When the filter and selection algorithms suggested
in Section 4 are used, the following state variables are defined in addition to the variables described previously.
Filter Register (peer.filter): This is a shift
register of NTP.SHIFT stages, where each stage stores a 3-tuple consisting of the measured delay, measured offset and calculated
dispersion associated with a single observation. These 3-tuples enter from the most significant (leftmost) right and are shifted
towards the least significant (rightmost) end and eventually discarded as new observations arrive.
Valid Data Counter (peer.valid): This is an integer
counter indicating the valid samples remaining in the filter register. It is used to determine the reachability state and when the
poll interval should be increased or decreased.
Offset (peer.offset): This is a signed, fixed-point
number indicating the offset of the peer clock relative to the local clock, in seconds.
Delay (peer.delay): This is a signed fixed-point
number indicating the roundtrip delay of the peer clock relative to the local clock over the network path between them, in seconds.
Note that this variable can take on both positive and negative values, depending on clock precision and skew-error
Dispersion (peer.dispersion): This is a signed
fixed-point number indicating the maximum error of the peer clock relative to the local clock over the network path between them, in
seconds. Only positive values greater than zero are possible.