RFC2493 - Textual Conventions for MIB Modules Using Performance History Based on

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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)", RFC1903, 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)", RFC1902, January 1996.

[3] Fowler, D., "Definitions of Managed Objects for the DS1, E1, DS2
and E2 Interface Types", RFC2495, January 1999.

[4] Fowler, D., "Definitions of Managed Objects for the DS3/E3
Interface Type", RFC2496, 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
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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.

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