User manual

Computer Gateway User Manual 4-95 5/96
4.8.1
Relative requests—Beginning and ending offset times apply to
only relative history requests. They are stated in the units of the
specified history type and are used to establish start time, search
direction, and the number of samples to be collected from the HM.
Further explanation of the use characteristics of offset times
follows:
Offset Units used for each of the history types are
History Type Units of Offset
5-second snapshots 5 seconds
10-second snapshots 10 seconds
20-second snapshots 20 seconds
60-second snapshots Minutes
Hourly averages Hours
Shift averages 8-hour shift is assumed
Daily averages Days
Monthly averages
(normal or fast interval) Months
User averages Number of user averages to skip
The number of samples returned when offset values are used is
calculated as the positive difference between the starting offset and
the ending offset plus one. If this difference exceeds 262, the
request is truncated at 262 samples and the return status is set to
five (complete with errors).
The 5-, 10-, or 20-second snapshots are synchronized with the
60-second (1-minute) snapshots and samples returned are relative
to the start of a minute.
Offset values less than one have special meanings. When the
starting or ending offset value is zero (i.e., current LCN time), in
the case of averages, the first sample returned is the current
running average for the period.
A starting offset of -1 has special meaning in the cases of
snapshots and user averages. In only those cases, LCN time is
rounded to the beginning of the last hour. This permits an ACP to
be sure of obtaining the last full hour of snapshots or user
averages. For calculating the number of samples returned, a -1 is
treated as a value of 0 and its number of samples and direction of
search follows those rules.
An ending offset of -1 for snapshots and user averages means the
search direction is forward and the ending time is on the hour
starting "n" units back from current time.
For history type 8 (the sampling rate inquiry), both the starting
and ending offsets should be set to zero.