Section 2 of RFC-1119, as well as much new material clarifying the
interpretation of timescales and leap seconds.

4.

Minor changes have been made in the Version-3 local-clock algorithms to
avoid problems observed when leap seconds are introduced in the UTC
timescale and also to support an auxiliary precision oscillator, such as
a cesium clock or timing receiver, as a precision timebase. In addition,
changes were made to some procedures described in Section 3 and in the
clock-filter and clock-selection procedures described in Section 4.
While these changes were made to correct minor bugs found as the result
of experience and are recommended for new implementations, they do not
affect interoperability with previous versions or existing
implementations in other than minor ways (at least until the next leap
second).

5.

In Version 3 changes were made to the way delay, offset and dispersion
are defined, calculated and processed in order to reliably bound the
errors inherent in the time-transfer procedures. In particular, the
error accumulations were moved from the delay computation to the
dispersion computation and both included in the clock filter and
selection procedures. The clock-selection procedure was modified to
remove the first of the two sorting/discarding steps and replace with an
algorithm first proposed by Marzullo and later incorporated in the
Digital Time Service. These changes do not significantly affect the
ordinary operation of or compatibility with various versions of NTP, but
they do provide the basis for formal statements of correctness as
described in Appendix H.
Table of Contents

1.       Introduction   1

1.1.     Related Technology     2

2.       System Architecture    4

2.1.     Implementation Model   6

2.2.     Network Configurations 7

3.       Network Time Protocol  8

3.1.     Data Formats   8

3.2.     State Variables and Parameters 9

3.2.1.   Common Variables       9

3.2.2.   System Variables       12

3.2.3.   Peer Variables 12

3.2.4.   Packet Variables       14

3.2.5.   Clock-Filter Variables 14

3.2.6.   Authentication Variables       15

3.2.7.   Parameters     15

3.3.     Modes of Operation     17

3.4.     Event Processing       19

3.4.1.   Notation Conventions   19

3.4.2.   Transmit Procedure     20

3.4.3.   Receive Procedure      22

3.4.4.   Packet Procedure       24

3.4.5.   Clock-Update Procedure 27

3.4.6.   Primary-Clock Procedure        28

3.4.7.   Initialization Procedures      28

3.4.7.1.         Initialization Procedure       29

3.4.7.2.         Initialization-Instantiation Procedure 29

3.4.7.3.         Receive-Instantiation Procedure        30

3.4.7.4.         Primary Clock-Instantiation Procedure  31

3.4.8.   Clear Procedure        31

3.4.9.   Poll-Update Procedure  32

3.5.     Synchronization Distance Procedure     32

3.6.     Access Control Issues  33

4.       Filtering and Selection Algorithms     34

4.1.     Clock-Filter Procedure 35