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Final draft ETSI EG V1.1.1 ( )
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1 Final draft EG V1.1.1 ( ) Guide Speech Processing, Transmission and Quality Aspects (STQ); User related QoS parameter definitions and measurements; Part 2: Voice telephony, Group 3 fax and modem data services
2 2 Final draft EG V1.1.1 ( ) Reference DEG/STQ Keywords Data, fax, modem, quality, user, voice 650 Route des Lucioles F Sophia Antipolis Cedex - FRANCE Tel.: Fax: Siret N NAF 742 C Association à but non lucratif enregistrée à la Sous-Préfecture de Grasse (06) N 7803/88 Important notice Individual copies of the present document can be downloaded from: The present document may be made available in more than one electronic version or in print. In any case of existing or perceived difference in contents between such versions, the reference version is the Portable Document Format (PDF). In case of dispute, the reference shall be the printing on printers of the PDF version kept on a specific network drive within Secretariat. Users of the present document should be aware that the document may be subject to revision or change of status. Information on the current status of this and other documents is available at If you find errors in the present document, send your comment to: Copyright Notification No part may be reproduced except as authorized by written permission. The copyright and the foregoing restriction extend to reproduction in all media. European Telecommunications Standards Institute All rights reserved. DECT TM, PLUGTESTS TM and UMTS TM are Trade Marks of registered for the benefit of its Members. TIPHON TM and the TIPHON logo are Trade Marks currently being registered by for the benefit of its Members. 3GPP TM is a Trade Mark of registered for the benefit of its Members and of the 3GPP Organizational Partners.
3 3 Final draft EG V1.1.1 ( ) Contents Intellectual Property Rights...5 Foreword Scope References Definitions and abbreviations Definitions Abbreviations General considerations Services covered Use of the parameters Reporting for different classes of customers Non standard levels of QoS Reporting for directly- and indirectly-serviced customers Data processing issues Data collection period Sampling and test calls Comparability of measurements Publication of QoS parameters QoS parameters for voice, data and fax services accessed via the PTN Unsuccessful call ratio Definition Application Measurement and statistics Further considerations Call set up time Definition Application Measurement and statistics Further considerations Speech connection quality Definition Application Results Further considerations Fax connection quality Definition Application Measurement and statistics Data rate of dial-up access to the internet Definition Application Measurement and statistics Further considerations...22 Annex A (normative): Annex B (normative): Annex C (normative): Combination of weekly or monthly results...24 Further explanation of "X % of"...25 Guidance on the selection of representative samples and test calls...26 Annex D (normative): Decision about the success of a call attempt...27 Annex E (normative): Relationship between the accuracy of the estimator of the unsuccessful call ratio and the number of calls to be observed...29
4 4 Final draft EG V1.1.1 ( ) E.1 Theory...29 E.2 Guidance...31 Annex F (normative): Annex G (normative): Annex H (normative): Method of calculating the number of observations required for measures of time...32 Standardized test chart for fax connection quality...33 General approach and basic principles for the determination of Speech Connection Quality...36 Annex I (informative): Bibliography...38 History...39
5 5 Final draft EG V1.1.1 ( ) Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to. The information pertaining to these essential IPRs, if any, is publicly available for members and non-members, and can be found in SR : "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to in respect of standards", which is available from the Secretariat. Latest updates are available on the Web server ( Pursuant to the IPR Policy, no investigation, including IPR searches, has been carried out by. No guarantee can be given as to the existence of other IPRs not referenced in SR (or the updates on the Web server) which are, or may be, or may become, essential to the present document. Foreword This Guide (EG) has been produced by Technical Committee Speech processing, Transmission and Quality aspects (STQ), and is now submitted for the standards Membership Approval Procedure. The present document is part 1 of a multi-part deliverable covering Speech Processing, Transmission and Quality Aspects (STQ); User related QoS parameter definitions and measurements, as identified below: Part 1: Part 2: Part 3: "General"; "Voice telephony, Group 3 fax and modem data services"; "QoS parameters specific to mobile services". Part 1 of the present document contains general user related QoS parameter definitions and measurement methods that can be applied to any service. Part 2 of the present document (this part) contains user related QoS parameter definitions and measurement methods for voice, data and fax services accessed via the public telecommunication network. The data parameters are specified for the case where an ITU-T Recommendation V.90/V.92 [17], [18] compliant modem is used since this kind of modem is in common use. Part 3 of the present document contains user related QoS parameter definitions and measurement methods for mobile specific services. The present document takes into account as far as practicable the following eight principles: 1) QoS parameters should be easily understood by the public, and be useful and important to them. 2) All parameters are applicable at the network termination point (where appropriate). 3) Where measurements are possible they should be made on the customer's premises, using in-service lines. NOTE: Literally principles 2 and 3 imply that all measurements must be carried out at the NTP, which would require co-operation by users and be excessively intrusive, as it would require many visits to the premises of users. Measurements at the subscriber side of the local exchange (e.g. at the MDF or other possible connection point/distribution frame in the access network) generally give an adequate representation of the quality that would be perceived at the NTP for the parameters defined in the present document, and so this approach is used because it is more practicable and meets the underlying objectives of these principles. 4) To be as realistic as possible, real traffic rather than test calls should be used as a basis of the measurements, wherever possible. 5) Parameters should be capable of verification by independent organizations. This verification might be made by direct measurements or by audit of service provider's measurements. 6) The accuracy of QoS values should be set to a level consistent with measurement methods being as simple as possible with costs as low as possible.
