Victor, Charlie, Victor, Charlie, welcome

Anyone who has ever set the date and time on a computer has seen the abbreviation UTC, but not everyone knows where this time really comes from and why it is so important.

A bit of history

UTC is a modern version of WET (Western European Time). UTC was introduced in 1964 and belongs to the Earth International Coordinate System (ITRS). The International Astronomical Coordinate System (ICRS) is used to calculate the time for celestial bodies.

GMT is quite enough in everyday life, but if more precise coordination is needed, then you cannot do without UTC. UTC is the link between the time on the Greenwich meridian (GMT) and International Atomic Time (TAI).

After installing the first ARPANET server (September 2, 1969), it became necessary to describe and transmit a single time over the network. For compatibility, the time described in the framework of the POSIX standard. The starting point was taken on January 1, 1970. Thus, the timer started in milliseconds from midnight on January 1, 1970. On January 30, 1970, after the first second of coordination, the POSIX time lag was UTC. Up until 1981, the backlog was corrected manually until David L. Miles invented the UTC and POSIX time synchronization protocol (NTP).

Subsequently, NTP began to be used not only within the ARPANET network, but also such networks as NSFNet, CSNET, and others. Currently, all modern computers can work with NTP.

International Earth Rotation Service

If earlier all roads led to Rome, now Paris can be called the center of time. It was in Paris that the International Earth Rotation Service (hpiers.obspm.fr) was formed in 1987, which is responsible for maintaining universal time.

From her work depends stable communication and work not only the Internet, but also satellite systems.

As for satellite systems (GLONASS, GPS, DORIS, QZSS, IRNSS, EGNOS, WAAS), they mainly serve to clarify astronomical calculations, as well as relay accurate time signals to the ground.

Observation of the rotation of the earth is mainly carried out using radio telescopes, seismic sensors located in different parts of the planet, as well as tacheometers and other equipment installed at observatories. With the help of all this equipment, specialists of the international time service track the speed of movement of lithospheric plates, which affects the value of Greenwich Mean Time (GMT).



The modern Internet is based on the TCP / IP protocol (RFC739, RFC791), at the transport level of which exact time is actively used. UTC plays a key role, allowing the network to work in a single coordinate system. The exact time source for a computer connected to the Internet is mainly a time server (SNTP, NTP), or a hardware clock (CMOS), which can be synchronized with a GPS satellite via a GPS device to receive the exact time from a satellite.



')

Problem number 1. Time synchronization in computer systems

In the last 40 years alone, the International Earth Rotation Service added 24 seconds to UTC. For developers of high-load systems and network administrators, every decision made by the International Earth Rotation Service may become another problem. Usually, at the time of adding a second coordination, administrators perform a scheduled server reboot in order to avoid abnormal load on the processor or after losing communication with the server.

Problem number 2. Time setting in computer systems

Another problem with using UTC that a developer of multi-tier systems based on Windows architecture may encounter is that the same program on computers with the same characteristics, but in different network infrastructure can work with different performance, and the source of the problem can be not a program at all, but TCP / IP settings. Not optimally set values ​​for TcpDelAskTicks (confirmation delay time) or TcpInitialRTT (wait time) can paralyze the network, as a result, client applications simply will not receive confirmation that the packet was successfully delivered to the server and will try to send it again. The problem may be exacerbated after installing the TcpMaxDataRetransmissions parameter on the server (the maximum number of retransmissions) on a slow channel to 1 and fast on 4294967295. In this case, the default TcpDelAskTicks can play a fatal role. It seems obvious that on fast channels the timeout parameter can be reduced, as well as the confirmation delay time parameter, while the channel capacity will increase. In fact, the characteristics of the communication channel may change during the day for various reasons, including due to the “second coordination”. To adapt the timeout value, use the Timestamps option (the Tcp1323Opts parameter), which allows you to automatically set the value for the retransmission timer.

Problem number 3. Problem 2038

The most well-known problem associated with UTC is the “2038 problem”, when the UTC value in computer systems goes beyond 32-bit. It will happen on January 19, 2038 at 3 hours 14 minutes and 8 seconds. In the case of using an NTP server, you can receive notifications about the upcoming coordination second via the network and make adjustments in real time, not after. In this case, you can reset the time counter in computer systems in advance, and start counting UTCv2. Computer systems without external synchronization will have to switch to UTCv2 after the onset of coordination seconds.

Alternative Time - BMT

There is also an alternative to UTC and its associated time zone - this is Biel Mean Time (hereinafter referred to as BMT). BMT is proposed to be used as a universal measure of time on the Internet. BMT time was officially announced on October 23, 1998, and is mainly funded by the Swiss company Swatch, so on the Internet, along with BMT, you can see the abbreviation SIT, which means Swatch Internet time. BMT is also related to GMT, as well as WET to UTC, but unlike WET is precisely tied to winter time, which corresponds to UTC + 1, therefore, calculating the BMT time, you must take into account not only time zones, but also the conversion of hours to summer time and back.





BMT does not have time zones due to the introduction of a single conventional unit for time - .beats. Conventionally, 1000 .beats is equal to one average solar day. Midnight in terms of .beat will be equal to 000 , and noon 500 .beats. BMT time is always three-digit and has no time zones.

Perhaps in the future, UTCv2 will be as simple as BMT and more accurate than POSIX time.