[Ntp] NTPv5 draft suggestion to move timescale offset into extension fields.

[David Venhoek <[e-mail]>]

Below attached is the diff of a PR on Miroslav's draft for NTPv5 for
moving the timescale offset field into a separate extension field.

In my view, doing so has several advantes:
 - We can use larger datatypes for offset, which makes it trivial to
allow larger than 1 second offsets for UT1 which might become
necessary if UTC stops doing leap seconds.
 - We gain more bits for both the flag and timescale fields, giving
additional flexibility for these fields.

Please let me know if you have any feedback on this.

Kind regards,
David Venhoek

--- a/ntp-ntpv5.xml
+++ b/ntp-ntpv5.xml
@@ -163,6 +163,12 @@
             describing the fractional part. The maximum value is
             16 seconds and the resolution is about 3.7 nanoseconds. Note that
             this is different from the 32-bit time format in NTPv4.</t>
+
+          <t hangText="time64"><vspace/>
+            A 64 bit signed fixed-point type containg values in
seconds. It has 32
+            signed integer bits, and 32 fractional bits. The sign
uses 2-complements
+            representation for negative numbers.
+          </t>

           <t hangText="timestamp64"><vspace/>
             A 64-bit unsigned fixed-point type containing a timestamp describes
@@ -199,9 +205,9 @@
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-|LI | VN  |Mode | Scale |Stratum|     Poll      |  Precision    |
+|LI | VN  |Mode |    Stratum    |     Poll      |  Precision    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-|     Flags     |      Era      |        Timescale Offset       |
+|              Flags            |      Era      |   Timescale   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Root Delay                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@@ -258,8 +264,8 @@
           <t hangText="Mode"><vspace/>
             A 3-bit field containing the value 3 (request) or 4 (response).</t>

-          <t hangText="Scale"><vspace/>
-            A 4-bit identifier of the timescale. In requests it is the
+          <t hangText="Timescale"><vspace/>
+            An 8-bit identifier of the timescale. In requests it is the
             requested timescale. In responses it is the timescale of the
             receive and transmit timestamps. Defined values are:

@@ -272,10 +278,12 @@
           </t>

           <t hangText="Stratum"><vspace/>
-            A 4-bit field containing the stratum of the server. Primary time
+            An 8-bit field containing the stratum of the server. Primary time
             servers have a stratum of 1, their clients have a stratum of 2, and
             so on. The value of 0 indicates an unknown or infinite stratum. In
-            requests it is always 0.</t>
+            requests it is always 0. Servers advertising a stratum above 16
+            should not be synchronized to except when the client is explicitly
+            configured to do so by the end-user.</t>

           <t hangText="Poll"><vspace/>
             An 8-bit signed integer containing the polling interval as a
@@ -289,7 +297,7 @@
             requests, which don't contain any timestamps, it is always 0.</t>

           <t hangText="Flags"><vspace/>
-            An 8-bit integer that can contain the following flags:
+            A 16-bit integer that can contain the following flags:

             <list style="hanging">
               <t hangText="0x1: Unknown leap"><vspace/>
@@ -773,6 +781,81 @@

       </section>

+      <section title="Timescale offset request">
+        <t>A clients request for the offset between two indicated
timescales.</t>
+
+        <t>The reference field MUST contain the timescale identifier of
+          the timescale with respect to which the client wants to know
+          the offset.</t>
+
+        <t>The target field MUST contain the timescale identifier of the
+          timescale for which the client wants to know an offset.</t>
+
+        <t>The reserved and placeholder fields MUST be set to 0
+          by the client, and MUST be ignored by a server</t>
+
+        <t>A server which does not know either the reference or target
+          timescale, or which does not know the offset between them, MUST
+          ignore the timescale request.</t>
+
+        <figure align="center" anchor="timescale-offset-request-ext-field"
+            title="Format of Timescale Offset Request Extension Field">
+          <artwork><![CDATA[
+ 0                   1                   2                   3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Type = [[TBD]] (draft 0xF509) |           Length = 16         |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|   Reference   |    Target     |           Reserved            |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|                                                               |
+|                  Offset placeholder (64 bits)                 |
+|                                                               |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+          ]]></artwork>
+        </figure>
+      </section>
+
+      <section title="Timescale offset response">
+        <t> The offset between two given timescales.</t>
+
+        <t>The reference field MUST contain the timescale identifier of
+          the timescale with respect to which the client wants to know
+          the offset.</t>
+
+        <t>The target field MUST contain the timescale identifier of the
+          timescale for which the client wants to know an offset.</t>
+
+        <t>The offset is given such that for a given timestamp in the
+          reference timescale, the timestamp in the target timescale
+          is the reference scale timestamp plus the offset. (i.e.
+          target = reference + offset)</t>
+
+        <t>The reserved bits MUST be set to 0 by the server, and MUST
+          be ignored by the client.</t>
+
+        <t>When the offset between the target and reference timescales
+          varies over time, the provided offset MUST be the servers
+          best approximation of this offset at the time exactly halfway
+          between the receive and transmit timestamps.</t>
+
+<figure align="center" anchor="timescale-offset-response-ext-field"
+            title="Format of Timescale Offset Response Extension Field">
+          <artwork><![CDATA[
+ 0                   1                   2                   3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+| Type = [[TBD]] (draft 0xF50A) |           Length = 16         |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|   Reference   |    Target     |           Reserved            |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|                                                               |
+|                  Offset (time64)                              |
+|                                                               |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+          ]]></artwork>
+        </figure>
+      </section>
     </section>

     <section title="Measurement Modes" anchor="measurement-modes">