CN111740800A

CN111740800A - Multi-precision clock synchronization method based on SDN framework 5G intelligent node

Info

Publication number: CN111740800A
Application number: CN202010752261.4A
Authority: CN
Inventors: 李传煌; 诸葛斌; 李军; 毛建洋; 张彬鑫; 梁刚; 陈青松; 鲁佳
Original assignee: Zhejiang Gongshang University; Sunwave Communications Co Ltd
Current assignee: Zhejiang Gongshang University; Sunwave Communications Co Ltd
Priority date: 2020-07-30
Filing date: 2020-07-30
Publication date: 2020-10-02
Anticipated expiration: 2040-07-30
Also published as: CN111740800B

Abstract

The invention discloses a multi-precision clock synchronization method based on an SDN framework 5G intelligent node, which comprises the following steps: 1) the synchronized 5G intelligent nodes are regarded as forwarding units in an SDN framework, clock synchronization logic function blocks are abstracted, and logic function description is realized by utilizing XML files; 2) developing specific operation programs for all operation interfaces in the XML file according to the definition of the clock synchronization logic function block; 3) under the unified coordination of the controllers, the controllers are used as master clock nodes, and all 5G intelligent nodes are used as slave clock nodes; 4) and the controller controls the clock synchronization logic function block instances of all synchronized 5G intelligent nodes through corresponding synchronization protocols according to different precision requirements of user clock synchronization, so that large-scale clock synchronization is realized. The method has the advantages of convenient arrangement, low cost and better compatibility, and can be applied to the requirement of large-scale terminal node multi-precision clock synchronization.

Description

Multi-precision clock synchronization method based on SDN framework 5G intelligent node

Technical Field

The invention belongs to the technical field of communication, and particularly relates to a multi-precision clock synchronization method based on an SDN framework 5G intelligent node.

Background

5G is the biggest hotspot in the telecommunication industry today and even in the whole ICT industry, and is also an important concern for national strategy. The 5G defines three major service scenarios of eMBB (enhanced mobile broadband), urrllc (high reliability and low latency) and mtc (large-scale machine connectivity), and almost covers the service application field which can be imagined today. Compared with the 4G, the key indexes of the 5G such as access rate, time delay and connection density are improved by 10 times, which is a significant technical progress. Reviewing the development history of mobile communication, the technical standards are upgraded every 10 years. In the last 80 th century, 1G is analog voice communication, in the last 90 th century, 2G is digital voice communication, in the third century, 3G enables a mobile network to be developed from TDM to IP, and in the fortuitous time of Jobs, a smart phone is invented, so that the era of mobile internet is met, and 4G provides a stronger network environment for the mobile internet, particularly mobile video. The 3G/4G mobile internet is still in the stage of consuming internet, and the application is mainly oriented to life and entertainment of individual users. Different from the past, the industrial internet is the next wave of internet development today, the development center of gravity and the business growth point of 5G are in the fields of industrial internet and internet of things, the realization of the intellectual association of everything is an ideal of 5G and also a maximum value of 5G, and the unique technical advantages of 5G have great attraction to the digital transformation of society and industry. The active contribution of 5G in the new coronary pneumonia epidemic prevention and control is witnessed, so that the remote medical treatment is strongly supported, and the remote medical treatment system plays an important role in the aspects of remote education, remote office, video live broadcast, media fusion, automatic driving, unmanned aerial vehicle application, complex work and complex production technical support and the like. In a word, 5G is not only the next generation of mobile communication, but 5G is the integration of various wireless, network and IT new technologies; 5G is not only a technical revolution, but also a new opportunity of industrial fusion, cross-border expansion and ecological reconstruction, and the 5G application is full of imagination space due to the interconnection of everything; 5G is a future large industry, and the industry boundary far surpasses the traditional mobile communication; 5G is a new battlefield of international science and technology competition, and countries and large enterprises are developing.

The development and evolution of the clock synchronization technology, which is a basic supporting technology of the digital communication network, is always driven by the development of the communication network technology. In the aspect of network, a communication network develops from analog to digital, and develops from a TDM network to a packet network; in terms of services, a multi-service mode mainly developed from TDM voice services to packet services, a multi-service mode mainly developed from fixed voice services to both fixed and mobile voice services, a multi-service mode developed from narrowband services to broadband services, and the like. In terms of transmission technologies that are very closely related to synchronous networks, the coaxial transmission is evolving to PDH, SDH, WDM and DWDM, and more recently OTN and PTN technologies. With the continuous development of new communication services and new technologies, the synchronization requirements are higher and higher, the basic clock technologies including clock sources, phase-locked loops and the like are updated and updated for many times, the synchronization technology is also continuously updated, and the time synchronization technology is the focus of attention in the current industry.

