and control of the information flow transmission on the information side, and aiming at the problem that the communication fault causes the information service to be lost and further the single fault to be worsened into the cascade fault, the cascade fault resisting mechanism on the power network side is mostly adopted at present, but the mechanism cannot effectively solve the problem, so that a route optimization strategy is needed to reduce the possibility that the emergency control service is blocked by the communication fault and causes the power system fault to evolve into the cascade fault.
Disclosure of Invention
In order to solve the technical problems, the invention provides a routing optimization method and a system based on a service function chain, which improve the phenomenon that high-importance information is concentrated in a local network by optimizing a routing strategy from an information side so as to achieve the technical effects of enhancing the robustness of information transmission and reducing the possibility that communication faults become cascading failure causes of an electric power system.
In a first aspect, the present invention provides a service function chain-based route optimization method, where the method includes:
calculating the importance of a functional chain of the service functional chain according to the information physical sensitivity of the power system and the cascading failure indication coefficient of the transmission line;
Calculating a link risk value of the physical link according to the importance of the functional link and the availability of the physical link, and calculating a risk routing weight value of the physical link according to the link risk value and the link length;
And establishing a service function link route optimization model according to the function link importance and the risk route weight value, and solving the service function link route optimization model to obtain an optimal route strategy of the power system.
Further, before the step of calculating the importance of the functional chain of the service functional chain according to the physical sensitivity of the information of the power system and the cascading failure indication coefficient of the transmission line, the method further comprises:
calculating information physical sensitivity of the power system according to the mapping relation between the information quantity and the physical quantity in the power system;
and calculating the cascade fault indication coefficient of the transmission line according to the limit power proximity and the power fluctuation amplitude of the transmission line in the power system.
Further, the step of establishing a service function link route optimization model according to the function link importance and the risk route weight value includes:
taking the risk route weight value as a weight value of a route decision variable, and establishing a first objective function according to the importance of the functional chain;
Determining an interruption indicating coefficient of a service function chain according to an uncertain variable of a link fault, and establishing a second objective function according to the importance of the function chain;
Establishing a route optimization objective function according to the first objective function and the second objective function;
establishing constraint conditions of a service function chain according to virtual network function node requirements, bandwidth resource requirements and routing selection requirements of the service function chain;
And taking the route optimization objective function and the constraint condition as a service function link route optimization model.
Further, the step of establishing the constraint condition of the service function chain according to the virtual network function node requirement, the bandwidth resource requirement and the selected route requirement of the service function chain includes:
establishing node constraint conditions according to node deployment uniqueness of virtual network functions in a service function chain;
establishing bandwidth resource constraint conditions according to the maximum value of the bandwidth resources of the service function chain;
establishing access sequence constraint conditions according to the node access sequence requirements of the selected route in the service function chain;
And establishing a route topology constraint condition according to the network topology requirement of the selected route in the service function chain.
Further, the information physical sensitivity is expressed by the following formula:
In the method, in the process of the invention, A vector representing a physical state variable; A vector representing the variable of the information, A vector representing the physical side control variable,A vector representing the information-side control variable;
the limit power proximity is expressed using the following formula:
In the method, in the process of the invention, Representing a pre-fault transmission lineThe power of the flow-through,Representing a transmission lineIs used for the reference power value of (a),Representing a transmission lineIs set at the power transmission limit of (c),Representing the total number of the transmission lines;
The power fluctuation amplitude is expressed by the following formula:
In the method, in the process of the invention, Representing a transmission linePost-fault power transmission linePower fluctuations caused thereon;
The cascade failure indication coefficient is expressed by the following formula:
In the method, in the process of the invention, Representing a transmission lineIs used for the cascade failure indication coefficient of (a),Representing the equalization factor;
the functional chain importance is expressed by the following formula:
In the method, in the process of the invention, The function chain importance of the kth service function chain is represented,Representing the physical sensitivity of the information of the kth service function chain,Representing a fault scenarioProbability of occurrence, S represents a fault matrix uncertainty set of the communication network,Representing a failure scenarioIs a transmission line of (2)Is a cascade failure indication coefficient of (a).
Further, the link risk value is expressed by the following formula:
In the method, in the process of the invention, Representing physical linksIs a link risk value of (a) and (b),Representing physical linksIs used in the present invention, the availability of (a) the availability of (c) the (b) the (c),Representing physical nodesAnd physical nodeThe physical link between the two-way network and the network,The function chain importance of the kth service function chain is represented;
the risk routing weight value is expressed by adopting the following formula:
In the method, in the process of the invention, Representing physical linksIs a risk routing weight value of (1),Representing physical linksIs provided for the length of (a),Indicating the link availability per unit length,Representing physical linksThe maximum risk value that can be carried,Representing a transmission lineMedium physical linkIs a link risk value for (a) a link risk value (b).
