5i'
PART IV
SUPPLEMENTS TO THE SERIES E RECOMMENDATIONS
RELATING TO TELEPHONE NETWORK MANAGEMENT
AND TRAFFIC ENGINEERING
MONTAGE: PAGE PAIRE = PAGE BLANCHE
Supplement No. 1
TABLE OF THE ERLANG FORMULA
Table of the
Erlang loss formula
(Erlang No. 1 formula, also called Erlang B formula)
Loss probabilities : 1%, 3%, 5%, 7%.
Let p = the loss probability y = the
traffic offered (in Erlangs) n = the number of cir
cuits v'2P' v'3p' Formula: E 1, n (y ) = p = $$2o
fIn !
________ $$3u1 + [Formula Deleted] !
_____ + fIn !
________ $$3e
H.T. [T1.1]
Unable to convert table Table 1 [T1.1], p.
Supplement No. 2
CURVES SHOWING THE
RELATION BETWEEN THE TRAFFIC OFFERED
AND THE NUMBER OF CIRCUITS REQUIRED
Figure 1, p.
Figure 2, p.
Supplement No. 3
INFORMATION ON TRAFFIC ROUTING IN THE INTERNATIONAL NETWORK
(Results from study in 19731976 of Question 11/XIII
concerning actual connections of international telephone calls
(For the text of this Supplement, see Supplement No. 7,
Volume II.2, Orange Book , Geneva, 1976)
Supplement No. 4
USE OF COMPUTERS FOR NETWORK PLANNING AND CIRCUIT
GROUP DIMENSIONING
(For the text of this Supplement, see Supplement No. 8,
Volume II.2, Orange Book , Geneva, 1976)
Supplement No. 5
TELETRAFFIC IMPLICATIONS FOR INTERNATIONAL SWITCHING AND
OPERATIONAL  PROCEDURES RESULTING FROM A FAILURE OF A
TRANSMISSION FACILITY
1 Very considerable changes have occurred in the international
network over the past decade. These changes have arisen mainly
from:
 the growth in the number of longdistance routes;
 the growth in the number of circuits forming
individual longdistance routes;
 the worldwide introduction of international
automatic operation;
 technological developments associated with all
aspects of the international network: switching unit design,
transmission facility design, and routing and operational stra
tegies;
 the integration into the international automatic
service of the more isolated geographical areas and of centres hav
ing lowcapacity international switching units.
2 The resultant multiplicity of circumstances and situations
arising within the international network is now such that it is no
longer possible to specify one single criterion for initiating
corrective action to counter the loss of a transmission facility.
Indeed, the failure of the whole, or part, of a transmission facil
ity may manifest itself in a different manner to each of several
Administrations affected by the failure.
3 Among the many aspects of international switching and opera
tional procedures which can influence the degree of curtailment of
service arising from a transmissionfacility failure, i.e. which
can reduce the ability of part of the international network to
carry its designed traffic load successfully, the following are
specifically stressed (their order has no particular significance):
 the introduction of fully automatic interna
tional operation, which means that the control of the network,
formerly completely operator controlled, now depends directly on
subscribers' habits;
 the number of routes that could be affected by
failure and their proportion of the total routes on the switching
unit to which they are directly connected: the range can be from
one whole route to a few circuits in each of many routes, depending
on the method of allocating circuits to transmission facilities;
 the influence of any route, for which no alterna
tive transmission facility exists, on the performance of the inter
national switching unit to which it is connected;
 the effect on the grade of service of the switch
ing unit itself due to the loss of a complete route or routes, or
parts of several routes, directly connected to it;
 the methods of limiting the effect of failure on
service by action within the switching unit or at preceding inter
national or national switching unit, e.g. by code blocking or
recorded announcements;
 the cause of the failure, and thus the possible
restoration time, relative to the 24hour traffic profile;
 the effect of a failure on overflow and automatic
alternative routing strategies ;
 the use of diversity of international switching
units;
 the use of diversity of international transmis
sion facilities.
4 Attention is also drawn to four major factors of maintaining
continuity of service:
 reliability ,
 diversity,
 network management , and
 any redundancy specifically provided to allow
restoration of service.
5 Clearly, no practical transmission facility provided will
give 100 per cent reliability, so it is inevitable that the other
three factors will be involved to varying degrees in maintaining
service. The interaction of these four factors will depend largely
on the emphasis placed upon each of them by each Administration,
thus reinforcing the view that the degree of corrective action that
can be taken will depend considerably upon the investment policy
(in materials and equipment) and forwardplanning objectives of
individual Administrations.
6 With respect to diversity, it is recommended that Adminis
trations give consideration to the provision of an adequate number
of paths for a particular route, with an adequate level of indepen
dence between the paths. Such independence could reduce the effect
of a breakdown or other adverse event by confining it, as far as
possible, to only one of the paths used by that route.
7 For the further assistance of Administrations in their study
of those teletraffic aspects of international switching and opera
tional procedure which influence the degree of curtailment of
service and which arise from a transmission facility failure, these
factors are included in Question 23/II related to continuity of
service, accepted for study during the 19851988 Study Period.
Supplement No. 6
TERMS AND DEFINITIONS FOR QUALITY OF SERVICE, NETWORK PERFORMANCE,
DEPENDABILITY AND TRAFFICABILITY STUDIES
CONTENTS
PART I  Dependability Vocabulary
1 Introduction
2 Related Recommendations
3 Basic concepts
4 Performances
5 Events and states
5.1 Defects
5.2 Failures
5.3 Faults
5.4 Errors and mistakes
5.5 States
6 Maintenance
7 Time concepts
7.1 Maintenance related times
7.2 Item state related times
7.3 Time concepts related to reliability perfor
mance
8 Measures of performances
8.1 Availability performance
8.2 Reliability performance
8.3 Maintainability performance
8.4 Maintenance support performance
9 Test, data, design and analysis
9.1 Test concepts
9.2 Data concepts
9.3 Design concepts
9.4 Analysis concepts
9.5 Improvement processes
10 Measure modifiers
PART II  Statistical vocabulary
1 Introduction
2 Terms and definitions
Annex A: Alphabetical list of definitions contained in this
Supplement
Annex B: Relations between defect, failure and fault con
cepts
Annex C: List of recommended symbols and abbreviations
PART I
Dependability Vocabulary
1 Introduction
A consistent set of terms and definitions is required for the
development and use of the various Recommendations addressing
aspects relating the specifications, planning, data collection,
analysis and evaluation of the dependability, including availabil
ity performance, reliability performance, maintainability perfor
mance and maintenance support performance. These needs address the
whole range of operational and maintenance aspects as applicable to
telecommunication networks, exchanges, transmission routes and
channels, etc., independent of the types of services supported,
including aspects of providing the necessary maintenance.
The vocabulary provided by this Supplement is also of impor
tance in the handling of concepts related to quality of service and
network performance. The conceptual relationships between quality
of service and network performance to dependability and other
itemrelated performances is shown in Figure 1. Further information
on these performances is found in Recommendation E.800.
The vocabulary also provides the necessary linking to the per
formances of components and building blocks (hardware and software)
of networks at any level of indenture (ref. definition 6019).
Figure 1, p.
For the quantitative application and determination of meas
ures, the terms and definitions of Part II also need to be con
sulted.
2 Related Recommendations
E.600  Terms and definitions of traffic engineering
E.800  Quality of service and dependability vocabulary.
3 Basic concepts
3001 item; entity
F: entite; individu
S: elemento; entidad; item
Any part, device, subsystem, functional unit, equipment or
system that can be individually considered.
Note 1  An item  ay consist of hardware, software or both,
and may also include people, e.g. operators in a telephone operator
system.
Note 2  In French, the term entite  eplaces the term
dispositif  reviously used in this meaning, because the term
dispositif is also the common equivalent for the English term "dev
ice".
Note 3  In French, the term individu  s used mainly in
statistics.
3002 repaired item
F: entite reparee
S: elemento reparado
A repairable item  hich is in fact repaired after a failure
.
3003 nonrepaired item
F: entite non reparee
S: elemento no reparado
An item  hich is not repaired after a failure .
Note  A nonrepaired item  ay be repairable or not.
3005 required function
F: fonction requise
S: funcion requerida
A function or a combination of functions of an item  hich is
considered necessary for the provisioning of a given service .
3006 functional mode
F: mode de fonctionnement
S: modo de funcionamiento
A subset of the whole set of possible functions of an item .
3007 instant of time
F: instant
S: instante (de tiempo)
A single point on a time scale.
Note  The time scale may be continuous as calendar time, or
discrete, e.g. number of use cycles.
3008 time interval
F: intervalle de temps
S: intervalo de tiempo
All instants of time  etween two given instants of time .
3009 (time) duration
F: duree
S: duracion
The difference between the end points of a time interval .
3010 accumulated time
F: duree cumulee
S: tiempo acumulado
The sum of time durations  haracterized by given conditions
over a given time interval .
3011 measure (as applied in the study of reliability per
formance and related areas)
F: caracteristique (probabilite); mesure (en fiabilite
et domaines connexes)
S: medida (aplicada en estudios de fiabilidad y de
aspectos conexos)
A function or quantity used to describe a random variable  r
a random process .
Note  For a random variable , examples of measures
 re the distribution function  nd the mean .
3012 operation
F: exploitation
S: explotacion; operacion
Combination of all technical and corresponding administrative
actions intended to allow an item  to perform a required function
, recognizing necessary adaptation to changes in external condi
tions.
Note  By external conditions are understood, for example,
service demand and environmental conditions.
3013 modification (of an item)
F: modification (d'une entite)
S: modificacion (de un elemento)
The combination of all technical and corresponding administra
tive actions intended to alter the capability of an item by chang
ing, adding or deleting one or more required functions .
4 Performances
4001 dependability
F: s  rete de fonctionnement
S: seguridad de funcionamiento
The collective term used to describe the availability perfor
mance  nd its influencing factors: reliability performance, main
tainability performance and maintenance support performance .
Note  Dependability is used only for general descriptions in
nonquantitative terms.
4002 availability performance
F: disponibilite
S: disponibilidad
The ability of an item  o be in a state to perform a
required function  t a given instant of time or at any instant of
time within a given time interval , assuming that the external
resources, if required, are provided.
Note 1  This ability depends on the combined aspects of the
reliability performance , the maintainability performance and the
maintenance support performance of an item .
Note 2  In the definition of the item  he external
resources required must be delineated.
Note 3  The term availability  s used as an availability
performance measure .
Note 4  Warning: the term availability has occasionally been
used in connection with the term item , but with an implied meaning
of item being entirely different from that of this Supplement.
