1、SII*ITU-T HDBK HQS-ENGL 1993 H 4862571 0682350 933 INTERNATIONAL TELECOMMUNICATION UNION - CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE HANDBOOK ON QUALITY OF SERVICE AND NETWORK PERFORMANCE Geneva, 1993 INTERNATIONAL TELECOMMUNICATION UN ION CCITT THE INTERNATIONAL TELEGRA
2、PH AND TELEPHONE CONSULTATIVE COMMITTEE HANDBOOK ON QUALITY OF SERVICE AND NETWORK PERFORMANCE Geneva, 1993 ISBN 92-61 -04741 -6 STDaITU-T HDBK HQS-ENGL 11773 48625L Ob82152 706 H O ITU 1993 Ail rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, e
3、lectronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. Si“i7MU-T HDBK HQS-ENGL 3993 4862593 b82153 b42 D CONTENTS Page Preface V . CHAPTER 1 - Introduction to quality of service and network performance 1 1.1 Overview of Quaiity of Servi ce . 1 1.2
4、Network performance aspects . 3 1.3 Description of QOS by NP parameters 4 1.4 Practical application of QOS and Np measures . 4 CHAPTER 2 - Source of information and data collection . 7 2.1 General aspects . 7 2.2 Source of information and data collection . 7 2.3 Evaluation procedures . 9 CHAPTER 3 -
5、 Recommendations and objectives on quality of service and network performance . 13 3.1 Quality of Service and network performance Recommendations . 13 3.2 Objectives . 13 CHAPTER 4 - Dependability planning . 15 4.1 Introduction 15 4.2 Dependability planning concepts and models 15 Annex A - Practical
6、 use of terms and definitions . Annex B - QOS and network performance parameters Annex C - Standard methods for data treatment Annex D - QOS Recommendation references Annex E - E-series Recommendations which include numerical objectives . Annex F - Mapping of QOS/“ measures and objectives Annex G -
7、Dependability planning Annex H - Useful addresses of standards organisations 16 22 37 45 49 53 57 72 Contents III - - STD-ITU-T HDBK HQS-ENGL 1993 4862593 Ob82154 589 9 PREFACE The CCiT Handbook on Quality of Service, Network Management and Network Maintenance was published in 1984. It describes the
8、 principles, rules and recommendations to be considered in organising and operating the telephone network and its telecommunications services with respect to Quality of Service, Network Management and Network Maintenance. Furthermore, the Handbook has proven to be a useful educational guide on these
9、 topics, between which there are very strong interrelationships. During the 1985-1988 period work continued to review and develop guidance in each of the areas covered by the Handbook. During this period there was considerable development on Quality of Service and Network Performance issues and cons
10、ideration was given to publishing an entirely new Handbook on these subjects. The resulting publication essentially replaces the Quality of Service sections of the 1984 Handbook but retains references to it where these are considered useful. The new Handbook contains a distillation of the ideas form
11、ulated during the 1984-1991 period but focuses, in the main, on the work which resulted in Recommendations carried in the 1989 Blue Book. However reference has been made, where necessary, to later work, especially those recent Recommendations which are currently being authorised under the new accele
12、rated procedure process. Other work, which has been included, but is not supported by Recommendations, is annotated to distinguish it from the majority of the material contained in the new Handbook. The new Handbook concentrates mainly on the Public Switched Telephone Network (PSTN). However the pri
13、ncipies and parameters of Quality of Service and Network Performance explained in the new Handbook may be applied to all services. The new Handbook can be applied to both national and international networks since in Quality of Service terms there is no difference. In addition the new Handbook contai
14、ns references to ISDN, although, as relevant Recommendations in this area are few in number at the time of writing, there is little scope for useful comment. It is hoped, however, to develop Addenda covering ISDN Quality of Service and Network Performance issues as these evolve. The new Handbook is
15、divided into two main parts, which, while being complete in themselves, are frequently cross-referenced. The fmt part consists of four Cbapters which can be considered as an overview of the subject for the general reader. The second part is made up of eight Annexes for those readers requiring more s
16、pecific information and for reference purposes. The new Handbook is aimed at all levels of management in telecommunication Administrations as well as other interested parties. Note - In this document, the expression “Administration” is used to denote both a telecommunication Administration and a rec
17、ognised private operating agency. Previous page is blank. Preface V STD-ITU-T HDBK HQS-ENGL 1773 4862571 Ob82155 415 m CHAPTER 1 INTRODUCTION TO QUALITY OF SERVICE AND NETWORK PERFORMANCE Abstract This chapter introduces briefly the concept of Quality of Service in a unified context with its related
18、 concepts and measures. The purpose is to apply Quality of Service activities in practice, utilizing CCIT Recommendations and Administrations own experiences. Reference is made to the Annexes in this Handbook. 1.1 Overview of Quality of Service Quality of Service (QOS) is a very broad concept which
19、comprises many performance aspects and numerous e collective effect of service performances which determine the degree of satisfaction of a user of the measures. According to Recommendation E.800 Quality of Service is: service. The purpose of Figure 1 (see Figure 1E.800) is to provide an overview of
