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 «bodies»: 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 «network», 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 qualit‚ 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: servibilit‚ (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: accessibilit‚ (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: continuabilit‚ (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: log¡stica 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: facilit‚ d'utilisation (d'un service) S: facilidad de utilizaci¢n (de un servicio) The ability of a service to be successfully and easily operated by a user. 3107 service integrity F: integrit‚ 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: qualit‚ de transmission Fascicle II.3 - Rec. E.800 PAGE1 S: calidad de transmisi¢n 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: qualit‚ technique du r‚seau 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: traficabilit‚; capacit‚ d'‚coulement du trafic S: aptitud para cursar tr fico 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: capacit‚; capabilit‚ (d'une entit‚) 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: caract‚ristiques de propagation S: caracter¡stica de propagaci¢n 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: efficacit‚ 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: interrupci¢n (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: dur‚e d'interruption S: duraci¢n de interrupci¢n The time duration of an interruption. 4104 mean time between interruptions (MTBI) F: dur‚e moyenne entre interruptions (DMEI) S: tiempo medio entre interrupciones The expectation of the time between interruptions. 4105 mean interruption duration (MID) F: dur‚e moyenne d'une interruption (DMI) S: duraci¢n media de una interrupci¢n The expectation of the interruption duration. 5 Measures of performances 5.1 Service support performance 5101 mean service provisioning time F: d‚lai moyen pour la fourniture d'un service S: tiempo medio de espera (para la prestaci¢n 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: probabilit‚ d'erreur de facturation S: probabilidad de error de facturaci¢n The probability of an error when billing a user of a service. 5103 incorrect charging or accounting probability F: probabilit‚ de taxation erron‚e S: probabilidad de tarificaci¢n o de contabilidad incorrectas The probability of a call attempt receiving incorrect charging or accounting treatment. 5104 undercharging probability F: probabilit‚ de sous-taxation S: probabilidad de subtarificaci¢n The probability that an effective call will be undercharged for any reason. 5105 overcharging probability F: probabilit‚ de surtaxation Fascicle II.3 - Rec. E.800 PAGE1 S: probabilidad de sobretarificaci¢n The probability that an effective call will be overcharged for any reason. 5106 billing integrity (probability) F: (probabilit‚ de) justesse de facturation S: integridad de la facturaci¢n (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: probabilit‚ 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: probabilit‚ d'erreur de num‚rotation S: probabilidad de error de marcaci¢n The probability that the user of a telecommunication network makes dialling mistakes during his call attempts. 5203 service user abandonment probability F: probabilit‚ d'abandon (d'accŠs … 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: probabilit‚ 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: accessibilit‚ (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: dur‚e moyenne d'accŠs 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: accessibilit‚ (d'un r‚seau) 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: accessibilit‚ S: accesibilidad de una conexi¢n 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: dur‚e moyenne d'accŠs 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 dur‚e d'accŠs 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: accessibilit‚ d'une communication … ‚tablir S: accesibilidad de una conexi¢n 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: probabilit‚ d'une transmission inacceptable S: probabilidad de transmisi¢n 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: probabilit‚ de non tonalit‚ 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: probabilit‚ d'acheminement errone S: probabilidad de encaminamiento err¢neo 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: continuabilit‚ (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: continuabilit‚ (d'une chaŒne de connexion) S: retenibilidad (de una conexi¢n) 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: continuabilit‚ d'une communication ‚tablie S: retenibilidad de una conexi¢n 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: probabilit‚ de lib‚ration pr‚matur‚e S: probabilidad de liberaci¢n 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: probabilit‚ de non-lib‚ration S: probabilidad de fallo de liberaci¢n 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: probabilit‚ d'ex‚cution correcte du service S: probabilidad de prestaci¢n 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: entit‚; individu S: elemento; entidad; ¡tem 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 entit‚ 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. 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