4003 reliability performance
F: fiabilite
S: fiabilidad
The ability of an item  o perform a required function 
nder given conditions for a given time interval .
Note 1  It is generally assumed that the item  s in a
state to perform this required function at the beginning of the
time interval .
Note 2  The term reliability  s used as a measure of reli
ability performance .
4004 maintainability performance
F: maintenabilite
S: mantenibilidad
The ability of an item  nder stated conditions of use, to be
retained in, or restored to, a state in which it can perform a
required
function , when maintenance is performed under given condi
tions and using stated procedures and resources.
Note  The term maintainability  s used as a measure
 f maintainability performance .
4005 maintenance support performance
F: logistique de maintenance
S: logistica de mantenimiento
The ability of a maintenance organization, under given condi
tions, to provide upon demand the resources required to maintain an
item , under a given maintenance policy .
Note  The given conditions are related to the item  tself
and to the conditions under which the item is used and maintained.
4006 durability
F: durabilite
S: durabilidad
The ability of an item  o remain in a condition where it can
perform a required function under stated conditions of use and
maintenance until a limiting state is reached.
Note  A limiting state of an item  ay be characterized by
the end of the useful life , unsuitability for any economic or
technological reasons, etc.
5 Events and states
5.1 Defects
5101 defect
F: defaut
S: defecto
Any departure of a characteristic of an item  rom require
ments.
Note 1  The requirements may or may not be expressed in the
form of a specification.
Note 2  A defect may or may not affect the ability of an
item  o perform a required function .
5102 bug
F: erreur de programmation; bogue
S: error de programacion
A software defect  aused by a mistake .
5103 critical defect
F: defaut critique
S: defecto critico
A defect  hat is assessed likely to result in injury to per
sons or significant material damage.
5104 noncritical defect
F: defaut non critique
S: defecto no critico
A defect  ther than a critical defect .
5105 major defect
F: defaut majeur
S: defecto mayor
A defect  hat is likely to result in a failure  r to
reduce materially the usability of the item for its intended pur
pose.
5106 minor defect; imperfection
F: defaut mineur; imperfection
S: defecto menor; imperfeccion
A defect other than a major defect .
5107 defective; defective item
F: defectueux; entite defectueuse
S: defectuoso; elemento defectuoso
An item  hich contains one or more defects .
5108 critical defective item
F: defectueux critique
S: elemento defectuoso critico
An item  hich contains one or more critical defect .
5109 major defective item
F: defectueux majeur
S: elemento defectuoso mayor
An item  which contains one or more major defects .
5110 minor defective item
F: defectueux mineur
S: elemento defectuoso menor
An item  hich contains one or more minor defects  ut no
major defects .
5111 design defect
F: defaut de conception
S: defecto de dise~o
A defect  ue to an inadequate design of an item .
5112 manufacturing defect
F: defaut de fabrication
S: defecto de fabricacion
A defect  ue to nonconformance in manufacture to the design
of an item or to specified manufacturing processes.
5.2 Failures
5201 failure
F: defaillance
S: fallo
The termination of the ability of an item  o perform a
required function .
Note  After failure  he item  as a fault.
5202 critical failure
F: defaillance critique
S: fallo critico
A failure  hich is assessed likely to result in injury to
persons or significant material damage.
5203 noncritical failure
F: defaillance non critique
S: fallo no critico
A failure  ther than a critical failure .
5204 misuse failure
F: defaillance par mauvaise utilisation
S: fallo por uso incorrecto
A failure  ue to induced stresses during use which are
beyond the stated capabilities of the item .
5205 mishandling failure
F: defaillance par fausse manoeuvre
S: fallo por manejo incorrecto
A failure  aused by incorrect handling or lack of care of
the item
5206 (inherent) weakness failure
F: defaillance par fragilite (inherente)
S: fallo por fragilidad (inherente)
A failure  ue to a weakness inherent in the item  tself
when subjected to stresses within the stated capabilities of the
item
5207 design failure
F: defaillance de conception
S: fallo de dise~o
A failure  ue to a design defect .
5208 manufacturing failure
F: defaillance de fabrication
S: fallo de fabricacion
A failure  ue to a manufacturing defect .
5209 ageing failure; wearout failure
F: defaillance par vieillissement; defaillance par
usure
S: fallo por envejecimiento; fallo por desgaste
A failure  hose probability of occurrence increases with the
passage of time, as a result of processes inherent in the item .
5210 sudden failure
F: defaillance soudaine
S: fallo repentino
A failure  hat could not be anticipated by prior examination
or monitoring.
5211 gradual failure; degradation failure; drift failure
F: defaillance progressive; degradation; defaillance par
derive
S: fallo gradual; fallo por degradacion; fallo por
deriva
A failure  ue to a gradual change in time of given charac
teristics of an item and that could be anticipated by prior exami
nation or monitoring.
Note  A gradual failure  an sometimes be avoided by
preventive maintenance .
5212 cataleptic failure; catastrophic failure (deprecated)
F: defaillance cataleptique
S: fallo cataleptico; fallo catastrofico  (desacon
sejado)
A sudden failure  hich results in a complete fault .
5213 relevant failure
F: defaillance pertinente; defaillance a prendre en
compte
S: fallo pertinente; fallo relevante
A failure  o be included in interpreting test or operational
results or in calculating the value of a reliability performance
measure .
Note  The criteria for the inclusion should be stated.
5214 nonrelevant failure
F: defaillance non pertinente; defaillance a ne pas
prendre en compte
S: fallo no pertinente; fallo irrelevante
A failure  o be excluded in interpreting test or operational
results or in calculating the value of a reliability performance
measure
Note  The criteria for the exclusion should be stated.
5215 primary failure
F: defaillance primaire
S: fallo primario
A failure  f an item , not caused either directly or
indirectly by the failure or the fault of another item .
5216 secondary failure
F: defaillance secondaire
S: fallo secundario
A failure  f an item , caused either directly or indirectly
by the failure  r the fault of another item .
5217 failure cause
F: cause de defaillance
S: causa de fallo
The circumstances during design, manufacture or use which have
led to a failure .
5218 failure mechanism
F: mecanisme de defaillance
S: mecanismo de fallo
The physical, chemical or other process which has led to a
failure .
5219 systematic failure; reproducible failure; determinis
tic failure
F: defaillance systematique; defaillance reproductible
S: fallo sistematico; fallo reproducible; fallo
deterministico
A failure  elated in a deterministic way to a certain cause,
which can only be eliminated by a modification of the design or
manufacturing process, operational procedures, documentation or
other relevant factors.
Note 1  Corrective maintenance  ithout modification will
usually not eliminate the failure cause .
Note 2  A systematic failure  an be induced at will by
simulating the failure cause .
5.3 Faults
5301 fault
F: panne; derangement
S: averia
The inability of an item  o perform a required function ,
excluding that inability due to preventive maintenance , lack of
external resources or planned actions.
Note  A fault  s often the result of a failure
 f the item itself, but may exist without prior failure .
5302 critical fault
F: panne critique
S: averia critica
A fault  hich is assessed likely to result in injury to per
sons or significant damage to material.
5303 noncritical fault
F: panne non critique
S: averia no critica
A fault , other than a critical fault .
5304 major fault
F: panne majeure
S: averia mayor
A fault  hich affects a function considered to be of major
importance.
5305 minor fault
F: panne mineure
S: averia menor
A fault  ther than a major fault .
5306 misuse fault
F: panne par mauvaise utilisation
S: averia por uso incorrecto
A fault  ue to induced stresses during use which are beyond
the stated capabilities of the item .
5307 mishandling fault
F: panne par fausse manoeuvre
S: averia por manejo incorrecto
A fault  aused by incorrect handling or lack of care of the
item .
5308 (inherent) weakness fault
F: panne par fragilite (inherente)
S: averia por fragilidad (inherente)
A fault  ue to a weakness inherent in the item  tself when
subjected to stresses within the stated capabilities of the item
5309 design fault
F: panne de conception
S: averia de dise~o
A fault  ue to a design defect .
5310 manufacturing fault
F: panne de fabrication
S: averia de fabricacion
A fault  ue to a manufacturing defect .
5311 ageing fault; wearout fault
F: panne par vieillissement; panne par usure
S: averia por envejecimiento; averia por desgaste
A fault  esulting from an ageing failure .
5312 programmesensitive fault
F: panne mise en evidence par le programme
S: averia dependiente del programa
A fault  hat is revealed as a result of the execution of
some particular sequence of instructions.
5313 datasensitive fault
F: panne mise en evidence par les donnees
S: averia dependiente de los datos
A fault  hat is revealed as a result of the processing of a
particular pattern of data.
5314 complete fault; function preventing fault
F: panne complete
S: averia completa
A fault  haracterized by complete inability to perform all
required functions of an item .
Note  The criteria for a complete fault  ave to be stated.
5315 partial fault
F: panne partielle
S: averia parcial
A fault  f an item  ther than a complete fault .
5316 persistent fault; permanent fault; solid fault
F: panne permanente
S: averia permanente
A fault  f an item  hat persists until an action of
corrective maintenance is performed.
5317 intermittent fault; volatile fault; transient fault
F: panne intermittente; panne temporaire
S: averia intermitente; averia transitoria
A fault of an item  hich persists for a limited time dura
tion
 ollowing which the item recovers the ability to perform a
required
function without being subjected to any action of corrective
maintenance
Note  Such a fault is often recurrent.
5318 determinate fault
F: panne franche
S: averia clara; averia determinable
For an item , which produces a response as a result of an
action, a fault for which the response is the same for all actions.
5319 indeterminate fault
F: panne indeterminee
S: averia indeterminable
For an item , which produces a response as a result of an
action, a fault such that the error affecting the response depends
on the action applied.
Note  An example would be a datasensitive fault .
5320 latent fault
F: panne latente
S: averia latente
An existing fault  hat has not yet been recognized.
5321 systematic fault
F: panne systematique
S: averia sistematica
A fault  esulting from a systematic failure .
5322 fault mode; failure mode (deprecated)
F: mode de panne; mode de defaillance  (terme
deconseille)
S: modo de averia; modo de fallo  (desaconsejado)
One of the possible states of a faulty item , for a given
required function .
5323 faulty
F: en panne
S: averiado
Property of having a fault .
5.4 Errors and mistakes
5401 error
F: erreur
S: error
A discrepancy between a computed, observed or measured value
or condition and the true, specified or theoretically correct value
or condition.
Note  An error  an be caused by a faulty item , e.g. a
computing error  ade by a faulty computer equipment.