Further, the first objective function is expressed using the following formula:
In the method, in the process of the invention, The function chain importance of the kth service function chain is represented, K represents the total number of service function chains,Representing physical nodesAnd physical nodeThe physical link between the two-way network and the network,Representing a set of physical links,Representing physical linksIs a risk routing weight value of (1),Representing logical nodes in a kth service function chainAnd logical nodeWhether the primary logical link between them needs to go through the physical link，Representing logical nodes in a kth service function chainAnd logical nodeWhether or not the backup logical link between them needs to go through the physical link，Representing logical nodesAnd logical nodeA logical link between the two,Representing a first threshold;
The second objective function is expressed using the following formula:
In the method, in the process of the invention, Representing physical linksIs used for the control of the state of (a),Representing physical link-based in kth service function chainInterrupt indication coefficient of the state of (2);
the route optimization objective function is expressed using the following formula:
In the method, in the process of the invention, Representing a second threshold, S representing a fault matrix uncertainty set of the communication network;
the constraint is expressed using the following formula:
In the method, in the process of the invention, Indicating whether an mth virtual network function is deployed on a physical node i, M indicating a set of virtual network functions in the communication network,Representing a collection of physical nodes in a communication network,Representing logical nodesWhether or not handled by the mth virtual network function,Representing the set of nodes in the logical topology of the kth service function chain,Representing the set of links in the logical topology of the kth service function chain,Representing physical linksIs used in the present invention,Representing the source node of the kth service function chain,Representing the destination node of the kth service function chain,Representing logical nodes in a kth service function chainAnd logical nodeWhether the primary logical link between them needs to go through the physical link，Representing logical nodes in a kth service function chainAnd logical nodeWhether or not the backup logical link between them needs to go through the physical link。
In a second aspect, the present invention provides a service function chain-based route optimization system, the system comprising:
The importance calculating module is used for calculating the importance of the functional chain of the service functional chain according to the information physical sensitivity of the power system and the cascading failure indication coefficient of the transmission line;
The weight value calculation module is used for calculating a link risk value of the physical link according to the importance of the functional link and the availability of the physical link, and calculating a risk route weight value of the physical link according to the link risk value and the link length;
And the route optimization module is used for establishing a service function link route optimization model according to the function link importance and the risk route weight value, and solving the service function link route optimization model to obtain an optimal route strategy of the power system.
Further, the importance calculating module is further configured to calculate information physical sensitivity of the electric power system according to a mapping relationship between information quantity and physical quantity in the electric power system; and calculating the cascade fault indication coefficient of the transmission line according to the limit power proximity and the power fluctuation amplitude of the transmission line in the power system.
Further, the route optimization module is further configured to use the risk route weight value as a weight value of a route decision variable, and establish a first objective function according to the importance of the functional chain; determining an interruption indicating coefficient of a service function chain according to an uncertain variable of a link fault, and establishing a second objective function according to the importance of the function chain; establishing a route optimization objective function according to the first objective function and the second objective function; establishing constraint conditions of a service function chain according to virtual network function node requirements, bandwidth resource requirements and routing selection requirements of the service function chain; and taking the route optimization objective function and the constraint condition as a service function link route optimization model.
The invention provides a route optimization method and a system based on a service function chain. According to the method, the high-importance SFC is preferentially distributed to the network paths with low risk values, the high-importance SFC can be prevented from being concentrated in the local network topology, meanwhile, uncertainty disturbance is introduced into the model, and the robustness of a routing mechanism is improved by searching a solution under the most serious fault scene, so that self-adaption under the fault scene is realized.
Drawings
FIG. 1 is a flow chart of a method for optimizing a route based on a service function chain in an embodiment of the invention;
FIG. 2 is a topology diagram of a communication network of an IEEE 30 node system in a simulation experiment in accordance with an embodiment of the present invention;
FIG. 3 is a graph showing comparison of information accessibility in simulation experiment analysis results in an embodiment of the present invention;
FIG. 4 is a graph showing the comparison of load loss rates in the results of simulation experiment analysis in the embodiment of the present invention;
FIG. 5 is a graph showing branch risk values in simulation experiment analysis results according to an embodiment of the present invention;
FIG. 6 is a graph showing the importance of the blocked SFC in the analysis result of the simulation experiment in the embodiment of the present invention;
Fig. 7 is a schematic structural diagram of a route optimization system based on service function chains in an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. 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.
Before describing the technical scheme of the invention, technical keywords related to the technical scheme are described:
NFV: network Function Virtualization, network function virtualization;
SFC: service Function Chain, service function chain;
VNF: virtualized Network Function, virtual network functions;
CFI: CASCADING FAILURE INDEX, linking fault indication coefficients;
SFC-RS: SFC-Routing Strategy, routing strategy of service function chain;
SPRM: short-Path Routing Model, shortest path routing algorithm.
Referring to fig. 1, a service function chain-based route optimization method according to a first embodiment of the present invention includes steps S10 to S30:
step S10, calculating the importance degree of a functional chain of a service functional chain according to the information physical sensitivity of the power system and the cascading failure indication coefficient of the transmission line;
step S20, calculating a link risk value of the physical link according to the importance of the functional link and the availability of the physical link, and calculating a risk route weight value of the physical link according to the link risk value and the link length;
And step S30, establishing a service function link route optimization model according to the function link importance and the risk route weight value, and solving the service function link route optimization model to obtain an optimal routing strategy of the power system.
