home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Internet Standards
/
CD2.mdf
/
ccitt
/
1992
/
e
/
e880.asc
< prev
next >
Wrap
Text File
|
1991-12-30
|
21KB
|
502 lines
Recommendation E.880
FIELD DATA COLLECTION AND EVALUATION ON THE PERFORMANCE
OF EQUIPMENT, NETWORKS AND SERVICES
1 Introduction
This Recommendation provides guidelines for the collection of field data
relating to dependability. It covers general aspects with an overview of sources,
measures and information that may be involved when collecting field data. It is
anticipated that specific practical needs of operation, maintenance and planning
staff, in applying these guidelines, will be dealt with in a handbook under
preparation.
The Recommendation emphasizes that meaningful data must include the data
on successes (operation without failures) as well as data on failures and faults.
In other words, this Recommendation is not intended to be only a failure
reporting guideline.
It is applicable, without any restriction, to different items ranging from
components to systems and networks (including hardware, software and people).
Terms and definitions used are in line with Recommendation E.800.
2 Scope
It is the intention of this Recommendation to provide guidelines for
setting up data collection and reporting schemes which can be applied either
during monitoring of samples of items or on a more widespread basis on almost all
items (of the same type) by large operational and maintenance organizations.
It is considered that, if such guidelines are followed, accuracy and
completeness of reporting are enforced and the quality of the monitored items and
their parts can be improved on a medium- to long-term basis. Moreover, such an
effort will facilitate the interchange of information between user and providers.
No recommendations are made on how to organize maintenance support. It is
nevertheless understood that some items are repaired on site, others only
replaced on site and possibly repaired at centralized facilities. Field data may
be obtained at each of those stages.
In order to obtain maximum efficiency from the collection of data, it is
suggested that the programmes of reporting, analysis and dissemination of results
be closely co-ordinated.
The items considered may either have been designed, manufactured, or
installed and may be operated by the same organization or by different
organizations. This Recommendation applies to all possible cases of provider-user
relations.
3 The need for data collection
Any data collection scheme must aim to provide the information required to
enable the correct decisions to be taken in order to reach specified objectives;
these objectives should be well defined and documented at the outset.
Fascicle II.3 - Rec. E.880 PAGE1
The specific objectives of the field data collection and presentation are
as follows:
a) to provide for a survey of the actual performance level of the items
monitored for information to management, operation and planning,
maintenance support, training of personnel, etc.;
b) to indicate a possible need for the improvement of:
- items already installed and in operation, or
- further items to be delivered;
c) to compare the specified or predicted characteristics of the item(s)
with the actual field performance;
d) to improve future designs;
e) to improve predictions (data bases and procedures);
f) to inform the provider about the performance of items on a regular or
on a single occasion basis;
g) to have a common reporting basis.
4 Sources and means of data collection
In the following, the various information sources are described and the
methods for systematically collecting information are outlined.
4.1 Sources of data
The following sources of data may generally be available:
- maintenance activities;
- repair activities (on site, repair and/or complaint centre);
- performance observation activities (e.g. anomaly reports, traffic
measurements);
- existing information (e.g. stocklist, installation list, modifications,
a regularly updated data base for configuration control purposes).
4.2 Means of collecting data
It is not intended to recommend any particular format for the recording
medium (e.g. paper based or computer data base), however it should be recognized
that early consideration of the format is necessary and important in setting up
an effective data collection scheme and also aids subsequent successful
processing.
Frequently the recording of data will be by manual means but automated and
interactive data collection systems may be also considered. The advantages to be
gained from holding data in a form suitable for processing by an electronic data
processing system include easy and accurate updating of information and the
possibility of performing new extended analyses.
Data may be collected by one or several of the following reporting means.
4.2.1 Operation reporting
Data reporting should be supported by information on the use of the items.
Where systems are in operation for the reporting of all failures, it is necessary
to collect data on the use of the whole population of items (the total number of
similar items under observation).
4.2.2 Failure reporting
At any level, failure reporting is dependent on the fault coverage test
resources used at the considered level: cases such as "fault not found" or "right
when tested" should be clearly mentioned.
