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Backported from ntp-dev-4.2.7p385
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diff -up ntp-4.2.6p5/ntpd/ntp_proto.c.rootdisp ntp-4.2.6p5/ntpd/ntp_proto.c
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--- ntp-4.2.6p5/ntpd/ntp_proto.c.rootdisp 2013-12-09 15:02:58.394459288 +0100
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+++ ntp-4.2.6p5/ntpd/ntp_proto.c 2013-12-09 15:10:05.770954848 +0100
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@@ -1667,10 +1667,34 @@ clock_update(
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sys_refid = peer->refid;
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else
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sys_refid = addr2refid(&peer->srcadr);
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- dtemp = sys_jitter + fabs(sys_offset) + peer->disp +
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- (peer->delay + peer->rootdelay) / 2 + clock_phi *
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- (current_time - peer->update);
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- sys_rootdisp = dtemp + peer->rootdisp;
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+ /*
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+ * Root Dispersion (E) is defined (in RFC 5905) as:
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+ *
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+ * E = p.epsilon_r + p.epsilon + p.psi + PHI*(s.t - p.t) + |THETA|
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+ *
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+ * where:
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+ * p.epsilon_r is the PollProc's root dispersion
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+ * p.epsilon is the PollProc's dispersion
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+ * p.psi is the PollProc's jitter
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+ * THETA is the combined offset
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+ *
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+ * NB: Think Hard about where these numbers come from and
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+ * what they mean. When did peer->update happen? Has anything
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+ * interesting happened since then? What values are the most
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+ * defensible? Why?
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+ *
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+ * DLM thinks this equation is probably the best of all worse choices.
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+ */
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+ dtemp = peer->rootdisp
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+ + peer->disp
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+ + sys_jitter
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+ + clock_phi * (current_time - peer->update)
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+ + fabs(sys_offset);
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+
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+ if (dtemp > sys_mindisp)
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+ sys_rootdisp = dtemp;
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+ else
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+ sys_rootdisp = sys_mindisp;
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sys_rootdelay = peer->delay + peer->rootdelay;
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sys_reftime = peer->dst;
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@@ -2810,15 +2834,36 @@ root_distance(
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double dtemp;
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/*
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+ * Root Distance (LAMBDA) is defined as:
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+ * (delta + DELTA)/2 + epsilon + EPSILON + phi
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+ *
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+ * where:
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+ * delta is the round-trip delay
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+ * DELTA is the root delay
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+ * epsilon is the remote server precision + local precision
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+ * + (15 usec each second)
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+ * EPSILON is the root dispersion
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+ * phi is the peer jitter statistic
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+ *
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+ * NB: Think hard about why we are using these values, and what
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+ * the alternatives are, and the various pros/cons.
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+ *
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+ * DLM thinks these are probably the best choices from any of the
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+ * other worse choices.
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+ */
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+ dtemp = (peer->delay + peer->rootdelay) / 2
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+ + LOGTOD(peer->precision)
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+ + LOGTOD(sys_precision)
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+ + clock_phi * (current_time - peer->update)
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+ + peer->rootdisp
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+ + peer->jitter;
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+ /*
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* Careful squeak here. The value returned must be greater than
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* the minimum root dispersion in order to avoid clockhop with
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* highly precise reference clocks. Note that the root distance
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* cannot exceed the sys_maxdist, as this is the cutoff by the
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* selection algorithm.
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*/
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- dtemp = (peer->delay + peer->rootdelay) / 2 + peer->disp +
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- peer->rootdisp + clock_phi * (current_time - peer->update) +
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- peer->jitter;
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if (dtemp < sys_mindisp)
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dtemp = sys_mindisp;
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return (dtemp);
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