proposed Local_Clock doc change - Externally Disciplined

[MLewis]

https://docs.ntpsec.org/latest/driver_local.html


Current Description

Note: We recommend against using this driver. A much more flexible 
replacement is described on the Orphan Mode page.

This driver was intended for use in an isolated network where no 
external source of synchronization such as a radio clock or modem is 
available. It allows a designated time server to act as a primary server 
to provide synchronization to other clients on the network. Pick a 
machine that has a good clock oscillator and configure it with this 
driver. Set the clock using the best means available, like 
eyeball-and-wristwatch. Then, point all the other machines at this one 
or use broadcast mode to distribute time.

Another application for this driver is if a particular server clock is 
to be used as the clock of last resort when all other normal 
synchronization sources have gone away. This is especially useful if 
that server has an ovenized oscillator. For this you would usually, but 
not necessarily, configure this driver at a stratum greater than any 
other likely sources of time, such as the default 5 for this driver, to 
prevent this driver taking over when legitimate sources elsewhere in the 
network are available. To further protect the Internet infrastructure 
from accidental or malicious exposure to this driver, the driver is 
disabled if another source is available and operating.


Proposed draft of a new paragraph to add to the above description.

This driver is used when the system clock is Externally Disciplined (not 
disciplined/adjusted by NTP) and the system clock needs to be available 
to NTP so the externally disciplined system clock can be provided to 
NTP-Clients. For example, when the system clock is externally 
disciplined by: Precision Time Protocol (PTP), a high resolution counter 
disciplined by a GPS receiver, the Digital Time Synchronization Service 
(DTSS), or a completely separate clock discipline algorithm and 
synchronization protocol, such as the Lockclock algorithm used with NIST 
Automated Computer Time Service (ACTS) modem synchronized time. See 
https://docs.ntpsec.org/latest/extern.html for more information.


Michael