6 6 Final draft EG V1.1.1 ( ) 7) The parameters are designed for both statistical and individual application. The statistical values should be derived by the application of a simple statistical function to the individual values. The statistical function should be specified in the standard. The standard should also contain guidelines on how statistically significant samples should be selected. 8) The statistical functions should be designed so QoS figures from different service providers can be compared easily by users and in particular consumers.
7 7 Final draft EG V1.1.1 ( ) 1 Scope The present document contains definitions and measurement methods for a range of user perceivable Quality of Service (QoS) parameters. The purpose of these parameters is to define objective and comparable measures of the QoS delivered to users/customers for use by users/customers. The present document applies to any telecommunication service, however, some parameters may have a limited application. The present document is intended to provide a menu from which individual items can be selected. There is no obligation to use any or all of the parameters. The QoS parameters are related primarily to services and service features and not to the technology used to provide the services. Therefore the parameters should be capable of use when the services are provided on new technologies such as IP and ATM or other packet switched technologies as well as on circuit switched technologies. The establishment of target values for QoS is beyond the scope of the present document. The QoS parameters listed in the present document are also not intended to assess the complete QoS of a telecommunication service. The present document provides a set of QoS parameters that covers specific user related QoS aspects rather than a complete list of QoS parameters. This set has been chosen to address areas where monitoring of QoS is likely to be most worthwhile, i.e. the areas that are most likely to be affected by any QoS problems. If stakeholders wish to examine other QoS aspects they are recommended to follow the general approach of this document - as far as practicable - as a basis for the development of definitions and measurement methods for new specific QoS parameters. The set of QoS parameters is designed to be understood by the users of various telecommunications services. Sub-sets of these parameters can be selected for use in different circumstances. For example a specific parameter might be relevant for many users in some countries or markets but the same parameter might not be of relevance in others. Therefore stakeholders - users, customers, regulators, service providers, network operators and other parties interested in the use of QoS parameters - should decide in co-operation, which parameters and which measures should be used in their particular situation. This decision should take account of: The precise purpose for which they will be used The general level of quality achieved by most operators/providers The degree to which the parameters will provide a reliable comparison of performance The cost of measuring and reporting each parameter Part 1 of the present document contains general user related QoS parameter definitions and measurement methods that can be applied to any telecommunications service. The QoS parameters in part 1 are focused on non call related QoS aspects. Part 2 of the present document (this part) contains user related QoS parameter definitions and measurement methods for voice, data and fax services accessed via public telecommunication networks. The QoS parameters in part 2 are focused on call related QoS aspects. The data parameters are specified for the case where an ITU-T Recommendation V.90/V.92 compliant modem is used. Part 3 of the present document contains user related QoS parameter definitions and measurement methods specific to mobile access.