5402 execution error; generated error
F: erreur d'execution
S: error de ejecucion
Error  roduced during the operation of a faulty item .
5403 interaction error (manmachine)
F: erreur d'interaction  (hommemachine)
S: error de interaccion  (hombremaquina)
An error  n the response of an item  aused by a mistake
 uring its use.
5404 propagated error
F: erreur propagee
S: error propagado
An error  n the response to erroneous data input to a
nonfaulty item .
5405 mistake; error (deprecated in this sense)
F: erreur (humaine); faute
S: equivocacion; error  (desaconsejado en este sen
tido)
A human action that produces an unintended result.
5.5 Item related states  see also Figure 2)
Figure 2, p.
5501 operating state
F: (etat de) fonctionnement
S: estado de funcionamiento; estado operacional
The state when an item  s performing a required function .
5502 nonoperating state
F: (etat de) nonfonctionnement
S: estado de no funcionamiento
The state when an item  s not performing a required function
.
5503 standby state
F: (etat d') attente
S: estado de espera (en reserva)
A nonoperating up state  uring the required time .
5504 idle state; free state
F: etat vacant; etat libre
S: estado de reposo; estado libre
A nonoperating up state  uring nonrequired time .
5505 disabled state; outage
F: etat d'incapicite
S: estado de incapacidad
A state of an item  haracterized by its inability to per
form a required function , for any reason.
5506 external disabled state
F: etat d'incapacite externe
S: estado de incapacidad externa
That subset of the disabled state  hen the item  s in an
up state , but lacks required external resources.
5507 down state; internal disabled state
F: etat d'indisponibilite; etat d'incapacite interne
S: estado de indisponibilidad; estado de incapacidad
interna
A state of an item  haracterized by a fault  r by a possi
ble inability to perform a required function during preventive
maintenance .
Note  This state relates to availability performance .
5508 up state
F: etat de disponibilite
S: estado de disponibilidad
A state of an item  haracterized by the fact that it can
perform a required function , assuming that the external resources,
if required, are provided.
Note  This state relates to availability performance .
5509 busy state
F: etat occupe; occupation
S: estado de ocupacion; estado de ocupado
The state of an item  n which it performs a required func
tion
 or a user and for that reason is not accessible by other users.
5510 critical state
F: etat critique
S: estado critico
A state of an item  ssessed likely to result in injury to
persons or significant material damage.
Note  A critical state  ay be the result of a critical
fault , but not necessarily.
6 Maintenance
6001 maintenance philosophy
F: philosophie de maintenance
S: filosofia de mantenimiento
A system of underlying principles for the organization and
execution of the maintenance .
6002 maintenance policy
F: politique de maintenance
S: politica de mantenimiento
A description of the interrelationship between the maintenance
echelons , the indenture levels and the levels of maintenance to be
applied for the maintenance of an item .
6003 maintenance
F: maintenance
S: mantenimiento
The combination of all technical and corresponding administra
tive actions, including supervision actions, intended to retain an
item in, or restore it to, a state in which it can perform a
required function .
6004 preventive maintenance
F: maintenance preventive; entretien
S: mantenimiento preventivo
The maintenance  arried out at predetermined intervals or
according to prescribed criteria and intended to reduce the proba
bility of failure or the degradation of the functioning of an item
.
6005 corrective maintenance; repair
F: maintenance corrective; reparation; depannage
S: mantenimiento correctivo; reparacion
The maintenance  arried out after fault recognition  nd
intended to restore an item to a state in which it can perform a
required function .
6006 deferred maintenance
F: maintenance differee
S: mantenimiento diferido
Such corrective maintenance  hich is not immediately ini
tiated after a fault recognition but is delayed in accordance with
given maintenance rules.
6007 scheduled maintenance
F: maintenance programmee; entretien systematique
S: mantenimiento programado
The preventive maintenance  arried out in accordance with an
established time schedule.
6008 unscheduled maintenance
F: maintenance non programmee
S: mantenimiento no programado
The maintenance  arried out, not in accordance with an esta
blished time schedule, but, for example, after reception of an
indication regarding the state of an item .
6009 onsite maintenance; in situ maintenance; field
maintenance
F: maintenance in situ
S: mantenimiento local; mantenimiento sobre el terreno
Maintenance  erformed at the premises where the item  s
used.
6010 offsite maintenance
F: maintenance deportee
S: mantenimiento no local
Maintenance  erformed at a place different from where the
item is used.
Note  An example is the repair  f a subitem at a mainte
nance centre.
6011 remote maintenance
F: telemaintenance
S: mantenimiento remoto; telemantenimiento
Maintenance  f an item  erformed without physical access
of the personnel to the item .
6012 automatic maintenance
F: maintenance automatique
S: mantenimiento automatico
Maintenance  ccomplished without human intervention.
6013 functionaffecting maintenance
F: maintenance affectant les fonctions
S: mantenimiento que afecta a la funcion
A maintenance action  hat affects one or more of the
required functions of a maintained item .
Note  Functionaffecting maintenance  s divided into
functionpreventing maintenance and functiondegrading maintenance
.
6014 functionpreventing maintenance
F: maintenancearr  t; maintenance emp  chant
l'accomplissement des fonctions
S: mantenimiento con discontinuidad de funciones
A maintenance action  hat prevents a maintained item
 rom performing a required function by causing complete loss of
all the functions.
6015 functiondegrading maintenance
F: maintenance avec degradation; maintenance degradant
les fonctions
S: mantenimiento con degradacion de funciones
A maintenance action  hat affects one or more of the
required functions  f a maintained item , but not to such extent
as to cause complete loss of all the functions.
6016 functionpermitting maintenance
F: maintenance en fonctionnement; maintenance en
exploitation
S: mantenimiento sin discontinuidad de funciones
A maintenance action  hat does not affect any of the
required functions  f a maintained item .
6017 level of maintenance
F: niveau de maintenance
S: nivel de mantenimiento
The maintenance action  o be carried out at a specified
indenture level .
Note  Examples of a maintenance action  re replacing a
component, a printed circuit board, a subsystem, etc.
6018 maintenance echelon; line of maintenance
F: echelon de maintenance
S: escalon de mantenimiento; linea de mantenimiento
The position in an organization where specified levels of
maintenance  re to be carried out on an item .
Note 1  Examples of maintenance echelons  re: field,
repair shop, manufacturer.
Note 2  The maintenance echelon  s characterized by the
skill of the personnel, the facilities available, the location,
etc.
6019 indenture level (for maintenance)
F: niveau d'intervention (pour la maintenance)
S: nivel de intervencion (para el mantenimiento)
A level of subdivision of an item  rom the point of view of
a maintenance action .
Note 1  Examples of indenture levels  ould be a subsystem,
a circuit board, a component.
Note 2  The indenture level  epends on the complexity of
the item's construction, the accessibility to subitems, skill
level of maintenance personnel, test equipment facilities, safety
considerations, etc.
6020 elementary maintenance activity
F: operation elementaire de maintenance
S: accion elemental de mantenimiento
The unit of work into which a maintenance activity may be bro
ken down at a given indenture level .
6021 maintenance action; maintenance task
F: operation de maintenance; t  che de maintenance
S: accion de mantenimiento; tarea de mantenimiento
A sequence of elementary maintenance activities  arried out
for a given purpose.
Note  Examples are fault diagnosis , fault localization
 nd function checkout or combinations thereof.
6022 supervision
F: surveillance; supervision
S: supervision
Activity, performed either manually or automatically, intended
to observe the state of an item .
Note  Automatic supervision  ay be performed internally or
externally to the item .
6023 controlled maintenance
F: maintenance dirigee
S: mantenimiento dirigido
A method to sustain a desired quality of service  y the sys
tematic application of analysis techniques using centralized super
visory facilities and/or sampling to minimize preventive mainte
nance and to reduce corrective maintenance .
6024 fault recognition
F: detection (de panne)
S: deteccion (de una averia )
The event when a fault  s recognized.
6025 fault diagnosis
F: diagnostic (de panne)
S: diagnostico (de una averia)
Actions taken for fault recognition , fault localization  nd
cause identification.
6026 fault localization; fault location (deprecated in this
sense)
F: localisation de panne
S: localizacion (de una averia)
Actions taken to identify the faulty subitem or subitems at
the appropriate indenture level .
6027 fault correction
F: correction (de panne)
S: correccion (de una averia)
Actions taken after fault localization  ntended to restore
the ability of the faulty item to perform a required function .
6028 function checkout
F: verification (de fonctionnement)
S: verificacion de funcionamiento
Actions taken after fault correction  o verify that the item
 as recovered its ability to perform the required function .
6029 restoration; recovery
F: retablissement
S: restablecimiento; restauracion
That event when the item  egains the ability to perform a
required function after a fault .
6030 maintenance entity
F: cellule de maintenance
S: cellula de mantenimiento; entidad de mantenimiento
A subitem of a given item  efined with the intention that
an alarm  caused by a fault in that subitem  will be unambigu
ously referrable to the subitem.
7 Time concepts (see also Figure 3)
7.1 Maintenance related times
7101 maintenance time
F: temps de maintenance
S: tiempo de mantenimiento
The time interval  uring which a maintenance action  s
performed on an item either manually or automatically, including
technical delays and logistic delays .
Note  Maintenance  ay be carried out while the item
 s performing a required function .
7102 maintenance manhours (MMH)
F: duree equivalente de maintenance
S: duracion equivalente de mantenimiento; horashombre
de mantenimiento
The accumulated durations of the maintenance times , expressed
in hours, used by all maintenance personnel for a given type of
maintenance action or over a given time interval .
Figure 3, p. 6
7103 active maintenance time
F: temps de maintenance active
S: tiempo de mantenimiento activo
That part of the maintenance time  uring which a maintenance
action  s performed on an item , either automatically or manu
ally, excluding logistic delays .
Note  Active maintenance may be carried out while the item
 s performing a required function .
7104 preventive maintenance time
F: temps de maintenance preventive
S: tiempo de mantenimiento preventivo
That part of the maintenance time  uring which preventive
maintenance  s performed on an item , including technical delays
and logistic delays inherent in preventive maintenance .
7105 repair time; corrective maintenance time
F: temps de reparation; temps de maintenance correc
tive
S: tiempo de reparacion; tiempo de mantenimiento
correctivo
That part of the maintenance time  uring which corrective
maintenance  s performed on an item , including technical delays
and logistic delays inherent in corrective maintenance .
7106 active preventive maintenance time
F: temps de maintenance preventive active
S: tiempo de mantenimiento preventivo activo
That part of the active maintenance time  uring which
actions of preventive maintenance are performed on an item .
