rfc1059.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

                   00      no warning (day has 86400 seconds)
                   01      +1 second (day has 86401 seconds)
                           seconds)
                   10      -1 second (day has 86399 seconds)
                           seconds)
                   11      alarm condition (clock not synchronized)

      In all except the alarm condition (11) NTP itself does nothing
      with these bits, except pass them on to the time-conversion
      routines that are not part of NTP.  The alarm condition occurs
      when, for whatever reason, the logical clock is not synchronized,
      such as when first coming up or after an extended period when no
      outside reference source is available.

   Stratum (sys.stratum, peer.stratum, pkt.stratum)

      This is an integer indicating the stratum of the logical clock.  A
      value of zero is interpreted as unspecified, one as a primary
      clock (synchronized by outside means) and remaining values as the
      stratum level (synchronized by NTP).  For comparison purposes a
      value of zero is considered greater than any other value.

   Peer Poll Interval (peer.ppoll, pkt.poll)

      This is a signed integer used only in symmetric mode and
      indicating the minimum interval between messages sent to the peer,
      in seconds as a power of two.  For instance, a value of six



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      indicates a minimum interval of 64 seconds.  The value of this
      variable must not be less than NTP.MINPOLL and must not be greater
      than NTP.MAXPOLL.

   Precision (sys.precision, peer.precision, pkt.precision)

      This is a signed integer indicating the precision of the logical
      clock, in seconds to the nearest power of two.  For instance, a
      60-Hz line-frequency clock would be assigned the value -6, while a
      1000-Hz crystal-derived clock would be assigned the value -10.

   Synchronizing Distance (sys.distance, peer.distance, pkt.distance)

      This is a fixed-point number indicating the estimated roundtrip
      delay to the primary clock, in seconds.


   Estimated Drift Rate (sys.drift, peer.drift, pkt.drift)

      This is a fixed-point number indicating the estimated drift rate
      of the local clock, in dimensionless units.

   Reference Clock Identifier (sys.refid, peer.refid, pkt.refid)

      This is a code identifying the particular reference clock or
      server.  The interpretation of the value depends on the stratum.
      For stratum values of zero (unspecified) or one (primary clock),
      the value is an ASCII string identifying the reason or clock,
      respectively.  For stratum values greater than one (synchronized
      by NTP), the value is the 32-bit Internet address of the reference
      server.

   Reference Timestamp (sys.reftime, peer.reftime, pkt.reftime)

      This is the local time, in timestamp format, when the logical
      clock was last updated.  If the logical clock has never been
      synchronized, the value is zero.

3.2.2.  System Variables

   The following variables are used by the operating system in order to
   synchronize the logical clock.

   Logical Clock (sys.clock)

      This is the current local time, in timestamp format.  Local time
      is derived from the hardware clock of the particular machine and
      increments at intervals depending on the design used.  An



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      appropriate design, including slewing and drift-compensation
      mechanisms, is described in Section 5.

   Clock Source (sys.peer)

      This is a selector identifying the current clock source.  Usually
      this will be a pointer to a structure containing the peer
      variables.

3.2.3.  Peer Variables

   Following is a list of state variables used by the peer management
   and measurement functions.  There is one set of these variables for
   every peer operating in client mode or symmetric mode.

   Peer State (peer.state)

      This is a bit-encoded quantity used for various control functions.

   Host Poll Interval (peer.hpoll)

      This is a signed integer used only in symmetric mode and
      indicating the minimum interval between messages expected from the
      peer, in seconds as a power of two.  For instance, a value of six
      indicates a minimum interval of 64 seconds.  The value of this
      variable must not be less than NTP.MINPOLL and must not be greater
      than NTP.MAXPOLL.

   Reachability Register (peer.reach)

      This is a code used to determine the reachability status of the
      peer.  It is used as a shift register, with bits entering from the
      least significant (rightmost) end.  The size of this register is
      specified as PEER.SHIFT bits.

   Peer Timer (peer.timer)

      This is an integer counter used to control the interval between
      transmitted NTP messages.

   Timer Threshold (peer.threshold)

      This is the timer value which, when reached, causes the timeout
      procedure to be executed.