The technical scheme of the invention is applied to a novel power system, the novel power system is a typical information physical coupling system and can be divided into two levels of a power network and a communication network, nodes and transmission lines of the power network and communication nodes and links of the transmission line and the communication network are two different entities which are positioned at the same spatial position and respectively belong to the power network and the communication network, wherein the power network can be described as a nodeAnd lineDrawing of constitution。
The communication network mainly reflects the feedback process from the local measurement to the decision of the control center of the information control system, and the information flow concerned is not the closed loop feedback of the local protection control, but the network flow which needs to consider the characteristics of the communication network nodes and the branches. In a network function virtualized NFV network, the communication layer comprises a physical topology network and a logical topology network characterizing service function chain SFC requests. Physical topology network is formed by undirected graphThe definition of the term "a" or "an" is,AndRepresenting a set of entity nodes and a set of links in a communication network respectively,Representing any two physical nodes that are to be connected,Representing nodesAndA physical link between; is composed of directed graph Definition, wherein,Represents the k-th SFC,AndRespectively representA set of nodes and a set of links in a logical topology,Representing any two of the logical nodes of the network,Representing a logical link between two nodes.
One or more ofIs composed of an ingress node, an egress node and several virtual network functions VNFs. The VNF is deployed on NFV, i.e. corresponds to a physical node of the communication network. Since the virtual functions that should be included in forming a specific network service have not been standardized, the present invention employs the following general expression to represent the functional chains and their constituent VNFs:
Definition of the definition For a set of VNFs in a communication network,Representing the mth NVF of the optical disc,. For any of the communication networksIt is defined as:
wherein, For the purpose ofI.e., the number of VNFs in the SFC,For the purpose ofIs the first of (2)And VNFs.
When the power grid fails, the station with blocked emergency control service cannot timely perform feedforward control on the failure, so that the scale of the failure is enlarged, and cascading failure is caused. In a preferred embodiment provided by the present invention, the importance of the SFC is calculated based on the physical sensitivity of the information of the power system and the cascade fault indication coefficient of the transmission line, and the specific calculation steps include:
calculating information physical sensitivity of the power system according to the mapping relation between the information quantity and the physical quantity in the power system;
and calculating the cascade fault indication coefficient of the transmission line according to the limit power proximity and the power fluctuation amplitude of the transmission line in the power system.
Considering the deep coupling of the power system and the communication system in the current digital development trend, the cascade fault process caused by the communication fault actually belongs to an information physical interaction process, and in order to quantify the influence of the blocked SFCs in the power system, an information physical sensitivity analysis method is adopted in the embodiment, and is used for representing the influence of the information flow on the physical state variables. Specifically, the information physical sensitivity can be obtained from the mapping relationship of the information amount to the change of the physical amount:
In the method, in the process of the invention, Is the firstThe vector of physical state variables for each control cycle,As a vector of information variables,Is a vector of physical side control variables,Is a vector of information-side control variables,For the sensitivity of the information variable to the physical state variable,In order to control the matrix of relationships,Mapping an optimization function from a measured variable to a control variable.
Because the importance of the physical state variables themselves in the information physical interaction process also has differences, the importance of the SFC is calculated by considering the information physical sensitivity and the importance of the physical state variables themselves at the same time. Therefore, the present embodiment describes the importance of the physical state variable itself by defining the cascade fault indication coefficient CFI to measure the risk of cascade faults of each branch in the power system affected by the information fault.
In case of a grid failure and loss of emergency control traffic, load transfer within the system will cause overload of part of the lines. Because the power transmission limits of the power transmission lines are different, the line with lower transmission limit is not always overloaded due to sharing the power on the failure line, and on the contrary, some lines with higher power transmission limit but heavy load are more prone to faults. Thus, the potential risk of a line failure can be measured by calculating the proximity of the line transmission power before failure compared to the line transmission limit.
To be transmitted to the lineThe approximation degree of the power in normal transmission compared with the transmission limit of the line, namely the limit power proximity is recorded as：
In the method, in the process of the invention,Representing a pre-fault transmission lineThe power of the flow-through,Representing a transmission lineIs used for the reference power value of (a),Representing a transmission lineIs set at the power transmission limit of (c),Representing the total number of transmission lines.
The power of the failure line will be redistributed in the network after the failure occurs, and recordedIs a power transmission linePower fluctuation amplitude after power flow redistribution:
In the method, in the process of the invention, Representing a transmission linePost-fault power transmission lineThe power fluctuation caused above is expressed as:
wherein, The distribution factor is broken for the branch,The power transfer distribution factor is transmitted for the generator,As a line before failurePower flowing upward; is hindered by Absolute value of power at the destination node.
After the two parameters are obtained, the power transmission lineIs a cascade failure indication coefficient of (2)Can be defined as:
wherein, Is an equalization factor.
By integrating the indicators of line power before and after the fault,The possibility of cascading failure of the normal line after the information physical coupling failure occurs can be reflected,The larger the line, the more likely the cascading failure occurs, i.e. the invention uses CFI to measure the importance of the physical state variable itself.
After calculating the physical sensitivity of the information and the importance of the physical state variables themselves,The importance of (i.e., the functional chain importance) can be defined as:
In the method, in the process of the invention, The function chain importance of the kth service function chain is represented,Representing the physical sensitivity of the information of the kth service function chain,Representing a fault scenarioThe probability of occurrence, the failure scenario of the power communication network can be expressed asS denotes a fault matrix uncertainty set of the communication network,Representing a failure scenarioIs a transmission line of (2)Is a cascade failure indication coefficient of (a).
