1、STD-ITU-T RECMN 0.15U-ENGL 1976 4862571 Ob21997 835 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU 0.150 SERIES O: SPECIFICATIONS OF MEASURING EQUIPMENT Equipment for the measurement of digital and an a log ue/d ig it al pa ram e te rs (05196) General req
2、uirements for instrumentation for performance measurements on digital transmission equipment ITU-T Recommendation O. 150 (Previously ”CCITT Recommendation”) - STD-ITU-T RECMN 0.150-ENGL 177b H 48b2571 Ob21798 771 ITU-T O-SERIES RECOMMENDATIONS SPECIFICATIONS OF MEASURING EQUIPMENT General R Maintena
3、nce access o. 1-0.9 O. 10-0.19 I Automatic and semi-automatic measuring systems 0.20-0.39 0.40-0.129 I Eaubment for the measurement of analogue uarameters For further details, please refer to ITU-T List of Recommendations. STD-ITU-T RECMN 0.15U-ENGL 1996 48b2591 Ob21797 bUA FOREWORD The ITU-T (Telec
4、ommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. Th
5、e World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure
6、 laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation 0.150 was revised by ITU-T Study Group 4 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 12th of May 1996. NOTE In this Recommendation, the expression “Administration” is used for con
7、ciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1996 Ail rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in
8、 writing fi-om the ITU. Recommendation 0.150 (05196) i STD-ITU-T RECMN 0.15O-ENGL L99b 48b2591 Ob22000 T28 1 2 3 4 5 6 7 CONTENTS Page Scope References Standardized test sequences . Properties of pseudo-random test sequences 4.1 Measurements through scramblers . Loss of sequence synchronization 4.2
9、4.3 “Framed” measurements . 4.4 Jitter measurements . Digital test sequences used in the O-Series Recommendations . 5 1 l-bit pseudo-random test sequence . 2047-bit pseudo-random test sequence . 32 767-bit pseudo-random test sequence 1 048 575-bit pseudo-random test sequence . 8 388 607-bit pseudo-r
10、andom test sequence . 536 870 91 1-bit pseudo-random test sequence . 2 147 483 647-bit pseudo-random test sequence Description of framed test sequences at different bit rates . 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 1 048 575-bit pseudo-random test sequence with zero suppression . 6.1 6.2 6.3 6.4 6.5 6.6 6
11、.7 6.8 6.9 6.10 6.1 1 General 6.1.1 Testing digital demultiplexers . Digital frames operating at bit rates of 1544 kbiih . 6.2.1 6.2.2 24 - Frame multiframe or extended superframe Digital frames operating at bit rates of 2048 kbits . 6.3.1 Frames without CRC-4 procedure and providing common channel
12、signalling 6.3.2 Frames without CRC-4 procedure and providing channel associated signalling 6.3.3 Frames with CRC-4 procedure and providing channel associated signalling . Digital frames operating at bit rates of 63 12 kbit/s . Digital frames operating at bit rates of 8448 kbits . Digital frames ope
13、rating at bit rates of 32 064 kbits Digital frames operating at bit rates of 34 368 kbits Digital frames operating at bit rates of 44 736 kbits Digital frames operating at bit rates of 97 728 kbits Digital frames operating at bit rates of 139 264 kbit/s 6.10.1 Digital frames operating at 139 264 kbi
14、t/s and multiplexing 34 368 kbits signals 6.10.2 Digital frames operating at 139 264 kbit/s and multiplexing 44 736 kbits signals Digital frames operating at STM-N bit rates i2 - Frame mutifiame or superframe . Block-oriented error performance measurements 7.1 Measurement of block errors 7.2 Block s
15、izes 7.2.1 Block sizes for out-of-service performance measurements on PDH systems . 7.2.2 7.2.3 Block sizes for out-of-service performance measurements on SDH systems . Block sizes for performance measurements on cell-based systems 8 Detection and clearance of AIS and LOS defects 1 1 2 2 2 2 3 3 3 3
16、 4 4 4 4 5 5 5 6 6 6 6 6 7 7 8 8 8 8 9 10 10 11 12 13 13 13 14 14 14 14 15 15 16 16 11 Recommendation 0.150 (05/96) SUMMARY This .Recommendation contains general requirements applicable to the O-Series Recommendations for instrumentation for performance measurements on digital transmission equipment
