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diff --git a/contrib/ntp/html/driver1.htm b/contrib/ntp/html/driver1.htm new file mode 100644 index 0000000..1f88e7d --- /dev/null +++ b/contrib/ntp/html/driver1.htm @@ -0,0 +1,157 @@ +<HTML> +<HEAD> + <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> + <META NAME="GENERATOR" CONTENT="Mozilla/4.01 [en] (Win95; I) [Netscape]"> + <TITLE>Undisciplined Local Clock +</TITLE> +</HEAD> +<BODY> + +<H3> +Undisciplined Local Clock</H3> + +<HR> +<H4> +Synopsis</H4> +Address: 127.127.1.<I>u</I> +<BR>Reference ID: <TT>LCL</TT> +<BR>Driver ID: <TT>LOCAL</TT> +<H4> +Description</H4> +This driver is 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 (Digital machines are good, Sun machines are not) +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 (not multicast) mode to distribute time. + +<P>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 configure this driver at a stratum +greater than any other likely sources of time (say 3 or 4) to prevent the +server taking over when legitimate sources are still available. + +<P>A third application for this driver is when an external discipline source +is available, such as the NIST <TT>lockclock</TT> program, which synchronizes +the local clock via a telephone modem and the NIST Automated Computer Time +Service (ACTS), or the Digital Time Synchronization Service (DTSS), which +runs on DCE machines. In this case the stratum should be set at zero, indicating +a bona fide stratum-1 source. In the case of DTSS, the local clock can +have a rather large jitter, depending on the interval between corrections +and the intrinsic frequency error of the clock oscillator. In extreme cases, +this can cause clients to exceed the 128-ms slew window and drop off the +NTP subnet. + +<P>In the case where a NTP time server is synchronized to some device or +protocol that is not external to the NTP daemon itself, some means should +be provided to pass such things as error and health values to the NTP daemon +for dissemination to its clients. If this is not done, there is a very +real danger that the device or protocol could fail and with no means to +tell NTP clients of the mishap. When ordinary Unix system calls like <TT>adjtime()</TT> +are used to discipline the kernel clock, there is no obvious way this can +be done without modifying the code for each case. However, when a modified +kernel with the <TT>ntp_adjtime()</TT> system call is available, +that routine can be used for the same purpose as the <TT>adjtime()</TT> +routine and in addition provided with the estimated error, maximum error, +and leap-indicator values. This is the preferred way to synchronize the +kernel clock and pass information to the NTP clients. + +<P>In the default mode the behavior of the clock selection algorithm is +modified when this driver is in use. The algorithm is designed so that +this driver will never be selected unless no other discipline source is +available. This can be overridden with the <TT>prefer</TT> keyword of the +<TT>server</TT> configuration command, in which case only this driver will +be selected for synchronization and all other discipline sources will be +ignored. This behavior is intended for use when an external discipline +source controls the system clock. See the <A HREF="prefer.htm">Mitigation +Rules and the <TT>prefer</TT> Keyword </A>page for a detailed description +of the exact behavior. + +<P>The stratum for this driver is set at 3 by default, but can be changed +by the <TT>fudge</TT> configuration command and/or the <TT>ntpdc</TT> utility. +The reference ID is <TT>LCL</TT> by default, but can be changed using the +same mechanisms. <B>*NEVER*</B> configure this driver to operate at a stratum +which might possibly disrupt a client with access to a bona fide primary +server, unless the local clock oscillator is reliably disciplined by another +source. <B>*NEVER NEVER*</B> configure a server which might devolve to +an undisciplined local clock to use multicast mode. + +<P>This driver provides a mechanism to trim the local clock in both time +and frequency, as well as a way to manipulate the leap bits. The <TT>fudge +time1</TT> parameter adjusts the time (in seconds) and the <TT>fudge time2</TT> +parameter adjusts the frequency (in parts per million). Both parameters +are additive and operate only once; that is, each command (as from <TT>ntpdc</TT>) +adds signed increments in time or frequency to the nominal local clock +time and frequency. +<H4> +Monitor Data</H4> +No <TT>filegen clockstats</TT> monitor data are produced by this driver. +<H4> +Fudge Factors</H4> + +<DL> +<DT> +<TT>time1 <I>time</I></TT></DT> + +<DD> +Specifies the time offset calibration factor, in seconds and fraction, +with default 0.0.</DD> + +<DT> +<TT>time2 <I>time</I></TT></DT> + +<DD> +Specifies the frequency offset calibration factor, in parts per million, +with default 0.0.</DD> + +<DT> +<TT>stratum <I>number</I></TT></DT> + +<DD> +Specifies the driver stratum, in decimal from 0 to 15, with default 3.</DD> + +<DT> +<TT>refid <I>string</I></TT></DT> + +<DD> +Specifies the driver reference identifier, an ASCII string from one to +four characters, with default <TT>LCL</TT>.</DD> + +<DT> +<TT>flag1 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag2 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag3 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + +<DT> +<TT>flag4 0 | 1</TT></DT> + +<DD> +Not used by this driver.</DD> + + +<P>Additional Information + +<P><A HREF="refclock.htm">Reference Clock Drivers</A></DL> + +<HR> +<ADDRESS> +David L. Mills (mills@udel.edu)</ADDRESS> + +</BODY> +</HTML> |
