[ntpsec commit] Add a glossary of NTP-speak.
Eric S. Raymond
esr at ntpsec.org
Mon Oct 19 17:28:05 UTC 2015
Module: ntpsec
Branch: master
Commit: 8e3df274e772cfe86b57128b4261e0b0f15ea3b2
Changeset: http://git.ntpsec.org/ntpsec/commit/?id=8e3df274e772cfe86b57128b4261e0b0f15ea3b2
Author: Eric S. Raymond <esr at thyrsus.com>
Date: Mon Oct 19 13:27:38 2015 -0400
Add a glossary of NTP-speak.
---
docs/includes/misc.txt | 1 +
docs/index.txt | 8 ++-
docs/ntpspeak.txt | 189 +++++++++++++++++++++++++++++++++++++++++++++++++
docs/pic/howland.jpg | Bin 0 -> 14570 bytes
4 files changed, 195 insertions(+), 3 deletions(-)
diff --git a/docs/includes/misc.txt b/docs/includes/misc.txt
index dd68afb..0c0dadf 100644
--- a/docs/includes/misc.txt
+++ b/docs/includes/misc.txt
@@ -1,5 +1,6 @@
== Miscellaneous Pages ==
* link:copyright.html[Copyright Notice]
+* link:ntpspeak.html[A Glossary of NTP-speak]
* link:decode.html[Event Messages and Status Words]
* link:kern.html[Kernel Model for Precision Timekeeping]
* link:msyslog.html[+{ntpd}+ System Log Messages]
diff --git a/docs/index.txt b/docs/index.txt
index 7c4d02c..b0d0750 100644
--- a/docs/index.txt
+++ b/docs/index.txt
@@ -175,9 +175,11 @@ The link:sitemap.html[Site Map] page contains a list of document
collections arranged by topic. The Program Manual Pages collection may
be the best place to start. The link:comdex.html[Command Index]
collection contains a list of all configuration file commands together
-with a short function description. A great wealth of additional
-information is available via the External Links collection, including a
-book and numerous background papers and briefing presentations.
+with a short function description. There is a
+link:ntpsleak.html[glossary of NTP-speak]. A great wealth of
+additional information is available via the External Links collection,
+including a book and numerous background papers and briefing
+presentations.
Background information on computer network time synchronization is on
the {millshome}exec.html[Executive Summary -
diff --git a/docs/ntpspeak.txt b/docs/ntpspeak.txt
new file mode 100644
index 0000000..364556c
--- /dev/null
+++ b/docs/ntpspeak.txt
@@ -0,0 +1,189 @@
+= A Glossary of NTP-speak =
+
+[cols="10%,90%",frame="none",grid="none",style="verse"]
+|==============================
+|image:pic/howland.jpg[]|
+{millshome}pictures.html[from 'Pogo', Walt Kelly]
+|==============================
+[glossary]
+
+//association::
+
+[[drift]]
+drift::
+ In an NTP context, refers to the frequency drift of a clock crystal
+ in an NTP host, expressed in a parts-per-million offset from its
+ nominal frequency. Changes, slowly, in response to environmental
+ factors (mainly ambient temperature). {ntpd} measures this by
+ sampling the clock and performing clock recovery against a
+ phase-locked loop. The drift measurement is occasionally stored
+ locally to a drift file so that when {ntpd} is stopped and restarted
+ it doesn't have to go through the entire resampling and resynchronization
+ process before providing reliable time.
+
+[[falseticker]]
+falseticker::
+ <<Mills-speak>> for a timeserver identified as not
+ reliable by statistical filtering. Usually this does not imply any
+ problem with the timeserver itself but rather with highly variable
+ and asymmetric network delays between server and client/
+
+[[fudge]]
+fudge::
+ Can have one of two senses. Either (1) an offset configured for
+ a <<refclock>> or server to correct its time, reversing a fixed or
+ nearly-fixed propagation delay, or (2) a "fudge bit" set in
+ a configuration file to change the refclock's behavior in some
+ driver-dependent way.
+
+[[fuzzball]]
+fuzzball::
+ Historical. An
+ https://www.eecis.udel.edu/~mills/database/papers/fuzz.pdf[operating
+ system] running on PDP-11s used for early time-service and Internet
+ routing experiments. Metonymously, a PDP-11 running the suite.
+ While some of these remained in service as late as 1988 they are
+ now long gone, but have left a few traces in the NTP codebase.
+
+[[GPSDO]]
+GPSDO::
+ GPS-constrained Oscillator. A very high-precision atomic clock,
+ usually a rubidium or cesium crystal oscillator, periodically
+ resynchronized to <<USNO>> time via <<PPS>>. The most accurate time
+ source generally available; the only better ones are the
+ custom-built atomic clocks maintained by national time authorities.
+ Only cost-effective for time service when intrinsic variability in
+ network delays is well under GPSDO accuracy; thus, unsuitable for
+ use on a WAN, for which plain GPSes with <<PPS>> are cheaper and
+ generally good enough.
+
+[[GPSD]]
+GPSD::
+ The http://www.catb.org/gpsd/[GPS Daemon], an open-source device
+ manager for GPSes and other geodetic sensors. Frequently used as
+ a clock source by Stratum 1 sites via the SHM
+ link:driver28.html[(Type 28)] interface.