17、. KEYWORDS Block sizes, block-oriented measurement, detection and clearance of Alarm Indication Signal (AIS), detection and clearance of Loss Of Signal (LOS), digital test sequences, performance measurements, pseudo-random test sequences; tester. iii Recommendation 0.150 (05796) - STD*ITU-T RECMN O-
18、L!iO-ENGL L77b LiAb257L Ob22002 ATO STD-ITU-T RECMN 0.150-ENGL 199b 48bZ.591 Ob22003 737 Recommendation 0.150 GENERAL REQUIREMENTS FOR INSTRUMENTATION FOR PERFORMANCE MEASUREMENTS ON DIGITAL TRANSMISSION EQUIPMENT (revised in 1996) 1 Scope This Recommendation contains general requirements applicable
19、 to instrumentation for performance measurements on digital transmission equipment. Such equipment is specified in the O-Series Recommendations. This Recommendation is intended to give general guidance in connection with specific O-Series Recommendations and is a help in finding the right measuremen
20、t conditions for different applications. This Recommendation defines such items as digital (pseudo-random) test sequences, block sizes for error performance measurements and the criteria for the detection and clearance of loss of frame and of alarm indication signal. 2 References The following Recom
21、mendations 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 to revision; all users of this Recommendation ar
22、e therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of currently valid ITU-T Recommendations is regularly published. Pl ITU-T Recommendation G.823 (1993), The control of jitter and wander within di
23、gital networks which are based on the 2048 kbits hierarchy. Pl CCITT Recommendation O. 153 (1992), Basic parameters for the measurement of error performance at bit rates below the primary rate. 31 CCITT Recommendation O. 152 (1992), Measuring equipment for bit rates of 64 kbits and N x 64 kbith. i41
24、 CCITT Recommendation O. 15 1 (1992), Error perf-ormance measuring equipment operating at the primary rate and above. PI ITU-T Recommendation G.826 (1 993), Error performance parameters and objectives for international, constant bit rate digitalpaths at or above theprimary rate. 161 ITU-T Recommenda
25、tion (3.704 (1999, Synchronous ffame structures used at 1544, 6312, 2048, 8488 and 44 736 kbits. i71 CCITT Recommendation G.752 (1988), Characteristics of digital multiplex equipments based on a second order bit rate of 6312 kbits and using positive justijcation. CCITT Recommendation G.751 (1988), D
26、igital multiplex equipments operating at the third order bit rate of 34 368 kbtis and the fourth order bit rate of 139 264 kbits and usingpositive justification. CCITT Recommendation G.703 (1 99 i), PhysicaUelectrical characteristics of hierarchical digital interfaces. ITU-T Recommendation G.775 (19
27、94), Loss Of Signal (LOS) and Alarm Indication Signal (MS) defect detection and clearance criteria. SI 191 lo 1 i American National Standard for telecommunications ANSI T1.107-1988, Digital hierarchy formats specifications. 121 CCIIT Recommendation (3.743 (1988), Second order digital multiplex equip
28、ment operating at 6312 kbits and using positive justification. Recommendation 0.150 (0996) 1 13 CCITT Recommendation G.742 (1988), Second order digital multiplex equipment operating at 8448 kbith and using positive justification. CCITT Recommendation G.755 (1988), Digital multiplex equipment operati
29、ng at 139 264 kbith and multiplexing three tributaries at 44 736 kbith. 141 3 Standardized test sequences Bit error measurements are important means to assess the performance of digital transmission equipment. So-called “true“ bit error measurements, during which every error can be detected, can onl
30、y be carried out if the bit sequence of the pattern used for the measurement is exactly known. Because of its random nature, this condition is normally not fulfilled by real traffic. Therefore, it is necessary to specie reproducible test sequences which simulate real traffic as closely as possible.