Failure reporting should cover all failures that have been observed. They
should also contain sufficient information to identify failures. Failures
considered to be attributable to any maintenance action should be so noted.
The failure reporting should be sufficiently comprehensive to cover the
requirements of detailed investigation of an individual failure and the resulting
fault. Where economic reasons or lack of resources make it undesirable to collect
all of the failure data indicated, it may be desirable to agree upon a shortened
form of report which can be used to collect limited data on all relevant
failures, with an option to call for the full report in specific cases.
4.2.3 Maintenance reporting
The maintenance report should contain all information relevant to the
manual or automatic action taken to restore the item.
When there is need to distinguish between corrective maintenance and
preventive maintenance reporting, if no replacements or repairs are made, the
action can be classified as a preventive maintenance report. If a preventive
maintenance action results in a replacement or repair, the report may be treated
as a corrective maintenance report even though the item has in fact not failed in
operation.
PAGE4 Fascicle II.3 - Rec. E.880
4.3 Storage, updating and checking procedures
Independently of the structure chosen for the data storage, data should be
checked at the time of input so as to ensure validity.
It is evident that every data bank needs an in-depth study appropriate to
its specific requirements, in order to define the most suitable method of data
checking, error correction, and updating.
5 List of dependability measures
The selection of the data to be collected is very dependent on the kind of
performance measures to be evaluated/estimated.
Field data reporting may have to be limited by economic necessity to the
minimum necessary to meet the requirement, whilst recognizing that collection
systems should be capable of future expansion.
It is likely that certain data may be needed for more than one purpose,
and careful consideration can therefore result in the most cost-effective data
collection scheme.
The dependability measures that might be taken into consideration are
listed as follows.
5.1 Reliability performance
Failure rate
Failure intensity
Replacement intensity
Mean operating time between failures
[.]1) Up time.
5.2 Maintainability performance
5.2.1 Time related performance
[.]1) Down time
[.]1) Technical delay
[.]1) Fault localization time
[.]1) Fault correction time
[.]1) Restart time
[.]1) Checkout time
[.]1) Repair time
[.]1) Active corrective maintenance time.
5.2.2 Probabilities
Probability of fault coverage
Probability of false alarm
Probability of fault nondetection
Probability of alarm detection
Probability of a failure being localized within a given number of
replaceable units.
5.3 Maintenance support performance
5.3.1 Time related performance
[.]2) Logistic time
[.]2) Administrative delay.
5.3.2 Probabilities
Spare parts shortage probability
Test resource shortage probability
Human resource shortage probability.
1) [.] indicates according to specific applications a mean value or a fractile.
2) [.] indicates according to specific applications a mean value or a fractile.
Fascicle II.3 - Rec. E.880 PAGE1
5.4 Availability performance
Steady state availability
[.]2) Accumulated down time.
6 Data required
Consideration of the foregoing objectives defines the need for a system
which provides for the collection of documented data covering:
a) the identity of items or population of items under observation;
b) operational conditions;
c) maintenance support conditions;
d) performance monitoring.
For each individual item, sufficient information has to be recorded to
clearly identify the item itself and its operating environment.
Depending on the item under consideration (e.g. equipment, printed circuit
board, component, personnel), and on the depth and kind of analysis of collected
data, the necessary item identification data shall be used, on a case by case
basis.
The item identification should also allow the analysis of the
relationships between the items for which data is collected.
In relation to the particular analysis to be done, some items may be
considered as equivalent, therefore separate small items need not to be collected
in such cases.
The following information may be needed and could be collected or will be
available from existing sources:
- type of item
- manufacture/provider
- item configuration
- individual No. or serial No.
- date of manufacture
- supplier
- delivery date
- installer (company)
- installation date
- customer (name)
- site (geographic)
- system.
Consideration should be given to possible limitations due to
non-completeness of collected data or possible difficulties in data collection or
particular assumptions made for the collection itself.
The choice of the kinds of data to be collected and the design of the
related collection procedure depend on many factors, some of which are:
- the required end-result;
- the diversity of components or systems;
- the duration of the data collection project;
- the data handling method (manual or computer based);
- a sufficient knowledge of the capability to collect the required
quantity of information and the accessibility to data to be gathered.
