Textual Conventions for MIB Modules Using Performance History Based on 15 Minute Intervals

Network Working Group                                     K. Tesink, Ed.
Request for Comments: 3593                        Telcordia Technologies
Obsoletes: 2493                                           September 2003
Category: Standards Track


     Textual Conventions for MIB Modules Using Performance History
                      Based on 15 Minute Intervals

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document defines a set of Textual Conventions for MIB modules
   that make use of performance history data based on 15 minute
   intervals.

   This memo replaces RFC 2493.  Changes relative to RFC 2493 are
   summarized in the MIB module's REVISION clause.

Table of Contents

   1.  Introduction .................................................  2
   2.  Note on Invalid Data and Proxies .............................  2
   3.  Note on xyzTimeElapsed .......................................  3
   4.  Note on xyzValidIntervals ....................................  3
   5.  Definitions ..................................................  4
   6.  Acknowledgments ..............................................  8
   7.  References ...................................................  8
       7.1.  Normative References ...................................  8
       7.2.  Informative References .................................  8
   8.  Security Considerations ......................................  9
   9.  Intellectual Property Statement ..............................  9
   10. Editor's Address .............................................  9
   11. Full Copyright Statement ..................................... 10

1.  Introduction

   In cases where a manager must obtain performance history data about
   the behavior of equipment it manages, several strategies can be
   followed in the design of a MIB that represents the managed
   equipment, including:

   0  The agent counts events on a continuous basis and, whenever
      desired, the manager obtains the value of the event counter and
      adjusts its understanding of the history of events at the agent.

   0  The agent allocates events to 'buckets' where each bucket
      represents an interval of time.

   Telecommunications equipment often makes use of the latter strategy.
   See [3][4][5][7][8] for examples.  In particular, for this equipment
   it is common that history data is maintained by the agent in terms of
   fifteen minute intervals.

   This memo does not attempt to compare the relative merits of
   different strategies used to obtain history data.  Differences may
   include polling policy, the amount of management traffic between
   manager and agent, agent simplicity, and 'data currentness' of the
   data obtained by the manager.  MIB designers should consider these
   aspects when choosing a particular strategy in a MIB design.
   Instead, this memo provides definitions that can be used in MIB
   modules that require history data based on fifteen minute intervals.

   When designing a MIB module, it is often useful to define new types
   similar to those defined in the SMI [2].  In comparison to a type
   defined in the SMI, each of these new types has a different name, a
   similar syntax, but more precise semantics.  These newly defined
   types are termed textual conventions, and are used for the
   convenience of humans reading the MIB module.  This is done through
   Textual Conventions as defined in RFC 2579 [1].  It is the purpose of
   this document to define the set of textual conventions to be used
   when performance history based on 15 minute intervals is kept.  The
   performance history textual conventions defined in this memo are
   based on 32 bit counts.  For high capacity performance history counts
   see [9].

2.  Note on Invalid Data and Proxies

   In this document, the word proxy indicates an application which
   receives SNMP messages and replies to them on behalf of the devices
   where the actual implementation resides, e.g., DS3/E3 interfaces.
   The proxy will have already collected the information about the
   DS3/E3 interfaces into its local database and may not necessarily
   forward requests to the actual DS3/E3 interface.  It is expected in
   such an application that there are periods of time where the proxy is
   not communicating with the DS3/E3 interfaces.  In these instances,
   the proxy will not necessarily have up-to-date configuration
   information, and will most likely have missed the collection of some
   data.  Missed data collection may result in some intervals in the
   interval table being unavailable.

3.  Note on xyzTimeElapsed

   While xyzTimeElapsed is defined as having a maximum, there may be
   cases (e.g., an adjustment in the system's time-of-day clock) where
   the actual value of the current interval would exceed this maximum
   value.

   Suppose that an agent which aligns its 15-minute measurement
   intervals to 15-minute time-of-day ("wall clock") boundaries has a
   time-of-day clock that systematically gains time, and that a manager
   periodically corrects the clock by setting it back.

   It is assumed that the agent's time-of-day clock is reasonably
   accurate, say within a few seconds per day.  Thus, the manager's
   periodic clock adjustments will normally be small, and if done
   frequently enough, need not ever exceed 10 seconds.  In this case,
   all interval durations will be within the allowed tolerance and none
   need be marked invalid, _if_ the ANSI procedure of ending measurement
   intervals at 15-minute time-of-day boundaries is followed [6].