+
+[[leapfile]]
+leapfile::
+ A local file containing the current leap-second offset, typically
+ fetched from <<USNO>> or <<NIST>> and potentially needing updates
+ near the very beginning or end of each quarter. Normally retrieved
+ by a cron(1) job, but some varieties of <<refclock>> (notably
+ GPses) update it themselves suring normal operation.
+
+[[Mills-speak]]
+Mills-speak::
+ Dr. David Mills, the original architect of NTP and its standards,
+ wrote in a vivid and idiosyncratic style which is still preserved in
+ much of NTP's documentation. He coined many neologisms which
+ connoisseurs refer to as "Mills-speak"; examples in this glossary
+ include <<falseticker>>, <<proventic>>, and <<truechimer>>.
+
+[[NIST]]
+NIST::
+ http://www.nist.gov/[National Institute of Standards and
+ Technology]. The civilian national time authority of the USA;
+ runs <<WWVB>>. Responsible for keeping U.S. civil time
+ coordinated with international UTC time. NIST time tracks <<USNO>>
+ time to within a few nanoseconds.
+
+[[NTP-classic]]
+NTP Classic::
+ The original reference implementation of NTP by Dave Mills, later
+ maintained by the Network Time Foundation. NTPsec forked from it
+ on June 6th, 2015.
+
+[[nonce]]
+nonce::
+ An arbitrary number that may only be used once. a random or
+ pseudo-random number issued in an authentication protocol (such as
+ NTP's) to ensure that old communications cannot be reused in replay
+ attacks.
+
+[[parse-driver]]
+parse driver::
+ A refclock link:driver8.html[(type 8)] which, uniquely, handles
+ multiple <<time radio>> protocols - two dozen mostly European
+ precision time radios mostly using DCF, the broadcast time from the
+ German national authority. Each clock type is internally represented
+ as a few parse methods and table entries in a table-driven parser.
+
+[[PPS]]
+PPS::
+ (Also as "1PPS") Pulse Per Second. A top-of-second pulse emitted
+ over RS232 handshake lines by some GPSes that, along with in-band
+ time delivered to 1-second accuracy, represents U.S. military time
+ (a very close approximation of UTC) to 50-nanosecond accuracy.
+ Nowadays the single most important time reference for most NTP
+ servers en outside the U.S.A.
+
+[[proventic]]
+proventic::
+ <<Mills-speak>> for "the transitive completion of the
+ authentication relstionship", defined in RFC5906. Time is proventic
+ if it is provided by a chain of time servers between which packets
+ are authenticated and the chain reaches back to Stratum 1.
+
+[[refclock]]
+refclock::
+ Shorthand for a "reference clock", a primary time source. A computer
+ with a refclock is implicitly Stratum 1.
+
+[[SADA]]
+SADA::
+ Sun Audio Driver API, a software interface to audio devices
+ directly supported by NTP and used by the Irig Audio Decoder (type
+ 6) and IRIG (type 7) refclocks. Originating in SunOS, it was later
+ implemented in Solaris and OpenSolaris, supported in the Linux OSS
+ sound layer, and is still used by the *BSD family of open-source
+ operating systems.
+
+[[stratum]]
+stratum::
+ A "stratum" is a layer in the hieratchy of time servers. a
+ <<refclock>> is considered stratum 0; a computer directly attached to
+ a refclock is stratum 1; and a client served by a stratum N is
+ stratum N+1. Often capitalized, especially when referring to all
+ members of a stratum. While strata up to 15 are defined, it is
+ unusual to see a public timeserver with stratum > 3, and thus
+ almost all NTP clients are at Stratum 4 or lower.
+
+[[time-radio]]
+time radio::
+ A radio receiver specialized for picking up accurate time reference
+ signals broadcast over the air by a national time authority; notable
+ ones include <<WWVB>> (U.S.), CHU (Canada), DCF (Germany), and MSF
+ (United Kingdom). Usable as a Stratum 1 time source; may be
+ qualified by "precision time radio" to distinguish from
+ consumer-grade "atomic clocks", which are time radios that normally
+ take radio synchronization just once a day and are _not_ accurate
+ enough to be used for Stratum 1. Precision time radios used to be
+ important time sources, but (especially in the U.S.) have been
+ largely obsolesced by GPS and <<GPSDO>>-based clocks.
+
+[[truechimer]]
+truechimer::
+ <<Mills-speak>> for a timeserver that provides time believed good,
+ that is with low jitter with respect to UTC. As with a
+ link#falseticker[falseticker], this is usually less a property of
+ the server itself than it is of favorable network topology.
+
+[[USNO]]
+USNO::
+ http://www.usno.navy.mil/USNO[The United States Naval Observatory],
+ one of tthe two U.S. national time authorities and the source of the
+ U.S. military time reference, now delivered primarily by GPS
+ signals. U.S. civil and military time agree to within nanoseconds.
+
+[[WWVB]]
+WWVB::
+ The U.S. national time radio station, run by <<NIST>> and
+ broadcasting a highly accurate U.S. civil-time reference. Formerly
+ an important primary time source, until NIST changed its modulation
+ in 2013 and obsolesced all then-existing U.S. precision time radios. No
+ WWVB-compatible precision time radios have been manufactured since,
+ though consumer-grade "atomic clocks" unaffected by the modulation
+ change are still made.
+
+// end
diff --git a/docs/pic/howland.jpg b/docs/pic/howland.jpg
new file mode 100644
index 0000000..017ff93
Binary files /dev/null and b/docs/pic/howland.jpg differ
More information about the vc
mailing list