1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T G.821TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (12/2002) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks Quality and availability targets Error performance of an international digital connection operating at a
2、 bit rate below the primary rate and forming part of an Integrated Services Digital Network ITU-T Recommendation G.821 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMO
3、N TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.
4、400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TESTING EQUIPMENTS G.500G.599 TRANSMISSION MEDIA CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 General aspects G.800G.809 Design objectives for digital networks G.810G.819 Quality an
5、d availability targets G.820G.829 Network capabilities and functions G.830G.839 SDH network characteristics G.840G.849 Management of transport network G.850G.859 SDH radio and satellite systems integration G.860G.869 Optical transport networks G.870G.879 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.90
6、0G.999 QUALITY OF SERVICE AND PERFORMANCE G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DIGITAL TERMINAL EQUIPMENTS G.7000G.7999 DIGITAL NETWORKS G.8000G.8999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.821 (12/2002) i ITU-T Recommendation G.82
7、1 Error performance of an international digital connection operating at a bit rate below the primary rate and forming part of an Integrated Services Digital Network Summary This Recommendation defines error performance parameters and objectives for international digital connections operating below t
8、he primary rate of the digital hierarchy, using equipment designed prior to the adoption of revised ITU-T Rec. G.826 on 14 December 2002. The objectives given are independent of the physical network supporting the connection. This Recommendation is based upon bit error and bit error ratio measuremen
9、ts. The events, parameters and objectives are defined accordingly. Annex A deals with the definition of availability of the connection. Source ITU-T Recommendation G.821 was revised by ITU-T Study Group 13 (2001-2004) and approved under the WTSA Resolution 1 procedure on 14 December 2002. Keywords E
10、rror Performance Objectives, Error Performance Parameters, Errored Second, Severely Errored Second. ii ITU-T Rec. G.821 (12/2002) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardiz
11、ation Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which m
12、eets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-T
13、s purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draw
14、s attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or
15、 others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not repr
16、esent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2003 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.821 (12/2002) iii CONTENTS Page 1 Scope 1
17、2 References. 1 3 Abbreviations 1 4 Definitions 2 4.1 Digital connections. 2 4.2 Error performance events and parameters 2 4.2.1 Events . 2 4.2.2 Parameters 2 4.3 Functions of error performance objectives. 2 5 Performance objectives. 3 6 Apportionment of overall objectives 3 6.1 Basic apportionment
18、principles 3 6.2 Apportionment strategy for the errored seconds requirement 5 6.3 Apportionment strategy for the severely errored seconds requirement 6 Annex A Criteria for entry and exit for the unavailable state. 7 A.1 Criteria for a single direction 7 A.2 Criterion for a bidirectional connection
19、. 7 A.3 Criterion for a unidirectional connection . 7 A.4 Consequences on error performance measurements 7 iv ITU-T Rec. G.821 (12/2002) Introduction This Recommendation takes into account that services are based on the concept of an Integrated Services Digital Network (ISDN). In digital networks, e
20、rrors are a major source of degradation in that they affect voice services in terms of distortion of voice, and data type services in terms of lost or inaccurate information or reduced throughput. In spite of the fact that voice services are likely to predominate the narrow-band ISDN, it is required
21、 to transport a wide range of service types and it is therefore desirable to have a unified specification. An explanation of network performance objectives and their relationship with design objectives is given in ITU-T Rec. G.102. 1 NOTE The application of this Recommendation is limited to internat
22、ional digital connections, operating below the primary rate of the digital hierarchy, that use equipment designed prior to the adoption of revised ITU-T Rec. G.826 on 14 December 2002. Background This Recommendation was adopted in 1980 and defined error performance parameters and objectives for ISDN
23、 connections operating at a bit rate of 64 kbit/s. Because it was the first Recommendation giving error performance objectives, it found wide application even in areas it was not developed for. One of these applications was error performance evaluation at bit rates higher than 64 kbit/s. In 1988, an
24、 Annex D was added to this Recommendation, which indicated how to derive error performance data of 64 kbit/s connections taking into account measurements performed at higher bit rates. Practical experience showed, however, that Annex D/G.821 lead in many cases to doubtful results. It became obvious
25、that a Recommendation was needed which dealt with error performance parameters and objectives for higher bit rates. To fill this gap, ITU-T Rec. G.826 3 was developed and was adopted in 1993. It gives error performance parameters and objectives for constant bit rate digital paths operating at bit ra
26、tes at and above the primary rate. ITU-T Rec. G.826 contains the statement that it “. is the only Recommendation specifying error performance parameters and objectives at bit rates at or above the primary rate.“ Considering this statement, this Recommendation had to be restricted to bit rates below
27、the primary rate and Annex D/G.821 had to be deleted. On the other hand, the bit rate range between 64 kbit/s and the primary rate was to be covered by this Recommendation. Another problem discovered in the practical use of this Recommendation was the applicability of the Degraded Minute parameter (
