drivers.txt

= NTPD driver retention analysis =
Eric S. Raymond <esr@thyrsus.com>
Version 1.4, 2015-06-30

== Summary ==

ntpd contains support for 42 driver types.  Of these: 2 are IPC drivers
which must be retained; 10 are for hardware that might, under very
generous assumptions, still be of use; and 30 can be discarded.

Out of that 10, the actual utility of some remains dubious, but the
cultural/political context of the project probably requires that we
retain them.  I discuss related issues in a concluding section.

== Technological context ==

NTP's driver inventory contains several different classes of precision
time sources.  The software is now around 40 years old, and some of
those classes are now obsolescent or semi-obsolescent.

See http://www.catb.org/gpsd/time-service-intro.html["Introduction to
Time Service"] for terminology, device classes, and accuracy.  The
summary version is that inexpensive 1PPS-capable GPS devices have a
nearly overwhelming cost-effectivenee advantage over older time source
types, and the utility of supporting those older types is accordingly
plummeting.

I think it is actually seriously questionable whether support for
*any* of these legacy devices is worth maintaining.  No hardware
drivers have been added since 2006, and possibly none since 2002.
NIST's modulation change in 2013 laid waste to the U.S. time-radio
industry. It may actually be the case that *all* the Stratum 1 sites
running non-custom ntpd instances are using GPSes now.

However, political reality - especially for a federally-funded project
with customers in a lot of .gov and .mil shops running very old iron -
does not necessarily allow the best technical move, which would be to
drop all the drivers, see who screams, and reinstate the fewest we
can.  I will return to this issue.

== Objectives and criteria ==

Two of our main objectives in the ntpd rescue are (1) to eliminate security
vulnerabilities and (2) move the code to a maintainable state.  An
effective way of accomplishing both would be to outright remove as
much code as possible from ntpd.

ntpd includes no fewer than 46 device drivers for local clock sources.
Some effective means of removing code would be to remove drivers which
are obsolescent by the following criteria:

INTRINSIC::
	Remove hardware that can no longer work for intrinsic technical reasons.

DEPRECATED::
	Remove deprecated drivers - that is, drivers which the ntpd
	documentation itself declares obsolete or no longer documents.

DISCONTINUED::
	Remove drivers for products that have been discontinued for
	more than seven years. (In the first version of this report
	the proposal was ten years.  Please see the final section
	on policy and conclusions.)

UNAVAILABLE::
	Remove drivers for products which cannot be found for sale
	with a web search. (I have noted when remaindered units are
	available on e-Bay and second-hand sites.)

REDUNDANT::
	Remove drivers that duplicate capabilities better provided by
	GPSD (or, in principle, other sensor managers).

INACCURATE::
	Remove GPS drivers and time radios for which the hardware offers no
	better source accuracy than a timing GPS available for less than
	$75 in 2015; that is, about 5&micro;s.  (However, do not necessarily
	remove poorer-performing GPS-conditioned *clocks*, as they continue
	to supply time in holdover mode when the GPS cannot get satellite lock.)

We should certainly keep drivers such as SHM and GPSD-NG that are IPC
methods for peer time-source programs in ntpd itself.

== First-round triage ==

The following lists the drivers in ntpd4, categorizes them, and
recommends a disposition for each. It's based on the master list
from the NTP Classic documentation.

Types 15, 23, 24, and 25 are not listed because they are reserved and
not in use.

=== Type 1: Undisciplined Local Clock ===

This driver type is described as deprecated.  It is in any case
obsolete anywhere with a sky view, where a GPS will do a better job.

Disposition: Fails tests DEPRECATED and INACCURATE; Remove.

=== Type 2:   Trak 8820 GPS Receiver

This driver still existed only as one mention in the ntp4
documentation.  There is no refclock implementation for it.

Web searches reach one copy of the technical manual dating from 1994
and preserved here:

http://www.to-way.com/tf/trak8820a.pdf

All other references are to copies of old ntpd documentation. I
conclude that this hardware is extremely obsolete and
discontinued well before before 2000.