Currently, conventional risk equalization strategies are important to divide by the S-type of information traffic, wherein,，Representing physical linksWhether a failure has occurred, but this approach ignores the fact that information belonging to the same traffic type is of different importance. Because the importance of different nodes to the power system in the actual operation of the power grid is different, the importance of the information flow of the nodes is also different. Therefore, the invention provides a more targeted risk balance strategy based on the SFC importance degree and applies the risk balance strategy to the SFC routing strategy.
Conventional risk equalization strategies linkIn this embodiment, in order to accurately identify different information under the same service type, SFC importance is used to replace importance divided according to service type, so the improved link risk value may be defined as:
In the method, in the process of the invention, Is of length ofPhysical link of (c)When a plurality of SFCs are carried on the physical link, the risk value is the accumulation of the risk values of the SFCs:
further, the present embodiment constructs the link risk value as a form of weight, so the link Risk routing weight value of (a)Is defined as:
In the method, in the process of the invention, Representing physical linksIs a risk routing weight value of (1),Representing physical linksIs provided for the length of (a),Indicating the link availability per unit length,Representing physical linksThe maximum risk value that can be carried,Representing a transmission lineMedium physical linkIs a link risk value for (a) a link risk value (b).
When the risk value of the link is increased, the corresponding weight value is obviously increased, so that the change condition of the state of the line can be sensitively reflected through the risk routing weight value.
As with conventional networks, network function virtualized NFV networks are also faced with reliability issues of information transfer, since virtual network functions VNFs are executed by software on virtualized platforms, such forms present a higher risk of failure than dedicated hardware. An effective way to ensure reliability is to provide redundant backups for SFCs, which will be activated when the primary VNF instance fails. Therefore, the invention provides a routing strategy SFC-RS of a service function chain, which optimizes the routing strategy of the power communication service function chain influenced by cascading faults of a power system by considering the combination problems of reliable deployment of main and standby routes of the SFC and balanced network risk and introducing the influence of uncertainty of fault scenes so as to achieve the aim of reducing concentrated distribution of high-importance information in local topology of the network while improving the robustness of information transmission, thereby avoiding the situation that single fault is deteriorated into cascading faults due to communication service blockage.
In this embodiment, an optimal routing policy considering cascade fault influence and risk balance policy is obtained by constructing a service function link routing optimization model, and the specific construction steps of the routing optimization model include:
taking the risk route weight value as a weight value of a route decision variable, and establishing a first objective function according to the importance of the functional chain;
Determining an interruption indicating coefficient of a service function chain according to an uncertain variable of a link fault, and establishing a second objective function according to the importance of the function chain;
Establishing a route optimization objective function according to the first objective function and the second objective function;
establishing constraint conditions of a service function chain according to virtual network function node requirements, bandwidth resource requirements and routing selection requirements of the service function chain;
And taking the route optimization objective function and the constraint condition as a service function link route optimization model.
In this embodiment, the SFC route deployment introducing the improved risk balance policy is modeled as a mathematical optimization problem, and binary variables are defined based on the model structure of the above-mentioned general expression for representing the functional chain and its constituent VNsTo represent the mth virtual network functionWhether or not to be deployed on the physical node i, and when the value is 1, the value indicatesDeployed at physical nodesAnd if not, 0; at the same time define binary variablesTo represent logical nodesWhether or not to be operated by the mth virtual network functionProcessing, representing a logical node when the value is 1From the following componentsProcessing, otherwise, 0; in addition, define binary variablesAndRespectively representIs a primary and backup logical link of (a)Whether or not to need to go through a physical linkThe value 1 needs to be taken, otherwise 0.
In order to achieve risk balance, in this embodiment, risk routing weight values are usedAs a decision variableAndAnd reflect virtual links based on dynamic updates of network stateThe bearing relationship, thereby constructing a first objective function as:
Where K denotes the total number of service function chains SFC, Represents a first threshold value, here,Is defined as a small value for guaranteeing that the objective function makes a decision on the primary route preferentially.
Considering the uncertainty influence of the fault, the present embodiment also introduces an uncertainty scene set of the link fault, which is taken as an uncertainty factor to promote the robustness of information transmission, so the second objective function is defined as:
In the method, in the process of the invention, Representing physical linksIs used for the control of the state of (a),Representing physical link-based in kth service function chainThe interrupt indication coefficient of the state of (2), 1 at the time of interrupt, or 0 otherwise,The value of (2) depends on an uncertainty variable：
Specifically, the variables are uncertainRepresenting physical linksThe state of (1) indicates the link is broken, otherwise, 0, each failure scenario corresponds to a specific set of; Auxiliary variableAndRespectively for representingIf the main and standby routes are interrupted, the interruption is 1, otherwise, the interruption is 0; Is a sufficiently large value.
Based on the two objective functions, the SFC-RC routing strategy provided by the invention can be constructed as a two-stage robust optimization problem, and the objective functions can be expressed as follows:
In the method, in the process of the invention, Representing a second threshold, S representing a fault matrix uncertainty set of the communication network, where,Is defined as a minute value for preferentially guaranteeing the robustness objective.
