1、 International Telecommunication Union ITU-T G.974TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2007) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Optical fibre submarine cable systems Characteristics of regenerative optical fi
2、bre submarine cable systems ITU-T Recommendation G.974 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVI
3、DUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450
4、G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 General G.900G.909 Parameters for optical fibre cable systems G.910G.919 Digital sections at hierarchical bit
5、 rates based on a bit rate of 2048 kbit/s G.920G.929 Digital line transmission systems on cable at non-hierarchical bit rates G.930G.939 Digital line systems provided by FDM transmission bearers G.940G.949 Digital line systems G.950G.959 Digital section and digital transmission systems for customer
6、access to ISDN G.960G.969 Optical fibre submarine cable systems G.970G.979 Optical line systems for local and access networks G.980G.989 Access networks G.990G.999 QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OV
7、ER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.974 (07/2007) i ITU-T Recommendation G.974 Characteristics of regenerative optical fibre submarine cab
8、le systems Summary ITU-T Recommendation G.974 is concerned primarily with the system performance and interface requirements of regenerative optical fibre submarine cable systems. The physical implementation of such systems is considered separately in Annex A. Common items relevant to all the optical
9、 fibre submarine cable systems and the characteristics of optical fibre submarine cables are described in ITU-T G.971, and ITU-T G.978, respectively. Source ITU-T Recommendation G.974 was approved on 29 July 2007 by ITU-T Study Group 15 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii IT
10、U-T Rec. G.974 (07/2007) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating
11、and 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
12、 Recommendations 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 R
13、ecommendation, 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
14、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
15、 compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU 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, va
16、lidity 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 re
17、quired 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 2007 All rights reserved. No part of this publication may be reprod
18、uced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.974 (07/2007) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 3.1 Terms defined elsewhere 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Characteristics and performance of the system 2 6.1 Charac
19、teristics and performance of the digital line sections 2 6.2 Characteristics and performance of the optical sections 3 6.3 System reliability performance. 4 7 Characteristics and performance of the terminal equipment 5 7.1 General . 5 7.2 Transmission performance . 5 7.3 Actions consequent to an ala
20、rm 5 7.4 Automatic switching. 5 8 Characteristics and performance of the repeater 6 8.1 Characteristics of the signal at the optical interface. 6 8.2 Jitter performance. 6 9 Characteristics and performance of the cable. 6 Annex A Implementation of regenerative optical fibre submarine cable systems .
21、 8 A.1 Introduction 8 A.2 System configuration 9 A.3 Characteristics of the line signal. 11 A.4 System operation 11 A.5 Repeater and branching unit characteristics . 12 ITU-T Rec. G.974 (07/2007) 1 ITU-T Recommendation G.974 Characteristics of regenerative optical fibre submarine cable systems 1 Sco
22、pe This Recommendation is concerned primarily with the system performance and interface requirements of regenerative optical fibre submarine cable systems. The physical implementation of such systems is considered separately in Annex A. Common information relevant to all the optical fibre submarine
23、cable systems is described in ITU-T G.971. Common information relevant to the characteristics of optical fibre submarine cables is also described in ITU-T G.978. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute
24、 provisions 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 Recomme
25、ndations and 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.652 ITU-T Recommendation G.652 (2005), C
26、haracteristics of a single-mode optical fibre and cable. ITU-T G.653 ITU-T Recommendation G.653 (2006), Characteristics of a dispersion-shifted single-mode optical fibre and cable. ITU-T G.654 ITU-T Recommendation G.654 (2006), Characteristics of a cut-off shifted single-mode optical fibre and cable
27、. ITU-T G.702 ITU-T Recommendation G.702 (1988), Digital hierarchy bit rates. ITU-T G.703 ITU-T Recommendation G.703 (2001), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.707 ITU-T Recommendation G.707/Y.1322 (2007), Network node interface for the synchronous digita
28、l hierarchy (SDH). ITU-T G.821 ITU-T Recommendation G.821 (2002), Error performance of an international digital connection operating at a bit rate below the primary rate and forming part of an Integrated Services Digital Network. ITU-T G.823 ITU-T Recommendation G.823 (2000), The control of jitter a
