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All drawings appearing in this Recommendation have been done in Autocad.
Recommendation E.8001)
QUALITY OF SERVICE AND DEPENDABILITY VOCABULARY
CONTENTS
1 Introduction
2 Related Recommendations
3 Performances
3.1 Service related performances
3.2 Item related performances
4 Interruptions
5 Measures of performances
5.1 Service support performance
5.2 Service operability performance
5.3 Service accessibility performance
5.4 Service retainability performance
5.5 Serveability performance
5.6 Transmission performance
6 Common concepts
Annex A - Alphabetical list of definitions contained in this Recommendation
1 Introduction2)
A consistent set of terms and definitions is necessary for the development
of Recommendations in the important areas of quality of service and network
performance by the numerous Study Groups responsible for the Recommendations.
Terminology standardization is also necessary to align the work of the various
groups and to avoid confusing the users of Recommendations by the introduction of
conflicting terms and definitions. Therefore, this Recommendation sets forth a
simple set of terms and definitions relating to the concept of the quality of
telecommunications services and network performance. These terms and definitions
apply to all telecommunications services and all network arrangements used to
provide the services.
The diagram in Figure 1/E.800 is intended to provide an overview of the
factors which contribute collectively to the overall quality of service as
perceived by the user of a telecommunication service. The terms in the diagram
can be thought of as generally applying either to the quality of service levels
actually achieved in practice, to objectives which represent quality of service
goals to be achieved, or to requirements which reflect design specifications.
The diagram in Figure 1/E.800 is also structured to show that one quality
of service factor can depend on a number of others. It is important to note -
although it is not explicitly stated in each of the definitions to follow - that
the value of a characteristic measure of a particular factor may depend directly
on corresponding values of other factors which contribute to it. This
necessitates, whenever the value of a measure is given, that all of the
conditions having an impact on that value be clearly stated.
An essential aspect of the global evaluation of a service is the opinion
of the users of the service. The result of this evaluation expresses the users'
degrees of satisfaction. This Recommendation establishes:
1) a general framework for the quality of service concept
2) the relationship between quality of service and network performance
3) a set of measures for these performances.
It is obvious that a service can be used only if it is provided, and it is
desirable that the provider have a detailed knowledge about the quality of the
offered service. From the provider's viewpoint, network performance is a concept
by which network characteristics can be defined, measured and controlled to
achieve a satisfactory level of service quality. The interests and the viewpoints
of users and providers are different, and usually require a compromise between
quality and economics.
In the utilization of a service the user identifies two ½bodies╗:
1) the "Organization(s)", i.e., the telecommunication Administration,
operating company, etc. providing the means and facilities for the
access to and the utilization of the service;
1) Formerly part of Recommendation G.106, Red Book, Fascicle III.1
2) Terms printed in italics in the text may be found with their related definitions in
Supplement No. 6 or in Recommendation E.600.
3) In some countries' terminals are not part of the network and are or may be
customer-provided
Fascicle II.3 - Rec. E.800 PAGE1
2) the ½network╗, i.e., the necessary means (terminals3), lines, switches,
etc.) actually used.
The contribution of the Organization to the quality of service is
characterized by one performance concept, service support performance, as shown
in Figure 1/E.800.
The contribution of the network to the quality of service is characterized
by three performance concepts, which are:
- service operability performance, i.e., the ease by which the service
can be used, including the characteristics of terminal equipment, the
intelligibility of tones and messages, etc.;
- serveability performance, the ability of a service to be obtained -
within specified tolerances and other given conditions - when requested
by the user and continue to be provided for the requested duration.
Thus, serveability performance describes the response of the network
during the establishment, retention and release of a service
connection;
- service integrity, the degree to which a service is provided without
excessive impairments, once obtained. Thus, service integrity is
primarily concerned with the level of reproduction of the transmitted
signal at the receiving end.