8 8 Final draft EG V1.1.1 ( ) 2 References The following documents contain provisions which, through reference in this text, constitute provisions of the present document. References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For a specific reference, subsequent revisions do not apply. For a non-specific reference, the latest version applies. [1] EG : "Speech Processing, Transmission and Quality Aspects (STQ); QoS parameter definitions and measurements; Parameters for voice telephony service required under the ONP Voice Telephony Directive 98/10/EC". [2] ETR 250: "Transmission and Multiplexing (TM); Speech communication quality from mouth to ear for 3,1 khz handset telephony across networks". [3] Directive 98/10/EC of the European Parliament and of the Council of 26 February 1998 on the application of open network provision (ONP) to voice telephony and on universal service for telecommunications in a competitive environment. [4] ITU-T Recommendation E.180: "Technical characteristics of tones for the telephone service". [5] ITU-T Recommendation E.425: "Internal automatic observations". [6] ITU-T Recommendation E.451: "Facsimile call cut-off performance". [7] ITU-T Recommendation E.452: "Facsimile modem speed reductions and transaction time". [8] ITU-T Recommendation E.453: "Facsimile image quality as corrupted by transmission-induced scan line errors". [9] ITU-T Recommendation E.800: "Terms and definitions related to quality of service and network performance including dependability". [10] ITU-T Recommendation G.107: "The E-Model, a computational model for use in transmission planning". [11] ITU-T Recommendation G.108: "Application of the E-model: A planning guide". [12] ITU-T Recommendation G : "Conversational impacts on end-to-end speech transmission quality - Evaluation of effects not covered by the E-model". [13] ITU-T Recommendation G.109: "Definition of categories of speech transmission quality". [14] ITU-T Recommendation G.114 (05/00): "One-way transmission time". [15] ITU-T Recommendation I.210: "Principles of telecommunication services supported by an ISDN and the means to describe them". [16] ITU-T Recommendation T.22: "Standardized test charts for document facsimile transmissions". [17] ITU-T Recommendation V.90: "A digital modem and analogue modem pair for use on the Public Switched Telephone Network (PSTN) at data signalling rates of up to bit/s downstream and up to bit/s upstream". [18] ITU-T Recommendation V.92: "Enhancements to Recommendation V.90". [19] ITU-T Recommendation Q.850: "Usage of cause and location in the Digital Subscriber Signalling System No. 1 and the Signalling System No. 7 ISDN User Part".
9 9 Final draft EG V1.1.1 ( ) 3 Definitions and abbreviations 3.1 Definitions For the purposes of the present document, the following definitions apply. access line: connection from the Network Termination Point to the entry point to the local switch or remote concentrator, whichever is the nearer NOTE: In many cases this is the main distribution frame. access network operator: organization that provides the access line NOTE: In many cases the access network operator will be the direct service provider, but if the line is unbundled, the direct service provider would be a separate organization call by call carrier selection: form of carrier selection where the user dials a carrier access code to indicate which carrier is to route the call carrier access code: code that the user may or must dial before the national (significant) number when dialling an access line in another telecommunications network, so that the call is routed by the carrier of his choice customer: party that pays for the telecommunication service(s) provided NOTE: Customers can generally be categorized as business or residential; the definition of business and residential customers is left to individual service providers. Service providers who receive interconnect services from other service providers are not considered to be customers for the purpose of the present document. The term "customer" is equivalent to "subscriber", which is used in Directive 98/10/EC [3]. data service: telecommunications service involving the transport of data via the PTN such that any user can use equipment connected to a network termination point to exchange data with another user of equipment connected to another termination point direct service: service where the service provider that provides the telecommunication service(s) also provides the access network or rents an unswitched local loop (unbundled local loop) to use for the provision of the service to the customer fax service: telecommunications service of transport of facsimile via the PTN such that any user can use equipment connected to a network termination point to exchange facsimiles with another user of equipment connected to another termination point indirect service: service where the service provider that provides the telecommunication service(s) does not provide the access network but is selected by the customer or user using a form of call by call carrier selection or carrier preselection network operator: organization that provides a network for the provision of a public telecommunication service NOTE: If the same organization also offers services it also becomes a service provider. Network Termination Point (NPT): physical point at which a user is provided with access to a public telecommunications network ported number: subscriber number (directory number) where the location of the NTP and/or the identity of the service provider has changed after the number was originally allocated preselection: form of carrier selection where the customer informs his access network operator which carrier is to route all or a particular subset of his calls, unless call by call carrier selection is used Public Telecommunications Network: telecommunications network used wholly or partly for the provision of publicly available telecommunications services
10 10 Final draft EG V1.1.1 ( ) Quality of Service (QoS): collective effect of service performance which determines the degree of satisfaction of a user of the service NOTE: (See ITU-T Recommendation E.800 [9].) service provider: organization that offers a telecommunication service to the customer and/or user NOTE: A service provider need not be a network operator. stakeholder: party having an interest in the level of quality of a service supplementary service: additional service that modifies or supplements a basic telecommunication service NOTE: Consequently, it cannot be offered to a customer as a stand-alone service; it has to be offered in association with a basic telecommunication service. The same supplementary service may be common to a number of basic telecommunication services. (See ITU-T Recommendation I.210 [15].) telecommunications: technical process of sending, transmitting and receiving any kind of message in the form of signs, voice, images or sounds by means of telecommunications systems telecommunication services: provision of telecommunications and the provision of other additional services that are closely related to the provision of telecommunications like e.g. billing, directory services telecommunications systems: technical equipment or systems capable of sending, transmitting, switching, receiving, steering or controlling as messages identifiable electromagnetic signals user: individuals, including consumers, or organizations using or requesting publicly available telecommunications services NOTE: (See Directive 98/10/EC [3].) voice service: telecommunications service of direct transport of real-time speech via the PTN such that any user can use equipment connected to a network termination point to communicate with another user of equipment connected to another termination point 3.2 Abbreviations For the purposes of the present document, the following abbreviations apply. ATM EG GSM IP ISDN ISP MDF NER NTP PTN QoS STQ Asynchronous Transfer Mode Guide Global System for Mobile communications Internet Protocol Integrated Services Digital Network Internet Service Provider Main Distribution Frame Network Effectiveness Ratio Network Termination Point Public Telecommunications Network Quality of Service Speech Transmission and Quality (Technical Committee)
