rfc2493.txt

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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:



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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.




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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



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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:     [phone]
              Fax:     [phone]
              E-mail:  [e-mail]"
          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



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RFC 2493        15 Minute Based Performance History TCs     January 1999


     --       "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