The synchronization technology includes two aspects of a frequency synchronization technology and a time synchronization technology, the time synchronization has an increasingly wide demand in the communication field, and the demand of various communication systems for the time synchronization can be divided into high-precision time demand (microsecond and nanosecond) and common-precision time demand (millisecond and second). Aiming at the time synchronization requirements with different precisions, the following existing time synchronization technologies are mainly applied in the communication network: (1) IRIG-B (InterRange instrumentation group) and DCLS (DC Level Shift); (2) ntp (network TIme protocol); (3) 1PPS (1 Pulseper Second) and serial port ASCII string; (4) PTP (precision Time protocol).

The protocols for transferring TIme in a computer network are mainly 3 types of TIme Protocol (TIme Protocol), TIme-of-day Protocol (DayTIme Protocol), and Network TIme Protocol (NTP). In addition, there is a Simple Network Time Protocol (SNTP) only for the user side. The time server on the network will continuously monitor the timing requirements using the above protocol on the different ports and send the time code in the corresponding format to the client. Among the above network time protocols, the NTP protocol is the most complex and the time accuracy that can be achieved is relatively high. The network structure, data format, authentication and weighting of the server, filtering algorithms, etc. running NTP are very fully specified in RFC-1305. NTP technology can be applied in local area networks and wide area networks, and the accuracy can only reach millisecond level or second level.

Improved NTPs have also emerged in recent years. Unlike traditional NTPs, the improved NTP generates and processes timestamp labels at the physical layer, which requires hardware modifications to existing NTP interfaces. The improved NTP still adopts the algorithm of NTP protocol, and can realize intercommunication with the existing NTP interface. Compared with the original NTP, the time precision of the NTP can be greatly improved. At present, the number of devices supporting the improved NTP is small, and the precision, the application scene and the like of the devices are still needed to be further researched. The improved row NTP number can reach tens of microseconds.

The PTP and NTP are realized based on bidirectional equivalent transmission time delay, and the biggest difference is the generation and processing link of time tags. PTP achieves much higher time accuracy than NTP by time-stamping the physical layer. The PTP technique based on IEEE-1588 was originally used for industrial control requiring strict timing coordination, and in order to comply with the rapid increase in the demand for high-precision time synchronization in a communication network, IEEE-1588 was developed from original release 1 to release 2, and has been applied to synchronization devices, optical transmission devices, and 3G base station devices.

In China, the PTP technology is mainly based on the high-precision time transmission of an optical transmission system, and domestic operators develop researches on the high-precision time transmission of the ground transmission system in recent years, perform a large number of experiments in laboratories and current networks, obtain certain achievements and exceed the research level in relevant aspects abroad. At present, the time transmission between PTP bureaus is realized in a network environment with a certain scale in China, and the precision can reach microsecond level.

However, the automation degree of the current clock synchronization process is generally not high, and the automation degree of the multi-precision clock synchronization protocol method can reach a very high level.

Disclosure of Invention

The invention aims to provide a multi-precision clock synchronization method based on an SDN framework 5G intelligent node aiming at the defects of the prior art.

The purpose of the invention is realized by the following technical scheme: a multi-precision clock synchronization method based on an SDN framework 5G intelligent node comprises the following steps:

1) the synchronized 5G intelligent nodes are used as forwarding units in an SDN framework, a clock synchronization logic function block is defined on each 5G intelligent node, each 5G intelligent node is an independent intelligent terminal, and management software of the clock synchronization logic function block is configured on each intelligent terminal; the clock synchronization logic function block comprises information reading, parameter configuration and event reporting functions of the 5G intelligent node, and function description of the clock synchronization logic function block is realized by utilizing an XML file; the method specifically comprises the following steps: the method comprises the steps that XML files are used for carrying out class and example description on clock synchronization logic function blocks, one class needs to be provided with one XML file description, the clock synchronization logic function blocks of the same class are provided with a plurality of examples of the clock synchronization logic function blocks, each example needs to be provided with one XML file description, and the XML files describe values of specific parameters in the examples of the clock synchronization logic function blocks, interfaces for reading and writing the clock synchronization logic function blocks and event reporting interfaces in the clock synchronization logic function blocks;

2) developing specific operation programs for all operation interfaces in the XML file according to the definition of the clock synchronization logic function block; the method specifically comprises the following steps: according to the definition of the clock synchronization logic function block, developing corresponding functions for all the examples of the clock synchronization logic function block, the interface for reading and writing the clock synchronization logic function block described by the XML file and the event reporting interface in the clock synchronization logic function block, and realizing the requirement of the corresponding interface by calling the function provided by the management software of the 5G intelligent node in the functions;

3) under the unified coordination of controllers in an SDN framework, the controllers are used as master clock nodes, and all 5G intelligent nodes are used as slave clock nodes;

