Research On Network Time Synchronization And Time Service Technologies

Time is one of the seven fundamental physical quantities in the International System of Units and the International System of Measurement.It plays an irreplaceable role in the country's economic construction,scientific research,national defense and security,and people's lives.The distribution of accurate synchronization has been a fundamental prerequisite for the correct operation of the telecommunications network for a long time.The recent development of communication networks(such as 5G,high-precision communication networks,etc.)has further increased the network's demand for accurate and reliable time synchronization.The need for time synchronization is continuously increasing in several industries other than Telecom,as they are building the infrastructure for a Smart Society.At present,high-precision synchronization requirements can only be met by building a dedicated synchronization network which is costly and cannot be accessed by customers.Towards the network time synchronization and network time service problem,this paper studies and proposes a software-defined time synchronization scheme,time compensation method,and network time service scheduling mechanism to form an environment for time-engineered applications and meet the customers' time requirements.The specific work and main contributions of this paper are as follows:1.A software-defined network time synchronization scheme is proposed.By constructing time synchronization as a network function,time message transmission and error compensation are decoupled to solve the problem of accurate time information and data information transmitted in the same network.First,based on the idea of network virtualization,this paper constructs time synchronization as a network function using SDN/NFV technology to separate time transmission and accuracy compensation operations.The packet network can provide application programming interface for time-engineered applications and improve the programmability and flexibility of network time synchronization through the synchronization controller and time synchr-onization function.Secondly,the time synchronization path management and security protection are jointly considered in the time synchronization process.The shortest path algorithm is combined with historical time synchronization path data to make the optimal backup path preconfigured to eliminate the impact of delayed attacks.Finally,the test results show that the proposed time synchronization scheme can effectively ensure the accuracy,safety,and reliability of time synchronization.2.A time error compensation method is proposed,combining the time synchronization packets' software and hardware timestamp information.It calculates the time error through the coordinated work of the time synchronization function,and the controller stabilizes the compensation operation through the neural network-based PID algorithm.First,the paper considers the impact of network element and link transmission errors on time synchronization under best-effort forwarding conditions,analyzes and establishes a time error model.Secondly,given the delay asymmetry introduced by the network,combined with the software and hardware timestamp information obtained by in-band measurement,a time error compensation mechanism based on the coordination of time synchronization VNF and controller is proposed.Then,the error compensation problem is modeled as a nonlinear control optimization problem,and a stability control optimization algorithm based on a neural network is proposed.What's more,the network element node that supports time synchronization networking is developed.Finally,experimental verification and analysis are carried out for the compensation performance.The experimental results show that the proposed time error compensation method has high compensation accuracy and realtime performance.3.Based on the concept of time as a service,a network time service orchestration mechanism is proposed,which uses service function chain technology to realize the deployment and orchestration of time synchronization network functions.First of all,the service function chain technology is introduced into the network time service,and the delay-constrained time service orchestration needs are considered.The programmable control and orchestration of the time synchronization VNF are realized to form a time service application environment.Second,this paper considers the coordination of remote cloud computing servers and edge cloud computing servers,computing resource costs,end-to-end delay guarantees to perform service chain orchestration,and builds the orchestration as a mixed-integer linear programming problem.To maximize the revenue of network time services,a priority-based heuristic algorithm is proposed to solve the problem.Simulation results show that the proposed time service orchestration mechanism can effectively reduce deployment costs and increase the success rate of user requests.Finally,the end-to-end network timing performance is analyzed and verified through experiments.