20、 the factors which contribute collectively to the overall Quality of Service as perceived by the user of a telecommunication service. As seen from Figure 1 there are four main factors which contribute to the overall Quality of Service. Each of these Service Performance aspects should be considered a
21、s a concept, an “umbrella” normally characterised by many measures or parameters. QOS depends on: - - - - At the next “level” Serveability depends on the properties of: - the Trafficability - - QOS can be structured in other ways than Figure 1. For example it may be represented just by numerous Howe
22、ver, - to give an overview, - to avoid confusion, - the Support, i.e. the secondary services such as information, provisioning, billing, etc. the Operability, i.e. the ease of use, etc. the Serveability, i.e. the access and retention of the service, etc. the Integrity, i.e. the transmission aspects,
23、 etc. the Propagation, i.e. radio transmission, etc. the Dependability aspects, i.e. availability, reliability, etc. measures and parameters which give a profile of QOS. to apply a consistent set of terms widely used within CCIT, this handbook is exclusively based on the structure according to Recom
24、mendation E.800 with its Supplement No. 6. Thus Figure 1 should be considered as the framework for the QOS concept. QOS characteristics should be applied - among other purposes - as tools for mapping a specific service seen from the customers viewpoint. Mapping (ref. Chapter 3 and Annex F) is intend
25、ed to give a profile of the numerous contributing measures. Chapter 1 1 STD-ITU-T HDBK HQS-ENGL 1773 E 4Bb2591 0bB235b 351 The user of a service generally identifies two ?bodies? when using a service: - - Very often the ?human related? aspects are most important to the user (even though not always r
26、ecognised by the Administration, i.e. the ?human related aspects? the Network, i.e. the ?technical related aspects?. the Administration). The ?human related? aspects are Concerned with ?Support? while ?technical related? aspects are mostly Operability (ease of use) is in fact technically related, bu
27、t is also a ?man-machine relationship? and as such concerned with ?Serveability? (including Accessibility and Retainability) and ?Integrity? (transmission etc). the user may relate it to the ?human aspects?. Quality of service Service support QoS Service operability performance I - I Service 1 I Ser
28、vice 1 accessibility rentainability performance performance Serveability performance I Service integrity Trafficability Availability performance performance Reliability performance Maintainability 1 1 Maint.int;yce performance performance I? II II I Dependability I TO2031 a92 FIGURE 1 Quality of Ser
29、vice and Network Performance concepts Propagation Transmission performance performance Note - Figure 1 includes a dashed line which is not used in Figure 1E.800. It is an approach to the integration of Figure 1E.800 and Figure 2E.800 in order to interpret the relationship between QOS and NP. 2 Chapt
30、er 1 STDmITU-T HDBK HQS-ENGL 1793 4862591 0682157 298 Quality of Service 1.2 Network performance aspects Network Performance A formal defintion of Network Performance (NP) was introduced in Recommendation E.800 in 1988 (the Blue Book). The concept, however, (without a definition) has been used previ
31、ously in many Recommendations. Network Performance is a very important element of Quaiity of Service because it defines - portion by portion - the “technical part” of the Quality of Service measures. According to Recommendation E.800 Network Performance is: The ability of a network or network portio
32、n to provide the functions related to communications between users. Service atibute Focus on user-observable effects Between (at) service access points NP applies to the Administrations planning, development, operations and maintenance and is the detailed It is up to the Administration to combine th
33、e network performance parameters in such a way that the economic requirements of the Administration as well as the satisfaction of the user are both fulfilled. Usually this requires a compromise between economy and QOS. technical part of QOS, excluding Service Support Performance and other Human Fac
34、tors. Many measures and parameters are common to QOS and NP. In many cases it is difficult or even impossible to identify whether a given measure is QOS or NP if the measuring points i.e. the access points are not known, or if the viewpoint i.e. the custorner/provider side is not defined. Annex B pr
35、esents a detailed list of QOSMP measures. An essential difference between QOS and NP measures is that QOS is user orientated while NP is network provider orientated. Thus QS focuses on user perceivable effects (not their causes) and NP on the efficiency of the network in providing services to the cu
36、stomer. The result is that QOS measures are relevant between service access points, usually on an end-to-end basis, while NP measures are relevant between borders of network portions. Figure 2 (see Recommendation 1.350) shows some important aspects in the distinction between QOS and NP. Furthermore
37、the dashed line in Figure 1 is drawn to show that, above the line, QOS is relevant, while underneath the line, NP is relevant. Connection element Focus on planning, development (design), operations and maintenance End-to-end or network connection element capabilities I User oriented I Provider orien
38、ted I FIGURE 2 Distinction between Quality of Service and Network Performance Note - Quality of a bearer service: A parameter measured between (or at) access point(s) of a bearer service is an NP parameter to the provider of the bearer service, but a QOS parameter to the user of the bearer service.