Further, according to requirements of nodes, bandwidth resources, routing and the like of the NFC network, SFC needs to be constrained, and the constructing steps of constraint conditions include:
establishing node constraint conditions according to node deployment uniqueness of virtual network functions in a service function chain;
establishing bandwidth resource constraint conditions according to the maximum value of the bandwidth resources of the service function chain;
establishing access sequence constraint conditions according to the node access sequence requirements of the selected route in the service function chain;
And establishing a route topology constraint condition according to the network topology requirement of the selected route in the service function chain.
In the present embodiment, the network function based on the power system virtualizes the NFC network, each VNF should be uniquely deployed on one physical node, and in the followingAt most one logical node corresponds to each VNF, and node constraints built based on this requirement can be expressed as:
In the method, in the process of the invention, Representing an mth virtual network functionWhether or not deployed on a physical node i, M represents a set of virtual network functions VNFs in the communication network,Representing a collection of physical nodes in a communication network,Representing logical nodesWhether or not to be operated by the mth virtual network functionThe processing is carried out by the method,Representing the kth service function chainIs defined in the logical topology of the node set.
For physical linksThe bandwidth resources occupied by SFC cannot exceed its available bandwidth: thus, the bandwidth resource constraint can be expressed as:
In the method, in the process of the invention, Representing physical linksIs used for the transmission of the data.
For each ofThe VNFs included in the selected path are guaranteed to be accessed in a specific order, and thus, the access order constraint may be defined as:
taking the example of a primary logical route as an example, Representing information flow from virtual node when 1Flow to virtual nodesIn this constraint, when a pathSelected, the start node of the pathThe corresponding VNF is accessed first, but only the nodeAs the next pathIs accessed, so that when a path is determined, the initial node of the path is always ensured to be accessed first, thereby ensuring the access sequence of VNF.
In addition, it should be ensured that the selected physical links are connected end to end in the network topology, and the main and standby paths of the SFC should not coincide, so the routing topology constraint condition may be defined as:
In the method, in the process of the invention, Representing the destination node of the kth service function chain,Representing logical nodes in a kth service function chainAnd logical nodeWhether the primary logical link between them needs to go through the physical link，Representing logical nodes in a kth service function chainAnd logical nodeWhether or not the backup logical link between them needs to go through the physical link。
Regarding constraints to guarantee link termination, for a source nodeThe information flow sent by the source node only has the output degree and has no input degree, and for the information flow k, the output degree of the source node is 1; similarly, at the destination nodeThe information flow only has an input degree and no output degree, and the output degree is-1; for the intermediate nodes, the out = in, and therefore takes a value of 0. When the circulation of information meets the requirement of respective access degree according to the node type, each section of link through which the information flows is naturally connected in an ending way, thereby forming a self-locking typeTo the point ofIs a complete path of (c).
And taking the constraint conditions as constraint conditions of the objective function, obtaining a complete service function link route optimization model, and then solving the route optimization model by using a solver, so as to obtain an optimal value of a decision variable, namely an optimal route strategy of the power system. The specific solution process may refer to a conventional model solution process, and will not be repeated here.
According to the service function chain routing strategy SFC-RS provided by the invention, the weight is dynamically updated according to the improved risk balance strategy and network change, the high importance SFC is preferentially distributed to the network path with a low risk value, the high importance information is prevented from being concentrated in the network local topology, meanwhile, uncertainty disturbance is introduced into the model, the robustness of a routing mechanism is improved by searching the solution under the most serious fault scene, and the self-adaption under the fault scene is realized.
The effect of the route optimization method provided by the invention is verified through a simulation experiment, and in the simulation experiment, the route optimization method provided by the invention is applied to an IEEE 30 node system and a communication network corresponding to the IEEE 30 node system, and the simulation result is analyzed. Specifically, according to the structure of the IEEE 30 node system, the communication network topology structure of the system is shown in fig. 2, where the IEEE 30 node system includes n nodes, respectively denoted by 1 to 30, the number of nodes corresponding to the communication network topology structure is 21, denoted by S1 to S20 and CCs, and according to the connectivity of the network, the node CC with the highest node degree is selected as the control master station. The Python 3.7.0 is used for simulation on a notebook computer carrying a AMD Ryzen 7 5800H processor and 16GB memory, and Gurobi.5.2 is called to solve the optimization problem. Convergence threshold of solverAnd a minute valueAre all set as. The VNF types in the network are set to 4 types, the lengths of SFCs are randomly distributed between 2 and 4, the same type of VNF is generated only once in each SFC, and the link bandwidth is set to 30. Since the main objective of SFC-RS is to affect the operation of the power system by regulation of the SFC path, communication delay issues are not considered here, allowing VNFs to be pre-deployed on communication nodes, representing the usage scenario of the shared communication infrastructure.
According to the related standard requirements, the production implementation control business is required to meet the planning target of N-2, and in the experiment, the power communication network fault is preset as an N-2 fault, and the power network fault is preset as an N-1 fault. When the physical links carrying the primary and backup paths of the SFC are both broken, the SFC transmission is blocked. In actual grid operation, the existing emergency control service route optimization is designed manually according to experience of operators mainly based on a shortest path model. Therefore, the experiment is to compare the effect of applying the shortest path routing algorithm SPRM in the IEEE 30 node system with the routing strategy SFC-RS of the service function chain provided by the invention.