Disposition: Fails tests DEPRECATED, DISCONTINUED, UNAVAILABLE; Remove.

=== Type 3: PSTI/Traconex 1020 WWV/WWVH Receiver (WWV_PST) ===

This device is described http://prc68.com/I/PST1020.shtml[here] with a
2005 note that it is "not very reliable" having drifted by a full minute.

Investigating the vendor site at U.S. Traffic Corp (now Peek Traffic)
reveals that this device was discontinued, probably before 2000.

According to this August 2001 post

https://groups.google.com/forum/#!topic/comp.protocols.time.ntp/0jOItglBTLE

the device required manual intervention every year and was not
designed for use after 2001.  Dave Mills replied to that one in a way
that implies he still has two of these and there is a workaround to
the problem described, but also says they have a service life of only
a few years due to a failure-prone component.

I could not find any for sale on the Web.  This hardware
would no longer work even if a specimen could be found, due to WWVB's
modulation change as described in the next entry.

Disposition: Fails tests INTRINSIC, DISCONTINUED, UNAVAILABLE, and 
INACCURATE; Remove.

=== Type 4: Spectracom WWVB/GPS Receivers (WWVB_SPEC) ===

Since WWVB changed its modulation scheme in January 2013
Spectracom WWVB receivers from before that date no longer function.
The models covered by this driver (Model 8170, Netclock/2 WWVB) are in
this category.  Spectracom has not produced any new time-radio gear
since the modulation change.

However, the Spectracom 9300 (still in production and support)
is a GPS clock that can emit the type 0 and 2 formats recognized
by this driver.

Disposition: Move to refclockd.

=== Type 5: TrueTime GPS/GOES/OMEGA Receivers (TRUETIME) ==

True Time was a product line of timer sources. The most recent manual
I can find is from 1997:

www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA324042

The devices can be found for sale, but only on e-Bay and electronics
remainder sites.  The vendor seems to be long gone.

Disposition: DISCONTINUED; Remove.

=== Type 6: IRIG Audio Decoder (IRIG_AUDIO) ===

This driver is a very, very bad idea given flesh. It demodulates an
*audio signal* emitted by several radio time sources, requiring custom
wiring to connect to a microphone or line-in port.  All for
accuracy two orders of magnitude worse (500&micro;s) than a cheap 1PPS GPS
and no holdover capability.

Disposition: INACCURATE; Remove.

=== Type 7: Radio CHU Audio Demodulator/Decoder (CHU) ===

A very bad idea similarly wired to Type 6, using a Canadian analog 
of WWVB.  Cited as 1ms accuracy without GPS calibration.

Disposition: INACCURATE; Remove.

=== Type 8: Generic Reference Driver (PARSE) ===

This is a driver supporting a large variety of time radios, some of
which (such as the Meinberg line) are still generally available.

Disposition: Move to refclockd.

=== Type 9: Magnavox MX4200 GPS Receiver (GPS_MX4200) ===

A line of GPSes produced by Magnavox, discontinued in 1994, with 
the surplus stock marketed by Leica Geosystems.  Leica no longer
sells them.  They shipped 1PPS.  I could find none available for sale.

Disposition: DISCONTINUED, UNAVAILABLE; Remove.

=== Type 10: Austron 2200A/2201A GPS Receivers (GPS_AS2201) ===

An obsolete line of 1PPS GPS receivers.  Austron was acquired some
time before 1996 and the product line apparently discontinued then.
A few units were still in hobbyist use in 2006, but there don't
seem to be more recent references even on the time-nuts list.
I could find none available for sale.

Disposition: Fails tests DISCONTINUED, UNAVAILABLE; Remove.

=== Type 11: Arbiter 1088A/B GPS Receiver (GPS_ARBITER) ===

Arbiter systems is still alive at http://www.arbiter.com/

With 100ns worst-case accuracy relative to 1PPS this is still a viable
time source.

Disposition: Move to refclockd.