11 11 Final draft EG V1.1.1 ( ) 4 General considerations 4.1 Services covered The QoS parameters of the present document cover aspects of telecommunications services which are typically provided via the public telecommunications network such as voice, fax or data services. These services may be accessed via terminals connected to fixed network termination points or via mobile accesses e.g. GSM. The definitions and measurement methods of the QoS parameters were elaborated primarily in order to assess QoS aspects of "standard" telecommunication services. Therefore mainly common aspects and applications of telecommunication services were considered and are reflected in the present parameters. In principle the QoS parameters may also be used for the investigation of special or non-standard telecommunication services but further enhancements/additions to the definitions and measurements methods may be necessary. Most parameters are in principle applicable to any service provided via the public telecommunication network. Some parameters are however only applicable to specific services depending on technical aspects of the provision of those services, e.g. mobile, data, fixed NTP. Depending on the set of QoS parameters used by the stakeholders the scope of the services covered may vary. The parameters are end-user/customer and end-to-end orientated and are not intended to address the quality of interconnect services explicitly. Any dependence on interconnect services is included implicitly in the measures of QoS provided to the end user. Separate Guides in this series deal with the QoS of interconnect arrangements. In many cases the provider of telecommunications services to the customer may depend on other providers for part of the service. An example is an international call where several service providers are normally involved. In such cases the provider of the service to the customer is responsible for all elements for which it receives payment from the customer. In order to provide satisfactory QoS, this service provider will need to ensure that adequate QoS is provided by the other interconnected service providers. QoS figures for the responsible service provider will reflect both its own capability and that of the interconnected service providers. 4.2 Use of the parameters The parameters may be used for various purposes including: Specifying the level of quality of service in customer telecommunication service contracts or in the description or terms and conditions of the service Comparing the quality of service of different service providers Comparing the quality of service aspects of different service offers Preparing long term studies on the quality of service aspects of a specific service 4.3 Reporting for different classes of customers For each parameter, statistics may be produced or requested that are aggregated over all classes of customer or, where a distinction between different classes is desired, e.g. residential and business, separate statistics may be used, or both. This recognizes the voluntary nature of these measures and the fact that some stakeholders may only wish to target specific sections or to provide a rough overview of the market. NOTE: Due to the fact that a variety of different service offers is available at the market, it is not always possible to clearly distinguish between classes of customers like residential or business. Furthermore it may not be fair to compare different service offers on the basis of different classes of customers because the results may be misleading. Also statistics may be falsified when aggregating over all classes of customers. (See also clause 4.9)
12 12 Final draft EG V1.1.1 ( ) 4.4 Non standard levels of QoS Statistics produced should normally be based on the standard level of QoS for each telecommunication service. The standard level is defined in the terms and conditions of the services as published by the service providers. Stakeholders may choose to produce or request specific statistics for cases where customers are able to pay more for enhanced or less for lower QoS. It is recommended to provide additional information on the kind and scope of services the QoS statistics are referring to when covering non-standard levels of QoS. 4.5 Reporting for directly- and indirectly-serviced customers The principle used is that the service provider who charges the customer should be responsible for the quality of the service and for providing QoS statistics relevant to the service provided. Thus, in the case of carrier selection, the indirect service provider has the responsibility for QoS and provision of QoS statistics when it is selected to carry a call. For each parameter in clause 5 a statement is made on whether it is applicable to indirect services. Some service providers provide both direct and indirect services. Where there are likely to be significantly different levels of performance for these two service types or where the services are understood as being two different not comparable service offers (even though the same telecommunication service is offered), the production of separate statistics for each service type is recommended. The treatment of direct and indirect services is summarized in the last column of table 1. NOTE: Where only a combined statistic for both types of service is specified, separate statistics for each service type may be provided in addition if the stakeholders to do so. 4.6 Data processing issues Where the measures are based on all actual occurrences rather than samples, the measuring party may prefer to process data on a weekly or monthly basis, discard the detailed data and use a statistical method such as that specified in annex A for combining the weekly or monthly results. For one parameter the statistic required is "X % of...". This statistic is explained in annex B. In some cases disasters, freak weather, etc. may distort measured QoS figures. Such occurrences may not necessarily damage a network, but could degrade QoS by inducing exceptional traffic levels etc. In these cases, service providers should provide the measured QoS and may additionally provide a second figure which excludes the effects of the exceptional circumstances. A note clearly explaining the difference should also be provided. Service providers covering large geographical areas are likely to be more prone to these effects than service providers serving smaller areas. The effect on the reported QoS of a service provider covering a small area is likely to be more severe, however, should such an event occur. 4.7 Data collection period Where the measurements are to be used for long term comparisons, it is recommended that QoS data should be collected and calculated on a quarterly basis starting on 1 January, 1 April, 1 July and 1 October. Stakeholders may also decide to use longer or shorter data collection periods. For most QoS parameters a data collection period on a quarterly basis is suitable, and will provide adequately up-to-date information. But there may also be cases were a longer period is more practicable, e.g. extensive customer surveys. Shorter periods are advisable for QoS aspects where frequent and fast changes in quality are likely to occur. 4.8 Sampling and test calls Where sampling and test calls are used the approach should ensure that the results adequately reflect the QoS perceived by customers for the period under review. Guidance on the choice of adequate test calls with respect to choice of origin, destination, traffic variations etc. may be found in annex C.