   If the time-of-day clock is systematically adjusted in small
   increments, then always ending measurement intervals at 15-minute
   time-of-day boundaries will result, in the long term, in the correct
   number of intervals with the correct average duration, irrespective
   of whether the clock is moved ahead or moved back.  Thus, if for some
   reason, such as an adjustment in the system's time-of-day clock, the
   current interval exceeds the maximum value, it is considered
   acceptable that the agent will return the maximum value.

4.  Note on xyzValidIntervals

   The overall constraint on <n> is 1 =< n =< 96.  Any additional
   constraints on n must be defined in the DESCRIPTION clause (e.g., see
   [5]).

5.  Definitions

   PerfHist-TC-MIB DEFINITIONS ::= BEGIN

   IMPORTS
      MODULE-IDENTITY,
      Gauge32, mib-2
          FROM SNMPv2-SMI
      TEXTUAL-CONVENTION
          FROM SNMPv2-TC;

   perfHistTCMIB MODULE-IDENTITY
        LAST-UPDATED "200308130000Z"
        ORGANIZATION "IETF AToM MIB WG"
        CONTACT-INFO
           "WG charter:
              http://www.ietf.org/html.charters/atommib-charter.html

            Mailing Lists:
              General Discussion: atommib@research.telcordia.com
              To Subscribe: atommib-request@research.telcordia.com

            Editor:  Kaj Tesink
            Postal:  Telcordia Technologies
                     331 Newman Springs Road
                     Red Bank, NJ 07701
                     USA
            Tel:     +1 732 758 5254
            E-mail:  kaj@research.telcordia.com"

        DESCRIPTION
         "This MIB Module provides Textual Conventions
          to be used by systems supporting 15 minute
          based performance history counts.

          Copyright (C) The Internet Society (2003).
          This version of this MIB module is part of
          RFC 3593;  see the RFC itself for full
          legal notices."
        REVISION      "200308130000Z"
        DESCRIPTION
         "Contact information and references updated.
          No technical changes have been applied.
          Published as RFC 3593."
        REVISION      "199811071100Z"
        DESCRIPTION
         "The RFC 2493 version of this MIB module."
        ::= { mib-2 58 }

   -- The Textual Conventions defined below are organized
   -- alphabetically

   -- Use of these TCs assumes the following:
   -- 0  The agent supports 15 minute based history
   --    counters.
   -- 0  The agent is capable of keeping a history of n
   --    intervals of 15 minute performance data.  The
   --    value of n is defined by the specific MIB
   --    module but shall be 0 < n =< 96.
   -- 0  The agent may optionally support performance
   --    data aggregating the history intervals.
   -- 0  The agent will keep separate tables for the
   --    current interval, the history intervals, and
   --    the total aggregates.
   -- 0  The agent will keep the following objects.
   --    If performance data is kept for multiple instances
   --    of a measured entity, then
   --    these objects are applied to each instance of
   --    the measured entity (e.g., interfaces).
   --
   -- xyzTimeElapsed OBJECT-TYPE
   --       SYNTAX  INTEGER (0..899)
   --       MAX-ACCESS  read-only
   --       STATUS  current
   --       DESCRIPTION
   --       "The number of seconds that have elapsed since
   --       the beginning of the current measurement period.
   --       If, for some reason, such as an adjustment in the
   --       system's time-of-day clock, the current interval
   --       exceeds the maximum value, the agent will return
   --       the maximum value."
   --       ::= { xxx }

   -- xyzValidIntervals OBJECT-TYPE
   --       SYNTAX  INTEGER (0..<n>)
   --       MAX-ACCESS  read-only
   --       STATUS  current
   --       DESCRIPTION
   --       "The number of previous near end intervals
   --       for which data was collected.
   --          [ The overall constraint on <n> is 1 =< n =< 96; ]
   --          [ Define any additional constraints on <n> here. ]
   --       The value will be <n> unless the measurement was
   --       (re-)started within the last (<n>*15) minutes, in which
   --       case the value will be the number of complete 15
   --       minute intervals for which the agent has at least
   --       some data.  In certain cases (e.g., in the case
   --       where the agent is a proxy) it is possible that some
   --       intervals are unavailable.  In this case, this
   --       interval is the maximum interval number for
   --       which data is available."
   --       ::= { xxx }