=== Type 12: KSI/Odetics TPRO/S IRIG Interface (IRIG_TPRO) ===

An obsolete clock source that connected directly to the SBus of a Sun
workstation. SBus was replaced rapidly by PCI after 1997; no hardware
based on SBus has been shipped for at least a decade and the last
of these were probably shipped before the year 2000. I could find
none of them for sale.

Disposition: DISCONTINUED, UNAVAILABLE; Remove.

=== Type 13: Leitch CSD 5300 Master Clock Controller (ATOM_LEITCH) ===

Documentation has been removed from the ntpd4 webpages.

A clock source that synchronized with the U.S. national time authority
via modem.  Leitch was acquired by Harris Broadcasting in 2005.

Propagation jitter in the POTS network dooms any chance this could
even match the performance of a cheap serial GPS. Remnant units are
available on eBay and electronics remainder sites.

Disposition: DEPRECATED, DISCONTINUED, and INACCURATE; already removed.

=== Type 14: EES M201 MSF Receiver (MSF_EES) ===

Documentation for this driver has been removed from the ntpd4 webpages.

All the references to it I can find on the Web point back
to old NTP documentation. I conclude that it is obsolete.

Disposition: Fails test DEPRECATED and DISCONTINUED; already removed.

=== Type 16: Bancomm GPS/IRIG Receiver (GPS_BANCOMM) ===

A discontinued VME board for Sun 4 systems.  The last VME-based 
Sun 4 issued in 1989 to be replaced by SBus systems also now
obsolete.

Disposition: DISCONTINUED; Remove.

=== Type 17: Datum Precision Time System (GPS_DATUM) ===

Documentation has been removed from the ntpd4 webpages.  There used to
be a company called Datum that sold clock sources, but it has left no
traces on the Web and I can find no evidence of surviving hardware.

Disposition: DEPRECATED, DISCONTINUED, UNAVAILABLE; already removed.

=== Type 18: NIST/USNO/PTB Modem Time Services (ACTS_MODEM) ===

The USNO timer service still nominally exists, but requires a
Hayes-compatible 1200bps modem, hardware now 20 years obsolete:

http://tycho.usno.navy.mil/modem_time.html

It claims 4ms jitter (before propagation delays in the POTS network).
Retain because it might be useful in holdover mode.

Disposition: Move to refclockd.

=== Type 19: Heath WWV/WWVH Receiver (WWV_HEATH) ===

Pre-1992 time-radio receiver, cited as worse than 100ms accuracy.
Undated web pages suggest that a few may survive in hobbyist use.

Disposition: DISCONTINUED, UNAVAILABLE, INACCURATE; Remove.

=== Type 20: Generic NMEA GPS Receiver (NMEA) ===

GPSD does this better.

Disposition: REDUNDANT; Remove

=== Type 21: TrueTime GPS-VME Interface (GPS_VME) ===

VME-bus time source for Sun workstations, long dead, documentation
removed.

Disposition: INTRINSIC, DEPRECATED, DISCONTINUED; already removed.

=== Type 22: PPS Clock Discipline (PPS) ===

I had this marked for retention in the 1.0 version of this document;
it could still have been potentially useful in some very odd
situations - the documentation mentions "the vicinity of Mars".

However, Hal Murray reports that the PPS support in ntpd is "kludgy"
and needs to be fixed.  That says to me that this driver is too
broken to be worth saving.

Disposition: INTRINSIC; Remove

=== Type 26: Hewlett Packard 58503A GPS Receiver (GPS_HP) ===

Support for two discontinued HP time sources, not updated since 2005.
Used units can be found on the Web.  Accuracy cited as better than 1&micro;s
when GPS-locked, drift of better than 10ms in holdover mode. Some
are available on eBay.

I had this marked for removal in the 1.0 version of this document,
but Hal Murray - who is credible when he says such things - reports
that (a) these were heavily used in cell towers before being 
discontinued, so surplus units are easy to find, and (b) they're
widely used in the time-hacker community.

Disposition: DISCONTINUED; move to refclockd.

