[ntpsec commit] New glossary entries.

[Eric S. Raymond]

Module:    ntpsec
Branch:    master
Commit:    6c6f0f1d2b2a70a9ecc4171dd6aef0d966b07621
Changeset: http://git.ntpsec.org/ntpsec/commit/?id=6c6f0f1d2b2a70a9ecc4171dd6aef0d966b07621

Author:    Eric S. Raymond <esr at thyrsus.com>
Date:      Wed Oct 21 06:47:51 2015 -0400

New glossary entries.

---

 docs/ntpspeak.txt | 63 +++++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 52 insertions(+), 11 deletions(-)

diff --git a/docs/ntpspeak.txt b/docs/ntpspeak.txt
index d4ee8c7..d80ca76 100644
--- a/docs/ntpspeak.txt
+++ b/docs/ntpspeak.txt
@@ -7,6 +7,16 @@
 |==============================
 [glossary]
 
+[[ACTS]]
+ACTS::
+  http://www.nist.gov/pml/div688/grp40/acts.cfm[NIST Automated
+  Computer Time Service]. NIST provides a civil time reference for
+  computers equipped with analog modems that can dial to its phone
+  lines.  Due to variability of delays in the analog phone network
+  accuracy is not very good, around 4 milliseconds compared to
+  around a microsecond for <<PPS>>. But the service is still
+  occasionally used as a backup to more precise sources.
+
 [[association]]
 association::
   An association is the relationship that an NTP client and server have
@@ -23,7 +33,7 @@ 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
+  factors (mainly ambient temperature). {ntpd} measures drift 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
@@ -35,7 +45,7 @@ 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/
+  and asymmetric network delays between server and client.
 
 [[fudge]]
 fudge::
@@ -54,6 +64,14 @@ fuzzball::
    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.
 
+[[GPS]]::
+   Global Positioning System; also, "a GPS" is a radio receiver
+   designed to get position and time fixes from the system. GPS fixes
+   are derived from spherical trigonometry using the precisely known
+   positions of satellities in a geocentric coordinate system. GPS
+   also provides time service; those that emit <<PPS>> are suitable
+   as clock sources for Stratum 1 timeservers.
+
 [[GPSDO]]
 GPSDO::
    GPS-constrained Oscillator. A very high-precision atomic clock,
@@ -73,6 +91,14 @@ GPSD::
    a clock source by Stratum 1 sites via the SHM
    link:driver28.html[(Type 28)] interface.
 
+[[holdover]]
+holdover::
+   In connection with a <<GPSD0>> or <<time radio>> that may lose
+   signal from its time source, holdover is its ability to continue
+   delivering accurate time from an internal oscillator. Due to
+   <<drift>> in the oscillator, accuracy drops as holdover time (time
+   since last signal lock) increases.
+
 [[leapfile]]
 leapfile::
    A local file containing the current leap-second offset, typically
@@ -125,7 +151,22 @@ PPS::
   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.
+  servers even outside the U.S.A.
+
+[[PTP]]
+PTP::
+  https://en.wikipedia.org/wiki/Precision_Time_Protocol[Precision Time
+  Protocol], which does for hosts on a local area network what NTP
+  does on the general Internet. By taking advantage of the (usually)
+  more controlled conditions of a LAN, it is capable of much higher
+  sustained accuracy than NTP, into the sub-microsecond range.
+
+[[pool]]
+pool::
+   In an NTP context, "the pool" is usually the
+   http://www.pool.ntp.org/en/[NTP Pool Project], a collection of
+   thousands of NTP servers accessible through hub servers that hand
+   out service addresses at random from the pool.
 
 [[proventic]]
 proventic::
@@ -162,14 +203,14 @@ stratum::
 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.
+  ones include <<WWVB>> (U.S.), CHU (Canada), DCF (Germany), MSF
+  (United Kingdom), and JJY (Japan).  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::