1、 Recommendation ITU-R S.1521-1(01/2010)Allowable error performance fora hypothetical reference digitalpath based on synchronousdigital hierarchyS SeriesFixed-satellite servicesii Rec. ITU-R S.1521-1 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient an
2、d economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are perfor
3、med by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to
4、 be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be fou
5、nd. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, rad
6、iodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management
7、SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2010 ITU 2010 All rights reserved. No part of th
8、is publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R S.1521-1 1 RECOMMENDATION ITU-R S.1521-1 Allowable error performance for a hypothetical reference digital path based on synchronous digital hierarchy (2001-2010) Scope The fixed-satellite service
9、 (FSS) plays an important role in providing reliable international digital communications. Because of the integration with the terrestrial facilities, a satellite link should be designed to fulfil requirements that are compatible with terrestrial systems. ITU-T Recommendation G.828 specifies perform
10、ance parameters and objectives for international synchronous digital paths which are intended to carry synchronous digital hierarchy (SDH) and asynchronous transfer mode (ATM) traffic. In response to those objectives, this Recommendation gives guidance on bit-error probability (BEP) or bit-error rat
11、e (BER) design masks which can fully comply with the requirements of ITU-T Recommendation G.828. The ITU Radiocommunication Assembly, considering a) that satellites operating in the fixed-satellite service play an important role in providing reliable international digital communications; b) that sat
12、ellite link performance must be sufficient to allow compliance with overall end-to-end performance objectives and in turn end-user quality objectives; c) that satellite link performance is generally distance independent; d) that Recommendation ITU-R S.1062 specifies satellite link performance object
13、ives which comply with the objectives specified in ITU-T Recommendation G.826; e) that the error performance for international constant bit-rate synchronous digital paths which are intended to carry ATM traffic as defined in ITU-T Recommendation I.356 has been specified in ITU-T Recommendation G.828
14、; f) that Recommendation ITU-R S.1429 specifies the error performance allowance due to interference between different satellite systems; g) that Recommendation ITU-R S.1323 specifies how to calculate the operating margins to allow for both fading and time-varying interference; h) that in defining er
15、ror performance criteria, it is necessary to take into account all error-inducing mechanisms, especially time-varying propagation conditions and interference; j) that satellite systems can be designed to meet a wide range of performance requirements, recommends 1 that satellite links within the publ
16、ic network and intended to carry SDH and ATM traffic should be designed to at least meet the specifications set forth in this Recommendation which is based upon ITU-T Recommendation G.828 (see Annex 1); 2 Rec. ITU-R S.1521-1 2 that the methodology explained in Annex 2 should be used to generate the
17、necessary BEP design masks, see also Note 2. To fully comply with ITU-T Recommendation G.828, the BEP divided by the average number of errors per burst (BEP/, see 3 of Annex 2) at the output of either end of a two-way hypothetical reference digital path (HRDP) should not exceed, during the total tim
18、e including the worst month, the design masks defined in Table 1 and also in the BEP masks given in Fig. 2 in Annex 2; TABLE 1 Bit rate (kbit/s) Percentage of total time (worst month) BEP/ 1 664 0.2 2.0 10.0 1 1091 1091 1092 240 0.2 2.0 10.0 1 1091 1091 1096 848 0.2 2.0 10.0 1 1097 10106 101048 960
19、0.2 2.0 10.0 1 1092 10101 1010150 336 0.2 2.0 10.0 1 1092 10109 1011601 334 0.2 2.0 10.0 To be determined To be determined To be determined 3 that the following Notes are a part of this Recommendation: NOTE 1 The HRDP referred to is specified in Recommendation ITU-R S.521. NOTE 2 The BEP ratios give
20、n in Table 1 could be estimated by a BER measurement taken over a sufficiently long period of time. A method for measuring BERs as a function of a shorter percentage of time is given in Annex 1 of Recommendation ITU-R S.1062. NOTE 3 For ease of application, the values given in Table 1 are in terms o