   Originate Timestamp (peer.org, pkt.org)

      This is the local time, in timestamp format, at the peer when its



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      latest NTP message was sent.  If the peer becomes unreachable the
      value is set to zero.

   Receive Timestamp (peer.rec, pkt.rec)

      This is the local time, in timestamp format, when the latest NTP
      message from the peer arrived.  If the peer becomes unreachable
      the value is set to zero.

3.2.4.  Packet Variables

   Following is a list of variables used in NTP messages in addition to
   the common variables above.

   Version Number (pkt.version)

      This is an integer indicating the version number of the sender.
      NTP messages will always be sent with the current version number
      NTP.VERSION and will always be accepted if the version number
      matches NTP.VERSION.  Exceptions may be advised on a case-by-case
      basis at times when the version number is changed.

   Transmit Timestamp (pkt.xmt)

      This is the local time, in timestamp format, at which the NTP
      message departed the sender.

3.2.5.  Clock Filter Variables

   When the filter and selection algorithms suggested in Section 4 are
   used, the following state variables are defined.  There is one set of
   these variables for every peer operating in client mode or symmetric
   mode.

   Filter Register (peer.filter)

      This is a shift register of PEER.WINDOW bits, where each stage is
      a tuple consisting of the measured delay concatenated with the
      measured offset associated with a single observation.
      Delay/offset observations enter from the least significant
      (rightmost) right and are shifted towards the most significant
      (leftmost) end and eventually discarded as new observations
      arrive.  The register is cleared to zeros when (a) the peer
      becomes unreachable or (b) the logical clock has just been reset
      so as to cause a significant discontinuity in local time.






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   Delay Estimate (peer.delay)

      This is a signed, fixed-point number indicating the latest delay
      estimate output from the filter, in seconds.  While the number is
      signed, only those values greater than zero represent valid delay
      estimates.

   Offset Estimate (peer.offset)

      This is a signed, fixed-point number indicating the latest offset
      estimate output from the filter, in seconds.

   Dispersion Estimate (peer.dispersion)

      This is a fixed-point number indicating the latest dispersion
      estimate output from the filter, in scrambled units.

3.2.6.  Parameters

   Following is a list of parameters assumed for all implementations
   operating in the Internet system.  It is necessary to agree on the
   values for these parameters in order to avoid unnecessary network
   overheads and stable peer associations.

   Version Number (NTP.VERSION)

      This is the NTP version number, currently one (1).

   NTP Port (NTP.PORT)

      This is the port number (123) assigned by the Internet Number Czar
      to NTP.

   Minimum Polling Interval (NTP.MINPOLL)

      This is the minimum polling interval allowed by any peer of the
      Internet system, currently set to 6 (64 seconds).

   Maximum Polling Interval (NTP.MAXPOLL)

      This is the maximum polling interval allowed by any peer of the
      Internet system, currently set to 10 (1024 seconds).

   Maximum Dispersion (NTP.MAXDISP)

      This is the maximum dispersion assumed by the filter algorithms,
      currently set to 65535 milliseconds.




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   Reachability Register Size (PEER.WINDOW)

      This is the size of the Reachability Register (peer.reach),
      currently set to eight (8) bits.

   Shift Register Size (PEER.SHIFT)

      When the filter and selection algorithms suggested in Section 4
      are used, this is the size of the Clock Filter (peer.filter) shift
      register, in bits.  For crystal-stabilized oscillators a value of
      eight (8) is suggested, while for mains-frequency oscillators a
      value of four (4) is suggested.  Additional considerations are
      given in Section 5.

   Dispersion Threshold (PEER.THRESHOLD)

      When the filter and selection algorithms suggested in Section 4
      are used, this is the threshold used to discard noisy data.  While
      a value of 500 milliseconds is suggested, the value may be changed
      to suit local conditions on particular peer paths.

   Filter Weight (PEER.FILTER)

      When the filter algorithm suggested in Section 4 is used, this is
      the filter weight used to discard noisy data.  While a value of
      0.5 is suggested, the value may be changed to suit local
      conditions on particular peer paths.