=== Type 27: Arcron MSF Receiver (MSF_ARCRON) ===

Obsolete time source, noted in 2003 posting

http://comp.protocols.time.ntp.narkive.com/0sT20Wjc/trimble-s-acutime-2000-compared-to-arcron-msf

to be "not very good" and inferior to a common Trimble GPS.  The
vendor is gone.  Web searches do not find units for sale.

Disposition: DISCONTINUED, UNAVAILABLE, INACCURATE; Remove.

=== Type 28: Shared Memory Driver (SHM) ===

IPC driver, to be retained.

=== Type 29: Trimble Navigation Palisade GPS (GPS_PALISADE) ===

GPSD does this better.

Disposition: REDUNDANT; Remove.

=== Type 30: Motorola UT Oncore GPS GPS_ONCORE) ===

GPSD does this better.

Disposition: REDUNDANT; Remove.

=== Type 31: Rockwell Jupiter GPS (GPS_JUPITER) ===

GPSD does this better.

Disposition: REDUNDANT; Remove.

=== Type 32: Chrono-log K-series WWVB receiver (CHRONOLOG) ===

Discontinued WWVB receiver described as "very old" in 2010.  Vendor
still exists but is now making blood-platelet counters rather than
clocks. Only 1 second accuracy.  Wouldn't work following the WWVB
modulation change, anyway.

Disposition: INTRINSIC, DISCONTINUED, UNAVAILABLE, INACCURATE; Remove.

=== Type 33: Dumb Clock (DUMBCLOCK) ===

I can find no evidence that non-GPS ASCII clocks of this kind still
exist. It is not clear to me that they *ever* existed except as custom
hobbyist rigs!  Precision 2000 times worse than a cheap serial GPS.

Disposition: INACCURATE; Remove.

=== Type 34: Ultralink WWVB Receivers (ULINK) ===

A discontinued time radio.  Most recent references on the
Web are from 2008; still on sale in 2004.  This posting

http://fixunix.com/ntp/337036-ultralink-325-wwvb-receiver.html

notes that accuracy is bad compared to a GPS.  Would no
longer work due to the WWVB modulation change.

Disposition: INTRINSIC, DISCONTINUED and INACCURATE; Remove.

=== Type 35: Conrad Parallel Port Radio Clock (PCF) ===

Obsolete port type, obsolete clock.  The vendor is still in business
but this product has been discontinued.  All web references I found,
except one 404, are pointers to ntpd documentation from before 2010.

Disposition: DISCONTINUED, UNAVAILABLE; Remove.

=== Type 36: Radio WWV/H Audio Demodulator/Decoder (WWV) ===

Yet another really bad idea based on audio signal demodulation. Only
accurate to 1ms; a cheap GPS can do 200 times better.

Disposition: INACCURATE; Remove.

=== Type 37: Forum Graphic GPS Dating station (FG) ===

Product discontinued, vendor vanished, more than 15 years old and
had a Y2K issue then.

Disposition: DISCONTINUED, INACCURATE; Remove.

=== Type 38: hopf GPS/DCF77 6021/komp for Serial Line (HOPF_S) ===

The list of all Hopf products at 

http://www.hopf.com/en/index_article_en.html

does not list the Hopf 6021. Because the 6039 still shipping issued
in 2001 or earlier it is almost certain that the 6021 was discontinued
sooner yet.

The manual for the 6039 mentions a 2ms accuracy limit for time radios
synchronized to DCF77, so the DCF77 variant is also INACCURATE.

Disposition: DISCONTINUED; Remove

=== Type 39: hopf GPS/DCF77 6039 for PCI-Bus (HOPF_P) ===

Still a live product - an industrial-grade timing receiver, or what
passed for one in 2001 (date of manual). At a claimed jitter of 2ms it
is 400 times less accurate than any common 1PPS device today and half
the accuracy of a $30 USB timing GPS. However, as a clock rather than
plain GPS the DCF77 variant evades the INACCURATE tag (just barely).

Disposition: Move to refclockd.

