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RFC 2493 - Textual Conventions for MIB Modules Using Performance


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Network Working Group                                K. Tesink, Editor
Request for Comments: 2493                                    Bellcore
Category: Standards Track                                 January 1999

     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 (1999).  All Rights Reserved.

Abstract

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

1. Table of Contents

   1 Table of Contents .....................................    1
   2 Introduction ..........................................    1
   3 Note on Invalid Data and Proxy ........................    2
   4 Note on xyzTimeElapsed ................................    3
   5 Note on xyzValidIntervals .............................    3
   6 Definitions ...........................................    3
   7 Acknowledgments .......................................    7
   8 References ............................................    7
   9 Security Considerations ...............................    8
   10 IANA Considerations ..................................    8
   11 Author's Address .....................................    8
   12 Intellectual Property ................................    8
   13 Full Copyright Statement .............................    9

2.  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] 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 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 a 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 RFC1903[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. See
   for example the Trunk MIB modules [3][4][5].

3.  Note on Invalid Data and Proxy

   In this document, the word proxy is meant to indicate 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.

4.  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.

5.  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]).

6.  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 "9811071100Z"
          ORGANIZATION "IETF AToMMIB and TrunkMIB WGs"
          CONTACT-INFO
                       "Kaj Tesink
              Postal:  Bellcore
                       331 Newman Springs Road
                       Red Bank, NJ 07701
                       USA
              Tel:     +1 732 758 5254
              Fax:     +1 732 758 2269
              E-mail:  kaj@bellcore.com"
          DESCRIPTION
           "This MIB Module provides Textual Conventions
             to be used by systems supporting 15 minute
             based performance history counts."
          ::= { 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

7.  Acknowledgments

   This document is a product of the AToMMIB and TrunkMIB Working
   Groups.

8.  References

   [1]  Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
        "Textual Conventions for Version 2 of the Simple Network
        Management Protocol (SNMPv2)", RFC 1903, January 1996.

   [2]  Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
        "Structure of Management Information for Version 2 of the Simple
        Network Management Protocol (SNMPv2)", RFC 1902, January 1996.

   [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 SONET/SDH
        Interface Type", Work in Progress.

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

9.  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.

10.  IANA Considerations

   Prior to publication of this memo as an RFC, IANA is requested to
   make a suitable OBJECT IDENTIFIER assignment.

11.  Author's Address

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

   Phone: (732) 758-5254
   EMail: kaj@bellcore.com

12.  Intellectual Property

   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.

13.  Full Copyright Statement

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
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   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
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   followed, or as required to translate it into languages other than
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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