1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.775 (1 0/98) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital transmission systems - Terminai equipments - Operations, administration and maintenance features of transmission e
2、q u i pmen t Loss of Signal (LOS), Alarm Indication Signal (AIS) and Remote Defect Indication (RDI) defect detection and clearance criteria for PDH signals ITU-T Recommendation G.775 (Previously CCITT Recommendation) ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND
3、NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS INTERNA TIONAL ANALOGUE CARRIER SYSTEM INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE WITH METALLIC LINES SYSTEMS ON RADIO-RELAY OR SATELLITE
4、LINKS AND INTERCONNECTION COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY TESTING EQUIPMENTS TRANSMISSION MEDIA CHARACTERISTICS DIGITAL TRANSMISSION SYSTEMS TERMINAL EQUIPMENTS General Coding of analogue signals by pulse code modulation Coding of analogue signals by methods other than PCM Principa
5、l characteristics of primary multiplex equipment Principal characteristics of second order multiplex equipment Principal characteristics of higher order multiplex equipment Principal characteristics of transcoder and digital multiplication equipment Operations, administration and maintenance feature
6、s of transmission equipment Principal characteristics of multiplexing equipment for the synchronous digital hierarchy Other terminal equipment DIGITAL NETWORKS DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G. 1 OO-G. 199 G.300-G.399 G.400-G.449 G.450-G.499 G.700-G.799 G .700-G . 709 G.710-G.719 G.720-G.7
7、29 G ,730-G . 739 G. 740-G ,749 G.750-G.759 G .760-G. 769 G.77-G .779 G.780-G.789 G. 7 90-G . 799 G.800-G.899 G ,900-G . 999 For further details, please rejr to ITU-T Lisi ofliecomniendations. ITU-T RECOMMENDATION G.775 Issue 10198 LOSS OF SIGNAL (LOS), ALARM INDICATION SIGNAL (AIS) AND REMOTE DEFEC
8、T INDICATION (RDI) DEFECT DETECTION AND CLEARANCE CRITERIA FOR PDH SIGNALS Notes First revision includes a correction to Figure 1, and the addition of text related to the RDI defect detection in a new clause 6 and Appendix 1.3. Summary This Recommendation gives the recommended criteria for the detec
9、tion and clearance of LOS, AIS and RDI defects at intra-station interfaces conforming to Recommendation G.703 and operating at bit rates described in Recommendation G.702. The information provided complements the information on fault and consequent action given in the G.730-, G.340- and G.750-series
10、 Recommendations. Appendix I contains examples of the criteria used in equipment that has been designed prior to the development of this Recommendation. 1 1/94 History Furthermore, editorial modifications are included to comply with Recommendation A.3. Initial version Source ITU-T Recommendation G.7
11、75 was revised by ITU-T Study Group 15 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 13“ October 1998. FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardi
12、zation Sector (ITU-T) is a permanent organ of the ITU. The 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 Conference (WTS
13、C), 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 laid down in WTSC Resolution No. 1. In some areas of inf
14、ormation technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating ag
15、ency. INTELLECTUAL PROPERTY RIGHTS The IT draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual P
16、roperty Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. Howe
17、ver, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 1998 Ail rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, inc
18、luding photocopying and microfilm, without permission in writing from the ITU. II Recommendation G.775 (10/98) CONTENTS 1 Scope 2 References 3 Abbreviations . 4 Criteria for detection and clearance of a Loss of Signal (LOS) defect . 5 Criteria for detection and clearance of an Alarm Indication Signa
19、l (AIS) defect condition . 6 Criteria for detection and clearance of a Remote Defect Indication (RDI) defect . Appendix I . Other criteria that have been used for the detectiodclearance of LOS. AIS or RDI defects . I . 1 LOS defect detectiodclearance criteria 1.2 AIS defect detectiordclearance crite