=== Type 40:  JJY Receivers (JJY) ===

The TriState and C-Dex devices this supports may still be live
products, though little information seems to be available in English.

Disposition: Move to refclockd.

=== Type 41: TrueTime 560 IRIG-B Decoder ===

Documentation has been removed from the ntpd4 web pages, but from web
searches and context this is another obsolete product in the
audio-decoder class from a dead vendor.

Disposition: DEPRECATED and DISCONTINUED; already removed.

=== Type 42: Zyfer GPStarplus Receiver ===

Live product with a supporting vendor.  100ns accuracy.

Disposition: Move to refclockd.

=== Type 43: RIPE NCC interface for Trimble Palisade ===

Requires custom hardware no longer being made.

Disposition: INTRINSIC.

=== Type 44: NeoClock4X - DCF77 / TDF serial line ===

This is a radio clock synchronized to DCF77 and thus has 2ms jitter.
I found a source page at http://www.linux-funkuhr.de/ that suggests it
was written by a small software company "Linum Software GmbH" for
Linux hosts.  It may still be available.

Disposition: Move to refclockd.

=== Type 45: Spectracom TSync PCI ===

Spectracom is a product line of of time sources that is still 
available and supported by a vendor.  The TSync is a GPS clock 
with a specified accuracy of 100ns.

Disposition: Move to refclockd.

=== Type 46: GPSD NG client protocol ===

IPC driver, to be retained.

== Summary

For hardware marked "<2000?" the date it was end-of-lifed cannot
be determined cetainly but was almost certainly in the last century.

.Hardware status summary 
|===============================================================
| 1  | DEPRECATED, INACCURATE
| 2  | DEPRECATED, DISCONTINUED (<2000?), UNAVAILABLE
| 3  | INTRINSIC, DISCONTINUED (<2000?), UNAVAILABLE, INACCURATE
| 4  | -
| 5  | DISCONTINUED (<2000?)
| 6  | INACCURATE
| 7  | INACCURATE
| 8  | -
| 9  | DISCONTINUED (1994), UNAVAILABLE
| 10 | DISCONTINUED (1996), UNAVAILABLE
| 11 | -
| 12 | UNDOCUMENTED, DISCONTINUED (<2000?), UNAVAILABLE
| 13 | DISCONTINUED (<2005), INACCURATE
| 14 | DEPRECATED and DISCONTINUED (<2000?)
| 16 | DISCONTINUED (<2000?)
| 17 | UNDOCUMENTED, DEPRECATED, DISCONTINUED (<2000?), UNAVAILABLE
| 19 | DISCONTINUED (<1992), UNAVAILABLE, INACCURATE
| 20 | REDUNDANT
| 21 | INTRINSIC, DEPRECATED, DISCONTINUED (<2000?)
| 26 | DISCONTINUED (2005?)
| 27 | DISCONTINUED (<2000?), UNAVAILABLE, INACCURATE
| 29 | REDUNDANT
| 30 | REDUNDANT
| 31 | REDUNDANT
| 32 | INTRINSIC, DISCONTINUED (<2000?), UNAVAILABLE, INACCURATE
| 33 | INACCURATE
| 34 | INTRINSIC, DISCONTINUED (>2004,<2015) and INACCURATE
| 35 | DISCONTINUED (<2010), UNAVAILABLE
| 36 | INACCURATE
| 37 | DISCONTINUED (<2000), INACCURATE
| 38 | DISCONTINUED (<2001).
| 39 | -
| 40 | -
| 41 | DEPRECATED, DISCONTINUED
| 42 | -
| 43 | INTRINSIC
| 44 | -
| 45 | -
|===============================================================