4) the controller controls the instances of the clock synchronization logic function blocks of the slave clock nodes to be synchronized through the master clock node by selecting a clock synchronization protocol corresponding to the precision requirement according to different precision requirements of the user clock synchronization, so as to realize clock synchronization; the method specifically comprises the following steps: after receiving the precision requirement of user clock synchronization and the range of the designated synchronization node, the master clock node firstly sends a corresponding clock synchronization protocol to the slave clock node with the synchronized designated range according to different precision requirements to create a required clock synchronization logic function block example, sets parameters related to the clock synchronization protocol in the example, then the master clock node sends related set and get commands to the slave clock node, the slave clock node returns a synchronized timestamp message to the master clock node, and the synchronization result of the designated range slave clock node is fed back to the user through the master clock node.

Furthermore, the 5G intelligent node is used as an intelligent terminal and is configured with a real-time operating system, management software is configured in the system and is used for realizing the function control and management of the clock synchronization logic function block, the 5G network is utilized for networking, and the controller performs centralized control on the 5G intelligent node through a 5G network communication protocol and supports distributed cooperative work.

Furthermore, a clock synchronization logic function block is defined for the function realized by the management software of the 5G intelligent node according to the method specified by the LFB model in the ForCES forwarding element.

The invention has the beneficial effects that: the multi-precision clock synchronization method based on the SDN framework 5G intelligent nodes has better compatibility, can be applied to intelligent terminals with different system versions, and can realize semi-automatic setting in large-scale 5G intelligent nodes. For example, the method is applied to large-scale unmanned aerial vehicle work and performance, and corresponding clock synchronization protocols can be switched according to different distances, so that resource utilization is optimized.

Drawings

FIG. 1 is a schematic diagram of a clock synchronization architecture;

FIG. 2 is a schematic diagram of a 5G intelligent node structure;

FIG. 3 is a schematic diagram of NTP timing;

fig. 4 is a diagram of a PTP protocol delayed response mechanism.

Detailed Description

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

The multi-precision clock synchronization method based on the SDN framework 5G intelligent node has good compatibility, can be applied to the multi-precision clock synchronization requirement of large-scale terminal nodes, and has high automation degree.

The invention utilizes 5G environment and SDN framework to perform centralized control and software definition on the low-cost intelligent network sensing nodes. With the rapid development of network applications, more and more protocols and servers need to be deployed in a network, and traditional routers need to manually complete the expansion of the services and the protocols, so that the efficiency is low. The advent of programmable networks has enabled the expansion of network protocols and services to be automated over an open, programmable network platform. Firstly, ForCES (ForCES) which is a programmable interface standard of IP network equipment is used for configuring the QoS (quality of service) function of a forwarding component for a control component in the IP network equipment, and then the precise clock synchronization of multiple network nodes in different ranges is realized through an NTP (network time protocol) or a PTP (precision time protocol) according to different precision requirements. The accurate clock synchronization can ensure the real-time performance of the system, combines the technical advantages of an SDN framework, combines the SDN centralized control technology and the accurate clock synchronization technology, and realizes the unified control of the controller on the clock synchronization of the sensing nodes.

By using the ultra-low delay characteristic of the 5G network as the communication basis of the intelligent network nodes in the smart city, as shown in FIG. 1, the controller is set as a master clock node, and all the other 5G intelligent nodes are set as slave clock nodes. All 5G intelligent nodes are designed based on an SDN framework, and an SDN controller realizes centralized control and software definition on the 5G intelligent nodes. All synchronized 5G intelligent nodes comprise various network node devices and network terminal devices, the intelligent nodes are interconnected through a 5G network, a real-time operating system of specific management software is installed, and clock synchronization logic function blocks are defined by the management software. The clock synchronization logic function block defines the functions which can be realized by the equipment management software according to the method specified by the forwarding element model in the clock synchronization protocol, and obtains interface definitions of equipment information reading, parameter configuration and event reporting functions. The method comprises the steps of utilizing XML files to carry out class and example description on clock synchronization logic function blocks, wherein one class needs to have one XML file description, the clock synchronization logic function blocks of the same class are provided with a plurality of examples of the clock synchronization logic function blocks, each example needs to be described by one XML file, and the XML files describe values of specific parameters in the examples of the clock synchronization logic function blocks, interfaces for reading and writing the clock synchronization logic function blocks and event reporting interfaces in the clock synchronization logic function blocks. For all the clock synchronization logic function block examples, the interface for reading and writing the clock synchronization logic function block described by the XML file and the event reporting interface in the clock synchronization logic function block develop corresponding functions, and the function calls the function provided by the management software of the equipment to realize the requirement of the corresponding interface.