The serveability performance is further subdivided into two terms:
- service accessibility performance, the ability of a service to be
obtained - within specified tolerances and other given conditions -
when requested by the user, further subdivided into (1) network
accessibility, which is the ability of the user to obtain access to the
network for a service request, and (2) connection accessibility, which
is the ability of the network to provide the user with a satisfactory
connection to the intended destination;
- service retainability performance, which is the ability of the service,
once obtained, to continue to be provided under given conditions for a
requested period of time. That is, service retainability performance
covers the proper retention of connections and the release
(disengagement) when requested by the user.
Serveability performance is divided into trafficability performance,
dependability and propagation performance as shown in Figure 1/E.800. The
trafficability performance is described in purely teletraffic engineering terms
(see Recommendation E.600). The measures are expressed in terms of losses and
delay times. Dependability is the combined aspects of availability, reliability,
maintainability and maintenance support performances and relates to the ability
of an item to be in a state to perform a required function (see Supplement No.
6). Propagation performance refers to the ability of the transmitting medium to
transmit the signal within intended tolerances.
Figure 1/E.800 - CCITT 31424
Measures for all of the above performances may be related to an instant of
time (instantaneous, etc.) or expressed as a mean value over a time interval.
These and other recommended qualifiers (measure modifiers) are found in
Supplement No. 6.
Supplement No. 6 further provides recommended statistical terms and
definitions for use in the application of measures related to all performances.
While dependability is used only for a general description in
non-quantitative terms, the actual quantification is done under the heading of
availability performance, reliability performance, maintainability performance
and maintenance support performance.
The most important of these dependability-related measures are found in
Supplement No. 6, Part I. The properties expressed by these measures impact the
measures related to quality of service and network performance and are thus
implicitly characterizations of these performances.
Measures are connected to events (failure, restoration, etc.), states
(fault, up state, down state, outage, etc.) or activities (e.g. maintenance),
with their time durations.
Part I of Supplement No. 6 provides necessary identification of times,
events, states and maintenance activities.
2 Related Recommendations and Supplements
Recommendation E.600: Terms and definitions of traffic engineering
PAGE12 Fascicle II.3 - Rec. E.800
Supplement No. 6: Terms and definitions for quality of service, network
performance, dependability and trafficability studies.
3 Performances
3.1 Service related performances
3101 quality of service
F qualité de service
S: calidad de servicio
The collective effect of service performances which determine the degree
of satisfaction of a user of the service.
Note 1 - The quality of service is characterized by the combined aspects
of service support performance, service operability performance, serveability
performance, service integrity and other factors specific to each service.
Note 2 - The term "quality of service" is not used to express a degree of
excellence in a comparative sense nor is it used in a quantitative sense for
technical evaluations. In these cases a qualifying adjective (modifier) shall be
used.
3102 serveability performance
F: servibilité (d'un service)
S: servibilidad (de un servicio)
The ability of a service to be obtained - within specified tolerances and
other given conditions - when requested by the user and continue to be provided
for a requested duration.
Note - Serveability performance may be subdivided into the service
accessibility performance and the service retainability performance.
3103 service accessibility performance
F: accessibilité (d'un service)
S: accesibilidad (de un servicio)
The ability of a service to be obtained, within specified tolerances and
other given conditions, when requested by the user.
Note - This takes into account the transmission tolerance and the combined
aspects of propagation performance, trafficability performance and availability
performance of the related systems.
3104 service retainability performance
F: continuabilité (d'un service)
S: retenibilidad (de un servicio)
The ability of a service, once obtained, to continue to be provided under
given conditions for a requested duration.
Note - Generally this depends on the transmission tolerances, the
propagation performance and reliability performance of the related systems. For
some services, for example packet switching, this also depends on the
trafficability performance and the availability performance of the related
systems.
3105 service support performance
F: logistique de service
S: logística del servicio
The ability of an organization to provide a service and assist in its
utilization.
Note - An example of service support performance is the ability to provide
assistance in commissioning a basic service, or a supplementary service such as
the call waiting service or directory enquiries service.
3106 service operability performance
F: facilité d'utilisation (d'un service)
S: facilidad de utilización (de un servicio)
The ability of a service to be successfully and easily operated by a user.
3107 service integrity
F: integrité de service
S: integridad del servicio
The degree to which a service is provided without excessive impairments,
once obtained.