7107 active repair time; active corrective maintenance time
F: temps de reparation active; temps de maintenance
corrective active
S: tiempo de reparacion activo; tiempo de manten
imiento correctivo activo
That part of the active maintenance time  uring which
actions of corrective maintenance are performed on an item .
7108 undetected fault time
F: temps de nondetection de panne
S: tiempo de no deteccion de una averia
The time interval  etween a failure  nd recognition of the
resulting fault .
7109 administrative delay (for corrective maintenance)
F: delai administratif (pour la maintenance correc
tive)
S: retardo administrativo (para el mantenimiento
correctivo); demora administrativa
The accumulated time  uring which an action of corrective
maintenance  n a faulty item is not performed due to administra
tive reasons.
7110 logistic delay
F: delai logistique
S: retardo logistico; demora logistica
That accumulated time  uring which a maintenance action
 annot be performed due to the necessity to acquire maintenance
resources, excluding any administrative delay .
Note  Logistic delays  an be due to, e.g. travelling to
unattended installations, awaiting the arrival of spare parts, spe
cialists or test equipment.
7111 fault correction time
F: temps de correction de panne
S: tiempo de correccion de una averia
That part of active repair time  uring which fault correc
tion
 s performed.
7112 technical delay
F: delai technique
S: retardo tecnico; demora tecnica
The accumulated time  ecessary to perform auxiliary techni
cal actions associated with the maintenance action itself.
7113 checkout time
F: temps de verification (du fonctionnement)
S: tiempo de verificacion (de funcionamiento)
That part of active repair time  uring which function
checkout  s performed.
7114 fault localization time; fault location time (depre
cated)
F: temps de localisation (de panne)
S: tiempo de localizacion de una averia
That part of active repair time  uring which fault localiza
tion  s performed.
7.2 Itemstate related times
7201 operating time
F: temps de fonctionnement
S: tiempo de funcionamiento
The time interval  uring which an item  s an operating
state .
7202 nonoperating time
F: temps de nonfonctionnement
S: tiempo de no funcionamiento
The time interval  uring which an item  s in a
nonoperating state .
7203 required time
F: periode requise
S: periodo requerido
The time interval  uring which the user requires the item
 o be in a condition to perform a required function .
7204 nonrequired time
F: periode non requise
S: periodo no requerido
The time interval  uring which the user does not require the
item  o be in a condition to perform a required function .
7205 standby time
F: periode d'attente
S: tiempo de espera (en reserva)
The time interval  uring which an item  s in a standby
state .
7206 idle time; free time
F: periode vacante; temps mort; temps libre
S: tiempo de reposo; tiempo muerto; tiempo libre
The time interval  uring which an item  s in a free state
.
7207 disabled time
F: temps d'incapacite
S: tiempo de incapacidad
The time interval  uring which an item  s in a disabled
state .
7208 down time
F: temps d'indisponibilite
S: tiempo de indisponibilidad
The time interval  uring which an item  s in a down state
.
7209 accumulated down time
F: duree cumulee d'indisponibilite
S: tiempo de indisponibilidad acumulado
The sum of the duration of down times  ver a given time
interval .
7210 external disabled time; external loss time
F: temps d'incapacite externe
S: tiempo de incapacidad externa
The time interval  uring which an item  s in an external
disabled state .
7211 up time
F: temps de disponibilite; temps de bon fonctionnement
S: tiempo de disponibilidad
The time interval  uring which an item  s in an up state .
7.3 Time concepts related to reliability performance
7301 time to first failure
F: duree de fonctionnement avant la premiere
defaillance
S: tiempo hasta el primer fallo
Total time duration  f the operating time  f an item
 rom the instant of time it is first put in an up state , until
failure .
7302 time to failure
F: duree de fonctionnement avant defaillance
S: tiempo hasta el fallo
Total time duration  f the operating time  f an item ,
from the instant of time it goes from a down state to an up state ,
after a corrective maintenance action , until the next failure .
7303 time between failures
F: temps entre defaillances
S: tiempo entre fallos
The time duration  etween two successive failures  f a
repaired item .
Note 1  Those parts of nonoperating time  hich are
included must be identified.
Note 2  In some applications only the up time  s con
sidered.
7304 time to restoration; time to recovery
F: temps de panne
S: tiempo de averia
The time interval  uring which an item  s in a down state
 ue to a failure .
7305 useful life
F: (duree de) vie utile
S: vida util
Under given conditions, the time interval  eginning at a
given instant of time , and ending when the failure intensity
becomes unacceptable or when the item is considered unrepairable as
a result of a fault .
7306 early failure period
F: periode initiale de defaillance
S: periodo de fallos inicial
That possible early period in the life of an item , beginning
at a given instant of time and during which the instantaneous
failure intensity for a repaired item or the instantaneous failure
rate for a nonrepaired item decreases rapidly.
Note  In any particular case, it is necessary to explain
what is meant by "decreases rapidly".
7307 constant failure intensity period
F: periode d'intensite constante de defaillance
S: periodo de intensidad de fallos constante
That possible period in the life of a repaired item  uring
which the failure intensity is approximately constant.
Note  In any particular case it is necessary to explain what
is meant by "approximately constant".
7308 constant failure rate period
F: periode de densite constante de defaillance; periode de
taux constant de defaillance
S: periodo de tasa de fallos constante
That possible period in the life of a nonrepaired item 
uring which the failure rate is approximately constant.
Note  In any particular case it is necessary to explain what
is meant by "approximately constant".
7309 wearout failure period
F: periode de defaillance par vieillissement; periode de
defaillance par usure
S: periodo de fallos por envejecimiento
That possible later period in the life of an item
 uring which the instantaneous failure intensity for a repaired
item or the instantaneous failure rate for a nonrepaired item
increases rapidly.
Note  In any particular case it is necessary to explain what
is meant by "increases rapidly".
8 Measures of performances
8.1 Availability performance
8101 instantaneous availability; pointwise availability;
A(t) (symbol)
F: disponibilite (instantanee), A(t)  symbole)
S: disponibilidad instantanea, A(t)  simbolo)
The probability  hat an item  s in an up state  t a
given instant of time , t .
Note  In French the term disponibilite  s also used to
denote the performance quantified by this probability .
8102 instantaneous unavailability; pointwise unavailabil
ity; U(t) (symbol)
F: indisponibilite (instantanee), U(t)  symbole)
S: indisponibilidad instantanea, U(t)  simbolo)
The probability that an item  s in a down state  t a given
instant of time , t .
8103 mean availability, A (tv1,  v2) (symbol)
F: disponibilite moyenne, A  (t1, t2) (symbole)
S: disponibilidad media, A  (t1, t2) (simbolo)
The normalized integral of the instantaneous availability  n
a given time interval (t1, t2).
Note  The mean availability  s related to the instantane
ous availability as
A  fR (t 1
, t 2) =
[Formula Deleted]
t 1
fIt 2
A (t ) dt .
8104 mean unavailability, U (tv1, tv2) (symbol)
F: indisponibilite moyenne, U  (t1,  fIt2) (sym
bole)
S: indisponibilidad media, U  (t1,  fIt2) (simbolo)
The normalized integral of the instantaneous unavailability 
n a stated time interval (t1,  fIt2).
Note  The mean unavailability  s related to the instan
taneous unavailability as
U  fR (t 1
, t 2) =
[Formula Deleted]
t 1
fIt 2
U (t ) dt .
8105 (asymptotic) availability; (steadystate) availabil
ity; A (symbol)
F: disponibilite asymptotique; disponibilite, A
 symbole)
S: disponibilidad (asintotica); disponibilidad (en
regimen permanente); A  simbolo)
The limit, if this exists, of the instantaneous availability
 hen the time tends to infinity.
Note  Under certain conditions, for instance constant
failure rate and constant repair rate, the asymptotic availability
may be expressed as:
A =
fIMUT + MDT
___________
where
MDT  s the mean down time
MUT  s the mean up time .
8106 asymptotic unavailability, U (symbol)
F: indisponibilite asymptotique, U  symbole)
S: indisponibilidad asintotica, U  simbolo)
The limit, if this exists, of the instantaneous unavailability
 hen the time tends to infinity.
Note  Under certain conditions, for instance constant
failure rate and constant repair rate, the asymptotic unavailabil
ity may be expressed as:
U =
fIMDT + MUT
___________
where
MDT  s the mean down time
MUT  s the mean up time .
8107 asymptotic mean availability, A (symbol)
F: disponibilite moyenne asymptotique, A  (symbole)
S: disponibilidad media asintotica, A  (simbolo)
The limit, if this exists, of the mean availability  ver a
time interval (t1,  fIt2) when t2tends to infinity.
Note 1  The asymptotic mean availability  s related to the
mean availability as
A  fR = lim A  fR (t 1, t 2)
A  fR = t 2 oo
Note 2  When such a limit exists it is not dependent on t1.
8108 asymptotic mean unavailability, U (symbol)
F: indisponibilite moyenne asymptotique, U  (sym
bole)
S: indisponibilidad media asintotica , U  (simbolo)
The limit, if this exists, of the mean unavailability  ver a
time interval  t1,  fIt2) when t2tends to infinity.
Note 1  The asymptotic mean unavailability  s related to
the mean unavailability  s
U  fR = lim U  fR (t 1, t 2)
U  fR = t 2 oo
Note 2  When such a limit exists it is not dependent on t1.
8109 mean up time (MUT)
F: temps moyen de disponibilite; duree moyenne de
disponibilite (TMD)
S: tiempo medio de disponibilidad (TMD)
The expectation  f the up time .
8110 mean accumulated down time (MADT)
F: duree cumulee moyenne d'indisponibilite
S: tiempo medio acumulado de indisponibilidad (TMAI)
The expectation  f the accumulated down time .
8111 instantaneous availability of a leased circuit
F: disponibilite instantanee d'un circuit loue
S: disponibilidad instantanea de un circuito arrendado
The probability  hat, under stated operating conditions, a
leased circuit can perform a required function when requested by
the subscriber.
8.2 Reliability performance
8201 reliability, R (symbol)
F: fiabilite, R  symbole)
S: fiabilidad, R  simbolo)
The probability  hat an item  an perform a required func
tion  nder stated conditions for a given time interval .
Note 1  It is generally assumed that the item  s in a
state to perform this required function at the beginning of the
time interval .
Note 2  In French, the term fiabilite  s also used to
denote the performance quantified by this probability .