39、The user may be the end user or another provider. The provider of the teleservice is responsible for the bearer service according to agreement with the bearer service provider, who is acting as a sub-provider (sub-supplier). Chapter 1 3 STD-ITU-T HDBK HQS-ENGL 1993 S 48625L Ob82158 124 111 Objective
40、s Business Operations 1.3 Description of QOS by NP parameters Design, dimensioning, target (within 5 years), CCI” recommended, etc., value Acceptable and unacceptable value by customer/Administration/authoriq, etc. DaiiyAong term mean, alarm value, action level value for maintenance, etc. The two ma
41、in concepts, Serveabiiity (access and retention) and Service Integrity (transmission) are described by numerous NP parameters. In principle the QOS measures for the relevant network are described user-end-to-end by combining ali the NP parameters - portion by portion - of the network under considera
42、tion. In many cases this “combining” might just be to sum up the individual values from each portiodelement of the considered network. NP parameters should be measurable or at least calculable (based on measurements). It should be realised that almost all measures are time dependent and should in pr
43、inciple be considered as random (stochastic) variables. As such the parameters can only be estimated. Ref. Chapter 2 and Annex C. A specific measure/parameter may be given one or more modifiers such as mean value and internationally recommended value. The following are typical practical examples of
44、modifiers: Modifiers Type r- I True, estimated, mean, maximum, minimum, fractile, instantaneous, etc., value FIGURE 3 Examples of modifiers for measuredparameters 1.4 Practical application of QOS and NP measures So far QOS and NP have mainly been considered from a conceptual viewpoint. QOS and NP ho
45、wever, are extremely useful tools for fulfilling administrations primary objective: To provide telecom services which satisfy the userdcustomers regarding both quality and price. QOS should be applied for mapping each specifk service from the customers point of view. A QOS “specification” or “declar
46、ation” means a systematic grouping of features and characteristics that may satisfy the customers need. The properties of the service should be described by values of relevant measures. In principle all these measures should be continuously monitored, mapped and compared with known values of accepta
47、ble thresholds. This is not feasible in practice of course. Guidelines and forms for this mapping are presented in Chapter 3 and Annex F. In various contexts, some misconception of QOS has occurred that QOS is equivalent to the users perception of a given service. According to the CCITT definition i
48、n Recommendation E.800, however, QOS is the profile (more or less complete) of the numerous values of the QOS measures, including both Administration and Network related measures. 4 Chapter 1 STDmITU-T HDBK HQS-ENGL 1993 4862593 Ob82157 Ob0 Customer perception Score (MOS) With this profile in mind a
49、 market segment of users can be interviewed about their expectation and perception of the QOS. This can be taken as a whole or for specifically target selected measures of the service. The customer satisfactiodperception with/of a given service or selected parameters may be assessed, for example by the Mean Opinion Score (MOS) as shown in Figure 4: Bad Poor Fair Good Excellent 1 2 3 4 5 Service integrity FIGURE 4 Estimation of customer satisfactiodperception Service integrity Figure 5 indicates that each service must be treated separately and sbows an overview of