21、f total time and represent the limits of a BEP performance model utilizing the method outlined in Annex 2. In arriving at the figures in Table 1 the errors occurring during the unavailable time have been excluded. The BEPs in Table 1 are not the only ones that meet the requirements of ITU-T Recommen
22、dation G.828. Other BEP masks may be used where appropriate to satisfy ITU-T Recommendation G.828. NOTE 4 This Recommendation applies to satellite systems operating below 15 GHz. The extension to systems operating at higher frequencies is the subject of further study. NOTE 5 A BEP value of 1 108has
23、been used as the unavailability threshold. Rec. ITU-R S.1521-1 3 NOTE 6 The objectives given in Table 1 are given in terms of percentage of the worst month. These monthly percentages correspond to the following yearly percentages: 10% of a month = 4.0% of year; 2% of a month = 0.6% of year; 0.2% of
24、a month = 0.04% of year. NOTE 7 In order to comply with Table 1 at frequencies greater than 10 GHz (see also Note 4), it may be advantageous to make use of fade countermeasures including adaptive forward error correction (FEC) coding, power control or site diversity. Information on site diversity op
25、eration is given in Annex 1, Recommendation ITU-R S.1061. NOTE 8 The preferred method of verifying digital satellite link performance is on the basis of in- service measurements. These measurements would utilize the block error detection schemes, which are related to the inherent SDH block size and
26、structure of the transmission system. FEC, scrambling and differential encoding have an impact on interpretation of the measurements (see Annex 2, 3). NOTE 9 The error performance described in Table 1 was developed based on the use of an HRDP in the international portion of the link (e.g. switched i
27、nternational gateway-to-switched international gateway). Other applications of the HRDP within the connection are possible (e.g. end office-to-end office) and the error performance objectives can be adjusted accordingly. NOTE 10 The methods described in this Recommendation may be applied to the desi
28、gn of satellite links in private networks. NOTE 11 The performance objectives shall be met for the required transmission rate not for any higher rate created to support multiplexing or error correction. For instance, if the transmission rate over a satellite link is 6 Mbit/s and the required transmi
29、ssion rate between the end points is 2 Mbit/s, then the performance objectives for 2 Mbit/s transmission apply. Annex 1 1 General ITU-T Recommendation G.828 defines error performance parameters and objectives for international synchronous digital paths which are intended to carry SDH and ATM traffic
30、. This Recommendation adopts all the definitions parameters and objectives defined therein. The objectives given in ITU-T Recommendation G.828 are defined as being independent of the physical network supporting the path. In-service measurement of error rates at the SDH layer is supported by bit inte
31、rleaved parity (BIP) codes carried in the SDH container headers. 1.1 Definitions For convenience, the definitions in ITU-T Recommendation G.828 are repeated here. Error performance measurements are based upon blocks whose size is consistent with the SDH frame structure and varies according to the bi
32、t rate, see Table 2. 4 Rec. ITU-R S.1521-1 1.1.1 A block A block is a set of consecutive bits associated with the path; each bit belongs to one and only one block. Consecutive bits may not be contiguous in time. 1.1.2 Error events Errored block (EB): A block in which one or more bits are in error. E
33、rrored second (ES): A 1 s period with one or more EBs or at least one defect. Defects and related performance criteria are listed in Annex B of ITU-T Recommendation G.828. Severely errored second (SES): A 1 s period which contains 30% EBs or at least one defect. SES is a subset of ES. To simplify me
34、asurements, the defect is used in the definition of SES instead of defining SES directly in terms of severe bit errors. However, it should be appreciated that there may exist error patterns that would not trigger a defect. Field experience will establish if this is a major problem in measuring error
35、s. Background block error (BBE): An EB not occurring as part of an SES. Severely errored period (SEP): A sequence of between 3 and 9 consecutive SESs. The period is terminated by a second that is not a SES. Thus the SEP event is the same as the consecutive SES (CSES) event, as defined in ITU-T Recom