As shown in fig. 2, after the controller sends the precision requirement of the user clock synchronization received by the application program, the controller sends a synchronization code corresponding to the precision requirement to the operation interfaces of all synchronized 5G intelligent nodes, and issues the parameters. Management is achieved on the master clock node by direct operation of the clock synchronization logic function of all synchronized slave clock nodes. When the controller receives the command, the set command and the get command are sent to the slave clock nodes, the slave clock nodes keep accurate synchronization at any moment through a clock synchronization protocol, synchronous data frames are sent between the master clock node and the slave clock nodes, the sending time and the receiving time information of the data frames are recorded, and the time information is added into the data frames. The slave clock node acquires the time information, calculates the time deviation between the slave clock node and the master clock node and the transmission delay between the network nodes, and corrects the local clock so as to synchronize the local clock with the master clock node. The method comprises the steps of carrying out centralized control and software definition on low-cost intelligent network sensing nodes by utilizing an SDN framework, and realizing accurate clock synchronization on multiple network nodes through an NTP protocol or a PTP protocol.

The most typical time service mode of NTP is a Client/Server mode. As shown in fig. 3, the client first sends to the server an NTP packet containing a timestamp T1 when the packet leaves the client, and when the server receives the packet, the timestamp T2 when the packet arrived and the timestamp T3 when the packet left are filled in sequence, and then immediately returns the packet to the client. The client, upon receiving the response packet, records the timestamp T4 returned by the packet. The client can calculate 2 key parameters with the above 4 time parameters: the round-trip delay d1 between T1 and T2 of the NTP packet, the round-trip delay d2 between T3 and T4, and the clock skew T between the client and the server. The client uses the clock offset to adjust the local clock to make its time coincide with the server time.

As shown in fig. 4, the basic procedure for using the PTP synchronization protocol is as follows: the master and slave clocks interact with each other to synchronize the message and record the receiving and sending time of the message, the round-trip total delay between the master and slave clocks is calculated by calculating the round-trip time difference of the message, if the network is symmetrical (namely the transmission delays in two directions are the same), half of the round-trip total delay is one-way delay, the one-way delay is the clock deviation between the master and slave clocks, and the slave clock adjusts the local time according to the deviation, thus realizing the synchronization with the master clock. The master clock sends a Sync message to the slave clock, and records the sending time t 1; after receiving the message from the clock, the time of reception t2 is recorded. After the master clock sends the Sync message, it sends a Follow _ Up message carrying t 1. The slave clock sends a Delay _ Req message to the master clock, is used for initiating the calculation of reverse transmission Delay and records the sending time t 3; after receiving the message, the master clock records the receiving time t 4. After receiving the Delay _ Req message, the master clock replies a Delay _ Resp message carrying t 4. At this time, the slave clock has four time stamps of t 1-t 4, so that the total round-trip delay between the master clock and the slave clock is calculated to be [ (t 2-t 1) + (t 4-t 3) ], and the one-way delay between the master clock and the slave clock is calculated to be [ (t 2-t 1) + (t 4-t 3) ]/2 because the network is symmetrical. Thus, the clock skew of the slave clock relative to the master clock is: offset = (t 2-t 1) - [ (t 2-t 1) + (t 4-t 3) ]/2 = [ (t 2-t 1) - (t 4-t 3) ]/2. Under the continuous development of the SDN, a future city is certainly an "everything interconnected" smart city, there are more and more smart terminals distributed in the smart city, and the systems and versions of the smart terminals are also various. The multi-precision clock synchronization method based on the SDN framework 5G intelligent node has good compatibility, can perfectly solve the problem, and can operate on different system versions, thereby carrying out centralized control. The terminals provided with the real-time operating system are used as 5G intelligent nodes, are controlled in a centralized mode through software definition, and have remote control and configuration functions.

The multi-precision clock synchronization method based on the SDN framework 5G intelligent node can realize semi-automatic setting in large-scale 5G intelligent nodes. For example, the method is applied to large-scale unmanned aerial vehicle work and performance, and corresponding synchronization protocols can be switched according to different distances, so that resource utilization is optimized.

The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are within the spirit of the invention and the scope of the appended claims.

Claims

1. A multi-precision clock synchronization method based on an SDN framework 5G intelligent node is characterized by comprising the following steps:

2. The multi-precision clock synchronization method based on the SDN architecture 5G intelligent nodes according to claim 1, wherein the 5G intelligent nodes are configured with a real-time operating system as an intelligent terminal, and management software is configured in the system for realizing function control and management of clock synchronization logic function blocks, and the 5G intelligent nodes are centrally controlled by a controller through a 5G network communication protocol to support distributed cooperative work by using 5G network networking.

3. The multi-precision clock synchronization method based on the SDN architecture 5G intelligent node as claimed in claim 1, wherein the clock synchronization logic function block is defined for the function implemented by the management software of the 5G intelligent node according to the method specified by the LFB model in ForCES forwarding element.