13 13 Final draft EG V1.1.1 ( ) 4.9 Comparability of measurements The following issues may affect the comparability of the measurement results: Measurement methods may be implemented differently (e.g. use of real traffic vs. test calls, choice of representative connections) Measurements based on signalling information or tones may be unreliable because the signalling systems and tones are not implemented in a fully standardized manner (e.g. different uses of cause values) Service offers that claim to be similar may differ in terms of significant service features/aspects. NOTE: The parameters were elaborated with respect to "standard" service offers and so special care should be taken for non-standard services Publication of QoS parameters Where measurements are made and published in accordance with the present document, it is recommended that an explicit reference to the present document should be given so that readers can be made aware of the background of the definitions and measurement methods. The reader should be enabled to understand the meaning, purpose and areas of application of the QoS parameters. It is important that the reader is aware of the scope of the parameters and with that of the correct application of the QoS statistics, otherwise there is a high risk that the measurement results are misinterpreted. A fair and justified comparison of the published data of different service offers, i.e. quality aspects of different telecommunication services, is only possible if the data is strictly used according to the scope of the defined QoS parameters. Stakeholders who publish QoS statistics in accordance with the present document should provide additional and explanatory text in order to facilitate the understanding of the statistics. It may be assumed that a reader who is interested in comparable QoS statistics and QoS parameters of different nature is willing and capable to understand technical and operational background information on telecommunication services. A balanced approach should be used taking into account on the one hand the need for easy understandable information and on the other hand the requirement of correctly edited data derived from the measurements. 5 QoS parameters for voice, data and fax services accessed via the PTN Table 1 summarizes the QoS parameters defined in the present document. NOTE: Many of the parameters have several subtleties associated with their definition, applicability and measurement. The parameters are fully explained in clause 5.
14 14 Final draft EG V1.1.1 ( ) Unsuccessful call ratio Table 1: Summary of QoS parameters Parameter Measure Measurement Method Application a) the percentage of unsuccessful Measurements on: calls for national calls - real traffic (all or b) the percentage of unsuccessful sample) calls for international calls - test calls c) the number of observations used for national and international calls together with absolute accuracy Call set up time Speech connection quality Fax connection quality Data rate of Dial-up access to the Internet a) the mean value in seconds for national calls b) the time in seconds within which the fastest 95 % of national calls are set-up c) the mean value in seconds for international calls d) the time in seconds within which the fastest 95 % of international calls are set-up e) the number of observations performed for national and international calls a) quality category according to ITU-T Recommendation G.109 [13] b) characteristics of terminals c) reference connections % successful fax transactions Test calls transmission rate of modem data of 80 % of connections in bit/s Measurements on: - real traffic (all or sample) - test calls Use of E-Model with input parameters either derived of measurements or planning values Test calls directly and indirectly accessed fixed and/or mobile voice services directly and indirectly accessed fixed and/or mobile voice services Directly and indirectly accessed fixed and/or mobile voice services directly and indirectly accessed fixed and/or mobile fax services Directly and indirectly accessed data services Table 2 summarizes the information to be provided from the perspective of the user, who may have both a direct service provider (whose service includes the access line) and one or more indirect service providers that may be selected for different calls using call-by-call carrier selection or pre-selection. For each parameter, the table shows what will be measured and which service provider will report an event covered by the parameter. Table 2: QoS parameters from the perspective of the user Parameter Measure Information provided by Unsuccessful call ratio Percentage of unsuccessful calls direct, indirect and mobile service provider Call set up time Time in seconds direct, indirect and mobile service provider Speech connection quality Quality category voice service provider Fax connection quality Percentage of successful fax transactions fax service provider Data rate of Dial-up access to the Internet Data transmission rate of 80 % of connections data service provider
