This MIB module defines textual conventions used by MIB
modules that define objects describing performance history
data based on a configurable reporting interval.

Use of these textual conventions assumes the following:

    - The SNMP entity supports performance history data
      collection based on a configurable interval.

    - The SNMP entity is capable of maintaining a history of N
      report intervals.  A MIB module using these textual
      conventions defines the value of N, which may be
      configurable.

    - The SNMP entity may optionally support aggregation of
      performance data maintained by historic report intervals.

    - A MIB module using these textual conventions may define
      separate tables for the current interval, historic
      intervals, and the aggregation of historic performance
      data.

    - A MIB module using these textual conventions must define
      the following objects:

      xxxReportInterval OBJECT-TYPE
          SYNTAX      Unsigned32 (0..4294967295)
          UNITS       'xxx-units'
          MAX-ACCESS  read-only
          STATUS      current
          DESCRIPTION
              'This object indicates the duration of a report
              interval.'
          ::= { xxx }

      xxxReportMaxIntervals OBJECT-TYPE
          SYNTAX      Unsigned32 (0..4294967295)
          UNITS       'report intervals'
          MAX-ACCESS  read-only
          STATUS      current
          DESCRIPTION
              'This object indicates the maximum number of
              report intervals.'
          ::= { xxx }

      xxxReportElapsedTime OBJECT-TYPE
          SYNTAX      Gauge32
          UNITS       'xxx-units'
          MAX-ACCESS  read-only
          STATUS      current
          DESCRIPTION
              'This object indicates the time that has elapsed
              since the beginning of the current report
              interval.'
          ::= { xxx }

      xxxReportIntervals OBJECT-TYPE
          SYNTAX      Gauge32
          UNITS       'report intervals'
          MAX-ACCESS  read-only
          STATUS      current
          DESCRIPTION
              'This object indicates the number of report
              intervals for which data has been collected.  The
              value of this column starts at 0 and increments
              at the end of each report interval until the 
              number of report intervals is equal to the 
              corresponding value of xxxReportMaxIntervals.'
          ::= { xxx }

      xxxReportInvalidIntervals OBJECT-TYPE
          SYNTAX      Gauge32
          UNITS       'report intervals'
          MAX-ACCESS  read-only
          STATUS      current
          DESCRIPTION
              'This object indicates the number of report
              intervals, in the range of 0 to the value of the
              corresponding instance of xxxReportValidIntervals,

              for which no data is available.  The value of this
              column will typically be 0, except in certain
              circumstances when some intervals are not
              available.
          ::= { xxx }

      Observe that if the MIB module defines tables that
      maintain performance data for multiple instances of a
      measured entity (e.g., an interface), then the definition
      of these objects need to allow for the maintenance of
      these objects per instance of the measured entity.

      A MIB module may choose to provide the write-access to
      xxxReportInterval and xxxReportMaxIntervals.  In this 
      case, the MIB module must consider the following:

      - The MIB module may want to refine the data type to
        something more concise.  Alternatively, an 
        implementation may specify variations in an agent
        capabilities.

      - If the definition of either of these objects specifies
        '0' as an acceptable value, then the descriptive text
        should describe the semantics of this value.

      - The descriptive text of xxxReportInterval must explain,
        'When this value changes, the SNMP entity should discard
        any previously collected report interval data.'

      - The descriptive text of xxxReportMaxIntervals must
        explain, 'When this value changes to a value less than
        its current value, the SNMP entity should discard older
        report intervals to comply with the new value.'