Fig. 3 shows the information transmission reachability when two methods cope with the N-2 failure of the communication system. Analysis of FIG. 3 shows that under the most severe fault scenario, SFC-RS has 3 nodes disconnected, and the number of the maximum disconnected nodes of SPRMs reaches 5. When the SFC-RS is used for dealing with N-2 faults, the SFC-RS only reaches the maximum node disconnection number under three scenes, the number of nodes disconnected under other scenes is not more than 2, and the number of times of the disconnection of more than two nodes of the SPRM is far less. In addition, when the number of blocked SFCs exceeds 3, i.e. the number of the disconnection nodes is more than 3, at least 15% of control services in the system are disabled, and when SPRM is applied, if 4 and 8 are failed simultaneously, 7 and 16 are failed simultaneously or 11 and 16 are failed simultaneously, the service interruption rate is up to 25%, and the safe and stable operation of the power system is seriously threatened.
In fig. 4, the load loss rate in response to a communication system N-2 failure is shown for both methods, with the average and maximum values being lower than SPRM when SFC-RS is applied. From the effects of the information accessibility rate and the load loss rate, the SFC-RS can be seen to effectively improve the robustness of the system.
Fig. 5 shows the SFC risk distribution carried by each physical link when two algorithms are applied in an IEEE 30 node communication network topology. Comparing fig. 5 (a) with fig. 5 (b) shows that when SPRM is used, the information is mainly concentrated on links 7 and 8, and the risk value of link 8 is far higher than that of other links, because SPRM preferentially selects the path with the least overhead, so that the information is collected on the shortest path, and the distribution of SFC is too concentrated. In contrast, because the SFC-RS takes the risk routing weight as the weight, and dynamically updates the risk weight in the network after distributing the path for the previous SFC, a path with the minimum risk weight is searched when distributing the path for the new SFC, but not a path with the minimum cost, and the information is prevented from being intensively distributed on a local area or a certain line of the network.
But the overall risk value of the network in fig. 5 (a) is slightly higher than in fig. 5 (b), because SFC-RS is also essentially a type of shortest path algorithm, except that this approach seeks a minimum link risk, which results in a longer path for a single SFC-RS allocation than when SPRMs are applied, resulting in an increased overall risk value. However, the SFC-RS is initially designed to reduce the possibility that a single fault on the grid side is deteriorated to a cascade fault due to a communication fault by effectively adjusting the information side, and for this purpose, the risk value of a local area or a single line is too high to be dangerous compared with a slight increase of the overall risk of the network, and if the information fault occurs, the system is seriously affected. The SFC-RS reduces the risk value of the local area or line, that is, the algorithm of the present invention trades the robustness of communication and the balance of network risk distribution at the cost of slightly improving the network average risk, avoiding the significant increase of single point risk value to induce more serious consequences after the occurrence of an information failure, which is quite worth the actual effect, and the comparison of (c) in fig. 5 with (d) in fig. 5 is more evidence of this fact.
In order to verify the effect of SFC-RS on reducing cascade fault probability in a power system, the invention provides a weighted fault risk entropy by utilizing the information entropy concept in combination with an application background to evaluate the optimization effect.
Calculating the sum of the importance of blocked SFCs in the N-2 fault scene, and giving a blocked SFC importance sequenceBy usingRepresenting importance levelThe number of fault scenes is within the intervalProbability of (2)The method comprises the following steps:
further defining weighted risk distribution entropy as:
wherein, Is of importanceAverage importance value of all scenes of (1), assuming thatComprisesA fault scenario, I mn represents importance in the nth fault scenario, then:
According to the definition of the entropy values, the corresponding entropy values are smaller when the high-risk scenes in the system are fewer, namely the probability of cascade faults in the system is lower.
Selecting blocked SFC with importance sequence ofBy traversing N-2 failure scenes of the IEEE 30 node system, importance values corresponding to SFCs of which the two methods are blocked respectively under the failure scenes are counted, as shown in FIG. 6. From the figure, it can be seen that the importance of SFC blocked when SFC-RS is applied is far less than when SPRM is applied, because of the robustness of information transmission and the effect of improving risk balance.
The weighted risk distribution entropy is adopted to calculate the data, and the calculated entropy value of the SFC-RS is 495.057, which is far smaller than the entropy value 601.126 of the SPRM, so that the SFC-RS can effectively reduce the risk of cascade faults caused by blocking of emergency control service due to communication faults in the system under the same condition, and the SFC-RS can effectively achieve the aim of the invention.
According to the route optimization method based on the service function chain, the joint problems of reliable deployment of main and standby routes of SFC and network risk balance are considered, and the influence of uncertainty of a fault scene is introduced, so that the route strategy based on the service function chain is provided.