6.1 Number of items to be considered
The number of items to be considered depends mainly on the characteristics
to be dealt with, the statistical aspect of the evaluation to be made and the
cost involved.
6.2 Information on items being considered
6.2.1 Operating conditions
6.2.1.1 Environment classes
a) Fixed (outdoors, indoors, underground, undersea, off-shore, etc.);
PAGE4 Fascicle II.3 - Rec. E.880
b) Portable (item specially built for easy transportation by one man
only);
c) Mobile (in motor vehicle, in ship, in aircraft);
d) Other (specify).
6.2.1.2 Specific environment data
a) Climatic conditions
- weather-protected,
- not weather protected,
- air temperature,
- air pressure,
- humidity;
b) Electrical environment (EMC);
c) Mechanical conditions (vibration, shocks, bumps);
d) Mechanically active substances (sand, dust, etc.);
e) Chemically active substances;
f) Biological conditions.
6.2.1.3 Mode of operation
a) Continuous;
b) Intermittent (give cycle);
c) Stand-by;
d) Single operation (e.g. one shot devices);
e) Storage.
6.2.1.4 Load conditions
a) Overload;
b) Other (specified).
6.3 Failure and fault description
- Fault recognition: symptoms and indications, fault detected, fault not
detected, false alarm.
- Item fault mode (identification of functions affected).
- Failure causes:
a) Inherent to item under observation;
b) Misuse failure;
c) Induced by maintenance or administrative action;
d) External to item under observation;
e) Secondary (caused by related item);
Fascicle II.3 - Rec. E.880 PAGE1
f) Other.
In cases where the failure immediately follows a period of transport,
storage or stand-by, the relevant conditions shall be stated.
- Fault consequences
- List (identification) and physical location of faulty replaced parts:
a) quantity of suspected replaceable items;
b) quantity of replaced items.
- Fault evidence and documentation (printouts, photograph, etc.).
- Action taken: Replacement, repair, adjustment, modification,
lubrication, etc.
- Active maintenance time (diagnostic + repair + tests + . . .).
- Downtime, including, where applicable:
- undetected fault time,
- fault localization time,
- reconfiguration time3),
- technical delay,
- logistic delay,
- administrative delay,
- fault correction time,
- checkout time,
- restart time.
6.4 Maintenance support data:
- spare resources shortage,
- test resources shortage,
- resources shortage.
7 Data presentation for evaluation
When collected data is offered for subsequent evaluation by using
approximate statistical methods, all conditions for their correct use and
understanding should be clearly stated.
These conditions should encompass the purpose of the data gathering
especially with respect to type and variation of the data chosen. Information on
the circumstances should also be provided such as when (e.g. busy hour
conditions), where (e.g. geographic considerations) and for how long the
collection took place. Specific situations, which may limit the data application
and use, should be indicated, e.g. difficulties encountered, particular
assumptions made, non-completeness.
Considerations should also be given to the form of presentation: where
appropriate, a condensed form (e.g. diagrams, histograms) may prevail over a
detailed raw data presentation.
8 Statistical methods for data treatment
In most cases the need for data treatment appears in connection with one
of the following activities:
- estimation,
- compliance evaluation,
- monitoring of performances,
- comparison of performances.
For each performance of interest, estimations, hypothesis tests, control
charts and comparison techniques are used for evaluating.
The application of a given statistical procedure usually requires the
fulfilment of some general conditions and assumptions which have to be carefully
investigated. Some of these preliminary investigations relate directly to the
properties and the characteristics of the (stochastic) process generating the
collected data, some other relate to the distribution underlying the collected
data.
Both preliminary investigations and data treatment may require statistical
procedures not dealt with in this Recommendation. International organizations
other than CCITT, e.g. IEC, have produced valuable material in this field [1].
Reference
3) Time required for automatic reconfiguration (if manual operations are needed, they are
integrated into technical delay).
PAGE4 Fascicle II.3 - Rec. E.880
[1] International Electrotechnical Commission - Catalogue of Publications, Ed.
1987.
Fascicle II.3 - Rec. E.880 PAGE1