Note - This service is characterized by the transmission performance of
the system.
3108 transmission performance
F: qualité de transmission
Fascicle II.3 - Rec. E.800 PAGE1
S: calidad de transmisión
The level of reproduction of a signal offered to a telecommunications
system, under given conditions, when this system is in an up state.
3.2 Item related performances
3201 network performance
F: qualité technique du réseau
S: calidad de funcionamiento de la red
The ability of a network or network portion to provide the functions
related to communications between users.
Note 1 - Network performance contributes to serveability performance and
service integrity (see Figure 2/E.800).
Note 2 - Network performance measures are meaningful to network providers
and are quantifiable at boundaries of network portions to which they apply.
Quality of service measures are only quantifiable at a service access point.
Figure 2/E.800 - T0201420-88
3202 trafficability performance
F: traficabilité; capacité d'écoulement du trafic
S: aptitud para cursar tráfico
The ability of an item to meet a traffic demand of a given size and other
characteristics, under given internal conditions.
Note - Given internal conditions refer, for example, to any combination of
faulty and not faulty sub-items.
3203 capability
F: capacité; capabilité (d'une entité)
S: capacidad
The ability of an item to meet a demand of a given size under given
internal conditions.
Note 1 - Internal conditions refer, for example, to any given combination
of faulty and not faulty sub-items.
Note 2 - This is also called trafficability performance.
3204 propagation performance
F: caractéristiques de propagation
S: característica de propagación
The ability of a propagation medium, in which a wave propagates without
artificial guide, to transmit a signal within the given tolerances.
Note - The given tolerances may apply to variations in signal level,
noise, interference levels, etc.
3205 effectiveness (performance)
F: efficacité
S: efectividad
The ability of an item to meet a service demand of a given size.
Note - This ability depends on the combined aspects of the capability and
the availability performance of the item.
4 Interruptions
4101 interruption; break (of service)
F: interruption; coupure (d'un service)
S: interrupción (de un servicio); corte (de un servicio)
Temporary inability of a service to be provided persisting for more than a
given time duration, characterized by a change beyond given limits in at least
one parameter essential for the service.
Note 1 - An interruption of a service may be caused by disabled states of
the items used for the service or by external reasons such as high service
demand.
Note 2 - An interruption of a service is generally an interruption of the
transmission, which may be characterized by an abnormal value of power level,
noise level, signal distortion, error rate, etc.
4102 time between interruptions
F: temps entre interruptions
S: tiempo entre interrupciones
The time duration between the end of one interruption and the beginning of
PAGE12 Fascicle II.3 - Rec. E.800
the next.
4103 interruption duration
F: durée d'interruption
S: duración de interrupción
The time duration of an interruption.
4104 mean time between interruptions (MTBI)
F: durée moyenne entre interruptions (DMEI)
S: tiempo medio entre interrupciones
The expectation of the time between interruptions.
4105 mean interruption duration (MID)
F: durée moyenne d'une interruption (DMI)
S: duración media de una interrupción
The expectation of the interruption duration.
5 Measures of performances
5.1 Service support performance
5101 mean service provisioning time
F: délai moyen pour la fourniture d'un service
S: tiempo medio de espera (para la prestación de un servicio)
The expectation of the duration between the instant of time a potential
user requests that an organization provides the necessary means for a service,
and the instant of time when these means are furnished.
5102 billing error probability
F: probabilité d'erreur de facturation
S: probabilidad de error de facturación
The probability of an error when billing a user of a service.
5103 incorrect charging or accounting probability
F: probabilité de taxation erronée
S: probabilidad de tarificación o de contabilidad incorrectas
The probability of a call attempt receiving incorrect charging or
accounting treatment.
5104 undercharging probability
F: probabilité de sous-taxation
S: probabilidad de subtarificación
The probability that an effective call will be undercharged for any
reason.
5105 overcharging probability
F: probabilité de surtaxation
Fascicle II.3 - Rec. E.800 PAGE1
S: probabilidad de sobretarificación
The probability that an effective call will be overcharged for any reason.
