1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU GENERAL ASPECTS OF DIGITAL TRANSMISSION SYSTEMS G.772 (03/93) PROTECTED MONITORING POINTS PROVIDED ON DIGITAL TRANSMISSION SYSTEMS ITU-T Recommendation G.772 (Previously “CCITT Recommendation”) ITU-T RECMN*G-
2、?2 (REV83) 73 Ei 4862573 0582373 343 W FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a vie
3、w to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn produce Recommendations on these topics. ITU-T Recommendation G.772
4、 was revised by the ITU-T Study Group XV (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunicati
5、on Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to references containing the a
6、cronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Recommenda
7、tion, the expression “Administration” is used for conciseness to indicate both a O ITU 1993 All 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 writing from t
8、he ITU. - - . . ITU-T RECMNrG.772 (REVS11 93 W 4862591 0582374 28T W CONTENTS General . 1.1 Definition 1.2 Location of protected monitoring points 1.3 Use of protected monitoring points 1.4 General electrical characteristics Electrical characteristics of protected monitoring points provided on trans
9、mission equipments of the plesiochronous digital hierarchy 2.1 Impedances at the protected monitoring points 2.2 Characteristics of monitoring points incorporated in transmission equipment . 2.3 Characteristics of monitoring points located between transmission equipments Electrical characteristics o
10、f protected monitoring points provided on transmission equipments of the synchronous digital hierarchy 3.1 Impedances at the protected monitoring points 3.2 Characteristics of monitoring points at 155 520 kbit/s incorporated in transmission equipment . 3.3 Characteristics of monitoring points at 155
11、 520 kbit/s located between transmission equipments 3.4 Other bit rates . Protection of the transmitted signal Resilience of the protected monitoring point . References . Page 1 1 1 2 2 Recommendation G.772 (03/93) i Recommendation G.772 - - MUX - PROTECTED MONITORING POINTS PROVIDED ON DIGITAL TRAN
12、SMISSION SYSTEMS - - - - - - MUX LTE DEMUX (Melbourne, 1988: amended at Helsinki, 1993) - 1 General - - - Regular signal monitoring is an important measure to maintain performance of digital networks. Existing transmission equipment does not have built-in devices providing extensive performance moni
13、toring capabilities. Monitoring points are an additional means to a telecommunication management network (TMN) for temporarily monitoring the transmitted signal for purposes of fault finding. 1.1 Definition A protected monitoring point (PMP) provides a digital interface at which it is possible to mo
14、nitor the transmitted digital signal without impairing it Protected monitoring points allow measurements to be made with suitable test equipment. i 1.2 Location of protected monitoring points Protected monitoring points may be provided in conjunction with electrical output interfaces of equipment co
15、rresponding to Recommendation G.703 or at points between an output and an input interface, e.g. at distribution frames. Figure 1 shows some examples for the implementation of digital protected monitoring points. PMP No. 1 Monitoring point at multiplexer aitput 2 Monitoring point at a distribution fr
16、ame 3 Monitoring point ai the output of line terminating equipment 4 Monitoring point at demultiplexer inputdistribution frame 5 Monitoring point at demultiplexer output FIGURE UG.772 Possible locations of monitoring points Recommendation 6.772 (03193) 1 ITU-T RECMN*G.772 (REV*1) 73 E7 48b2.591 0582
17、376 052 1.3 Use of protected monitoring points In the long term, protected monitoring points will be used primarily for measurements that are not scheduled (e.g. failure detection and fault localization) or made on an infrequent basis. Protected monitoring points offer an interface at which digital
18、test equipment may be connected. Equipments specified in the O-Series Recommendations are preferred examples. (See Recommendations 0.133,0.151,0.152,0.161,0.162 2.) External test equipment connected to protected monitoring points may permit performance monitoring on linkdpaths not provided with thes
19、e functions built into terminal equipment, or might give the ability to monitor additional parameters. Scanner devices may be used with protected monitoring points to provide nearly continuous monitoring of transmission systems and terminals. Special switching matrices may allow the connection of m
20、external instruments to IZ protected monitoring points. Concerning the maintenance of circuits at 64 kbit/s, an additional use of the protected monitoring points on the primary order digital path is to allow monitoring of individual time slots. This will permit, for example, measurement of analogue
