1、CCITT RECMN*E.432 92 9 48b2591 O573580 334 = INTERNATIONAL TELECOMMUN KATION UN ION CCITT E.432 THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING CONNECTION QUALITY Recommendation E.432 Geneva, 1
2、992 CCITT RECMN*E*432 92 E 48b259L 0573581 270 E INTERNATIONAL TELECOMMUNICATION UNION CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEPHONE NETWORK AND ISDN QUALITY OF SERVICE, NETWORK MANAGEMENT AND TRAFFIC ENGINEERING E.432 CONNECTION QUALITY Recommendation E.432 Geneva
3、, 1992 - - - - - - - - - CCITT RECMN*E*432 92 4862591 0573582 107 POREWORD The CCIIT (the International Telegraph and Telephone Consultative Committee) is the permanent organ of the International Telecommunication Union 0. CCII“ is responsible for studying technical, operating and tariff questions a
4、nd issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CC which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members
5、 of CCIT between Plenary Assemblies is covered by the procedure laid down in CCIT Resolution No. 2 (Melbourne, 1988). Recommendation E.432 was prepared by Study Group II and was approved under the Resolution No. 2 procedure on the 16th of June 1992. CCiT NOTE In this Recommendation, the expression “
6、Administration” is used for conciseness to indicate both a telecommunication Administration and a recognized private operating agency. O IT 1992 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopyin
7、g and microfilm, without permission in writing from the ITU. CCITT RECflN*E.432 92 W 4862573 0573583 043 Recommendation E.432 CONNECTION QUALITY 1 Introduction This Recommendation suggests parameters, measurements and standards to capture the customer perception of connection quality for ail service
8、s on the public switched telephone network (PSTN) and the evolving integrated services digital network (ISDN). In principle, when a new service is to be implemented, a market analysis has to be undertaken to gain information on the service quality that has to be offered to the users at a given tarif
9、f. Here a problem appears to arise: users show their satisfaction in a non-technical way: they judge connection quality ranging from poor to excellent. The same problem applies to existing services. The intention of the Recommendation is to provide a guideline to obtain end-to-end connection of acce
10、ptable quality? that satisfies the end users. 2 Scope in considering “connection quality”, it is important to recognize that the “user” must already have a complete end-to-end connection, i.e. a distant end answer signal has been received before the connection quality can be assessed. “Connection qu
11、ality” does not include call set-up delays, etc. The “connection quality” has to be considered from the users perspective and will be influenced by the subjective perception of the user, the destination and route chosen, the transmission media used and the total ressources available and applicable t
12、o the end-to-end connection. As a result, this Recommendation considers the user perspective fmt, and then develops the network parameters and objectives. 3 Definitions connection quality The degree to which a connection reproduces the offered signal under stated conditions, as a sum of transmission
13、 performance, service integrity, service retainability performance, propagation performance. connection transmission quality The level of reproduction of a signal offered to a telecommunication system, under given conditions, when this system is in an up-state. 4 User perspective 4.1 methods, a serv
14、ice can assess users satisfaction in a quantitative and reproducible way. The user perspective is the key issue in connection quality. Users opinions are subjective but by appropriate During an established cail the user( may notice degradation of the intelligibility. The cause of this may be increas
15、ed attenuation, inadmissible distortion, strong noise, etc. Recommendation E.432 1 -. CCITT RECMN*E.432 72 4862573 O573584 TBT = The speech quality is influenced by ther performance and the user conditions applicable to the complete connection from speaker to listener. In general, speech quality is
16、treated by dividing it into sending quality, transmission quaiity and receiving quality. Among them, the transmission quality is the main factor which can be controlled by the Administration. The other two factors vary widely with the ability of speakers, listeners and the conditions under which spe
17、ech is sent and received. Low level pulsive noise, produced in a switching system, and group delay distorsion on a transmission line, do not cause any substantial trouble for the telephony service. These impairments are more likely to impact non- telephony applications, such as data and facsimile. I
18、t should be noted that there are many other impairments factors that affect non-telephony applications. For most services, it is the network and terminal equipement that have the major impact on user opinion. Figure 1B.432 illustrates the general network arrangement required to provide international
19、 voiceband services. Terminai Terminai - User User t-, equipment Nework f-, equipment t ; Telephone : Telephone National International National network , network network terminal . Data terminai Data : : TZO232-91 FaX FaX terminal terminal FIGURE 1E.432 General network arrangement required to provid
20、e international voice-band serviees The next step is to relate user of the connection quality to the relevant network or terminal conditions that can be studied or monitored by the service provider. 5 Customer perceived parameters in relation to network parameters and terminal equipement transmissio