8202 (instantaneous) failure rate, \(t) (symbol)
F: densite (temporelle) (instantanee) de defaillance;
taux (instantane) de defaillance, \(t)  (symbole)
S: tasa (instantanea) de fallos, \(t)  simbolo)
The limit, if this exists, of the ratio of the conditional
probability  hat the time to failure , T , of an item falls
within a given time interval , (t ,  fIt +?63t ), to the length of
this interval, ?63t , when ?63t tends to zero, given that the item
is in a state to perform a required function at the beginning of
the time interval .
Note  The instantaneous failure rate  s expressed by for
mula as:
\ (t ) = lim \ (t ) = ?63 (t ) 0+ 63t
____________________________
where T  s the instant of time  f failure .
The formula is also applicable if T  enotes the time to
failure .
8203 mean failure rate, \ (tv1,  v2) (symbol)
F: taux moyen de defaillance; densite (temporelle) moyenne
de defaillance, \  (t1,  fIt2) (symbole)
S: tasa media de fallos, \  (t1,  fIt2) (simbolo)
The normalized integral of the instantaneous failure rate 
ver a given time interval , (t1,  fIt2).
Note  The mean failure rate  elates to instantaneous
failure rate as
\
(t 1
, t 2) =
[Formula Deleted]
t 1
fIt 2 \ (t ) dt .
8204 (instantaneous) failure intensity, z(t) (symbol)
F: intensite (instantanee) de defaillance, z(t)
 (symbole)
S: intensitad (instantanea) de fallos, z(t) 
(simbolo)
The limit, if this exists, of the ratio of the mean number of
failures  f a repaired item in a time interval , (t ,  fIt 
 63t ), to the length of this interval, ?63t , when the length of
the time interval tends to zero.
Note  The instantaneous failure intensity  s expressed by
formula as:
z (t ) = lim z (t ) = ?63t 0+ 63t
_______________________
where N  t ) is the number of failures  n the time interval 
(0,  fIt ).
8205 mean failure intensity, z (tv1,  v2) (symbol)
F: intensite moyenne de defaillance, z  (t1,  fIt2)
(symbole)
S: intensidad media de fallos, z  (t1,  fIt2)
(simbolo)
The normalized integral of the instantaneous failure intensity
 over a given time interval  (t1,  fIt2).
Note  The mean failure intensity  s related to instantane
ous failure intensity as:
z  fR (t 1
, t 2) =
[Formula Deleted]
t 1
fIt 2 z (t ) dt .
8206 mean time to first failure (MTTFF)
F: duree moyenne de fonctionnement avant la premiere
defaillance (MTTFF)
S: tiempo medio hasta el primer fallo (MTTFF)
The expectation  f the time to first failure .
8207 mean time to failure (MTTF)
F: duree moyenne de fonctionnement avant defaillance
(MTTF)
S: tiempo medio hasta el fallo (MTTF)
The expectation  f the time to failure .
8208 mean time between failures (MTBF)
F: moyenne des temps entre defaillances (MTBF)
S: tiempo medio entre fallos (MTBF)
The expectation  f the time between failures .
8209 failure rate acceleration factor
F: facteur d'acceleration de la densite de defaillance;
facteur d'acceleration du taux de defaillance
S: factor de aceleracion de la tasa de fallos
The ratio of the accelerated testing failure rate  o the
failure rate under stated reference test conditions.
Note  Both failure rates  efer to the same time period in
the life of the tested items .
8210 failure intensity acceleration factor
F: facteur d'acceleration de l'intensite de defaillance
S: factor de aceleracion de la intensidad de fallos
In a time interval  f given duration , whose beginning is
specified by a fixed age of a repaired item , the ratio of the
number of failures obtained under two different sets of stress con
ditions.
8.3 Maintainability performance
8301 maintainability
F: maintenabilite
S: mantenibilidad
The probability  hat a given active maintenance action , for
an item  nder given conditions of use can be carried out within a
stated time interval , when the maintenance is performed under
stated conditions and using stated procedures and resources.
Note  In French the term maintenabilite  s also to denote
the performance quantified by this probability .
8302 (instantaneous) repair rate, u(t) (symbol)
F: densite (temporelle) (instantanee), de reparation,
u (t)  symbole)
S: tasa (instantanea) de reparaciones, u(t) 
simbolo)
The limit, if this exists, of the ratio of the conditional
probability  hat the corrective maintenance action terminates in
a time interval , (t , t +?63t ) to the length of this time inter
val , when ?63t tends to zero, given that the action had not ter
minated at the beginning of the time interval .
Note  The instantaneous repair rate  s expressed by for
mula as:
u (t ) = lim u (t ) = ?63 (t ) 0 63t
____________________________
where T  is the instant of time  f restoration .
T  ay also represent the time to restoration .
8303 mean repair rate, u (tv1,  v2) (symbol)
F: densite (temporelle) moyenne de reparation, u  fR
(t1,  fIt2) (symbole)
S: tasa media de reparaciones, u  fR (t1,  fIt2)
(simbolo)
The normalized integral of the instantaneous repair rate 
ver a given time interval (t1,  fIt2).
Note  The mean repair rate  s related to instantaneous
repair rate as:
u
(t 1
, t 2) =
[Formula Deleted]
t 1
fIt 2 u
(t ) dt .
8304 mean maintenance manhours
F: duree moyenne equivalente de maintenance
S: duracion media equivalente de mantenimiento; media
de horashombre de mantenimiento
The expectation  f the maintenance manhours .
8305 mean down time (MDT)
F: temps moyen d'indisponibilite; duree moyenne
d'indisponibilite (TMI)
S: tiempo medio de indisponibilidad (TMI)
The expectation  f the down time .
8306 mean repair time (MRT)
F: duree moyenne de reparation
S: tiempo medio de reparacion
The expectation  f the repair time .
8307 pfractile repair time
F: quantilep de la duree de reparation
S: cuantilp del tiempo de reparacion
The pfractile  alue of the repair time .
8308 mean active repair time (MART)
F: duree moyenne de reparation active
S: tiempo medio de reparacion activa
The expectation  f the active repair time .
8309 pfractile active repair time
F: quantilep de la duree de reparation active
S: cuantilp del tiempo de reparacion activa
The pfractile  alue of the active repair time .
8310 mean time to restoration (MTTR); mean time to
recovery; mean time to repair (deprecated)
F: duree moyenne de panne; moyenne des temps pour la t
 che de reparation (MTTR)
S: tiempo medio hasta el restablecimiento (MTTR)
The expectation  f the time to restoration .
8311 fault coverage
F: couverture de pannes
S: cobertura de averias
The proportion of faults  f an item  hat can be recognized
under given conditions.
8312 repair coverage
F: couverture des reparations
S: cobertura de reparaciones
The proportion of faults  f an item  hat can be success
fully removed.
8.4 Maintenance support performance
8401 mean administrative delay (MAD)
F: duree moyenne du delai administratif
S: retardo medio administrativo; demora media adminis
trativa
The expectation  f the administrative delay .
8402 pfractile administrative delay
F: quantilep du delai administratif
S: cuantilp del retardo administrativo; cuantilp de la
demora administrativa
The pfractile  alue of the administrative delay .
8403 mean logistic delay (MLD)
F: duree moyenne du delai logistique
S: retardo medio logistico; demora media logistica
The expectation  f the logistic delay .
8404 pfractile logistic delay
F: quantilep du delai logistique
S: cuantilp del retardo logistico; cuantilp de la demora
logistica
The pfractile  alue of the logistic delay .
9 Test, data, design and analysis
9.1 Test concepts
9101 test
F: essai
S: prueba
An experiment made in order to measure or classify a charac
teristic .
9102 compliance test
F: essai de conformite
S: prueba de conformidad
A test  sed to show whether or not a characteristic  f an
item  omplies with the stated requirements.
9103 determination test
F: essai de determination
S: prueba de determinacion
A test  sed to establish the value of a characteristic .
9104 laboratory test
F: essai en laboratoire
S: prueba de laboratorio
A compliance test  r a determination test  ade under
prescribed and controlled conditions which may or may not simulate
field conditions.
9105 field test
F: essai dans des conditions d'exploitation
S: prueba en condiciones de explotacion; prueba en
condiciones reales
A compliance test  r determination test  ade in the field
where operating, environmental, maintenance and measurement condi
tions are recorded.
9106 endurance test
F: essai d'endurance
S: prueba de resistencia
A test  arried out over a time interval  o investigate how
the properties of an item are affected by the application of stated
stresses and by their time duration .
9107 accelerated test
F: essai accelere
S: prueba acelerada
A test  n which the applied stress level is chosen to exceed
that stated in the reference conditions in order to shorten the
time duration required to observe the stress response of the item ,
or to magnify the responses in a given time duration .
Note  To be valid, an accelerated test  hall not alter the
basic fault modes and failure mechanisms , or their relative pre
valence.
9108 step stress test
F: essai sous contrainte echelonnee
S: prueba de esfuerzo escalonado
A test  onsisting of several stress levels applied sequen
tially for periods of equal time duration  o an item , in such a
way that during each time interval a stated stress level is applied
and the stress level is increased from one time interval to the
next.
9109 screening test
F: essai de selection
S: prueba de seleccion
A test , or combination of tests , intended to remove or
detect unsatisfactory items  r those likely to exhibit early
failures .
9110 time acceleration factor
F: facteur d'acceleration temporelle
S: factor de aceleracion temporal
The ratio between the time durations  ecessary to obtain the
same stated number of failures  r degradations in two equal size
samples under two different sets of stress conditions involving the
same failure mechanisms and fault modes and their relative pre
valence.
Note  One of the two sets of stress conditions should be a
reference set.
9111 maintainability verification
F: verification de la maintenabilite
S: verificacion de la mantenibilidad
A procedure applied for the purpose of determining whether the
requirements for maintainability performance measures for an item
has been achieved or not.
Note  The procedures may range from analysis of appropriate
data to a maintainability demonstration .
9112 maintainability demonstration
F: verification experimentale de maintenabilite
S: demostracion de la mantenibilidad
A maintainability verification  erformed as a compliance
test .
9.2 Data concepts
9201 observed data
F: valeur observee; donnee observee
S: datos observados; valores observados
Values related to an item  r a process obtained by direct
observation.
Note  Values referred to could be events, time instants,
time intervals , etc.
9202 test data
F: donnees d'essai
S: datos de prueba
Observed data  btained during tests .
9203 field data
F: donnee d'exploitation
S: datos de explotacion
Observed data  btained during field operation.
9204 reference data
F: valeur de reference; donnees de reference
S: datos de referencia; valores de referencia
Data, which by general agreement may be used for prediction
 nd/or comparison with observed data .
9.3 Design concepts
9301 redundancy
F: redondance
S: redundancia
In an item , the existence of more than one means for perform
ing a required function .
