China Shinco Net Time Synchronization Solution
I. Overview
In the field of communications, the concept of “synchronization†refers to the synchronization of frequencies, that is, the clock frequency and phase of each node of the network are synchronized, and the error should comply with the relevant standards. At present, in the communication network, the frequency and phase synchronization problems have been basically solved, and the time synchronization has not been well resolved. Time synchronization means that the clock time and time interval of each node clock of the network and each application interface connected through the network are synchronized with the coordinated universal time (UTC), at least in a local area or metropolitan area network and synchronized with Beijing time. The time synchronization network is the basis for ensuring time synchronization. The time synchronization network can be wired or wireless. Here we mainly introduce the Internet time synchronization technology and products, that is, through the network time server supporting the NTP protocol (Zhongxinchuang DNTS series) to achieve network time synchronization.
The basic unit of time is seconds, which is one of the seven basic units of the International System of Units (SI system). The 1986 International Conference on Quantity Measurement (CGDM) gave a new second definition: "Seconds are 9,192,631,770 cycles of radiation corresponding to transitions between two hyperfine levels of the 133 (133Cs) atom in the 0K temperature ground state. The duration of time, "atomic seconds" (TAI). The current Coordinated Universal Time is actually atomic seconds adjusted by the leap second.
Currently used at the international benchmarks and national benchmarks are the rubidium atomic clocks. The frequency reproducibility of the atomic atomic clock of the cold atomic fountain, established by the China Institute of Metrology, is 5×10-15, which is close to the international advanced level. In fact, such a high time and frequency accuracy is not needed at the application level. Different applications have different requirements for accuracy. Table 1 lists the time accuracy requirements of some typical applications (errors of the application interface time with respect to UTC time).
Table 1: Application of Time Accuracy to Some Typical Applications
application
Time accuracy requirements
Computers and Servers for Banking, Securities, Stocks and Futures Trading
1 second
Power line fault diagnosis
1 microsecond
Switch and billing system
1 second
CDMA2000 and TD-SCDMA
10 milliseconds
Network Management System
500 milliseconds
No. 7 Signaling Monitoring System
1 millisecond
Second, time synchronization network technology
At present, there are various kinds of time synchronization technologies, each of which has its own characteristics. There are also large differences in the time synchronization accuracy of different technologies, as shown in Table 2:
Table 2: Various commonly used time synchronization techniques
Time synchronization technology
Accuracy
Coverage
Shortwave timing
1 to 10 milliseconds
global
Long wave timing
1 millisecond
area
GPS
5 to 500 nanoseconds
global
Telephone dialing time
100 milliseconds
global
Internet Time Service (NTP)
1 to 50 milliseconds
global
SDH transmission network timing
100 nanoseconds
long haul
1, long and short wave timing synchronization technology
The use of radio signal timing has a history of more than 80 years. Longwave time internationally mainly uses the Roland-C system. The domestic launch station is located in the coastal areas and is mainly used for military and navigation purposes. It is not yet civilian.
2, telephone dialing time synchronization technology
The equipment used for telephone dialing time (ACTS) is relatively simple, requiring only telephone lines, analog modems, PCs, and client software. At present, this kind of computer is mainly used for calibrating home personal computer time, and it is not real-time at the same time.
3, GPS time synchronization technology
GPS time synchronization technology is currently more mature and widely used in the world of time synchronization technology. At present, in addition to the United States GPS, there are the former Soviet Union's GLANASS system and China's "Beidou" system. Due to economic reasons, GLANASS system has a limited number of healthy stars, and stability and reliability cannot be guaranteed. The "Beidou" system has not yet been used by civilians and cannot be covered in real time. At present, GPS is a relatively mature and reliable system.
4, Internet time synchronization technology
Using the Internet to synchronize the computer's time is very convenient. At present, this method is widely used in the local area network. Microsoft has embedded the Network Time Protocol (NTP) into Windows XP. As long as the computer is connected to the network, it can perform computer time calibration on the LAN or WAN. The standard NTP protocol uses the RFC 1350 standard, and the simplified network time protocol (SNTP) uses the RFC 1769 standard. The NTP protocol contains a 64-bit Coordinated Universal Time (UTC) timestamp with a time resolution of 200ps and can provide 1 to 50ms of time accuracy (depending on network load). However, experiments have shown that the accuracy of this technique in intercontinental calibration can only reach the order of a few hundred milliseconds or even only seconds. Therefore, primary and secondary time servers should be set up in large networks to solve the problem of accuracy.