31、Reproducible test sequences are also a prerequisite to perform end-to-end measurements. Pseudo-random sequences with a length of 2“ - 1 bits are the most common answers to this problem. In addition to strings of n consecutive ZEROs (so-called inverted signai) and n- 1 consecutive ONEs, such sequence
32、s contain any possible combination of ZEROs and ONEs within a string length depending on n. (For the value of n see Clauses 4 and 5.) Pseudo-random sequences of different lengths are specified in this Recommendation. 4 The properties of a test sequence should meet the requirements of the system unde
33、r test. In general, the length of a pseudo-random sequence shall increase with the bit rate at which measurements are performed. This avoids the sequence repetition fiequency becoming too high which would not be in accordance with the situation found in practice. Pseudo-random sequences may be produ
34、ced by means of shift registers with appropriate feedback. If the shift register has n stages, the maximum sequence length will be 2“ - 1 bits. If the digital signal is directly taken from the output of the shift register (non-inverted signal) the longest string of consecutive ZEROs will be equal n
35、- 1. If the signal is inverted, n consecutive ZEROs will be produced. It is possible to generate pseudo-random sequences with these properties by other means than shift registers. Properties of pseudo-random test sequences 4.1 Measurements through scramblers The unit under test may contain scrambler
36、s. This may yield unexpected measurement results if the value n as described in clause 4 has common integer multiples with the number of stages of the scrambler. To reduce the probability that this problem will occur, the value of n for test sequences specified more recently is a prime number. 4.2 L
37、oss of sequence synchronization Bit error measurements using pseudo-random sequences can only be performed if the reference sequence produced on the receiving side of the test Set-up is correctly synchronized to the sequence coming from the object under test. In order to achieve compatible measureme
38、nt results, it is necessary that the sequence synchronization characteristics are specified. The following requirement is applicable to all O-Series Recommendations dealing with error performance measurements using pseudo-random sequences. Sequence synchronization shall be considered to be lost and
39、resynchronization shall be started if: a) the bit error ratio is 2 0.20 during an integration interval of 1 second; or b) it can be unambiguously identified that the test sequence and the reference sequence are out of phase. NOTE - One method to recognize the out-of-phase condition is the evaluation
40、 of the error pattern resulting from the bit-by-bit comparison. If the error pattern has the same structure as the pseudo-random test sequence, the out-of-phase condition is reached. 2 Recommendation 0.150 (05196) STD-ITU-T RECMN O*150-ENGL 177b 48b2591 0b22005 50T 209 - i 21 - 1 215- I 220 - 1 4.3
41、“Framed” measurements 8 10 15 19 0.153 0.152 O. 151 O. 1 5 3 Error measurements on data circuits at bit rates up to 14 400 bit/s Error and jitter measurements at bit rates of 64 kbits and N x 64 kbits Error and jitter measurements at bit rates of 1544,2048, 6312,8448,32 064 and 44 736 kbit/s Error m
42、easurements on data circuits at bit rates up to 72 kbit/s Certain measurements require that the test sequence is transmitted as “payload” within a valid frame. In this case, transmission of the test sequence shall be stopped when the frame alignment signal is transmitted. More detailed information i
43、s given in clause 6. 220- 1 223 - i 229 - i 231 - 1 4.4 Jitter measurements 14 23 29 - Specific measurement tasks 31 - Specific measurement tasks O. 15 1 O. 15 i Error and jitter measurements at bit rates of 1544,63 12, 32 064 and 44 736 kbits Error and jitter measurements at bit rates of 34 368 and
44、 139 264 kbitk Digital test sequences are not only used in error measurements but also for measuring the jitter transfer function or tolerable input jitter. Special attention should be paid in this case to the length of the test sequence used in the measurement. If the sequence is too short (high se
45、quence repetition frequency), the spectral distribution of the test signal may differ substantially from the properties of real traffic. In this case, the measurement results will not reflect the practical situation. See Annex pJG.823 i in this connection. 5 Digital test sequences used in the O-Seri
46、es Recommendations This clause describes the digital test sequences used in the O-Senes Recommendations and their main applications. Table 1 gives a summary. TABLE 110.150 Digital test sequences used in the O-Senes Recommendations I Used in Rec. I Length of Consecutive sequence (bits) zeros Use of s
47、equence 5.1 511-bit pseudo-random test sequence This sequence is primarily intended for error measurements on data circuits at bit rates up to 14 400 bits (see Recom- mendation O. 153 2). The sequence may be generated in a nine-stage shift register whose 5th and 9th stage outputs are added in a modu
48、lo-two addition stage, and the result is fed back to the input of the first stage. The sequence begins with the first ONE of 9 consecutive ONES. - Number of shift register stages 9 - Length of pseudo-random sequence 29- 1 =511 bits - Longest sequence of zeros 8 (non-inverted signal) Recommendation 0
49、.150 (05/96) 3 STD-ITU-T RECMN O*150-ENGL Ob220b 5.2 2047-bit pseudo-random test sequence This sequence is primarily intended for error and jitter measurements on circuits operating at bit rates of 64 kbits and N x 64 kbi/s (see Recommendations 0.152 3 and 0.153 2). The sequence may be generated in an eleven-stage shift register whose 9th and 11th stage outputs are added in a modulo-two addition stage, and the result is fed back to the input of the first stage. - Number of shift register stages 11 - Length of pseudo-random sequence 2l
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