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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:

Tesink, Ed. Standards Track [Page 1] RFC 2493 15 Minute Based Performance History TCs January 1999

 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.

Tesink, Ed. Standards Track [Page 2] RFC 2493 15 Minute Based Performance History TCs January 1999

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

Tesink, Ed. Standards Track [Page 3] RFC 2493 15 Minute Based Performance History TCs January 1999

        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 }
  1. - The Textual Conventions defined below are organized
  2. - alphabetically
  1. - Use of these TCs assumes the following:
  2. - 0 The agent supports 15 minute based history
  3. - counters.
  4. - 0 The agent is capable of keeping a history of n
  5. - intervals of 15 minute performance data. The
  6. - value of n is defined by the specific MIB
  7. - module but shall be 0 < n =< 96.
  8. - 0 The agent may optionally support performance
  9. - data aggregating the history intervals.
  10. - 0 The agent will keep separate tables for the
  11. - current interval, the history intervals, and
  12. - the total aggregates.
  13. - 0 The agent will keep the following objects.
  14. - If performance data is kept for multiple instances
  15. - of a measured entity, then
  16. - these objects are applied to each instance of
  17. - the measured entity (e.g., interfaces).
  18. -
  1. - xyzTimeElapsed OBJECT-TYPE
  2. - SYNTAX INTEGER (0..899)
  3. - MAX-ACCESS read-only
  4. - STATUS current
  5. - DESCRIPTION

Tesink, Ed. Standards Track [Page 4] RFC 2493 15 Minute Based Performance History TCs January 1999

  1. - "The number of seconds that have elapsed since
  2. - the beginning of the current measurement period.
  3. - If, for some reason, such as an adjustment in the
  4. - system's time-of-day clock, the current interval
  5. - exceeds the maximum value, the agent will return
  6. - the maximum value."
  7. - ::= { xxx }
  1. - xyzValidIntervals OBJECT-TYPE
  2. - SYNTAX INTEGER (0..<n>)
  3. - MAX-ACCESS read-only
  4. - STATUS current
  5. - DESCRIPTION
  6. - "The number of previous near end intervals
  7. - for which data was collected.
  8. - [ The overall constraint on <n> is 1 =< n =< 96; ]
  9. - [ Define any additional constraints on <n> here. ]
  10. - The value will be <n> unless the measurement was
  11. - (re-)started within the last (<n>*15) minutes, in which
  12. - case the value will be the number of complete 15
  13. - minute intervals for which the agent has at least
  14. - some data. In certain cases (e.g., in the case
  15. - where the agent is a proxy) it is possible that some
  16. - intervals are unavailable. In this case, this
  17. - interval is the maximum interval number for
  18. - which data is available."
  19. - ::= { xxx }
  1. - xyzInvalidIntervals OBJECT-TYPE
  2. - SYNTAX INTEGER (0..<n>)
  3. - MAX-ACCESS read-only
  4. - STATUS current
  5. - DESCRIPTION
  6. - "The number of intervals in the range from
  7. - 0 to xyzValidIntervals for which no
  8. - data is available. This object will typically
  9. - be zero except in cases where the data for some
  10. - intervals are not available (e.g., in proxy
  11. - situations)."
  12. - ::= { 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

Tesink, Ed. Standards Track [Page 5] RFC 2493 15 Minute Based Performance History TCs January 1999

             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

Tesink, Ed. Standards Track [Page 6] RFC 2493 15 Minute Based Performance History TCs January 1999

         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.

Tesink, Ed. Standards Track [Page 7] RFC 2493 15 Minute Based Performance History TCs January 1999

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.

Tesink, Ed. Standards Track [Page 8] RFC 2493 15 Minute Based Performance History TCs January 1999

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
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 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
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Tesink, Ed. Standards Track [Page 9]

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