[2085] Fix root distance and root dispersion calculations

bk: 52118107xRXAZMfq-iw0s5WgRmyttg

diff --git a/ChangeLog b/ChangeLog
index d333820ca45d92e689c149bc7b5b92ac221c7ad3..d2d999c32808e4fc2e5f09d3e7e9d731e5d9e2c7 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,4 @@
+* [2085] Fix root distance and root dispersion calculations.
 (4.2.7p384) 2013/08/18 Released by Harlan Stenn <stenn@ntp.org>
 * [Bug 2450] --version has bogus short option.
 (4.2.7p383) 2013/08/10 Released by Harlan Stenn <stenn@ntp.org>

diff --git a/ntpd/ntp_proto.c b/ntpd/ntp_proto.c
index ae05982ec408a47ed59edb81762aa53079fb513f..f2d6970ec92a17caef0f80503018e6ea8923dc89 100644 (file)
--- a/ntpd/ntp_proto.c
+++ b/ntpd/ntp_proto.c
@@ -1827,9 +1827,30 @@ clock_update(
                sys_refid = peer->refid;
        else
                sys_refid = addr2refid(&peer->srcadr);
-       dtemp = fabs(sys_offset) + peer->disp + peer->rootdisp +
-           (peer->delay + peer->rootdelay) / 2 + clock_phi *
-           (current_time - peer->update) + sys_jitter;
+       /*
+        * Root Dispersion (E) is defined (in RFC 5905) as:
+        *
+        * E = p.epsilon_r + p.epsilon + p.psi + PHI*(s.t - p.t) + |THETA|
+        *
+        * where:
+        *  p.epsilon_r is the PollProc's root dispersion
+        *  p.epsilon   is the PollProc's dispersion
+        *  p.psi       is the PollProc's jitter
+        *  THETA       is the combined offset
+        *
+        * NB: Think Hard about where these numbers come from and
+        * what they mean.  When did peer->update happen?  Has anything
+        * interesting happened since then?  What values are the most
+        * defensible?  Why?
+        *
+        * DLM thinks this equation is probably the best of all worse choices.
+        */
+       dtemp   = peer->rootdisp
+               + peer->disp
+               + sys_jitter
+               + clock_phi * (current_time - peer->update)
+               + fabs(sys_offset);
+
        if (dtemp > sys_mindisp)
                sys_rootdisp = dtemp;
        else
@@ -2923,6 +2944,30 @@ root_distance(
 {
        double  dtemp;
 
+       /*
+        * Root Distance (LAMBDA) is defined as:
+        * (delta + DELTA)/2 + epsilon + EPSILON + phi
+        *
+        * where:
+        *  delta   is the round-trip delay
+        *  DELTA   is the root delay
+        *  epsilon is the remote server precision + local precision
+        *          + (15 usec each second)
+        *  EPSILON is the root dispersion
+        *  phi     is the peer jitter statistic
+        *
+        * NB: Think hard about why we are using these values, and what
+        * the alternatives are, and the various pros/cons.
+        *
+        * DLM thinks these are probably the best choices from any of the
+        * other worse choices.
+        */
+       dtemp = (peer->delay + peer->rootdelay) / 2
+               + LOGTOD(peer->precision)
+                 + LOGTOD(sys_precision)
+                 + clock_phi * (current_time - peer->update)
+               + peer->rootdisp
+               + peer->jitter;
        /*
         * Careful squeak here. The value returned must be greater than
         * the minimum root dispersion in order to avoid clockhop with
@@ -2930,9 +2975,6 @@ root_distance(
         * cannot exceed the sys_maxdist, as this is the cutoff by the
         * selection algorithm.
         */
-       dtemp = (peer->delay + peer->rootdelay) / 2 + peer->disp +
-           peer->rootdisp + clock_phi * (current_time - peer->update) +
-           peer->jitter;
        if (dtemp < sys_mindisp)
                dtemp = sys_mindisp;
        return (dtemp);