36、mendation G.784, with the lower threshold set to 3 s. Table 2 gives the relationships between block sizes, bit rates, error detection code (EDC) and path types. TABLE 2 Block sizes versus bit rates Bit rate (kbit/s) Path type SDH block size used in ITU-T Recommendation G.828 (bits) EDC 1 664 VC-11,
37、TC-11 832 BIP-2 2 240 VC-12, TC-12 1 120 BIP-2 6 848 VC-2, TC-2 3 424 BIP-2 48 960 VC-3, TC-3 6 120 BIP-8 150 336 VC-4, TC-4 18 792 BIP-8 601 344 VC-4-4c, TC-4-4c 75 168 BIP-8 2 405 376 VC-4-16c, TC-4-16c 300 672 BIP-8 9 621 504 VC-4-64c, TC-4-64c 1 202 688 BIP-8 1.1.3 Error performance parameters E
38、rror performance should only be evaluated whilst the path is in the available state. For a definition of the entry/exit criteria for the unavailable state, see ITU-T Recommendation G.828, Annex A. Errored second ratio (ESR): The ratio of ES to total seconds in available time during a fixed measureme
39、nt interval. Severely errored second ratio (SESR): The ratio of SES to total seconds in available time during a fixed measurement interval. Rec. ITU-R S.1521-1 5 Background block error ratio (BBER): The ratio of BBE to total blocks in available time during a fixed measurement interval. The count of
40、total blocks excludes all blocks during SESs. Severely errored period intensity (SEPI): The number of SEP events in available time, divided by the total available time in seconds. Thus the SEPI parameter has a unit of 1/s. 1.1.4 Block based measurements Each block is monitored by means of a BIP EDC
41、carried in the SDH header. When an error state is detected, it is not possible to determine whether a block or its controlling EDC bits are in error. Therefore if there is a discrepancy between the EDC and its controlled block, it shall always be assumed that the block is in error. 2 Error performan
42、ce objectives 2.1 End-to-end objectives Table 3 specifies the end-to-end objectives for a 27 500 km hypothetical reference path (HRP). The objectives applicable to a real path are derived from Table 3 using the allocation principles detailed in 6.2 of ITU-T Recommendation G.828. Each direction of th
43、e path shall independently satisfy the allocated objectives for all parameters. The objectives are long-term objectives to be met over an evaluation period of typically 30 consecutive days. TABLE 3 End-to-end error performance objectives for a 27 500 km international synchronous digital HRP as defin
44、ed in ITU-T Recommendation G.828 Bit rate (kbit/s) Path type Blocks/sESR SESR BBER(1)SEPI(2)1 664 VC-11, TC-11 2 000 0.01 0.002 5 1050.0002/s 2 240 VC-12, TC-12 2 000 0.01 0.002 5 1050.0002/s 6 848 VC-2, TC-2 2 000 0.01 0.002 5 1050.0002/s 48 960 VC-3, TC-3 8 000 0.02 0.002 5 1050.0002/s 150 336 VC-
45、4, TC-4 8 000 0.04 0.002 1 1040.0002/s 601 344 VC-4-4c, TC-4-4c 8 000 (3) 0.002 1 1040.0002/s (1)This BBER objective corresponds to an equivalent BER of 8.3 1010, an improvement over the BER of 5.3 109for the VC-4 rate. Equivalent BER is valuable as a rate-independent indication of error performance
46、, as BBER objectives cannot remain constant as block sizes increase.(2)Provisional value requiring further study. (3)ESR objectives tend to lose significance for high bit rates and are therefore not specified for paths operating above 160 Mbit/s. However, a significant increase in ESR indicates a de
47、grading transmission system. Therefore, for maintenance purposes ES monitoring should be implemented.6 Rec. ITU-R S.1521-1 Synchronous digital paths operating at bit rates covered by this Recommendation may be carried by digital sections operating at higher bit rates. Such systems must meet their en
48、d-to-end objectives. For example, in SDH, an STM-1 section may carry a VC-4 path and therefore the STM-1 section should be designed to ensure compliance with the objectives of the VC-4 path. Objectives are allocated to the national and international portions of a path. In the above example, if the S
49、TM-1 section does not form a complete national or international portion, the corresponding national/international allocation must be subdivided to determine the appropriate allocation for the digital section. This is outside the scope of this Recommendation. 2.2 Apportionment of end-to-end objectives The levels of performance expected are apportioned between international and national portions of an HRP. Further subdivision of these objectives is beyond the scope
