Application of NTP network time server (PTP clock synchronization) in it network

NTP Network time server (ptp Clock synchronization ) stay IT Applications in the network
NTP Network time server (ptp Clock synchronization ) stay IT Applications in the network
Beijing Zhun provides the original text
Preface
in recent years , With the improvement of computer automation system , In major computer monitoring systems 、 Microcomputer protection device 、 Microcomputer fault recorder and various data management machines have been widely used , And there's an automatic timing for these devices . When the system fails , It can not only realize the operation monitoring and post accident fault analysis of all systems in the whole station under the unified time benchmark , It can also be done through various protective actions 、 Switch on and off sequence and accurate time to analyze the cause and process of the accident , It is convenient to analyze and trace various events in operation , Improve the automation level of the system .
One 、 summary
　　 In the field of Communications ,“ Sync ” The concept refers to the synchronization of frequencies , That is, the clock frequency and phase synchronization of each node in the network , The error should be in accordance with the relevant standards . at present , In communication network , The problem of frequency and phase synchronization has been basically solved , The synchronization of time has not been well solved . Time synchronization refers to the time and time interval of the clock of each node in the network and the clock of each application interface connected through the network and coordinated universal time （UTC） Sync , At least in a local area or metropolitan area network to synchronize with Beijing time . Time synchronization network is the basis of time synchronization , The time synchronization network can be constructed in wired way , It can also be done wirelessly . Here we mainly introduce Internet time synchronization technology and products , That is, through support NTP The network time server of the protocol realizes network time synchronization .
　　 The basic unit of time is seconds , It is the international system of units （SI The system of units ） One of the seven basic units of .1967 International Conference on Metrology （CGDM） A new definition of second is given ：“ Second is cesium 133（133Cs） The atom is in 0K The radiation corresponding to the transition between two hyperfine levels of the temperature ground state 9 192 631 770 The duration of a cycle ”, namely “ Atomic seconds ”（TAI）. Now the commonly used coordinated universal time is actually an atomic second adjusted by leap seconds .
　　 At present, cesium atomic clock is mainly used at the level of international benchmark and national benchmark . The frequency reproducibility of the cesium atomic clock in the cold atomic fountain established by the Chinese Academy of metrology is 5×10－15, It is close to the international advanced level . Actually , At the application level, there is no need for such high time and frequency accuracy as national benchmarks . Different applications have different requirements for accuracy , surface 1 The requirements of time accuracy for some typical applications are listed （ Application interface time is relative to UTC Time error ）.

surface 1： Some typical applications of time accuracy
application Time accuracy requirements
For bank 、 negotiable securities 、 Computers and servers for stock and futures trading 1 second
Power line fault diagnosis 1 Microsecond
Switch and billing system 1 second
CDMA2000 and TD-SCDMA 10 millisecond
Network management system 500 millisecond
7 Signaling monitoring system 1 millisecond

Two 、 Network time synchronization technology
At present, there are many kinds of time synchronization technologies , Each technology has its own characteristics , There are also great differences in the time synchronization accuracy of different technologies , As shown in the table 2 Shown ：

surface 2： Various commonly used time synchronization technologies
Time synchronization technology Accuracy Coverage
Shortwave timing 1～10 millisecond The global
Long wave timing 1 millisecond Area
GPS 5～500 nanosecond The global
Telephone dial-up time service 100 millisecond The global
Internet time service （NTP） 1～50 millisecond The global
SDH Transmission network timing 100 nanosecond long-distance
1、 Long and short wave timing and time synchronization technology
The use of radio signal timing has 80 Years of history , Roland is mainly used in international long wave timing -C System , The domestic launch pad is located in the coastal area , Mainly used for military and navigation , Not yet .
2、 Telephone dialing time synchronization technology
Telephone dial-up time service （ACTS） The equipment used is relatively simple , Just a phone line 、 Analog modem 、PC And client software . At present, this kind of computer is mainly used to calibrate the time of home personal computer , At the same time, it does not have real-time .
3、 GPS Time synchronization technology
GPS Time synchronization technology is a mature and widely used time synchronization technology in the world . At present, in addition to the United States GPS And the former Soviet Union GLANASS System and China's “ Beidou ” System .GLANASS The system is due to economic reasons , The number of health stars is limited , Stability and reliability cannot be guaranteed .“ Beidou ” The system has not been used yet , And can not achieve real-time coverage . at present GPS It belongs to a relatively mature and reliable system .
4、 Internet time synchronization technology
It is very convenient to use the Internet to synchronize the time of the computer , At present, this method is widely used in LAN . Microsoft has made the network time protocol （NTP） Embedded in Windows XP In the system , As long as computers can be connected to the Internet , Computer time calibration in LAN or WAN can be carried out . The standard NTP The protocol is based on RFC 1350 standard , Simplified network time protocol （SNTP） It's using RFC 1769 standard .NTP The agreement contains a 64bit Coordinated universal time （UTC） Time stamp , Time resolution 200ps, And can provide 1~50ms Time accuracy of （ Rely on network load ）. But experiments show that the calibration accuracy of this technology between continents can only reach hundreds of milliseconds or even seconds . therefore , In the huge network, primary and secondary time servers should be set up to solve the problem of accuracy .
in addition , There are two relatively simple 、 Low precision Internet Time Protocol ：Time agreement （RFC868） and Daytime agreement （RFC867）, Can provide 1s Wan time synchronization for calibration accuracy .

3、 ... and 、GPS Network time server
The network time server is GPS The combination of time synchronization technology and Internet time synchronization technology . use 19 Inch 1U Rack design , built-in GPS Receiver , With GPS Satellite time is the standard time source , Support NTP agreement （V2.0/V3.0/V4.0） and SNTP agreement . It can be used for hundreds of computers in the LAN 、 Routers, etc. provide time calibration . The following figure for GPS Application scheme of network time server ：
In the scheme above , From the provincial central network to the local municipal network, the time synchronization of the application interface needs to be maintained . If only one network time server is set up in the provincial network, the client in the prefecture and municipal network can not guarantee the required accuracy due to network delay and other reasons , Then this problem can be solved by setting up a network time server in the prefecture level network , But if the network conditions are good , This error NTP It can be automatically compensated during the agreement ;