15 15 Final draft EG V1.1.1 ( ) 5.1 Unsuccessful call ratio Definition Unsuccessful call ratio is defined as the ratio of unsuccessful calls to the total number of call attempts in a specified time period. An unsuccessful call is a call attempt to a valid number, properly dialled following dial tone, where neither called party busy tone, nor ringing tone, nor answer signal, is recognized at the access of the calling user within 30 seconds from the instant when the last digit of the destination subscriber number is received by the network. NOTE: The unsuccessful call ratio is comparable to the Network Effectiveness Ratio (NER) as defined in ITU-T Recommendation E.425 [5] Application The QoS parameter is applicable to directly and indirectly accessed fixed and/or mobile services Measurement and statistics The following statistics should be provided separately: a) The percentage of unsuccessful calls for national calls, together with the number of observations used and the absolute accuracy limits for 95 % confidence calculated from this number. b) The percentage of unsuccessful calls for international calls, together with the number of observations used and the absolute accuracy limits for 95 % confidence calculated from this number. The statistics should be calculated from: a) measurements on all real traffic; or b) measurements on real traffic for outgoing calls in a representative population of local exchanges to a representative set of destinations; or c) test calls in a representative population of local exchanges or NTPs to a representative set of destinations; or d) a combination of the above. Guidance on the choice of adequate origin and destination NTPs and/or local exchanges may be found in annex C. NOTE 1: These alternative methods each have different advantages and disadvantages. The use of test calls is often expensive. Observations based on signalling information can be a low cost alternative but may be unreliable because in real equipments cause values may not be assigned exactly in accordance with the standards and therefore extra care should be taken. NOTE 2: Measurements may be based on the analysis of tones or on signalling information or on a combination of them. Extra care should be taken to set up the measuring equipment adequately in order to receive comparable results. Methods for deciding if a call is unsuccessful are given in annex D. Measurements should be scheduled so as to reflect accurately traffic variations over the hours of a day, the days of the week and the months of the year. When measuring values for different destination categories (national or international) this applies to each destination category separately. In the case of test calls the choice of destination exchanges (or NTPs) should be traffic weighted. The number of observations may be chosen by the reporting operator and will determine the absolute accuracy to be given with the results but: a) shall fulfil the Laplace criterion for the applicability of calculations based on the normal distribution (see annex E), but b) is not required to exceed a test call rate of 1 in
16 16 Final draft EG V1.1.1 ( ) Annex E gives information on how to calculate the absolute accuracy based on the measured result, the confidence level and the number of observations. NOTE 3: This approach has been chosen because of the cost implications of trying to specify the accuracy level. Operators will improve the accuracy by using more observations but may decide themselves how many observations are worth taking. For directly connected customers service providers should exclude from the statistics calls that they deliver to an indirect service provider who then completes the call and charges the customer. For indirectly connected customers, either: a) Measurements should be based on call data from the processor of the originating local exchange for real calls, or b) measurements should be made from the subscriber line side of the local exchange in the access network, or c) measurements should be made from the NTP Further considerations This parameter has been formulated in a general manner. In practice measurements and reporting should be focused on particular services, e.g. normal geographic services or freephone numbers, and the scope of the measurements identified explicitly in any reporting. NOTE 1: The indirect service provider may have to pay the access network operator to make measurements or special test calls from the local exchange. Special confidentiality requirements may apply to this information. NOTE 2: Care should be taken not to degrade the customer's service by making an excessive number of test calls in periods of high traffic levels NOTE 3: No intrusive measurements should be made by the access network operator without the agreement of the indirect service provider. The first two arrangements for indirectly connected customers will require co-operation by the access network operator in making the measurements or providing the call data. For the third arrangement there is no co-operation with the access network operator necessary. Both the second and third arrangement may involve disturbance to the customer. 5.2 Call set up time Definition The call set up time is the period starting when the address information required for setting up a call is received by the network and finishing when the called party busy tone or ringing tone or answer signal is received by the calling party. Where overlap signalling is used the measurement starts when sufficient address information has been received to allow the network to begin routeing the call. NOTE: Information on characteristics of tones may be found in ITU-T Recommendation E.180 [4] Application The QoS parameter is applicable to directly and indirectly accessed fixed and/or mobile services.