9302 active redundancy
F: redondance active
S: redundancia activa
That redundancy  herein all means for performing a required
function  re intended to operate simultaneously.
9303 standby redundancy
F: redondance en attente; redondance passive; redondance
en secours
S: redundancia pasiva; redundancia de reserva
That redundancy  herein one means for performing a required
function  s intended to operate, while the alternative means are
inoperative until needed.
9304 fail safe
F: protege contre defaillances (critique); a s  rete
integree
S: prevencion de fallos
A designed property of an item  hich prevents its failures
 rom resulting in critical faults .
9305 fault tolerance
F: tolerance aux pannes
S: tolerancia a las averias
The attribute of an item  hat makes it able to perform a
required function  n the presence of certain given subitem
faults .
9306 fault masking
F: masquage de panne
S: enmascaramiento de averia
The condition in which a fault  xists in a subitem of an
item  ut cannot be recognized because of a feature of the item or
because of another fault of the subitem or of another subitem.
9.4 Analysis concepts
9401 prediction
F: prevision; prediction
S: prevision; prediccion
1) The process of computation used to obtain (a)
predicted
 alue(s) of a quantity.
2) The predicted  alue(s) of a quantity.
9402 reliability model
F: modele de fiabilite
S: modelo de fiabilidad
A mathematical model used for prediction  r estimation  f
reliability measures  f an item or for similar purposes.
9403 fault modes and effects analysis (FMEA)
F: analyse des modes de panne et de leurs effets
(AMDE)
S: analisis de los modos de averia y de sus efectos
(AMAE)
A qualitative method of reliability  nalysis which involves
the study of the fault modes  hich can exist in every subitem of
the item and the determination of the effects of each fault mode on
other subitems of the item and on the required functions of the
item .
9404 fault modes, effects and criticality analysis (FMECA)
F: analyse des modes de panne, de leurs effets et de leur
criticite (AMDEC)
S: analisis de los modos de averia, sus efectos y su cri
ticidad (AMAEC)
Fault modes and effect analysis  ogether with a considera
tion of the probability  f occurrence and a ranking of the seri
ousness of the fault .
9405 fault tree analysis (FTA)
F: analyse par arbre de panne
S: analisis en arbol de averias
An analysis to determine which fault modes  f the subitems
or external events, or combinations thereof, may result in a stated
fault mode of the item , resulting in a fault tree .
9406 stress analysis
F: analyse de contraintes
S: analisis de esfuerzos
A quantitative or qualitative determination of the physical,
chemical or other stresses an item  s subjected to under given
use conditions.
9407 reliability block diagram
F: diagramme de fiabilite
S: diagrama de bloques de fiabilidad
Block diagram showing, for one or more functional modes  f a
complex item , how faults  f the subitems represented by the
blocks, or combinations thereof, result in a fault of the item .
9408 fault tree
F: arbre de panne
S: arbol de averias
A logic diagram showing which fault modes  f subitems or
external events, or combinations thereof, result in a given fault
mode of the item .
9409 statetransition diagram
F: diagramme de transition
S: diagrama de transicion de estados
A diagram showing the set of possible states of an item  nd
the possible one step transitions between these states.
9410 stress model
F: modele de contraintes
S: modelo de esfuerzos
A mathematical model which describes how a reliability perfor
mance measure  f an item  aries as a function of the applied
stresses.
9411 fault analysis
F: analyse des pannes
S: analisis de averias
The logical, systematic examination of an item  r its
diagram(s) to identify and analyse the probability , causes and
consequences of potential and real faults .
9412 maintainability model
F: modele de maintenabilite
S: modelo de mantenibilidad
A mathematical model used for prediction  r estimation  f
maintainability performance measures of an item or for similar pur
poses.
Note  An example is the maintenance tree .
9413 maintainability prediction
F: prevision de maintenabilite; prediction de
maintenabilite
S: prevision de la mantenibilidad; prediccion de la
mantenibilidad
An activity performed with the intention to forecast the
numerical values of a maintainability performance measure of an
item , taking into account the maintainability performance and
reliability performance measures of its subitems, under given
operational and maintenance conditions.
9414 maintenance tree
F: arbre de maintenance
S: arbol de mantenimiento
A logic diagram showing the pertinent alternative sequences of
elementary maintenance activities  o be performed on an item and
the conditions for their choice.
9415 maintainability allocation; maintainability apportion
ment
F: repartition de la maintenabilite
S: distribucion de la mantenibilidad; asignacion de la
mantenibilidad
A procedure applied during the design of an item  ntended to
apportion the requirements for maintainability performance measures
for an item to its subitems according to given criteria.
9.5 Improvement processes
9501 learning process
F: apprentissage
S: aprendizaje
Growth in experience and familiarity by personnel with design
or constructional techniques, which reduces the risk of future mis
takes .
9502 burnin
F: rodage
S: rodaje
A process of reliability improvement  f hardware, employing
operation of every item  n a prescribed environment, with succes
sive fault correction , replacement or removal at every failure ,
during the steeply falling failure intensity period within the
early failure period .
9503 reliability growth
F: croissance de la fiabilite
S: crecimiento de la fiabilidad; incremento de la fia
bilidad
A condition characterized by a progressive improvement of a
reliability performance measure  f an item , or population of
similar items , with time.
Note  A growth can result either from active improvement or
from burnin .
9504 reliability improvement
F: amelioration de fiabilite
S: mejora de la fiabilidad
A process undertaken with the deliberate intention of promot
ing reliability growth  y the elimination of systematic faults .
9505 maintainability programme
F: programme de maintenabilite
S: programa de mantenibilidad
A detailed plan, including the human and material resources,
procedures, tasks and responsibilities during the life of an item ,
intended to determine the fulfilment of the requirements for main
tainability performance measures for an item and facilitate the
planning of the maintenance .
10 Measure modifiers
1001 true  ..
F: ...  rai
S: ...  erdadero
The ideal value which characterizes a quantity perfectly
defined under the conditions which exist at the moment when that
quantity is observed, or the subject of a determination.
Note  This value could be arrived at only if all causes of
measurement error were eliminated.
1002 predicted  ..
F: ...  redit; ...  revu
S: ...  revisto; ...  redicho
The numerical value assigned to a quantity, before the quan
tity is actually observable, computed on the basis of earlier
observed or estimated values of the same quantity or of other quan
tities using a mathematical model.
1003 extrapolated  ..
F: ...  xtrapole
S: ...  xtrapolado
The predicted  alue based on estimated  alues for one or a
set of conditions, intended to apply to other conditions such as
time, maintenance and environmental conditions.
1004 estimated  ..
F: ...  stime
S: ...  stimado
The value obtained as the result of an estimation .
Note  The result may be expressed either as a single numeri
cal value, a point estimate, or as a confidence interval .
1005 intrinsic  ..; inherent  ..
F: ...  ntrinseque; ...  nherent
S: ...  ntrinseco; ...  nherente
Value of a measure  etermined when maintenance and opera
tional conditions are assumed to be ideal.
1006 operational  ..
F: ...  perationnel
S: ...  peracional
Value determined under given operational conditions.
1007 mean  ..; average  .. (deprecated)
F: ...  oyen (adjectif)
S: ...  edio (adjetivo); promedio  desaconsejado)
1) The value obtained as the expectation  f a
random variable .
2) The normalized integral of a time dependant
quantity.
1008 pfractile  ..
F: ...  uantilep
S: cuantilp de  ..
The value obtained as the pfractile  f the distribution of
a random variable .
1009 instantaneous  ..
F: ...  nstantane
S: ...  nstantaneo
The value of a measure  etermined for a given instant of
time .
PART II
Statistical vocabulary
1 Introduction
The quantitative applications of measures for quality of ser
vice, network performance, dependability and trafficability perfor
mance requires a fundamental set of statistical concepts.
This Part provides the terms and definitions for such applica
tions.
2 Terms and definitions
2001 characteristic
F: caractere (statistique)
S: caracteristica
A property which helps to differentiate between the individu
als of a given population.
Note  The differentiation may be either quantitative (by
variables) or qualitative (by attributes).
2002 probability
F: probabilite
S: probabilidad
For practical reasons, it may be considered that, whenever the
conditions of a test  an be reproduced, the probability Pr (E) 
of an event E  ccurring is the value around which the occurrence
frequency of the latter oscillates and towards which it tends when
the number of tests are indefinitely increased.
Note  The concept of probability  ay be introduced in
either of two forms, depending on whether it is intended to desig
nate a degree of belief or whether it is considered as the limit
value of a frequency. In both cases, its introduction requires that
some precautions be taken which cannot be developed within the con
text of an International Standard and for which users should refer
to specialized literature.
2003 random variable; variate
F: variable aleatoire
S: variable aleatoria
A variable which may take any of the values of a specified set
of values and with which is associated a probability distribution.
Note  A random variable  hich may take only isolated
values is said to be "discrete". A random variable  hich may take
all the values of a finite or infinite interval is said to be "con
tinuous".
2004 random process
F: processus aleatoire; processus stochastique
S: proceso aleatorio; proceso estocastico
A collection of timedependent random variables  here the
values are governed by a given set of multivariate distributions
for all combinations of the random variables .
2005 distribution function
F: fonction de repartition
S: funcion de distribucion
A function giving, for every value x , the probability  hat
the random variable X  s less than or equal to x :
F (x ) = Pr (X x ).
2006 probability density function
F: densite de probabilite
S: funcion densidad de probabilidad
The derivative, if this exists, of the distribution function :
f (x ) =
X
____ .
2007 pfractile; pquantile (of a probability distribution)
F: quantile d'ordre p; quantilep (d'une loi de
probabilite)
S: cuantilp; cuantil de orden p (de una ley de
distribucion de probabilidades)
If p  s a number between 0 and 1, the pfractile  s the
value of the random variable  or which the distribution function
equals p or "jumps" from a value less than or equal to p to a value
greater than p .
Note  It is possible that the distribution function
 quals p throughout the interval between consecutive possible
values of the variate. In this case, any value in this interval may
be considered as the pfractile .
2008 expectation (of a random variable); mean (of a random
variable)
F: esperance mathematique (d'une variable aleatoire);
moyenne (d'une variable aleatoire)
S: esperanza matematica (de una variable aleatoria);
media (de una variable aleatoria)
a) For a discrete random variable X  aking the
values xiwith the probabilites pi,
E (X ) = ~" p
i x
i
the sum being extended over all the values xiwhich can be
taken by X .
b) For a continuous random variable X  aving the
probability density function f (x ),
E (X ) =
x f (x ) dx
the integral being extended over all values of the interval
of variation of X .
