Implementation and application of time synchronization system

The meaning of time synchronization

The timing of various communication devices or computer equipment on the communication network (time and minutes) is limited to a sufficiently small range (such as 100ms) based on UTC (Coordinated world time), which is called time synchronization.

In general, the most widely used time synchronization applications are computers on the Internet. Computer clocks are used to record time information about events, such as e-mail messages, file creation and access times, database processing times, and so on. Clocks are also used to control the operation of backups, to automatically construct a compiler for the design to check for changes in files, and other applications. If the computer clock is not accurate, many of these applications will not work properly. Time-sensitive computer systems, such as financial sector servers, EDI, large distributed commercial databases, aerospace control computers, and so on, require high precision time information. The time display system of the transportation industry, such as the subway timetable display system, the airport timetable display system, if the deviation is large, may affect the traveller's travel.

The CDMA base station needs UTC information. In CDMA systems, which rely on GPS satellite time synchronization, the time synchronization between base stations is based on public CDMA, which is synchronized with UTC time by receiving GPS timing. BTS requires absolute time to obtain the CDMA signal sent from Ms. In a soft switch, a message instruction mismatch may occur in the selector due to a BS message path queue delay. To prevent this mismatch, all BTS and BSc must have time synchronization.

The time synchronization function is also applied to telephone billing because of the presence of multiple carriers and the existence of a phased rate. Network billing inconsistency caused by the single loss, the use of time synchronization can be reduced or even eliminated. For example, when Telecom and Unicom exchange, is through the gate billing, if the telecommunications side billing starting point for 20:58 (half the time period before), and Unicom side billing starting point for 21:01 (after half the time period), then the telecommunications, Unicom billing will appear errors, the usual practice is to discard the statement, the loss by both operators to bear. If the absolute Moment (TOD) provided by Bits can be received on both sides of the switch, the billing error of both sides can be controlled at the millisecond level, fundamentally avoiding the differences in the speech orders. Even if only one side of the switch can receive Tod, then in the statement decision, the party can occupy the ruling position, to eliminate the loss for their own. As a result, the Tod solution is a synchronized new technology that operators pay close attention to.

The alarms and logs of the network management system also need to accurately record the exact time of events and alarms in order to perform the fault and performance analysis. For example, the alarm time generated by the network Management center may not be the exact time when the switch actually generates alarms. In addition, when multi-point logging is used in the network Management center, if the time of each node is not synchronized, it will cause the confusion of log records. Accurate time is essential if this information is to be quickly and accurately located.

Ii. acquisition of UTC time Benchmarks

The standard timescale used in most countries of the world is Coordinated Universal Time UTC based on the astronomical time of the Earth's rotation and the atoms that are based on atomic oscillations. UTC time is spread through a number of channels, including wireless and satellite navigation systems, telephone modems and portable timers.

The time datum of the satellite navigation system is the timing of the ground time datum source of the respective country, so the UTC time can be conveniently obtained by using the GPS GLONASS Beidou receiver. The HJ201 HJ204 receiver can directly output 1PPS, RS-232 and irig-b format signals, which lays a foundation for the wide application of time information at present.

In order to realize the propagation of time information and ensure the propagation accuracy, the distributed Network Time protocol is needed. These protocols ensure that time synchronization network meta devices read the server correctly, pass readings to one or more customers, and adjust each customer's time as needed. These protocols include: Network Time Protocol (NTP), Digital time synchronization Protocol (DTSS), and so on.

Three, UTC time Transmission mode

The time information that transmits UTC, usually has the wireless transmission way (high-frequency or low-frequency radio signal), the Wired Transmission Way (DCN, PSTN, DDN and so on), in general, the telecommunication network uses the wired transmission way to solve the UTC time transmission.

With the development of computer network, the network Time Protocol (NTP) protocol becomes a member of the TCP/IP protocol family. The time server (NTP) that currently has the NTP software installed on the Internet provides the time service benchmark for its client computers, and the first time server (NTP) obtains the absolute moment information of UTC from the GPS receiver (using the RS-232 interface), the low Level time server (NTP) Obtain UTC time from a parent server through a TCP/ip-based DCN network. All client computers that require time obtain UTC time information from a specified time server (such as the HJ210 NTP Network time server) by installing an NTP client program to calibrate their current time information.

The NTP protocol in the Internet in 1998 has more than 230 first-time servers (NTP) synchronized through wireless, satellite and modem, and far more than 100,000 secondary servers and clients. In addition, there are thousands of private networks in government, associations and institutions. They act as a subtree or subnet in the synchronization network, where the tier one server is the root and the secondary server and client are on the growing lower level.

Using NTP protocol to provide TOD, suitable for users with DCN network, investment in the province, precision to meet billing, E-commerce, network management needs.

Four, time synchronization network scheme

1, the time synchronization between the Bureau

The inter-local time synchronization network structure is a primary time server (NTP) (stratum 1), two-level time server (NTP) (stratum 2) 、......、 15-level time Server (NTP) (stratum 15).

Superior time Server (NTP) preferred the use of DCN network, usually superior and subordinate time server (NTP) between the set for the number of transfer less fixed route, transmission distance is not particularly long, so this way has the most investment, good performance, easy installation, no maintenance and other characteristics, Fully able to meet the telecommunications user and business to the second-level accuracy of the basic requirements (after tracking can achieve far higher than 100ms precision). If you do not have a DCN network, you can also set up a dedicated time synchronization DCN network for the transmission of NTP packets, such as DDN line, PSTN line (need to use modem) or E1 special line. As long as the transport channel between the servers is working properly, it is sufficient to allow the level of time server (NTP) to have millisecond precision.

2, the Inside time synchronization

A computer with client-side NTP software, which obtains a UTC time reference from the Network time server (NTP) and calculates local UTC time information, and a client computer installs a software program based on NTP or SNTP to obtain synchronization information.

This shows that the time server (NTP) in the same building computer users, through TCP/IP LAN is the most efficient way to get tod time, so this way has investment province, software installation convenience, high precision characteristics, the most easy to promote the use of a large number.

Computers that cannot be on a LAN LAN can only transmit the UTC information individually via the physical interface of the user device that is connected to it (such as irig-b, RS-232, etc.).

Therefore, NTP protocol is the best choice to meet the accuracy requirements of alarm, log, billing, file recording and so on for most network management center and communication Equipment (workstation, server, maintenance terminal, switch) of communication network. The existing data network load will not have much impact (generally does not exceed 2% of the total load), while installation or upgrade maintenance is very convenient.

The time server (NTP) uses the standard NTP protocol, its interface is also standard, the other Synchronized Time server (NTP) and users do not have to use the same as the head time Server (NTP) the same operating system and software, You can use the NTP service provided by Synlock simply by providing a standard NTP interface. Huawei offers other levels of Time server (NTP) hardware and software to provide time server (NTP) for other Windows NT network management centers or sun workstations.

The communication network between Time Server (NTP) and synchronous equipment can use the existing private network, and it can be constructed by the PSTN, DDN and other communication networks. Because the network interface, the Protocol interface adopts the standard protocol, the expansibility, the compatibility is good, may conveniently, the economical use the equipment to provide the accurate time for each time.