Information about Time Transfer
Time transfer describes methods for transferring reference clock synchronization from one point to another, often over long distances. Radio-based navigation systems are frequently used as time transfer systems.
In some cases, multiple measurements are made over a period of time, and exact time synchronization only determined retrospectively.
In particular, time synchronization has been accomplished by using pairs of radio telescopes to listen to a pulsar, with the time transfer accomplished by comparing time offsets of the received pulsar signal.
In a one-way time transfer system, one end transmits its current time over some communication channel to one or more receivers.[1] The receivers will, at reception, decode the message, and either just report the time, or adjust a local clock which can provide hold-over time reports in between the reception of messages. The advantage of one-way systems is that they can be technically simple and serve many receivers, as the transmitter is unaware of the receivers. A drawback of the system is that propagation delays of the communication channel remain uncompensated except in some advanced systems. Examples of a one-way time transfer system are the clock on a church or town building and the ringing of their time-indication bells; Radio clock signals such as LORAN, DCF77 and MSF; and finally the Global Positioning System which uses multiple one-way time transfers from different satellites, with positional information and other advanced means of delay compensations to allow receiver compensation of time and position information in real time.
In a two-way time transfer system, the two peers will both transmit, and will also receive each others messages, thus performing two one-way time transfer measurements where the difference of the remote clock compared to the local clock is being noted.[2] The sum of these time differences will become the sum of the delay between the two nodes. It is often assumed that this delay is evenly distributed between the directions between the peers. Under this assumption, the difference between the measured delays divided by two will provide the time difference between the clocks without being affected by propagation delay. The advantage of the two-way time transfer system is that propagation delays gets compensated, but the drawback is that there needs to be means for bi-directional communication (of preferably symmetrical propagation delay) between the directions. Another drawback is that the source of reference needs to be actively measuring slaves, which can become a scale issue. The Two-Way Satellite Time and Frequency Transfer (TWSTFT) system being used in comparison among some time laboratories uses a satellite for a common link between the laboratories. The Network Time Protocol uses packet based messages over an IP network.
In some cases, multiple measurements are made over a period of time, and exact time synchronization only determined retrospectively.
In particular, time synchronization has been accomplished by using pairs of radio telescopes to listen to a pulsar, with the time transfer accomplished by comparing time offsets of the received pulsar signal.
In a one-way time transfer system, one end transmits its current time over some communication channel to one or more receivers.[1] The receivers will, at reception, decode the message, and either just report the time, or adjust a local clock which can provide hold-over time reports in between the reception of messages. The advantage of one-way systems is that they can be technically simple and serve many receivers, as the transmitter is unaware of the receivers. A drawback of the system is that propagation delays of the communication channel remain uncompensated except in some advanced systems. Examples of a one-way time transfer system are the clock on a church or town building and the ringing of their time-indication bells; Radio clock signals such as LORAN, DCF77 and MSF; and finally the Global Positioning System which uses multiple one-way time transfers from different satellites, with positional information and other advanced means of delay compensations to allow receiver compensation of time and position information in real time.
In a two-way time transfer system, the two peers will both transmit, and will also receive each others messages, thus performing two one-way time transfer measurements where the difference of the remote clock compared to the local clock is being noted.[2] The sum of these time differences will become the sum of the delay between the two nodes. It is often assumed that this delay is evenly distributed between the directions between the peers. Under this assumption, the difference between the measured delays divided by two will provide the time difference between the clocks without being affected by propagation delay. The advantage of the two-way time transfer system is that propagation delays gets compensated, but the drawback is that there needs to be means for bi-directional communication (of preferably symmetrical propagation delay) between the directions. Another drawback is that the source of reference needs to be actively measuring slaves, which can become a scale issue. The Two-Way Satellite Time and Frequency Transfer (TWSTFT) system being used in comparison among some time laboratories uses a satellite for a common link between the laboratories. The Network Time Protocol uses packet based messages over an IP network.
See also
- Global Positioning System
- LORAN
- Radio clock
- radio-controlled watch
- Atomic clocks
- International Earth Rotation and Reference Systems Service
- Network Time Protocol
- Two-Way Satellite Time and Frequency Transfer
- Time signal
References
1. ^ Jones, T (2000). Splitting the second. Institute of Physical Publishing, 116.
2. ^ Jones, T (2000). Splitting the second. Institute of Physical Publishing, 118.
2. ^ Jones, T (2000). Splitting the second. Institute of Physical Publishing, 118.
Synchronization (or Sync) is a problem in timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time.
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radio telescope is a form of directional radio antenna used in radio astronomy and in tracking and collecting data from satellites and space probes. In their astronomical role they differ from optical telescopes in that they operate in the radio frequency portion of the
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Pulsars are highly magnetized rotating neutron stars which emit a beam of detectable electromagnetic radiation in the form of radio waves. Their periods range from 1.5 ms to 8.5 s[1].
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A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time
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Loran can refer to one of the following:
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- LORAN, the terrestrial radio-based navigation system.
- Loran (cassette), a brand of blank audio cassette made out of Lexan plastic.
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DCF77 is a longwave time signal and standard-frequency radio station. Its primary and backup transmitter are located in Mainflingen, about 25 km south-east of Frankfurt, Germany.
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MSF may refer to:
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- National Physical Laboratory (MSF) time signal
- Mail Summary File(.msf), file extension used by Earthlink, Mozilla Thunderbird, and Netscape mail clients.
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Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its
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Two-Way Satellite Time and Frequency Transfer (TWSTFT) is a high-precision long distance time and frequency transfer mechanism used between time bureaux to determine and distribute time and frequency standards.
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The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP port 123 as its transport layer. It is designed particularly to resist the effects of variable latency (jitter).
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Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its
..... Click the link for more information.
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Loran can refer to one of the following:
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- LORAN, the terrestrial radio-based navigation system.
- Loran (cassette), a brand of blank audio cassette made out of Lexan plastic.
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A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time
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Atomic Clock is a type of clock that uses an atomic resonance frequency standard to feed its counter. Early atomic clocks were masers with attached equipment. Today's best atomic frequency standards (or clocks) are based on absorption spectroscopy of cold atoms in atomic fountains.
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International Earth Rotation and Reference Systems Service is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Parameter (EOP) and International Celestial Reference System (ICRS) groups.
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The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP port 123 as its transport layer. It is designed particularly to resist the effects of variable latency (jitter).
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Two-Way Satellite Time and Frequency Transfer (TWSTFT) is a high-precision long distance time and frequency transfer mechanism used between time bureaux to determine and distribute time and frequency standards.
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A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.
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Audible and visible time signals
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