20、ria . 1.3 RDI defect detectiodclearance criteria Page 1 1 2 2 3 5 . Recommendation G.775 (10/98) 111 Recommendation G.775 LOSS OF SIGNAL (LOS), ALARM INDICATION SIGNAL (AIS) AND REMOTE DEFECT INDICATION (RDI) DEFECT DETECTION AND CLEARANCE CRITERIA FOR PDH SIGNALS (revised in 1998) 1 Scope This Reco
21、mmendation provides the recommended criteria for the detection and clearance of LOS, AIS and RDI defects at intra-station interfaces conforming to Recommendation G.703 and operating at bit rates described in Recommendation G.702. The criteria given in this Recommendation should be applied to new equ
22、ipment designs. Appendix I contains examples of the criteria used in equipment designed prior to the development of this Recommendation. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recom
23、mendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other re
24、ferences listed below. A list of the currently valid ITU-T Recommendations is regularly published. CCITT Recommendation G.702 (1988), Digital hierarchy bit rates. ITU-T Recommendation G.703 (1 998), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T Recommendation G.704 (1
25、 998), Synchronous fiame structures used at 1544, 631 2, 2048, 8448 and 44 736 kbit/s hierarchical levels. CCITT Recommendation G.734 (1988), Characteristics of synchronous digital multiplex equipment operating at 1544 kbit/s. CCITT Recommendation G.742 (1 988), Second order digital multiplex equipm
26、ent operating at 8448 kbit/s and using positive just flcation. CCITT Recommendation G.743 (1 988), Second order digital multiplex equipment operating at 631 2 kbit/s and using positive justification. CCITT Recommendation G.747 (1 988), Second order digital multiplex equipment operating at 6312 kbit/
27、s and multiplexing three tributaries at 2048 kbit/s. CCITT Recommendation G.75 1 (1 988), Digital multiplex equipments operating at the third order bit rate of 34 368 kbits and the fourth order bit rate of 139 264 kbitls and using positive justification. CCITT Recommendation G.752 (1988), Characteri
28、stics of digital multiplex equipments based on a second order bit rate of 6312 kbit/s and usingpositive justiJication. CCITT Recommendation G.753 (1 988), Third order digital multiplex equipment operating at 34 368 kbit/s and using positive/zero/ negative justiJcation. Recommendation 6.775 (10198) 1
29、 - CCITT Recommendation G.755 (1 988), Digital multiplex equipment operating ut 139 264 kbitls and multiplexing three tributaries ut 44 736 kbitls. CCITT Recommendation M.20 (1 992), Maintenance philosophy for telecommunication networks. - 2 048 6 312 3 Abbreviations This Recommendation uses the fol
30、lowing abbreviations: AIS Alarm Indication Signal CAS Channel Associated Signalling LOS Loss of Signal RDI Remote Defect Indication 9 35 9 35 4 Criteria for detection and clearance of a Loss of Signal (LOS) defect 4.1 A Loss of Signal (LOS) defect at 64 kbWs interfaces is detected when the incoming
31、signal has “no transitions“, i.e. when the signal level is less than or equal to a signal level of B dB below nominal, for N consecutive pulse intervals, where 10 5 N 5 255. The LOS defect is cleared when the incoming signal has “transitions“, i.e. when the signal level is greater than or equal to a
32、 signal level of A dB below nominal, for N consecutive pulse intervals, where 10. I N 5255. NOTE - The values of A and B are for further study. (Values of A = 6 and B = 35 have been proposed.) 4.2 A LOS defect at 2048 kbit/s, 6312 kbit/s, 8448 kbits, 34 368 kbits and 139 264 kbits interfaces is dete
33、cted when the incoming signal has “no transitions“, i.e. when the signal level is less than or equal to a signal level of Q dB below nominal, for N consecutive pulse intervals, where 10INI255. The LOS defect is cleared when the incoming signal has “transitions“, i.e. when the signal level is greater
34、 than or equal to a signal level of P dB below nominal, for N consecutive pulse intervals, where 10 IN I 255. A signal with “transitions“ corresponds to a G.703 compliant signal. Values for P and Q are given in Table 1 a Figure 1 illustrates the relationship of the various signal levels. 7 34 368 15
35、 35 139 264 15 35 I 8 448 I 9 I 35 I 2 Recommendation G.775 (10/98) - STD-ITU-T RECMN Nominal value Maximum cable loss t 3 dB ,“Transition condition“ must be detected /?/ / olerance range “No transition condition“ or “transition condition“ may be detected . . . . . . . Q A %tran/sitik con/ditik“ mGt