Referring to fig. 7, based on the same inventive concept, a route optimization system based on service function chains according to a second embodiment of the present invention includes:
An importance calculating module 10, configured to calculate a function chain importance of the service function chain according to the information physical sensitivity of the power system and the cascading failure indication coefficient of the transmission line;
The weight calculating module 20 is configured to calculate a link risk value of the physical link according to the functional link importance and the availability of the physical link, and calculate a risk route weight value of the physical link according to the link risk value and the link length;
And the route optimization module 30 is configured to establish a service function link route optimization model according to the function link importance and the risk route weight value, and solve the service function link route optimization model to obtain an optimal route policy of the power system.
In a preferred embodiment, the present invention further comprises:
The importance degree calculating module 10 is further configured to calculate information physical sensitivity of the electric power system according to a mapping relationship between information quantity and physical quantity in the electric power system; and calculating the cascade fault indication coefficient of the transmission line according to the limit power proximity and the power fluctuation amplitude of the transmission line in the power system.
In another preferred embodiment, the present invention further comprises:
the route optimization module 30 is further configured to take the risk route weight value as a weight value of a route decision variable, and establish a first objective function according to the functional link importance; determining an interruption indicating coefficient of a service function chain according to an uncertain variable of a link fault, and establishing a second objective function according to the importance of the function chain; establishing a route optimization objective function according to the first objective function and the second objective function; establishing constraint conditions of a service function chain according to virtual network function node requirements, bandwidth resource requirements and routing selection requirements of the service function chain; and taking the route optimization objective function and the constraint condition as a service function link route optimization model.
The technical features and technical effects of the route optimization system based on the service function chain provided by the embodiment of the invention are the same as those of the method provided by the embodiment of the invention, and are not repeated here. The various modules in the service function chain-based route optimization system described above may be implemented in whole or in part by software, hardware, and combinations thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.
In summary, the embodiment of the invention provides a route optimization method and a system based on a service function chain, wherein the method calculates the importance of the function chain of the service function chain according to the information physical sensitivity of a power system and the cascading failure indication coefficient of a transmission line; calculating a link risk value of the physical link according to the importance of the functional link and the availability of the physical link, and calculating a risk routing weight value of the physical link according to the link risk value and the link length; and establishing a service function link route optimization model according to the function link importance and the risk route weight value, and solving the service function link route optimization model to obtain an optimal route strategy of the power system. The invention introduces the influence of uncertainty of fault scene by considering the joint problems of reliable deployment of main and standby routes of SFC and balanced network risk, and provides a routing strategy based on service function chain, which preferentially distributes high importance SFC to network paths with low risk value, the method and the device avoid the concentration of high importance information in the network local topology, and simultaneously improve the robustness of a routing mechanism and realize the self-adaption in a fault scene by searching the solution in the most serious fault scene, thereby avoiding the situation that a single fault is deteriorated to be a cascade fault due to the blocking of communication services.
In this specification, each embodiment is described in a progressive manner, and all the embodiments are directly the same or similar parts referring to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments. It should be noted that, any combination of the technical features of the foregoing embodiments may be used, and for brevity, all of the possible combinations of the technical features of the foregoing embodiments are not described, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The foregoing examples represent only a few preferred embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the application. It should be noted that modifications and substitutions can be made by those skilled in the art without departing from the technical principles of the present application, and such modifications and substitutions should also be considered to be within the scope of the present application. Therefore, the protection scope of the patent of the application is subject to the protection scope of the claims.
Claims (6)
1. A method for optimizing a route based on a service function chain, comprising:
calculating information physical sensitivity of the power system according to the mapping relation between the information quantity and the physical quantity in the power system;
calculating a cascading failure indication coefficient of a transmission line according to the limit power proximity and the power fluctuation amplitude of the transmission line in the power system;
calculating the importance of a functional chain of the service functional chain according to the information physical sensitivity of the power system and the cascading failure indication coefficient of the transmission line;
Calculating a link risk value of the physical link according to the importance of the functional link and the availability of the physical link, and calculating a risk routing weight value of the physical link according to the link risk value and the link length;
establishing a service function link route optimization model according to the function link importance and the risk route weight value, and solving the service function link route optimization model to obtain an optimal route strategy of the power system;
the step of establishing a service function link route optimization model according to the function link importance and the risk route weight value comprises the following steps:
taking the risk route weight value as a weight value of a route decision variable, and establishing a first objective function according to the importance of the functional chain;
Determining an interruption indicating coefficient of a service function chain according to an uncertain variable of a link fault, and establishing a second objective function according to the importance of the function chain;
Establishing a route optimization objective function according to the first objective function and the second objective function;
establishing constraint conditions of a service function chain according to virtual network function node requirements, bandwidth resource requirements and routing selection requirements of the service function chain;
And taking the route optimization objective function and the constraint condition as a service function link route optimization model.
2. The service function chain-based route optimization method according to claim 1, wherein the step of establishing the constraint condition of the service function chain according to the virtual network function node requirement, the bandwidth resource requirement and the selected route requirement of the service function chain comprises:
establishing node constraint conditions according to node deployment uniqueness of virtual network functions in a service function chain;
establishing bandwidth resource constraint conditions according to the maximum value of the bandwidth resources of the service function chain;
establishing access sequence constraint conditions according to the node access sequence requirements of the selected route in the service function chain;
And establishing a route topology constraint condition according to the network topology requirement of the selected route in the service function chain.