5106 billing integrity (probability)
F: (probabilité de) justesse de facturation
S: integridad de la facturación (probabilidad de)
The probability that the billing information presented to a user correctly
reflects the type, destination and duration of the call.
5.2 Service operability performance
5201 service user mistake probability
F: probabilité d'erreur d'un usager
S: probabilidad de error de un usuario (de un servicio)
Probability of a mistake made by a user in his attempt to utilize a
service.
5202 dialling mistake probability
F: probabilité d'erreur de numérotation
S: probabilidad de error de marcación
The probability that the user of a telecommunication network makes
dialling mistakes during his call attempts.
5203 service user abandonment probability
F: probabilité d'abandon (d'accès à un service par un usager)
S: probabilidad de abandono de un servicio por un usuario
The probability that a user abandons the attempt to use a service.
Note - Abandonments may be caused by excessive user mistake rates, by
excessive service access delays, etc.
5204 call abandonment probability
F: probabilité d'abandon (d'une tentative d'appel)
S: probabilidad de abandono de una tentativa de llamada
The probability that a user abandons the call attempt to a
telecommunication network.
5.3 Service accessibility performance
5301 service accessibility; service access probability
F: accessibilité (d'un service)
S: accesibilidad de un servicio; probabilidad de acceso a un servicio
The probability that a service can be obtained within specified tolerances
and other given operating conditions when requested by the user.
5302 mean service access delay
F: durée moyenne d'accès
S: retardo medio de acceso a un servicio; demora media de acceso a un
servicio
The expectation of the time duration between an initial bid by the user
for the acquisition of a service and the instant of time the user has access to
the service, the service being obtained within specified tolerances and other
given operating conditions.
5303 network accessibility
PAGE12 Fascicle II.3 - Rec. E.800
F: accessibilité (d'un réseau)
S: accesibilidad (de una red)
The probability that the user of a service after a request receives the
proceed-to-select signal within specified conditions.
Note - The proceed-to-select signal is that signal inviting the user to
select the desired destination.
5304 connection accessibility
F: accessibilité
S: accesibilidad de una conexión
The probability that a connection can be established within specified
tolerances and other given conditions following receipt by the exchange of a
valid code.
5305 mean access delay
F: durée moyenne d'accès
S: retardo medio de acceso; demora media de acceso
The expectation of the time duration between the first call attempt made
by a user of a telecommunication network to reach another user or a service and
the instant of time the user reaches the wanted other user or service, within
specified tolerances and under given operational conditions.
5306 p-fractile access delay
F: quantile-p de la durée d'accès
S: cuantil-p del retardo de acceso; cuantil-p de la demora de acceso
The p-fractile value of the duration between the first call attempt made
by a user of a telecommunication network to reach another user or a service and
the instant of time the user reaches the wanted other user or service, within
specified tolerances and under given operational conditions.
5307 accessibility of a connection to be established
F: accessibilité d'une communication à établir
S: accesibilidad de una conexión por establecer
The probability that a switched connection can be established, within
specified transmission tolerances, to the correct destination, within a given
time interval, when requested by the user.
Note 1 - For user-originated calls, it could express the probability of a
successful call establishment on the first attempt. For operator-handled calls,
it could represent the probability of having a satisfactory connection
established within a given time duration.
Note 2 - In general, the tolerances should correspond to a level of
transmission performance which makes the connection unsatisfactory for service
such that, for example, a substantial percentage of users would abandon the
connection.
5308 unacceptable transmission probability
F: probabilité d'une transmission inacceptable
S: probabilidad de transmisión inaceptable
The probability of a connection being established with an unacceptable
speech path transmission quality.
Fascicle II.3 - Rec. E.800 PAGE1
5309 no tone probability
F: probabilité de non tonalité
S: probabilidad de ausencia de tono
The probability of a call attempt encountering no tone following receipt
of a valid code by the exchange.
5310 misrouting probability
F: probabilité d'acheminement errone
S: probabilidad de encaminamiento erróneo
The probability of a call attempt being misrouted following receipt by the
exchange of a valid code.