Note 1  No distinction is made between the expectation
 f a random variable  nd that of a probability distribution.
Note 2  The term mean  s also used with other meanings,
for example as the normalized integral over a time interval .
2009 variance (of a random variable)
F: variance (d'une variable aleatoire)
S: varianza (de una variable aleatoria)
The expectation  f the square of the difference between a
random variable  nd the expectation of this variable.
2010 standard deviation, ` (symbol)
F: ecarttype, ` (symbole)
S: desviacion tipica, ` (simbolo)
The positive square root of the variance .
2011 observed value (in statistics)
F: valeur observee (en statistique)
S: valor observado (en estadistica)
The value of a characteristic  etermined as the result of an
observation or test .
2012 relative frequency
F: frequence (statistique)
S: frecuencia relativa
The ratio of the number of times a particular value, or a
value falling within a given class, is observed to the total number
of observations.
2013 statistical test
F: test (statistique)
S: prueba estadistica
A procedure that is intended to decide whether a hypothesis
about the distribution of one or more populations should be
rejected or not rejected (accepted).
Note 1  The decision taken is a result of the value of an
appropriate statistic  r statistics , calculated from values
observed in samples taken from the populations under consideration.
As the value of the statistic is subject to random variations,
there is some risk of error when the decision is taken.
Note 2  It is important to note that, generally speaking, a
test  ssumes a priori  hat certain assumptions are fulfilled
(for example, assumption of independence of the observations,
assumption of normality, etc.). These assumptions serve as a basis
of the test .
2014 onesided test
F: test unilateral
S: prueba unilateral
A statistical test  n which the statistic  sed is
onedimensional and the critical region is the set of values lower
than, or the set of values greater than, a given number.
2015 twosided test
F: test bilateral
S: prueba bilateral
A statistical test  n which the statistic  sed is
onedimensional and in which the critical region is the set of
values lower than a first given number and the set of values
greater than a second given number.
2016 null hypothesis, Hv0 (symbol)
F: hypothese nulle, H0(symbole)
S: hipotesis nula, H0(simbolo)
The hypothesis to be rejected or not rejected (accepted) at
the outcome of the statistical test .
2017 alternative hypothesis, Hv1 (symbol)
F: hypothese alternative, H1  symbole)
S: hipotesis alternativa, H1  simbolo)
The hypothesis, usually composite, which is opposed to the
null hypothesis
2018 critical region
F: region critique
S: region critica
The set of possible values of the statistic  sed such that,
if the value of the statistic  hich results from the observed
values belongs to the set, the null hypothesis will be rejected,
whereas it will not be rejected (accepted) if the opposite is the
case.
2019 critical values
F: valeurs critiques
S: valores criticos
The given value(s) which limit the critical region .
2020 error of the first kind
F: erreur de premiere espece
S: error de primera clase
The error  ommitted in rejecting the null hypothesis ,
because the statistic  akes a value which belongs to the critical
region , when the null hypothesis is true.
2021 type I risk
F: risque de premiere espece
S: riesgo de tipo I
The probability  f committing the error of the first kind ,
which varies according to the real situation (within the framework
of the null hypothesis ). Its maximum value is the significance
level of the statistical test .
2022 error of the second kind
F: erreur de seconde espece
S: error de segunda clase
The error  ommitted in failing to reject (accept) the null
hypothesis  because the value of the statistic does not belong to
the critical region ), when the null hypothesis is not true (the
alternative hypothesis therefore being true).
2023 type II risk
F: risque de seconde espece
S: riesgo de tipo II
The probability , designated , of committing the error of the
second kind . Its value depends on the real situation and can only
be calculated if the alternative hypothesis is adequately speci
fied.
2024 operating characteristic curve; OC curve (for a sta
tistical test plan)
F: courbe d'efficacite (d'un plan de test)
S: curva caracteristica de funcionamiento (para un
plan de prueba estadistica)
A curve showing, for a given statistical test  lan, the pro
bability of acceptance  s a function of the actual value of a
given measure .
2025 producer's risk (point)
F: (point du) risque du fournisseur
S: (punto de) riesgo del proveedor
A point on the operating characteristic curve  orresponding
to some predetermined and usually low probability of rejection .
2026 consumer's risk (point)
F: (point du) risque du client
S: (punto de) riesgo del consumidor
A point on the operating characteristic curve  orresponding
to a predetermined and usually low probability of acceptance .
2027 power of the test
F: puissance du test
S: potencia de la prueba
The probability  f not committing the error of the second
kind , equal to 1  (em  (*a, and thus the probability of reject
ing the null hypothesis when this hypothesis is false.
2028 significance level (of a statistical test), ( (symbol)
F: niveau de signification (d'un test); seuil de sig
nification, (  (symbole)
S: nivel de significacion (de una prueba estadistica);
umbral de significacion, (  (simbolo)
The given value which limits the probability  f the null
hypothesis  eing rejected, if the null hypothesis is true.
Note  The critical region  s determined in such a way that
if the null hypothesis  s true, the probability of this null
hypothesis being rejected should be not more than this given value.
2029 probability of acceptance
F: probabilite d'acceptation
S: probabilidad de aceptacion
The probability  hat an item  ill be accepted by a given
statistical test  lan.
2030 probability of rejection
F: probabilite de rejet
S: probabilidad de rechazo
The probability  hat an item  ill not be accepted by a
given statistical test  lan.
2031 confidence interval
F: intervalle de confiance
S: intervalo de confianza
The random interval limited by two statistics  r by a single
statistic , such that the probability that a parameter to be
estimated is covered by this interval is equal to a given value 1 
(em  (*a, where ( is the significance level .
2032 statistical tolerance interval
F: intervalle statistique de dispersion
S: intervalo estadistico de tolerancia
A random interval limited by two statistics  r by a single
statistic , such that the probability that a fraction of the popu
lation, equal to or greater than a given value between 0 and 1, is
covered by this interval is equal to a given value 1  (em  (*a,
where ( is the significance level .
2033 confidence limit
F: limite de confiance
S: limite de confianza
Each of the limits of a twosided confidence interval , or the
single limit of a onesided confidence interval .
2034 estimation
F: estimation (de parametres)
S: estimacion (de parametros)
The operation made for the purpose of assigning, from the
observed values in a sample, numerical values to the parameters of
the distribution chosen as the statistical model of the population
from which this sample is taken.
2035 estimate
F: estimation
S: estimacion
The result of an estimation .
Note  This result may be expressed either as a single numer
ical value (point estimation) or as a confidence interval .
2036 estimator
F: estimateur
S: estimador
A statistic  ntended to estimate a population parameter.
2037 confidence coefficient; confidence level
F: niveau de confiance
S: coeficiente de confianza; nivel de confianza
The value 1  (em  (*a of the probability  ssociated with a
confidence interval  r a statistical tolerance interval , where (
is the significance level .
2038 statistic
F: statistique
S: estadistico
A function of the observed values  erived from a sample.
2039 acceptable level (of a measure)
F: niveau acceptable (d'une caracteristique)
S: nivel aceptable (de una medida)
A level for a measure  f a given performance which in a test
 lan corresponds to a specified but relatively high probability
of acceptance .
ANNEX A
(to Supplement 6)
Alphabetical list of definitions contained in this
Supplement
2 col 9107 accelerated test
2039 acceptable level
7209 accumulated down time
3010 accumulated time
7107 active corrective maintenance time
7103 active maintenance time
7106 active preventive maintenance time
9302 active redundancy
7107 active repair time
7109 administrative delay
5209 ageing failure
5311 ageing fault
2017 alternative hypothesis
8105 asymptotic availability
8106 asymptotic unavailability
8107 asymptotic mean availability
8108 asymptotic mean unavailability
6012 automatic maintenance
8105 availability
4002 availability performance
1007 average (deprecated)
5102 bug
9502 burn in
5509 busy state
5212 cataleptic failure
5212 catastrophic failure (deprecated)
2001 characteristic
7113 checkout time
9102 compliance test
5314 complete fault
2037 confidence coefficient
2031 confidence interval
2037 confidence level
2033 confidence limit
7307 constant failure intensity period
7308 constant failure rate period
2026 consumer's risk (point)
6023 controlled maintenance
6005 corrective maintenance
7105 corrective maintenance time
5103 critical defect
5108 critical defective item
5202 critical failure
5302 critical fault
2018 critical region
5510 critical state
2019 critical value
5313 data sensitive fault
5101 defect
5107 defective
5107 defective item
6006 deferred maintenance
5211 degradation failure
4001 dependability
5111 design defect
5207 design failure
5309 design fault
5318 determinate fault
9103 determination test
5219 deterministic failure
5505 disabled state
7207 disabled time
2005 distribution function
5507 down state
7208 down time
5211 drift failure
4006 durability
3009 duration
7306 early failure period
6020 elementary maintenance activity
9106 endurance test
3001 entity
5401 error
5505 error (deprecated sense)
2020 error of the first kind
2022 error of the second kind
2035 estimate
1004 estimated .  
2034 estimation
2036 estimator
5402 execution error
2008 expectation
5506 external disabled state
7210 external disabled time
7210 external loss time
1003 extrapolated .  
9304 fail safe
5201 failure
5217 failure cause
8204 failure intensity
8210 failure intensity acceleration factor
5218 failure mechanism
5322 failure mode (deprecated)
8202 failure rate
8209 failure rate acceleration factor
5301 fault
9411 fault analysis
6027 fault correction
7111 fault correction time
8311 fault coverage
6025 fault diagnosis
6026 fault localization
7114 fault localization time
6024 fault location (deprecated)
7114 fault location time (deprecated)
9306 fault masking
5322 fault mode
9404 fault modes, effects and criticality analysis (FMECA)
9403 fault modes and effects analysis (FMEA)
6024 fault recognition
9305 fault tolerance
9408 fault tree
9405 fault tree analysis (FTA)
5323 faulty
9203 field data
6009 field maintenance
9105 field test
9403 FMEA (fault modes and effects analysis)
9404 FMECA (fault modes, effects and criticality analysis)
5504 free state
7206 free time
9405 FTA (fault tree analysis)
6013 function affecting maintenance
6028 function checkout
6015 functiondegrading maintenance
6016 function permitting maintenance
5314 function preventing fault
6014 functionpreventing maintenance
3006 functional mode
5402 generated error
5211 gradual failure
5504 idle state
7206 idle time
5106 imperfection
6019 indenture level
5319 indeterminate fault
5206 inherent weakness failure
1005 inherent .  
5308 inherent weakness fault
6009 in situ maintenance
3007 instant of time
1009 instantaneous .  