   -- xyzInvalidIntervals OBJECT-TYPE
   --     SYNTAX  INTEGER (0..<n>)
   --     MAX-ACCESS  read-only
   --     STATUS  current
   --     DESCRIPTION
   --       "The number of intervals in the range from
   --        0 to xyzValidIntervals for which no
   --        data is available.  This object will typically
   --        be zero except in cases where the data for some
   --        intervals are not available (e.g., in proxy
   --        situations)."
   --       ::= { xxx }

   PerfCurrentCount ::= TEXTUAL-CONVENTION
         STATUS  current
         DESCRIPTION
            "A counter associated with a
             performance measurement in a current 15
             minute measurement interval.  The value
             of this counter starts from zero and is
             increased when associated events occur,
             until the end of the 15 minute interval.
             At that time the value of the counter is
             stored in the first 15 minute history
             interval, and the CurrentCount is
             restarted at zero.  In the
             case where the agent has no valid data
             available for the current interval the
             corresponding object instance is not
             available and upon a retrieval request
             a corresponding error message shall be
             returned to indicate that this instance
             does not exist (for example, a noSuchName
             error for SNMPv1 and a noSuchInstance for
             SNMPv2 GET operation)."
          SYNTAX  Gauge32

   PerfIntervalCount ::= TEXTUAL-CONVENTION
         STATUS  current
         DESCRIPTION
            "A counter associated with a
             performance measurement in a previous
             15 minute measurement interval.  In the
             case where the agent has no valid data
             available for a particular interval the
             corresponding object instance is not
             available and upon a retrieval request
             a corresponding error message shall be
             returned to indicate that this instance
             does not exist (for example, a noSuchName
             error for SNMPv1 and a noSuchInstance for
             SNMPv2 GET operation).
             In a system supporting
             a history of n intervals with
             IntervalCount(1) and IntervalCount(n) the
             most and least recent intervals
             respectively, the following applies at
             the end of a 15 minute interval:
             - discard the value of IntervalCount(n)
             - the value of IntervalCount(i) becomes that
               of IntervalCount(i-1) for n >= i > 1
             - the value of IntervalCount(1) becomes that
               of CurrentCount
             - the TotalCount, if supported, is adjusted."
          SYNTAX  Gauge32

   PerfTotalCount ::= TEXTUAL-CONVENTION
         STATUS  current
         DESCRIPTION
            "A counter associated with a
             performance measurements aggregating the
             previous valid 15 minute measurement
             intervals.  (Intervals for which no valid
             data was available are not counted)"
          SYNTAX  Gauge32

   END

6.  Acknowledgments

   This document is a product of the AToM MIB Working Group.  The editor
   would like to acknowledge Mike Heard for his many valuable
   contributions to this memo.

7.  References

7.1.  Normative References

   [1]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
        M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58,
        RFC 2579, April 1999.

   [2]  McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
        M. and S. Waldbusser, "Structure of Management Information
        Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

7.2.  Informative References

   [3]  Fowler, D., "Definitions of Managed Objects for the DS1, E1, DS2
        and E2 Interface Types", RFC 2495, January 1999.

   [4]  Fowler, D., "Definitions of Managed Objects for the DS3/E3
        Interface Type", RFC 2496, January 1999.

   [5]  Tesink, K., "Definitions of Managed Objects for the Synchronous
        Optical Network/Synchronous Digital Hierarchy (SONET/SDH)
        Interface Type", RFC 3592, September 2003.

   [6]  American National Standard for Telecommunications - Digital
        Hierarchy - Layer 1 In-Service Digital Transmission Performance
        Monitoring, ANSI T1.231-1997, September 1997.

   [7]  Bathrick, G. and F. Ly, "Definitions of Managed Objects for the
        ADSL Lines", RFC 2662, August 1999.

   [8]  Ray, B., and R. Abbi, "Definitions of Managed Objects for High
        Bit-Rate DSL - 2nd generation (HDSL2) and Single-Pair High-Speed
        Digital Subscriber Line (SHDSL) Lines", RFC 3276, May 2002.

   [9]  Ray, B. and R. Abbi, "High Capacity Textual Conventions for MIB
        Modules Using Performance History Based on 15 Minute Intervals",
        Work in Progress.

8.  Security Considerations

   This memo defines textual conventions for use in other MIB modules.
   Security issues for these MIB modules are addressed in the memos
   defining those modules.

9.  Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

10.  Editor's Address

   Kaj Tesink
   Telcordia Technologies
   331 Newman Springs Road
   P.O. Box 7020
   Red Bank, NJ  07701-7020

   Phone: +1 732 758 5254
   EMail: kaj@research.telcordia.com

11.  Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.