17 17 Final draft EG V1.1.1 ( ) Measurement and statistics The following statistics should be provided separately a) the mean value in seconds for national calls b) the time in seconds within which the fastest 95 % of national calls are set-up c) the mean value in seconds for international calls d) the time in seconds within which the fastest 95 % of international calls are set-up e) The number of observations performed for national and international calls. Calls that are classified as unsuccessful calls should be excluded. Calls to ported numbers should be included. The statistics should be calculated from: a) measurements on real traffic for outgoing calls; or b) measurements on real traffic for outgoing calls in a representative population of local exchanges to a representative set of destinations; or c) test calls in a representative population of local exchanges or NTPs to a representative set of destinations; or d) a combination of the above. Guidance on the choice of adequate origin and destination NTPs and/or local exchanges may be found in annex C. Measurements should be scheduled so as to reflect accurately traffic variations over the hours of a day, the days of the week and the months of the year. Call monitoring can be done by monitoring every K th call where K is to be calculated from the total expected number of calls in the relevant time intervals and from the needed number of observations. When measuring values for different destination categories (national or international) this applies to each destination category separately. In the case of test calls the choice of destination exchanges (or NTPs) must be traffic weighted. NOTE 1: These alternative methods each have different advantages and disadvantages. The use of test calls is expensive and provides only an estimate of the actual performance but involves measurement at the access line side of the local exchange. Observations performed at the exchange processor are cheaper and more data can be obtained giving more accurate estimates, but the data does not come from so close to the NTP. NOTE 2: Measurements may be based on the analysis of tones or on signalling information or on a combination of them. Extra care should be taken to set up the measuring equipment adequately in order to receive comparable results. Annex F gives a formula for calculating the number of observations needed. For directly connected customers service providers should exclude from the statistics calls that they hand over to an indirect service provider who then completes the call and charges the customer For indirectly connected customers, either: a) measurement should be based on call data from the processor of the originating local exchange for real calls, or b) measurement should be made from the subscriber line side of the local exchange in the access network, or c) measurement should be made from the NTP. In addition the statistics should state if en bloc, overlap dialling or a mixture was used and if connections between fixed NTPs, mobile NTPs or a combination of fixed/mobile NTPs were measured. Separate statistics may be produced for the above listed dialling procedures and connection scenarios. Where there are likely to be significantly different levels of performance, the production of separate statistics is recommended.
18 18 Final draft EG V1.1.1 ( ) Further considerations This parameter has been formulated in a general manner. In practice measurements and reporting should be focused on particular services, e.g. normal geographic services or freephone numbers, and the scope of the measurements identified explicitly in any reporting. NOTE 1: The indirect service provider may have to pay the access network operator to make measurements or special test calls from the local exchange. Special confidentiality requirements may apply to this information. NOTE 2: Care should be taken not to degrade the customer's service by making an excessive number of test calls in periods of high traffic levels NOTE 3: No intrusive measurements should be made by the access network operator without the agreement of the indirect service provider. The first two arrangements for indirectly connected customers will require co-operation by the access network operator in making the measurements or providing the call data. For the third arrangement there is no co-operation with the access network operator necessary. Both the second and third arrangement may involve disturbance to the customer. When overlap signalling is used the measuring party has to know when the network starts routeing the call, i.e. the number of digits of the subscriber number that must be at least transmitted to the network. This number depends on the setting of the switches and therefore this information is normally only available at the access network provider. For the performance levels of call set up times in fixed circuit switched networks offering traditional telephone service it may be assumed that quality problems are not likely to occur. There are however scenarios that could decrease the performance levels, e.g: routing of calls via several networks, e.g. national calls may not be routed directly to the destinations (especially in combination with number portability), connections from and to mobile networks, use of packet based/switched networks. 5.3 Speech connection quality Definition Speech connection quality is a quality measure of end-to-end (mouth to ear) speech quality for conversational speech of a voice service call. It is expressed in terms of quality categories: best, high, medium, low and poor quality. NOTE: The perception of speech quality during a voice service call is primarily a "subjective" judgement. The above mentioned quality categories represent an estimate of end users' perception of end-to-end speech quality. They are not made for actual user opinion predictions, but allow for relative comparisons of transmission conditions of various connection scenarios Application The QoS parameter is applicable to all voice services providing 3,1 khz handset telephony accessed via the public telecommunication network irrespective whether they are provided via fixed and/or mobile networks and whether they are accessed directly or indirectly.
