Table 4 shows the 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. The following parameters are assumed fixed and applicable to all associations.
Version Number (NTP.VERSION): This is the current NTP version number (3).
NTP Port (NTP.PORT): This is the port number (123) assigned by the Internet Assigned Numbers Authority to NTP.
Maximum Stratum (NTP.MAXSTRATUM): This is the maximum stratum value that can be encoded as a packet variable, also interpreted as infinity or unreachable by the subnet routing algorithm.
Maximum Clock Age (NTP.MAXAGE): This is the maximum interval a reference clock will be considered valid after its last update, in seconds.
Maximum Skew (NTP.MAXSKEW): This is the maximum offset error due to skew of the local clock over the interval determined by NTP.MAXAGE, in seconds. The ratio NTP.MAXSKEW over NTP.MAXAGE is interpreted as the maximum possible skew rate due to all causes.
Maximum Distance (NTP.MAXDISTANCE): When the selection algorithm suggested in Section 4 is used, this is the maximum synchronization distance for peers acceptable for synchronization.
Minimum Poll Interval (NTP.MINPOLL): This is the minimum poll interval allowed by any peer of the Internet system, in seconds to a power of two.
Maximum Poll Interval (NTP.MAXPOLL): This is the maximum poll interval allowed by any peer of the Internet system, in seconds to a power of two.
Minimum Select Clocks (NTP.MINCLOCK): When the selection algorithm suggested in Section 4 is used, this is the minimum number of peers acceptable for synchronization.
Maximum Select Clocks (NTP.MAXCLOCK): When the selection algorithm suggested in Section 4 is used, this is the maximum number of peers considered for selection.
Minimum Dispersion (NTP.MINDISPERSE): When the filter algorithm suggested in Section 4 is used, this is the minimum dispersion increment for each stratum level, in seconds.
Maximum Dispersion (NTP.MAXDISPERSE): When the filter algorithm suggested in Section 4 is used, this is the maximum peer dispersion and the dispersion assumed for missing data, in seconds.
Reachability Register Size (NTP.WINDOW): This is the size of the reachability register (peer.reach), in bits.
Filter Size (NTP.SHIFT): When the filter algorithm suggested in Section 4 is used, this is the size of the clock filter (peer.filter) shift register, in stages. Filter Weight (NTP.FILTER): When the filter algorithm suggested in Section 4 is used, this is the weight used to compute the filter dispersion.
Select Weight (NTP.SELECT): When the selection algorithm suggested in Section 4 is used, this is the weight used to compute the select dispersion.