== Second-round triage ==

.Potentially viable drivers
|==========================================================
|Type 4: Spectracom WWVB/GPS Receivers (WWVB_SPEC)
|Type 8: Generic Reference Driver (PARSE)
|Type 11: Arbiter 1088A/B GPS Receiver (GPS_ARBITER)
|Type 18: NIST/USNO/PTB Modem Time Services (ACTS_MODEM)
|Type 26: Hewlett Packard 58503A GPS Receiver (GPS_HP)
|Type 28: Shared Memory Driver (SHM)
|Type 39: hopf GPS/DCF77 6039 for PCI-Bus (HOPF_P)
|Type 40: JJY Receivers (JJY)
|Type 42: Zyfer GPStarplus Receiver
|Type 44: NeoClock4X - DCF77 / TDF serial line
|Type 45: Spectracom TSync PCI
|Type 46: GPSD NG client protocol
|==========================================================

The Type 4 driver supports recent Spectracom GPS clocks, if I can
believe their protocol documentation.  But Spectracom no longer
makes WWVB receivers; this needs to be renamed "Spectracom Type 2 
protocol".

Types 28 and 46 are no-brainers to keep.  We will eventually want to
deprecate the SHM driver in favor of the JSON one.  That needs to be
described as a future direction in the documentation.

Kludgy PPS support in ntpd may compromise types 4, 8, and 45. This
is an issue we need to keep an eye on.

== Policy consequences ==

The 1.0 version of this document contained a technical policy proposal
but no conclusions.  It was, essentially, to remove all drivers tagged
INTRINSIC, DEPRECATED, OBSOLETE, REDUNDANT, and INACCURATE, but
allow for reinstatement of merely OBSOLETE drivers on demonstration of 
a real-world use case.

At that time the proposed obsolescence timeout was ten years.  I noted
that there is only one driver for hardware that has been discontinued,
but possibly too recently - Type 35; the date it was end-of-lifed is
unclear.  I have continued to designate it OBSOLETE, as its reliance
on a parallel port means it is extremely likely to have been
discontinued before 2008.

Susan Sons, acting as program manager, changed the timeout to seven
years.  She endorsed the exception that obsolete drivers may be 
reinstated if and when specific users demonstrate a need for them.

To date, there has been one such reinstatement: the Hewlett Packard
58503A (type 26), requested by Hal Murray.

Accordingly, the list under "Potentially viable drivers" is the list
to be retained in the cleanup release of NTP.  This list may be 
revised as we receive new information.

== Appendix: Test equipment available ==

Harlan Stenn reports:

-------------------------------------------------------------------
Here at my lab I have:

- Meinberg LANtime M600
- SEL-2407
- Sure GPS
- ublox

At ISC we have:

- Meinberg GPS167BGT
- - IRIG Audio
- - Serial with no PPS
- - Serial with PPS
- - DCF77 output
- Meinberg DCF77 receiver
- Trimble Acutime 2000

I think we have a Trimble Acutime Gold as well, but no cable for it.

> |==========================================================
> |Type 4: Spectracom WWVB/GPS Receivers (WWVB_SPEC)
> |Type 11: Arbiter 1088A/B GPS Receiver (GPS_ARBITER)

Dave Mills might have these two, but I have no idea if they're up and
running and there's no good way to access them at his place.  If they
are up and running I might be able to get logs for you.

> |Type 42: Zyfer GPStarplus Receiver

I had one of these back when I wrote the driver, but I haven't seen one
since.  There is no maintainer for this refclock, so if a problem is
found with it I'll ping the manufacturer and either they'll fix it or
I'll deprecate the driver.  I wrote this driver because Zyfer had a
customer (the NSA) who asked for it.  I haven't heard a word about this

-------------------------------------------------------------------

== History ==

Version 1.0, 2015-03-03::
	Initial version.

Version 1.1, 2015-03-06::
	Dropped type 22, reinstated type 26. Added hardware status summary.

Version 1.2, 2015-03-10::
	Added section on policy and conclusions. ACTS is still used
	for backup at government Stratum 1 sites, so keep it.

Version 1.3, 2015-06-16::
	Minor typo fixes.

Version 1.4, 2015-06-30::
	Add DEPRECATED tags to three refclocks because they are
	undocumented. Note that driver 2 was already gone and that
	13, 14, 17, 21, and 41 have already been removed.

// end