In addition, there are two relatively simple, low-precision Internet Time Protocols: the Time Protocol (RFC868) and the Daytime Protocol (RFC867), which provide wide-area network time synchronization with 1s calibration accuracy.
Third, China Netcom's network time server
Since the beginning, Zhongxin Chuangke has devoted itself to the development of network time servers and has gained recognition from customers. The current product is divided into 6 models to meet the needs of network time synchronization in different industries. At the same time, the new DNTS series of network time servers in China Shinco has been widely used in power, railway, military, telecommunications, government agencies and other industries.
The new DNTS time server in the company is a combination of GPS time synchronization technology and Internet time synchronization technology. 19-inch 1U rack-mount design, built-in GPS receiver, GPS satellite time as standard time source, support NTP protocol (V2.0/V3.0/V4.0) and SNTP protocol. Can provide time calibration for hundreds of computers, routers, etc. in the LAN.
In the previous Internet time synchronization technology, it was mentioned that the inter-continental calibration accuracy can only reach the order of a few hundred milliseconds or even only seconds due to network load and delay. Therefore, a large-scale network needs a secondary network time server to solve the problem of calibration accuracy and redundancy.In the above scenario, the time synchronization of the application interface needs to be maintained from the provincial center network to the local municipal networks. If only one network time server is set up in the provincial network, then the clients in the municipal network cannot ensure the required accuracy due to network delays, etc., then by setting up a network time server in the city network This problem, because in this case GPS receivers around the time when we receive more than 3 satellite signals when everyone's time source is the current standard time, so the consistency of the time source is guaranteed. At the same time, even if the GPS receiver in a certain location is faulty, the local network time server can act as a NTP client to the primary time server of the provincial network at the top level, and the standard time continues to provide accurate time source for the client of the local network. Provide calibration services. In extreme cases, when the primary-level time server GPS set up in the provincial network also fails, the primary time server has a highly accurate self-preserving time function (1×10 -12 punctuality accuracy, ie, 30 year error 1 s). Can provide accurate time source. The first-level time server in the scheme adopts China Shinco Co., Ltd. DNTS-6 type, and the second-level time server adopts DNTS-3 type.
In addition, China Shinco provides time and frequency products for mobile communications, satellite communications and digital broadcast television systems. For example, it can be used as a CDMA clock source to provide clock sources for CDMA base stations. It can provide 19.6608MHZ square wave signals, PP2S signals, 10M sine Wave signal or square wave signal. Applications such as digital trunking can be customized to signal 16.384 MHz, 14.4 MHz. And support re-timing function as a re-timing device.
China Shincoe Time Server Parameters and Performance Features:
Ensure that all computers in the intranet/Internet are synchronized
Support protocol ARP, UDP, IP, TCP, Telnet, ICMP, SNMP, DHCP, TFTP, NTP, SNTP, Time/UDP
NTP V4, V3, V2; NTP Server or NTP Client can be selected
Two independent Ethernet speeds 10/100M, protocol compatibility: Ethernet 2.0/IEEE 802.3
One RS232/RS485 output standard time and position signal (NMEA 0183)
One RS232 input can be used as external time source
1PPS output
Local dry node alarm function
12-channel GPS receiver, finder time less than 10 seconds
Built-in high-precision clock can output standard time signal under GPS signal loss
Network accuracy is less than 10ms
Can be used for WIN95/98/ME/NT/2000, Unix, Linux
Provide MD5 encryption verification to prevent illegal acquisition time
Provide UDP broadcast protocol, can be connected to LED display
Perfect SNMP network management function
Input power supply 220VAC/50Hz, -48VDC, 24VDC, 10W
Model:DNTS-3
Model: DNTS-7 Series
Beijing Zhongxinchuang Technology Co., Ltd. Contact: Wenxin
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