21、type parameters (signal level, quantizing distortion, etc.) using appropriate measuring equipment Other circuits to be monitored are signalling links of a common channel signalling system at a point on the exchange boundary, independent of the switching equipment itself. It is necessary to distingui
22、sh between access points and protected monitoring points. The use of access points for testing, i.e. insertion and retrieval of signals, will disturb the transmission on the accessed link (the accessed link must be out of service). On the contrary, the use of protected monitoring points for retrieva
23、l of signals shoud not disturb the transmission (the monitored link will be in service). The use of protected monitoring points is optional. 1.4 General electrical characteristics Concerning the general characteristics of the protected monitoring points, namely bit rate; number of pairs; code at the
24、 interface; nominal pulse shape, the relevant specifications of Recommendation G.703 shall apply 4. accordance with Recommendation G. 703 only for the purpose of signal monitoring. NOTE - For transmission equipment with optical interfaces it not required to provide a digital signal which is encoded
25、in The monitoring point for this signal may provide an attenuated NRZ signal as available at the input/output of the electro-/optical converter. 2 Electrical characteristics of protected monitoring points provided on transmission equipments of the plesiochronous digital hierarchy This clause applies
26、 to equipments operating in accordance wfth the plesiochronous digital hierarchy (PDH) as given in Recommendation G.702 3. Monitoring points already available on existing transmission equipment may output lower levels. NOTE - Subclauses 2.2.1 and 2.3.2 below specify a maximum signal attenuation of 2
27、0 dB at protected monitoring points. Providers of measuring equipment shall take this into account. 2.1 Impedances at the protected monitoring points The output and terminating impedances at the protected monitoring points shall be in accordance with Table 1. The return loss shall be 2 14 dB over a
28、frequency range corresponding to 5% to 150% of the relevant bit rate. 2 Recommendation 6.772 (03/93) _- ITU-T RECMN*G-772 (REV*1) 93 m 4862591 0582377 T99 m Bit rate (kbivs) 64 2 048 8 448 34 368 139 264 1 s44 TABLE UG.772 Impedance, return loss and output signal balance of protected monitoring poin
29、ts Impedance Impedance symmetrical coaxial 120 n - 120 n 75 n - 75 n - 75 n - 75 n loo Q - 32 064 44 736 I 75n I 1 6312 1 110n - 75 n - 75 n If applicable, the output siganal balance shall be 2 30 dB measured in accordance with Recommendation 0.9 over a frequency range corresponding to 5% to 150% of
30、 the relevant bit rate. NOTE - For bit rates up to 8448 kbitls, a simple resistive protection network presenting an impedance not complying with this table is acceptable. The input impedance of the connected test equipment must always comply with the values specified in the table. 2.2 2.2.1 Characte
31、ristics of monitoring points incorporated in transmission equipment Monitoring points at 64 kbis, 1544 kbis, 2048 kbis, 6312 kbis, 8448 kbis, 32 O64 kbis, 34 368 kbis, 44 736 kbis and 139 264 kbis The nominal voltage at the protected monitoring points when terminated in the nominal impedance as give
32、n in Table 1 shall be 2 1/10 of the voltage specified in Recommendation G.703. This means that the output signal at the protected monitoring point shall be attenuated not more than 20 dB referred to the output signal at a G.703 interface. 2.3 characteristics of monitoring points located between tran
33、smission equipments In this case, protected nionitoring points may be provided. for example, at digital distribution frames. 2.3.1 The digital signals presented at the protected monitoring points shall be as defined in 2.2.1 above but modified by the characteristics of the interconnecting cable. The
34、 attenuation of these cables shall be assumed to follow a Jf law. In accordance with Recommendation G.703, the attenuation at a frequency equivalent to half the nominal bit rate shall be as given below: Monitoring points at 64 kbis, 2048 kbis, 8448 kbis, 34 368 kbis and 139 264 kbit/s 0 I attenuatio
35、n I3 dB for 64 kbiih. O I attenuation I 6 dB for 2048 kbit/s and 8448 kbit/s. 0 I attenudtion I 12 dB for 34 368 kbit/s and 139 264 kbit/s. 2.3.2 The digital signals presented at protected monitoring points located at digital distribution frames shall be shaped as defined in 2, 3,4 and YG.703. Howev
36、er, when terminated in the nominal impedance as given in Table 1, the nominal voltage shall be 2 1/10 of the volmge specified in Recommendation G.703. This means that the output signal at the monitoring point shall be attenuated not more than 20 dB referred to the output signal at a G.703 interface.