3. The service function chain-based route optimization method of claim 1, wherein the information physical sensitivity is expressed by the following formula:
In the method, in the process of the invention, A vector representing a physical state variable; A vector representing the variable of the information, A vector representing the physical side control variable,A vector representing the information-side control variable;
the limit power proximity is expressed using the following formula:
In the method, in the process of the invention, Representing a pre-fault transmission lineThe power of the flow-through,Representing a transmission lineIs used for the reference power value of (a),Representing a transmission lineIs set at the power transmission limit of (c),Representing the total number of the transmission lines;
The power fluctuation amplitude is expressed by the following formula:
In the method, in the process of the invention, Representing a transmission linePost-fault power transmission linePower fluctuations caused thereon;
The cascade failure indication coefficient is expressed by the following formula:
In the method, in the process of the invention, Representing a transmission lineIs used for the cascade failure indication coefficient of (a),Representing the equalization factor;
the functional chain importance is expressed by the following formula:
In the method, in the process of the invention, The function chain importance of the kth service function chain is represented,Representing the physical sensitivity of the information of the kth service function chain,Representing a fault scenarioProbability of occurrence, S represents a fault matrix uncertainty set of the communication network,Representing a failure scenarioIs a transmission line of (2)Is a cascade failure indication coefficient of (a).
4. The service function chain-based route optimization method according to claim 1, wherein the link risk value is expressed by the following formula:
In the method, in the process of the invention, Representing physical linksIs a link risk value of (a) and (b),Representing physical linksIs used in the present invention, the availability of (a) the availability of (c) the (b) the (c),Representing physical nodesAnd physical nodeThe physical link between the two-way network and the network,The function chain importance of the kth service function chain is represented;
the risk routing weight value is expressed by adopting the following formula:
In the method, in the process of the invention, Representing physical linksIs a risk routing weight value of (1),Representing physical linksIs provided for the length of (a),Indicating the link availability per unit length,Representing physical linksThe maximum risk value that can be carried,Representing a transmission lineMedium physical linkIs a link risk value for (a) a link risk value (b).
5. The service function chain-based route optimization method of claim 1, wherein the first objective function is expressed by the following formula:
In the method, in the process of the invention, The function chain importance of the kth service function chain is represented, K represents the total number of service function chains,Representing physical nodesAnd physical nodeThe physical link between the two-way network and the network,Representing a set of physical links,Representing physical linksIs a risk routing weight value of (1),Representing logical nodes in a kth service function chainAnd logical nodeWhether the primary logical link between them needs to go through the physical link，Representing logical nodes in a kth service function chainAnd logical nodeWhether or not the backup logical link between them needs to go through the physical link，Representing logical nodesAnd logical nodeA logical link between the two,Representing a first threshold;
The second objective function is expressed using the following formula:
In the method, in the process of the invention, Representing physical linksIs used for the control of the state of (a),Representing physical link-based in kth service function chainInterrupt indication coefficient of the state of (2);
the route optimization objective function is expressed using the following formula:
In the method, in the process of the invention, Representing a second threshold, S representing a fault matrix uncertainty set of the communication network;
the constraint is expressed using the following formula:
In the method, in the process of the invention, Indicating whether an mth virtual network function is deployed on a physical node i, M indicating a set of virtual network functions in the communication network,Representing a collection of physical nodes in a communication network,Representing logical nodesWhether or not handled by the mth virtual network function,Representing the set of nodes in the logical topology of the kth service function chain,Representing the set of links in the logical topology of the kth service function chain,Representing physical linksIs used in the present invention,Representing the source node of the kth service function chain,Representing the destination node of the kth service function chain,Representing logical nodes in a kth service function chainAnd logical nodeWhether the primary logical link between them needs to go through the physical link，Representing logical nodes in a kth service function chainAnd logical nodeWhether or not the backup logical link between them needs to go through the physical link。
6. A service function chain-based route optimization system, comprising:
The importance degree calculating module is used for calculating the information physical sensitivity of the electric power system according to the mapping relation between the information quantity and the physical quantity in the electric power system; calculating a cascading failure indication coefficient of a transmission line according to the limit power proximity and the power fluctuation amplitude of the transmission line in the power system; calculating the importance of a functional chain of the service functional chain according to the information physical sensitivity of the power system and the cascading failure indication coefficient of the transmission line;
The weight value calculation module is used for calculating a link risk value of the physical link according to the importance of the functional link and the availability of the physical link, and calculating a risk route weight value of the physical link according to the link risk value and the link length;
The route optimization module is used for establishing a service function link route optimization model according to the function link importance and the risk route weight value, and solving the service function link route optimization model to obtain an optimal route strategy of the power system;
The route optimization module is further configured to use the risk route weight value as a weight value of a route decision variable, and establish a first objective function according to the importance of the functional chain; determining an interruption indicating coefficient of a service function chain according to an uncertain variable of a link fault, and establishing a second objective function according to the importance of the function chain; establishing a route optimization objective function according to the first objective function and the second objective function; establishing constraint conditions of a service function chain according to virtual network function node requirements, bandwidth resource requirements and routing selection requirements of the service function chain; and taking the route optimization objective function and the constraint condition as a service function link route optimization model.
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