8101 instantaneous availability
8111 instantaneous availability of a leased circuit
8204 instantaneous failure intensity
8202 instantaneous failure rate
8302 instantaneous repair rate
8102 instantaneous unavailability
5403 interaction error
5317 intermittent fault
5507 internal disabled state
1005 intrinsic .  
3001 item
9104 laboratory test
5320 latent fault
9501 learning process
6017 level of maintenance
6018 line of maintenance
7110 logistic delay
8301 maintainability
9415 maintainability allocation
9415 maintainability apportionment
9112 maintainability demonstration
9412 maintainability model
4004 maintainability performance
9413 maintainability prediction
9506 maintainability programme
9111 maintainability verification
6003 maintenance
6021 maintenance action
6018 maintenance echelon
6030 maintenance entity
7102 maintenance manhours (MMH)
6001 maintenance philosophy
6002 maintenance policy
4005 maintenance support performance
6021 maintenance task
7101 maintenance time
9414 maintenance tree
5105 major defect
5109 major defective item
5304 major fault
5112 manufacturing defect
5208 manufacturing failure
5310 manufacturing fault
8110 MADT (mean accumulated down time)
8308 MART (mean active repair time)
8401 MAD (mean administrative delay)
8305 MDT (mean down time)
2008 mean
1007 mean .  
8110 mean accumulated down time (MADT)
8308 mean active repair time (MART)
8401 mean administrative delay (MAD)
8103 mean availability
8305 mean down time (MDT)
8203 mean failure rate
8205 mean failure intensity
8403 mean logistic delay (MLD)
8304 mean maintenance manhours
8303 mean repair rate
8306 mean repair time (MRT)
8208 mean time between failures (MTBF)
8207 mean time to failure (MTTF)
8206 mean time to first failure (MTTFF)
8310 mean time to recovery
8310 mean time to repair (deprecated)
8310 mean time to restoration (MTTR)
8104 mean unavailability
8109 mean up time (MUT)
3011 measure
5106 minor defect
5110 minor defective item
5305 minor fault
5205 mishandling failure
5307 mishandling fault
5405 mistake
5204 misuse failure
5306 misuse fault
8403 MLD (mean logistic delay)
7102 MMH (maintenance manhours)
8306 MRT (mean repair time)
8208 MTBF (mean time between failures)
8207 MTTF (mean time to failure)
8206 MTTFF (mean time to first failure)
8310 MTTR
8109 MUT (mean up time)
3013 modification
5104 noncritical defect
5203 noncritical failure
5303 noncritical fault
5214 nonrelevant failure
3003 nonrepaired item
5502 nonoperating state
7202 nonoperating time
7204 nonrequired time
2016 null hypothesis
9201 observed data
2011 observed value
2024 OC curve
6010 offsite maintenance
2014 onesided test
6009 onsite maintenance
2024 operating characteristic curve
5501 operating state
7201 operating time
3012 operation
1006 operational .  
5505 outage
5315 partial fault
5316 permanent fault
5316 persistent fault
2007 pfractile (of a probability distribution)
1008 pfractile .  
8309 pfractile active repair time
8402 pfractile administrative delay
8404 pfractile logistic delay
8307 pfractile repair time
8101 pointwise availability
8102 pointwise unavailability
2027 power of the test
1002 predicted .  
9401 prediction
6004 preventive maintenance
7104 preventive maintenance time
5215 primary failure
2002 probability
2006 probability density function
2029 probability of acceptance
2030 probability of rejection
2025 producer's risk (point)
5312 programmesensitive fault
5404 propagated error
2007 pquantile
2004 random process
2003 random variable
6029 recovery
9301 redundancy
9204 reference data
8201 reliability
9407 reliability block diagram
9503 reliability growth
9504 reliability improvement
9402 reliability model
4003 reliability performance
2012 relative frequency
5213 relevant failure
6011 remote maintenance
6005 repair
8312 repair coverage
8302 repair rate
7105 repair time
3002 repaired item
5219 reproducible failure
3005 required function
7203 required time
6029 restoration
6007 scheduled maintenance
5216 secondary failure
9109 screening test
2028 significance level
5316 solid fault
2010 standard deviation
9303 standby redundancy
5503 standby state
7205 standby time
9409 statetransition diagram
2038 statistic
2013 statistical test
2032 statistical tolerance interval
8105 steadystate availability
9108 step stress test
9406 stress analysis
9410 stress model
5210 sudden failure
6001 supervision
5219 systematic failure
Blanc
5321 systematic fault
7112 technical delay
9101 test
9202 test data
9110 time acceleration factor
7303 time between failures
3009 time duration
7302 time to failure
7301 time to first failure
3008 time interval
7304 time to recovery
7304 time to restoration
5317 transient fault
1001 true .  
2015 twosided test
2021 type I risk
2023 type II risk
7108 undetected fault time
5508 up state
7211 up time
6008 unscheduled maintenance
7305 useful life
2009 variance
9203 variate
5317 volatile fault
5206 weakness failure
5308 weakness fault
5209 wearout failure
5311 wearout fault
7309 wearout failure period
Blanc
ANNEX B
(to Supplement 6, Part I)
Relations between defect, failure and fault concepts
H.T. [T1.6]
TABLE B1
______________________________________________________________________________
Defect Failure Fault
______________________________________________________________________________
Critical defect Critical failure Critical fault
Noncritical defect Noncritical failure Noncritical fault
Major defect  Major fault
Minor defect  Minor fault
 Misuse failure Misuse fault
 Mishandling failure Mishandling fault
 Inherent weakness failure Inherent weakness fault
Design defect Design failure Design fault
Manufacturing defect Manufacturing failure Manufacturing fault
 Ageing failure Ageing fault
 Sudden failure 
 Gradual failure 
 Cataleptic failure 
 Relevant failure 
 Nonrelevant failure 
 Primary failure 
 Secondary failure 
 Failure cause 
 Failure mechanism 
  Programmesensitive fault
  Datasensitive fault
  Complete fault
  Partial fault
  Persistent fault
  Intermittent fault
  Fault mode
  Determinate fault
  Indeterminate fault
  Latent fault
 Systematic failure Systematic fault
Bug  
______________________________________________________________________________








































































































































Table B1/Sup. 6 [T1.6], p.
Blanc
ANNEX C
(to Supplement 6, Part I)
List of recommended symbols and abbreviations
( Significance level
 Type II risk
\(t ) Instantaneous failure rate
\ (t1,  fIt2) Mean failure rate [in time interval (t1, 
fIt2)]
u(t ) Instantaneous repair rate
u  (t1,  fIt2) Mean repair rate [in time interval (t1, 
fIt2)]
` Standard deviation
A Asymptotic availability
A (t ) Instantaneous availability
A  Asymptotic mean availability
A  (t1,  fIt2) Mean availability [in time interval (t1,
 fIt2)]
ASR Answer seizure ratio
E (X ) Mean (of X )
f (x ) Probability density function
F (x ) Distribution function
FMEA Fault modes and effect analysis
FMECA Fault modes, effects and criticality analysis
FTA Fault tree analysis
H0 Null hypothesis
H1 Alternative hypothesis
MAD Mean administrative delay
MADT Mean accumulated down time
MART Mean active repair time
MDT Mean down time
MLD Mean logistic delay
MMH Maintenance manhours
MRT Mean repair time
MTBF Mean time between failures
MTTF Mean time to failure
MTTFF Mean time to first failure
MTTR Mean time to restoration
MUT Mean up time
N (t1, t2) Number of failures [in time interval (t1, 
fIt2)]
R Reliability
U Asymptotic unavailability
U (t ) Instantaneous unavailability
U  Asymptotic mean unavailability
U  (t1,  fIt2) Mean unavailability [in time interval
(t1,  fIt2)]
z (t ) Instantaneous failure intensity
z  (t1,  fIt2) Mean failure intensity [in time interval
(t1,  fIt2)]
Blanc
Supplement No. 7
GUIDE FOR EVALUATING AND IMPLEMENTING  fR ALTERNATE ROUTING
NETWORKS
A systematic procedure consisting of a number of distinct
steps is used for the evaluation of alternate routing networks.
These steps are given in the flowchart of Annex A and are pro
vided as guidance. Administrations may wish to expand, delete or
change the order of these steps to meet circumstances.
The steps may be grouped into the following six processes:
 Identification of alternate route.
 Preliminary screening.
 Data gathering.
 Evaluation.
 Implementation.
 Monitoring.
1 Identification of alternate route
A terminal Administration selects an alternate route.
A tentative agreement is reached with the opposite terminal
Administration to use the selected alternate route, and both termi
nal Administrations reach tentative agreement with the transit
Administration to explore the use of its network as an alternate
route.
If no tentative agreements are reached, another alternate
route is selected or if none is available, the procedure is aban
doned.
2 Preliminary screening
Using available data, the organizational elements of the ter
minal Administrations responsible for transmission, routing and
call completion, analyse the feasibility of utilizing the alternate
route.
If an objection is raised, another alternate route is selected
or, if none is available, the procedure is abandoned.
3 Data gathering
A questionnaire is issued to all Administrations involved to
obtain additional information before an evaluation is made of the
proposed alternate route.
The questionnaire can include requests for transmission, rout
ing, call completion rates, traffic profiles, circuit costs, and
transit charges.
If there is no response to the questionnaire or if the infor
mation provided indicates that the alternate route is unsuitable,
another alternate route is selected or, if none is available, the
procedure is abandoned.
4 Evaluation
The alternate routing network is dimensioned according to
Recommendation E.522.
If additional circuits are required on the alternate route,
and the required increment exceeds the available capacity, another
alternate route is selected. If no other alternate route is
available Administrations may choose to retain the selected alter
nate route and accept a cost disadvantage.
5 Implementation
Final negotiations are carried out and approval of all
Administrations involved in the alternate route network is sought.
The negotiations would include the reporting procedure and
responsibility for recording traffic overflowing to the alternate
route.
If final agreement cannot be reached, another alternate route
is selected or, if none is available, the procedure is abandoned.
6 Monitoring
Traffic volumes and performance data for the alternate route
are recorded and exchanged at regular intervals.
ANNEX A
(to Supplement No. 7)
Flowchart of evaluation and implementation procedure for alternate
routing networks
Figure A1, p.
Blanc
Figure A2, p.