1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T L.25 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2015) SERIES L: CONSTRUCTION, INSTALLATION AND PROTECTION OF CABLES AND OTHER ELEMENTS OF OUTSIDE PLANT Optical fibre cable network maintenance Recommendation ITU-T L
2、.25 Rec. ITU-T L.25 (01/2015) i Recommendation ITU-T L.25 Optical fibre cable network maintenance Summary Recommendation ITU-T L.25 deals with general features in relation to the maintenance and operation of optical fibre cable networks. This is the latest revision of a Recommendation that was first
3、 published in 1996. This revision is intended to be appropriate for the current situation with respect to optical fibre cable network maintenance and related Recommendations. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T L.25 1996-10-18 6 11.1002/1000/3889 2.0 ITU-T L.25 2
4、015-01-13 15 11.1002/1000/12411 _ * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T L.25 (01/2015) FOREWORD The International T
5、elecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating an
6、d tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce R
7、ecommendations 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-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Rec
8、ommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interop
9、erability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that
10、 compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTSITU draws 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, val
11、idity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or 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 req
12、uired to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2015 All rights reserved. No part of this publication may be reprodu
13、ced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T L.25 (01/2015) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recommendation . 1 4 Abbreviations and acronyms 2 5 Conventions 2 6 Gen
14、eral features of optical fibre cable network maintenance 2 6.1 Maintenance category . 2 6.2 General functions of optical fibre cable network maintenance 3 7 Relationship between recommendations relevant to maintenance of optical fibre cable networks 4 Appendix I Japanese experience . 6 I.1 Introduct
15、ion 6 I.2 Scope 6 I.3 Concept of optical fibre cable network maintenance . 6 I.4 Functions required for optical fibre cable network maintenance . 10 Appendix II UK experience 13 II.1 Introduction 13 II.2 Preventative maintenance surveillance 13 II.3 Preventative maintenance testing 13 II.4 Preventat
16、ive maintenance control 14 II.5 Post-fault maintenance surveillance 14 II.6 Post-fault maintenance testing . 14 II.7 Post-fault maintenance remedy . 14 Bibliography. 15 Rec. ITU-T L.25 (01/2015) 1 Recommendation ITU-T L.25 Optical fibre cable network maintenance 1 Scope This Recommendation describes
17、 the general features and definitions for the maintenance and operation of optical fibre cable networks for use in telecommunication services. The objective of this Recommendation is to identify the general functions of optical fibre cable network maintenance, and to provide information on relevant
18、Recommendations in the field of maintenance and operation of optical fibre cable networks. This Recommendation deals with non-gas pressurized cable networks. The maintenance and operation of the transmission equipment and facility management are not dealt with in this Recommendation. Submerged optic
19、al fibre cable such as that used in submarine systems is also not dealt with in this Recommendation, which is described in, for example, ITU-T G.979. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions
20、of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and
21、 other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.979 Recommendation ITU-T G.979 (2012), Characteristi
22、cs of monitoring systems for optical submarine cable systems. 3 Definitions 3.1 Terms defined elsewhere This Recommendation does not use terms defined elsewhere. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms relevant to optical fibre cable network maintenan
23、ce: 3.2.1 control: Activities to make arrangements on NEs for the purpose of maintenance. 3.2.2 customer service operation: A service operation designed to handle requests and complaints from customers. 3.2.3 fault: An undesirable event occurring in NEs, fibres or cables that provide telecommunicati
24、on services. It includes events that interrupt services and their causes. 3.2.4 fibre identification: To identify a target optical fibre in an optical fibre cable network. 3.2.5 fibre transfer: To splice one fibre to an alternate fibre during cable repair work, re-routing or network reconfiguration.
