Internet
Click on the red underlined text to get to the source
... 24], but has evolved in significant ways
since publication of that document. NTP is built on the Internet
Protocol (IP) [10] and User Datagram Protocol ...
... 11], but is
specifically designed to maintain accuracy and robustness, even when
used over typical Internet paths involving multiple gateways and
unreliable nets.
...
... NTP packet formats are shown in Appendices A and B.
Appendix C presents the results of a survey of about 5500 Internet
hosts showing how their clocks compare with primary reference sources
using three different time protocols, including NTP ...
...
Other mechanisms have been specified in the Internet protocol suite
to record and transmit the time at which an event takes place,
including the Daytime protocol ...
... 9]. Experimental
results on measured times and roundtrip delays in the Internet are
discussed in [14], [23 ...
... strongly influenced the design of NTP, Hellospeak itself is not an
Internet protocol and is unsuited for use outside its local-net
environment.
...
... process requires a broadcast capability, which is not a ubiquitous
feature of the Internet. While this model has been extended to
support hierarchical configurations in which a slave on one network
...
... algorithms require large numbers of messages,
especially when large numbers of clocks are involved, and are
designed to detect faults that have rarely been found in the Internet
experience. For these reasons they are not considered further in
this document.
...
... In practice it is not possible to determine the truechimers from the
falsetickers on other than a statistical basis, especially with
hierarchical configurations and a statistically noisy Internet.
Thus, the approach taken in this document and its predecessors
involves mutually coupled oscillators and maximum-likelihood
...
... polling, filtering and selection functions which tailor the dynamics
of the system to fit the ubiquitous Internet environment.
...
...
Following is a list of parameters assumed for all implementations
operating in the Internet system. It is necessary to agree on the
values for these parameters in order to avoid unnecessary network
...
...
This is the minimum polling interval allowed by any peer of the
Internet system, currently set to 6 (64 seconds).
Maximum Polling Interval (NTP ...
...
This is the maximum polling interval allowed by any peer of the
Internet system, currently set to 10 (1024 seconds).
Maximum Dispersion (NTP ...
... host maintains a table with as many entries as active peers. Each
entry includes a code uniquely identifying the peer (e.g., Internet
address and port), together with status information and a copy of the
timestamps ...
... the NTP message is returned by the recipient unaltered, as when
testing with an Internet-echo server, this convention still allows at
least the roundtrip time to be accurately determined without special
...
...
If the above is not the case, the source and destination Internet
addresses and ports in the IP and UDP ...
... algorithm is not an integral part of the NTP
specification; however, one found to work well in the Internet
environment is described in Section 4.
When a primary clock is connected to the host ...
... NTP specification. A clock
selection algorithm found to work well in the Internet environment is
described in Section 4, while a logical clock procedure is described
in Section 5. The clock selection algorithm ...
... algorithms suggested in this section were developed and refined over
several years of operation in the Internet under widely varying net
configurations and utilizations. While these algorithms are believed
...
... host, which means its reference clock
identifier (peer.refid) must not match the Internet address of
this host. This is analogous to the split-horizon rule used in
...
... As NTP service matures in the Internet, the resulting network traffic
can become burdensome, especially in the primary service ...
... synchronization mechanism itself.
Considerable experience with the Internet environment suggests the
values of CLOCK.MAX tabulated in Table 5.1 as appropriate. In
practice, these values are exceeded with a single time-server source
...
... Defense Advanced Research Projects Agency, "Internet Protocol", RFC-791std5, USC/Information Sciences Institute, September 1981. ...
... Defense Advanced Research Projects Agency, "Internet Control Message Protocol", RFC-792std5, USC/Information Sciences Institute, September 1981. ...
... In the case of type 2 and greater (secondary reference), this
is the 32-bit Internet address of the reference host.
...
... Following publication of RFC-956 and after further development and
experimentation using typical Internet paths, a better algorithm was
found for casting out outlyers from a continuous stream ...
... hop counts continue to increase, the points should begin to fill in
the wedge as it expands even further rightward. This behavior is in
fact what is observed on typical Internet paths involving ARPANET,
NSFNET ...
... ubiquitous NTP service in the Internet system. Section E.1 describes
the NTP primary service ...
... gateway services as
well. Table E.1 shows the name, Internet address, type of clock,
operating institution and identifying code.
...