37、 Monitoring points at 1 544 kbis, 6 312 kbis, 32 064 kbis and 44 736 kbis Recommendation 6.772 (03/93) 3 ITU-T RECMNaG-772 (REV*l) 93 6 48b2591 0582378 925 3 Electrical characteristics of protected monitoring points provided on transmission equipments of the synchronous digital hierarchy This clause
38、 applies to equipments operating in accordance with the synchronous digital hierarchy (SDH) as given in Recommendations G.707 5, G.708 6 and G.709 7. The overhead bytes specified in Recommendations G.708 and G.709 provide extensive capabilities to monitor performance. These capabilities can be utili
39、zed by the telecommu- nications management network (TMN). In addition, protected monitoring points may be provided for temporarily monitoring the transmitted signal with the aid of external measuring equipment. 3.1 Impedances at the protected monitoring points The output and terminating impedances a
40、t the protected monitoring points shall be in accordance with Table 2. The return loss shall be 2 14 dB over a frequency range corresponding to 5% to 150% of the relevant bit rate. TABLE 2/G.772 Impedance and return loss of protected monitoring points Bit rate Impedance (kbitk) coaxial 155 520 15 i2
41、 3.2 Characteristics of monitoring points at 155 520 kbit/s incorporated in transmission equipment The nominal voltage at the protected monitoring point when terminated in a nominal impedance of 75 R shall be 2 1/10 of the voltage specified in Recommendation G.703. This means that the output at the
42、protected monitoring point shall be attenuated not more than 20 dB referred to the output signal at a G.703 interface. 3.3 Characteristics of monitoring points at 155 520 kbit/s located between transmission equipments The digital signals presented at the protected monitoring points shall be as defie
43、d in 3.1 above but modified by the characteristics of the interconnecting cable. The attenuation of these cables shall be assumed to follow a fi law. In accordance with Recommendation G.703, the attenuation at a frequency of 77 760 kHz shall be between 0 and 12 dB. Monitoring points at other bit rat
44、es are under study. 3.4 Other bit rates Monitoring points at other bit rates are under study. 4 Protection of the transmitted signai Installation of protected monitoring points shall not result in degradation of the transmitted signal exceeding the limits specified in Recommendation G.703. When conn
45、ecting any passive load to the protected monitoring point, including short and open circuit, the pulse shape of the signal on the monitored path shall still comply with Recommendation G.703. With any passive load, the voltage of the transmitted signal measured at a frequency equivalent to half the n
46、ominal bit rate shall not be different from the voltage without load by more than 0.7 dB. 4 Recommendation 6.772 (03/93) 5 Resilience of the protected monitoring point With regard to overvoltage protection, the protected monitoring points shall comply with Annex B/G.703. No damage shdl result from t
47、he application of any load impedance, including short and open circuits, to the protected monitoring points. Properly screened coaxial or balanced cables shall be used for the installation of the protected monitoring points to minimize electroniagnetic susceptibility and generation of interfering si
48、gnals. The protection against the inadvertent application of external voltages to the protected monitoring points is under study. References i 21 CCIT O-Series Recommendations. 131 4 SI 6 7 CCITT Recommendation M.60 Maintenance terttzfzology and definitions. CCIT Recommendation G.702 Digital hierarc
49、hy bit rates. CCITT Recommendation G.703 Pliysical/electrical characteristics of hierarchical digital inteq5aces. CCITT Recommendation G.707 Synchronoits digital hierarchy bit rates. CCITT Recommendation G.708 Network node irzteq5ace for the synchronoiis digital hierarchy. CCITT Recommendation G.709 Synchroizoits niitltiplexing structure. Recommendation G.772 (03/93) 5