5.4 Service retainability performance
5401 service retainability
F: continuabilité (d'un service)
S: retenibilidad (de un servicio)
The probability that a service, once obtained, will continue to be
provided under given conditions for a given time duration.
5402 connection retainability
F: continuabilité (d'une chaîne de connexion)
S: retenibilidad (de una conexión)
The probability that a connection, once obtained, will continue to be
provided for a communication under given conditions for a given time duration.
5403 retainability of an established connection
F: continuabilité d'une communication établie
S: retenibilidad de una conexión establecida
The probability that a switched connection, once established, will operate
within specified transmission tolerances without interruption for a given time
interval.
5404 premature release probability; cut-off call probability
F: probabilité de libération prématurée
S: probabilidad de liberación prematura; probabilidad de corte de una
llamada
The probability that an established connection will be released for a
reason other than intentionally by any of the parties involved in the call.
5405 release failure probability
F: probabilité de non-libération
S: probabilidad de fallo de liberación
The probability that the required release of a connection will not take
place.
PAGE12 Fascicle II.3 - Rec. E.800
5.5 Serveability performance
5501 probability of successful service completion
F: probabilité d'exécution correcte du service
S: probabilidad de prestación satisfactoria de un servicio
The probability that a connection can be established, under satisfactory
operating conditions, and retained for a given time interval.
5.6 Transmission performance
5601 bit error ratio (BER)
F: taux d'erreur sur les bits (TEB)
S: tasa de errores en los bits; tasa de error en los bits (TEB)
The ratio of the number of bit errors to the total number of bits
transmitted in a given time interval.
5602 error free seconds (EFS)
F: secondes sans erreur (SSE)
S: segundos sin error (SSE)
The ratio of the number of one-second intervals during which no bits are
received in error to the total number of one-second intervals in the time
interval.
Note 1 - The length of the time interval needs to be specified.
Note 2 - This ratio is usually expressed as a percentage.
6 Common concepts
The following concepts are used in the definitions of this Recommendation.
Others used, such as probability, measure, up state, disabled state, time
duration, user and connection may be found in Recommendation E.600 and in
Supplement No. 6.
6001 service
F: service
S: servicio
A set of functions offered to a user by an organization.
6002 item; entity
F: entité; individu
S: elemento; entidad; ítem
Any part, device, subsystem, functional unit, equipment or system that can
be individually considered.
Note 1 - An item may 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 entité replaces the term dispositif
previously used in this meaning, because the term dispositif is also the common
equivalent for the English term "device".
Note 3 - In French, the term individu is used mainly in statistics.
Fascicle II.3 - Rec. E.800 PAGE1
ANNEX A
(to Recommendation E.800)
Alphabetical list of definitions contained in this Recommendation
5307accessibility of a connection 5
to be established 309 no tone probability
5102billing error probability 5105 overcharging probability
5106billing integrity 5306 p-fractile access delay
(probability) 5404 premature release probability
5601bit error ratio 5501 probability of successful
5204call abandonment probability service completion
3203capability 3204 propagation performance
5304connection accessibility 3101 quality of service
4101break (of service) 5405 release failure probability
5402connection retainability 5403 retainability of an
5404cut-off call probability established connection
5202dialling mistake probability 3102 serveability performance
3205effectiveness (performance) 6001 service
6002entity 5301 service access probability
5602error free seconds (EFS) 5301 service accessibility
5103incorrect charging or 3103 service accessibility
accounting probability performance
4103interruption duration 3107 service integrity
4101interruption 3106 service operability
6002item performance
5305mean access delay 5401 service retainability
4105mean interruption duration 3104 service retainability
5302mean service access delay performance
5101mean service provisioning time 3105 service support performance
4104mean time between 5203 service user abandonment
interruptions probability
5310misrouting probability 5201 service user mistake
5303network accessibility probability
3201network performance 4102 time between interruptions
3202 trafficability performance
3108 transmission performance
5308 unacceptable transmission
probability
5104 undercharging probability
PAGE12 Fascicle II.3 - Rec. E.800