36、 be detected T1517720-95 Level below Nominal NOTE 1 - The signai level P is (maximum cable loss +3) dB below nominal. NOTE 2 - The signal level Q is greater than the maximum expected cross-talk level. Figure VG.775 - Criteria for determination of transition conditions 4.3 A LOS defect at a 1544 kbit
37、/s interface is detected when the incoming signal has no transitions over a period of 175 I 75 contiguous pulse intervals. The LOS defect is cleared when the incoming signal has an average pulse density of at least 12.5% over a period of 175 L 75 contiguous pulse intervals starting with the receipt
38、of a pulse. 4.4 A LOS defect at a 44 736 kbit/s interface is detected when the incoming signal has no transitions over a period of 175 +_ 75 contiguous pulse intervals. The LOS defect is cleared when the incoming signal has an average pulse density of at least 33% over a period of 175 f 75 contiguou
39、s pulse intervals starting with the receipt of a pulse. Other equivalent algorithms that are based on the 33% average pulse density criteria are also acceptable. 5 Criteria for detection and clearance of an Alarm Indication Signal (AIS) defect condition 5.1 The criteria for detection of an AIS defec
40、t at a 64 kbit/s interface, other than for the channel associated signalling Time Slot (TS) which is described in 5.1 .l, is for further study. 5.1.1 An AIS defect for the 64 kbit/s channel associated signalling signal in TS-16, in the frame format of Recommendation G.704, is detected when the incom
41、ing TS-16 signal has three (3) or less ZEROs in each of two consecutive multiframe periods. The defect is cleared when each of two consecutive multiframe periods contains four (4) or more ZEROs, or when the multiframe alignment signal has been found. 5.2 An AIS defect at a 2048 kbit/s interface is d
42、etected when the incoming signal has two (2) or less ZEROs in each of two consecutive double frame periods (5 12 bits). The defect is cleared when each of two consecutive double frame periods contains three (3) or more ZEROs or when the Frame Alignment Signal (FAS) has been found. Recommendation G.7
43、75 (10/98) 3 5.3 An AIS defect at 6312 kbit/s (frame format per Recommendation G.747 ), 8448 kbit/s, 34 368 kbits and 139 264 kbits interfaces is detected when the incoming signal has X or less ZEROs in each of two consecutive frame periods (Y bits per frame). The defect is cleared when each of two
44、consecutive frame periods contains Z or more ZEROs, or when the frame alignment signal has been found. The values of X, Y and Z are given in Table 2. X (No. of ZEROs) Table 2/6.775 - Number of ZEROs for detectiodclearance of AIS defect Y (bidframe) I Bit rate (kbit/s) I 34 368 I 34 368 I 139 264 I 1
45、39 264 4 1 840(G.747) 4 I 848(G.742) 4 I 1536 (G.75 1) 5 I 2148 (G.753) 5 I 954(G.755) 5 I 2928 (G.751) Z (No. of ZEROs) 5 5 5 6 6 6 5.4 An AIS defect at a 1544 kbit/s interface (frame format per Recommendation G.704 or Recommendation G.734) is detected when the incoming signal is an unframed signal
46、 with ONEs density of at least 99.9% present for a time equal to or greater than T, where T is 3 ms to 75 ms. The AIS defect is cleared within a time period T when the incoming signal does not meet either the ONEs density or the unframed signal criteria, where T is 3 ms to 75 ms. 5.5 An AIS defect a
47、t a 6312 kbits (frame format per Recommendation G.704 or Recommendation G.743) interface is detected when the incoming signal has two (2) or less ZEROs in a sequence of 3 156 bits (0.5 ms). The AIS signal defect is cleared when the incoming signal has three (3) or more ZEROs in a sequence of 3 156 b
48、its (0.5 ms). 5.6 An AIS defect at a 44 736 kbit/s interface (frame format per Recommendation G.704 or Recommendation G.752) is detected when the AIS signal (defined in Recommendation G.704 for a frame format per Recommendation G.704 and defined in Recommendation M.20 for a frame format per Recommen
49、dation G.752) is present in contiguous M-fiames for a time equal to or greater than T, where T is 0.2 ms to 100 ms. The AIS defect is cleared when AIS signal is not detected in contiguous M-frames for a time equal to or greater than time T, where T is 0.2 ms to 100 ms. 5.7 An AIS defect at a 32 064 kbits interface is detected when the incoming signal has two (2) or less ZEROs in a sequence of 1920 bits (see Recommendation G.752). The AIS defect is cleared when the incoming signal has three (3) or more ZEROs in a sequence of 1920 bits. 5.8 An AIS signal