19 19 Final draft EG V1.1.1 ( ) Results The following results should be provided separately: a) The quality category of the speech connection quality of the voice service should be provided, i.e. best, high, medium, low and poor quality according to ITU-T Recommendation G.109 [13]. b) The kind/characteristics of terminals underlying these calculations. c) The reference configurations. The determination of the speech connection quality is based on the so-called "E-Model", a transmission rating model for assessing the combined effects of variations in several transmission parameters that effect speech quality. When assessing the quality of a voice service care should be taken to apply the E-Model correctly and to refer to the relevant ITU-T Recommendations. NOTE: Annex H gives a brief introduction on how to determine the speech connection quality and provides references to relevant ITU-T Recommendations. The speech connection quality of a call may vary depending on the specific connection scenario, i.e. the user will perceive different levels of quality when making a voice call. Typical connection scenarios resulting in different levels of speech quality are e.g. calls within circuit switched networks, mobile networks, packet switched networks and any combination of it. Differences are also likely to occur when considering local, national and international calls or specific destinations. If there are significant differences in quality, service providers should prepare separate results for each connection scenario Further considerations It is important to understand the concept and application of the E-Model. The most important aspects are that the E-Model rates the quality on an end-to-end (mouth to ear) basis, i.e. it gives a combined quality rating of both the terminals at both sides and the network(s). Furthermore the combined influence of a variety of important transmission parameters is taken into account. On the one hand the E-Model has the advantage to provide a single output parameter that can be easily transformed into a category of speech quality. This is user friendly and allows for direct comparison of different services even for the naïve user. On the other hand the correct application of the E-Model requires a detailed knowledge of the measurement methods and understanding of transmission planning. Because of the complexity of the model the possibility is high that the model is applied incorrectly or that assumptions are made that lead to incomparable results (e.g. reference configurations). Hence in order to provide a fair comparison of different services and meaningful quality values, supplementary information has to be included in the results. A statement of a speech connection quality category for a certain voice service is only useful to the user, if he has at least some basic knowledge on the underlying network configuration and planning principles. This kind of information does of course demand technical understanding of telecommunications; the interested user however will be able to understand and assess the meaning of the information. Thus the speech connection quality parameter reflects the ability and effort of the voice service provider to offer a good quality service to the user. Voice service providers have normally no influence on the type and quality of terminals that are used. The end-to-end speech quality, however, is heavily influenced by the performance of the terminals at each end of the call. Thus the choice of the terminals, i.e. the respective terminal related input parameter values of the E-Model, has a significant influence on the results. When determining the speech connection quality adequate and typical, i.e. broadly used by users, terminals should be chosen; if necessary connection scenario specific terminals have to be chosen. Because of these dependencies information on the terminal and reference connections are included in the results. Additional explanatory text may be necessary in order to give advice to the naïve user. If a user is not able to understand the interworking between terminals and networks and thus is not aware of the influence of the choice of terminals on the resulting speech quality, he is advised to use the same kind of terminal as the service provider has in his results in order to achieve the reported speech quality category.
20 20 Final draft EG V1.1.1 ( ) There are several effects on transmission quality that are not covered by the E-Model at the moment, e.g. wideband voice services and effects of packet loss. Work on these topics is going on and the E-Model will be constantly revised and upgraded. Therefore stakeholders should take not of the developments in this area and use the up-to-date documentation. NOTE: Information on transmission quality effects not covered by the E-Model may be found in ITU-T Recommendation G [12]. The speech quality categories allow for a rough rating within determined classes of quality. The categories represent a quality perception to be expected by the average user. Quality is a subjective judgement such that exact assignments cannot be made. Therefore the quality rating will always provide an averaged view and exact quality statements concerning the resulting quality of a specific connection are not possible. The speech quality rather allows for a comparable categorization of speech quality of different services and give an indication on how well designed a network and therefore the resulting voice service is. 5.4 Fax connection quality Definition Fax transaction success ratio is defined as the ratio of successful fax transactions between Group 3 facsimile terminals [14] to the total number of attempted fax transactions. An successful fax transaction is defined as a transaction of the standardized test chart as defined in annex G that: completes (i.e. all pages are sent), take place at the highest mutual transmission speed of the send and receive fax machines, and has no severely errored pages. NOTE: In case any further guidance is needed to decide on the completeness, transmission speed and errored pages the following ITU-T Recommendations should be taken into account: - E.451 (call cut off performance) [6], - E.452 (facsimile modem speed reduction and transmission times) [7], - E.453 (Facsimile Image Quality) [8] Application The QoS parameter is applicable to fax services irrespective whether they are accessed directly or indirectly and via fixed or mobile accesses Measurement and statistics The following statistics should be provided separately: a) the percentage of successful fax transactions, b) the number of test calls. The statistics should be calculated from test calls in a representative population of local exchanges or NTPs to a representative set of destinations. NOTE: Guidance on the choice of adequate origin and destination NTPs may be found in annex C. The result, expressed as a % successful fax transactions (to one decimal place), can be derived from: Total number effective transactions x 100. Total number of observations