28、DM). In practice, this event was hardly detected and it was therefore decided to delete it from this Recommendation. In summary, the following modifications are now included in this Recommendation: this Recommendation has been restructured in accordance with ITU-T Rec. A.15; this Recommendation is a
29、pplicable to bit rates below the primary rate of the digital hierarchy; the Degraded Minute parameter is deleted; Annex D/G.821 (1988) is deleted; otherwise, there are no technical changes to this Recommendation. After ITU-T Rec. G.826 3 was adopted, work on this Recommendation continued and compari
30、sons between the performance objectives for digital connections in this Recommendation and digital paths in ITU-T Rec. G.826 were made. From these comparisons it became apparent that inconsistencies existed between the two Recommendations. ITU-T Rec. G.821 (12/2002) v The performance of N 64 kbit/s
31、(1 N 24 or 31 respectively) international digital connections using equipment designed after the adoption of revised ITU-T Rec. G.826 on 14 December 2002 shall be governed by revised ITU-T Rec. G.826. ITU-T Rec. G.821 (12/2002) 1 ITU-T Recommendation G.821 Error performance of an international digit
32、al connection operating at a bit rate below the primary rate and forming part of an Integrated Services Digital Network 1 Scope This Recommendation specifies error performance events, parameters and objectives of a N 64 kbit/s circuit-switched digital connection (1 N 24 or 31 respectively) used for
33、voice traffic or as a “Bearer Channel“ for data-type services. The application of this Recommendation is limited to international digital connections, operating below the primary rate of the digital hierarchy, that use equipment designed prior to the adoption of revised ITU-T Rec. G.826 on 14 Decemb
34、er 2002. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject t
35、o revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document withi
36、n this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 1 ITU-T Recommendation G.102 (1988), Transmission performance objectives and Recommendations. 2 ITU-T Recommendation G.801 (1988), Digital transmission models. 3 ITU-T Recommendation G.826 (2002), End-
37、to-end error performance parameters and objectives for international, constant bit-rate digital paths and connections. 4 ITU-T Recommendation I.325 (1993), Reference configurations for ISDN connection types. 5 ITU-T Recommendation I.340 (1988), ISDN connection types. 6 ITU-T Recommendation G.921 (19
38、88), Digital sections based on the 2048 kbit/s hierarchy. 3 Abbreviations This Recommendation uses the following abbreviations: BER Bit Error Ratio ES Errored Second ESR Errored Second Ratio HRDP Hypothetical Reference Digital Path HRX Hypothetical Reference Connection ISDN Integrated Services Digit
39、al Network SES Severely Errored Second SESR Severely Errored Second Ratio 2 ITU-T Rec. G.821 (12/2002) 4 Definitions This Recommendation defines the following terms: 4.1 Digital connections The performance objectives are stated for each direction of a N 64 kbit/s circuit-switched connection (1 N 24
40、or 31 respectively) used for voice traffic or as a “Bearer Channel“ for data-type services. ITU-T Rec. I.325 4 gives reference configurations for the ISDN connection types listed in ITU-T Rec. I.340 5. In the context of error performance of 64 kbit/s circuit-switched connection types and the allocat
41、ion of performance to the connection elements, an all digital hypothetical reference configuration (HRX) is given in Figure 1. It encompasses a total length of 27 500 km and is a derivative of the standard hypothetical reference configuration given in Figure 1/G.801 2 and of the reference configurat
42、ion given in Figure 3/I.325. 4.2 Error performance events and parameters 4.2.1 Events Error performance parameters are derived from the following events: 4.2.1.1 errored second (ES): It is a one-second period in which one or more bits are in error or during which Loss of Signal (LOS) or Alarm Indica
43、tion Signal (AIS) is detected. 4.2.1.2 severely errored second (SES): It is a one-second period which has a bit error ratio 1.103or during which Loss of Signal (LOS) or Alarm Indication Signal (AIS) is detected. 4.2.2 Parameters It should be noted that total observation time (Stotal) is split into t
44、wo parts, namely, time for which the connection is deemed to be available (Savail) and that time when it is unavailable (Sunavail). Error performance should only be evaluated whilst the connection is in the available state. See Annex A. Parameters are: 4.2.2.1 errored second ratio (ESR): The ratio o
45、f ES to total seconds in available time during a fixed measurement interval. 4.2.2.2 severely errored second ratio (SESR): The ratio of SES to total seconds in available time during a fixed measurement interval. 4.3 Functions of error performance objectives The performance objectives aim to serve tw
46、o main functions: a) to give the user of national and international digital networks an indication as to the expected error performance under real operating conditions, thus facilitating service planning and terminal equipment design; b) to form the basis upon which performance standards are derived
47、 for transmission equipment and systems in an ISDN connection. The performance objectives represent a compromise between a desire to meet service needs and a need to realize transmission systems taking into account economic and technical constraints. The performance objectives, although expressed to
48、 suit the needs of different services are intended to represent a single level of transmission quality. Since the performance objectives are intended to satisfy the needs of the digital network, it must be recognized that such objectives cannot be readily achieved by all of todays digital equipment
49、and systems. The intent, however, is to establish equipment design objectives that are compatible with the objectives in this Recommendation. ITU-T Rec. G.821 (12/2002) 3 It is further urged that all technologies, wherever they appear in the network, should preferably be designed to better standards than those indicated here in order to minimize the possibility of exceeding the end-to-end objectives on significant numbers of real connections. The objectives relate to a very long connection and recogniz