21、n parameters The Table 1B.432 gives, for general information, examples of relationships between user-perceived quality and technical aspects of networWor terminai equipment. This is not intended to be an exhaustive list. 2 Recommendation E.432 6 TABLE 1m.432 Relationship of customer/network/terminal
22、 parameters I I Customer perceivable parameters Network parameters Terminal equipement parameters VOICE LOUdneSS Circuit loss Telephone design Noise Circuit noise, impulse noise, Noise acoustic Interruptions crosstalk (unintelligible) environment Terminal balance, echo control devices, Echo (talker
23、and listener) Terminal balance and singing delay, loss, stability Impedance Delay Propagation time, digital processing Digital processing Sidetone Impedance Telephone design Local distortion Fidelity Quantization, non-linear and attenuation distortions and bandwidth Bandwidth I Speech detectors para
24、meters, switched loss clipping, I interruptions, freeze-out, fading Chopped speech l Crosstalk (intelligible) Power loads on cables and carriers, leakage, imbalances NON-VOICE - Impulse noise, frame slips, jitter, Frame slips, drop-outs, Lost-errored hits, drop-outs, distodon, circuit loss, distorsi
25、on, data crosstalk, interruptions, etc., degradation due to burst errors, echo compression algorithms Throughput Delay (and above impairments) - Response time Delay Delay Fax image Above impairments, Above quality out of synchronism plus out of synchronism Noise, intemptions, out of synchronism, gro
26、up delay distortion, impulsive noise Echo control devices, out of synchronism Retransmission Measuring methods The following methods of measuring the connection quality are available: i) 2) testcalls; 3) customers interviews; 4) trouble reports; 5) transmission quality index VQI). service observatio
27、ns on live traffk; Recommendation E.432 3 x_ -_ _- CCITT RECMN*E-432 92 486259L O573586 852 Measures using test calls on live traffic can be taken manually or by automatic means. The automatic methods are considered as objective measurements, for example, the non-intrusive methods on live traffic an
28、d the envelope methodology for speech quality on test calk. TQI, model to assess the global user perception of the level of transmission quality, is described in Recommendation P.ll. This model expresses the resulting effect by an overail index, which can be directly derived from the objective measu
29、rements on the network of elementary transmission quality parameters, Measures using customer interviews and trouble reports are considered to be subjective measurements along with the manual methods for service observations and test cai categories. The following method is available for the assessme
30、nt of subjective measurements: Mean opinion score (MOS) Users of the observers - in a sufficiently large sample - express their satisfaction about connection quality according to a five-category scale frome 4 to O: excellent, good, fair, poor and bad, The MOS value is obtained by averaging scores. A
31、s an example: from Figure uE.432, it can be seen that an MOS of 2.5 relates to 90% satisfaction in the fair or better curve. It also means that 50% of the users are considering the quality as good or excellent. If the target for “good or exceient” quality is 75%, then the MOS should be 3. O 1 2 3 4
32、MOS (Mean opinion score) 0202330-91 PIGURE m.432 Cumulative MOS characteristic3 Recommendation E.432 CCITT RECMNaE-432 72 4862591 0573587 797 The modern trend is to carry out automatic measurements for the following reasons: - - continuous observation is possible; - operating cost is minimized (staf
33、f reduction); it is possible to take a larger sample; - human error is eliminated, - - conversational privacy is ensured; - automatic processing of data is facilitated; the time at which observations are made can be recorded. On the other hand, manual observations can permit the detection of a numbe
34、r of abnormalities which cannot easily be detected automatically, and whose assessment is largely subjective, e.g. voice clipping. 7 Objectives and CCIIT Recommendations Objectives provide an effective means for managing Quality of Service. The use of objectives will guide actions to be taken to ens
35、ure that Quality of Service is consistent with the requirements and perceptions of end users. Objectives need to be reviewed and revised periodically as networks and technologies evolve and user expectations for Quality of Service change. Guidance in setting objectives for specific aspects of Qualit
36、y of Service can be found in various CCI“ Recommendations, including those listed below. Recommendations on transmission quality, including both network and terminal equipment aspects, may be found in Volume V (P-Series) and IlT.1 (G-Series, Fascicle 1); and the Handbook of Telephonometry, Recommen-
37、 dations P.ll and G.113 are especially helpful regarding transmission impairments. Page XI of the G-Series, Fascicle III.1, gives a useful index of transmission performance Recommendations, grouped by the type of impairment (e.g. noise, level, delay). The Q-Series of Recommendations give Recommendat
38、ions for exchanges (Fascicle VI.1). The M-Series of Recommendations give Recommendations for leased circuits (Fascicle rV.2). Recommendations G.821 and G.921 give requirements for bit error ratios in digital circuits and sections. Finally, rhe Hadbook on Quality of Service and Network Performance (1992), contains comprehensive tables for cross-referencing Network Performance and Quality of Service parameters to Recommendations. Recommendation E.432 5
