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service
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The service environment consists of the implementation model and service
model described in Section 2. The implementation model is based on a
multiple-process operating system ...
...
The service environment consists of the implementation model and service
model described in Section 2. The implementation model is based on a
multiple-process operating system architecture ...
... architecture, although other
architectures could be used as well. The service model is based on a
returnable-time design which depends only on measured clock offsets, but
does not require reliable message delivery ...
... algorithms. Appendix H analyzes the sources and propagation of errors
and presents correctness principles relating to the time-transfer
service. Appendix I illustrates C-language code segments for the clock-
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... The Digital Time Service (DTS) [DEC89] has many of the same service
objectives as NTP. The DTS design places heavy emphasis on configuration
...
... cluster environment, while NTP places heavy emphasis on the accuracy
and stability of the service operated in an unmanaged, global-internet
environment. In DTS a synchronization subnet ...
... facilities are provided or necessary.
Duplicate detection is inherent in the processing algorithms. The
service can operate in a symmetric mode, in which servers and clients
are indistinguishable, yet maintain a small amount of state ...
... synchronization, possibly via other secondary servers, from a primary
server over network paths possibly shared with other services. Under
normal circumstances it is intended that the synchronization subnet ...
... synchronization subnet. Reliable
time service can usually be maintained with two peers at the next lower
stratum level and one peer at the same stratum level, so the rate of
ongoing polls is usually not significant, even when connectivity is lost
...
... -unavailable error message if a
service is not implemented or resources are not available; however, in
the case of NTP the resources required are minimal, so there is little
...
... Digital Time Service Functional Specification Version T.1.0.5. DigitalEquipment Corporation, 1989. ...
... Time and Frequency Dissemination Services. NBS Special Publication 432,U.S. Department of Commerce, 1979. ...
... Originate Timestamp: This is the local time at which the request
departed the client host for the service host, in 64-bit timestamp
format ...
...
Receive Timestamp: This is the local time at which the request arrived
at the service host, in 64-bit timestamp format ...
...
Transmit Timestamp: This is the local time at which the reply departed
the service host for the client host, in 64-bit ...
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There are two ways a reference clock can be attached to a NTP service
host, as an dedicated device managed by the operating system and as a
...
... algorithms, and another [MIL90] describing
the service model, algorithmic analysis and operating experience. In
previous versions these two objectives were combined in one document.
...
... the first of the two sorting/discarding steps and replace with an
algorithm first proposed by Marzullo and later incorporated in the
Digital Time Service. These changes do not significantly affect the
ordinary operation of or compatibility with various versions ...
... and through occasional use of portable atomic clocks. Most
seafaring nations of the world operate some sort of broadcast time
service for the purpose of calibrating chronographs, which are used in
conjunction with ephemeris data to determine navigational position. In
many countries the ...
... for the purpose of calibrating chronographs, which are used in
conjunction with ephemeris data to determine navigational position. In
many countries the service is primitive and limited to seconds-pips
broadcast by marine communication stations at certain hours. For
instance, a chronograph error of one second represents a longitudinal
...
... National Institute of Standards and Technology (NIST - formerly
National Bureau of Standards) operates three radio services for the
dissemination of primary time and frequency information. One of these
uses high-frequency (HF or CCIR band 7) transmissions on frequencies of
...
... BLA74]. Some countries
in western Europe operate similar services which use transmissions on 60
kHz from Rugby, U.K. (MSF), and on 77.5 kHz from Mainflingen, West
...
...
The third service operated by NIST uses ultra-high frequency (UHF or
CCIR band 9) transmissions on about 468 MHz from the Geosynchronous
...
... coordinates within a degree and UTC time within five seconds from an
external source before operation begins. There are several other VLF
services intended primarily for worldwide data communications with
characteristics similar to OMEGA. These services can be used in a manner
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... external source before operation begins. There are several other VLF
services intended primarily for worldwide data communications with
characteristics similar to OMEGA. These services can be used in a manner
similar to OMEGA, but this requires specialized techniques not suited
for unattended, automatic operation.
...
... Note that not all transmission formats used by NIST radio broadcast
services [NBS79] and no currently available radio clocks include
provisions for year information and leap-second warning. This
...
... variable f bounded by the interval <$E[-~phi ,~phi ]>, where <$Ephi>
represents the maximum frequency tolerance of the oscillator throughout
its service life. While f for a particular clock is a random variable
with respect to the population of all clocks, for any one clock it
ordinarily changes only slowly with time and can usually be assumed a
...
... In order to minimize the occurrence of errors due to incorrect clocks
and maximize the reliability of the service, NTP relies on multiple
peers and disjoint peer paths whenever possible. In the previous
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The algorithm proposed by DEC for use in the Digital Time Service
[DEC89] is based on these principles. For the scenario illustrated in
...