25、 3.2.6 maintenance support, testing and monitoring system: Systemized functions for optical fibre cable network maintenance. 2 Rec. ITU-T L.25 (01/2015) 3.2.7 optical fibre cable network: A network between transmission equipment that is composed of network elements (NEs): optical fibres and cables;
26、optical components such as optical splitters; and test access devices. 3.2.8 optical fibre identification: A technique for fibre identification by measuring certain optical characteristics to avoid incorrect cutting and/or connection of an optical fibre at a worksite. 3.2.9 optical fibre line: The o
27、ptical path between terminal equipment. 3.2.10 outside plant database: A facility database of optical fibre distribution that contains information on all physical cables and supporting infrastructures. 3.2.11 post-fault maintenance: Tasks performed after fault recognition. It includes tasks for iden
28、tifying fault locations and restoring the network to an operational condition such that it is capable of providing telecommunication services. 3.2.12 preventative maintenance: (Also known as preventive maintenance) Tasks performed to ensure that NEs are fully operational and capable of providing tel
29、ecommunication services. It includes tasks for detecting faults that affect (or have the potential to affect) telecommunication services. 3.2.13 surveillance: Activities to monitor NEs for the purpose of observing the operational condition. 3.2.14 test access device: A coupler for launching a test l
30、ight into an optical fibre line. 3.2.15 testing: Activities for evaluating faults and the condition of NEs after installation, and for identifying fault locations. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: B-OTDA Brillouin Optical fibre Time Doma
31、in Analysis NE Network Element NEC Network Element Control OLT Optical Line Terminal OTDR Optical Time Domain Reflectometry PDS Passive Double Star PON Passive Optical Network SEM System Element Manager WDM Wavelength Division Multiplexing 5 Conventions None. 6 General features of optical fibre cabl
32、e network maintenance 6.1 Maintenance category Tasks performed by telecommunication operators with respect to the maintenance of optical fibre cable networks fall into two categories: preventative maintenance and post-fault maintenance. Rec. ITU-T L.25 (01/2015) 3 6.1.1 Preventative maintenance Prev
33、entative maintenance activities consist of surveillance, testing and control. These activities shall be planned and are undertaken before major failures occur or are based on network provisioning. When preventative maintenance is performed under in-service conditions, care should be taken to avoid i
34、nterfering with telecommunication services, except when it involves planned construction where fibres require cutting. 6.1.2 Post-fault maintenance Post-fault maintenance activities consist of surveillance, testing and control. Depending on the seriousness of the fault, the restoration shall be perf
35、ormed immediately after a fault occurs or deferred in accordance with given maintenance rules. Post-fault maintenance is triggered by the detection of a fault from, for example, transmission systems (detecting alarms from transmission equipment), customer operation systems (detecting a complaint fro
36、m a customer) or as the result of preventative maintenance. Some appropriate interface is required that is not limited to systematic approaches. 6.2 General functions of optical fibre cable network maintenance The general functions for each category are listed in Table 1. Functions in preventative m
37、aintenance are optionally selected in accordance with maintenance rules established by the telecommunication operators. Functions in post-fault maintenance are normally required. 6.2.1 Surveillance The faults in optical fibre cable network have a number of origins. Fibre loss increase, fibre strain
38、increase and change in reflectance are considered as typical origins of faults. Furthermore, water penetration into closures, which has the potential to cause such problems as mechanical degradation, a hydrogen loss increase in optical fibre and a connector loss increase, is also considered to induc
39、e faults. Surveillance is performed by monitoring optical fibre/optical components, periodically or continuously, to detect faults and their origins as part of a programme of preventative maintenance. Monitoring the condition of the transmission equipment or reports from customer service operation s
40、ystems is considered to constitute surveillance in post-fault maintenance. 6.2.2 Testing Testing is performed to identify the location of faults and their origins or the condition of optical fibre cable networks. If a fault that affects service occurs, action should be taken to determine whether the
41、 fault is in the transmission equipment or the optical fibre cable network. Testing is also performed to confirm the condition after the installation and restoration of an optical fibre cable network. 6.2.3 Control Control involves making certain arrangements for an optical fibre cable network for t
42、he purpose of maintenance. Optical fibre between transmission equipment and a customer is sometimes transferred as a result of planned construction or restoration. Such fibre transfer is considered to be a control operation. If restoration is necessary, optical fibre has to be repaired, re-routed or
43、 replaced. To perform a control activity, the optical fibre must be identified at any location in the optical fibre cable network. Fibre identification is performed in conjunction with the use of outside plant database. An appropriate interface or support system is required with such systems. 4 Rec.
44、 ITU-T L.25 (01/2015) Table 1 General functions of optical fibre cable network maintenance Maintenance category Maintenance activity Functions Status Preventative maintenance Surveillance (e.g., periodic testing) Detection of fibre loss increase Detection of fibre deterioration Detection of water pe
45、netration Optional Optional (Note 1) Optional Testing (e.g., fibre degradation testing) Measurement of fibre fault location Measurement of fibre strain distribution Measurement of water location Optional Optional (Note 1) Optional Control (e.g., network element control) Fibre identification Fibre tr
46、ansfer Optional Optional (Note 2) Post-fault maintenance Surveillance (e.g., reception of transmission system alarm or customer trouble report) Interface with transmission operation system Interface with customer service operation Required Required Testing (e.g., fibre fault testing) Fault distincti
47、on between transmission equipment and fibre network Measurement of fibre fault location Confirmation of fibre condition Required Required Optional (Note 3) Control (e.g., cable repair/removal) Restoration/permanent repair Fibre identification Fibre transfer Required Required Required (Note 2) NOTE 1
48、 Further study is required. NOTE 2 Fibre transfer may be achieved in a variety of ways, for example: by use of fibre transfer splicing (optionally synchronous); by switching the transmission equipment to prior connected standby circuits which may be provided by a ring topology or diverse or duplicat
49、ed fibre feeds. NOTE 3 Confirmation after installation is recommended. 7 Relationship between recommendations relevant to maintenance of optical fibre cable networks Relationships between the various Recommendations relevant to the maintenance of optical fibre cable networks are shown in Figure 1. Rec. ITU-T L.25 (01/2015) 5 L . 2 5 (1 5 )_ F 0 1Ma i n t en an cew av el en g t hb -I T U -T L . 4 1 In -s er v i ce t es t i n gb -I T U -T L . 6 6 PO N s an d ri n gn et w o rk sb -I T U -T L . 5 3 H i g h p o w ers