29、nd wander within digital networks which are based on the 2048 kbit/s hierarchy. ITU-T G.921 ITU-T Recommendation G.921 (1988), Digital sections based on the 2048 kbit/s hierarchy. ITU-T G.971 ITU -T Recommendation G.971 (2007), General features of optical fibre submarine cable systems. ITU-T G.972 I
30、TU-T Recommendation G.972 (2004), Definition of terms relevant to optical fibre submarine cable systems. ITU-T G.978 ITU-T Recommendation G.978 (2006), Characteristics of optical fibre submarine cables. 2 ITU-T Rec. G.974 (07/2007) 3 Definitions 3.1 Terms defined elsewhere Terms used in this Recomme
31、ndation are defined in ITU-T G.972. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: BER Bit Error Ratio BU Branching Unit CTE Cable Terminating Equipment DLS Digital Line Section PFE Power Feeding Equipment TTE Terminal Transmission Equipment UBM Under
32、sea Branching Multiplexer 5 Conventions This clause is intentionally left blank. 6 Characteristics and performance of the system 6.1 Characteristics and performance of the digital line sections The digital line sections provided by the system should be in accordance with the relevant ITU-T Recommend
33、ations. 6.1.1 Characteristics of the digital signals at the system interface The recommended interface bit rates are given in ITU-T G.702, ITU-T G.703, ITU-T G.707, etc. Several interface bit rates may coexist for one single optical fibre submarine cable system. 6.1.2 Overall error performance The e
34、rror performance of an optical fibre submarine cable system should conform to ITU-T G.821 for the design life of the system. The relevant parameters are degraded minutes, severely errored seconds, and errored seconds. They are derived from ITU-T G.821 in conjunction with the performance at 64 kbit/s
35、 on a per kilometre basis. Information on the mapping of system performance at 64 kbit/s level is given in ITU-T G.821. 6.1.3 System availability The unavailable time performance is derived from ITU-T G.821, on a per kilometre basis. The DLS allocation is obtained by multiplying the per kilometre al
36、location by the digital line section (DLS) length. The system availability depends on the combined aspects of the reliability performance, the maintainability performance and the maintenance support performance of the system equipment, and particularly of the system terminal equipment. As per ITU-T
37、G.821, a period of unavailable time begins when the bit error ratio (BER) in each second is worse than l l03for a period of ten consecutive seconds. These ten seconds are ITU-T Rec. G.974 (07/2007) 3 considered to be unavailable time. The period of unavailable time terminates when the BER in each se
38、cond is better than l l03for a period of ten consecutive seconds. These ten seconds are considered to be available time. The unavailability specification applies to unavailable time caused by system component failure, and includes, for example, laser switching, terminal faults, and supervisory and m
39、aintenance operation leading to interruptions of ten seconds or longer. It does not include faults caused by trawlers or other external factors including system power feed reconfiguration time and any period during which the system is depowered for repair. Similarly, faults requiring ship interventi
40、on are not included in the unavailable time calculation. 6.1.4 Jitter performance The jitter performance of an optical fibre submarine cable system should follow ITU-T G.823 for the system design life. This applies in particular to: the jitter tolerance, for each digital line section, at the system
41、input interface; the maximum output jitter, for each digital line section, at the system output interface; the jitter transfer characteristic, for each digital line section, between the input and the output system interface. 6.1.5 Performance allocation between portions of the system The end-to-end
42、performance for a given DLS is obtained by multiplying the specified per km allocation by the DLS length. When it is necessary to allocate performance degradation to various portions in the DLS, an amount corresponding to a fixed length (usually 125 km) is allocated to each station terminal equipmen
43、t, and the submarine portion is allocated on a per kilometre basis an amount equal to the difference between the DLS specification and the terminal allocation. 6.2 Characteristics and performance of the optical sections 6.2.1 Optical power budget The errors created along the submarine portions of sy
44、stems equipped with regenerators accumulate and thus the overall error performance depends on the error performance of each optical section. The optical performance of one optical section is characterized by its optical power budget, which is the difference between the mean optical powers, expressed
45、 in dBm, at the two ends of optical section, as can be obtained taking into account the characteristics of the optical components in the equipment at both ends of the cable section. The optical power budget can be used to calculate the length of elementary cable section which permits fulfilment of t
46、he overall error performance requirement for each digital line section in the submarine optical fibre cable system. Several approaches can be used to calculate the optical power budget. They can be classified into worst-case approach, statistical approach, and semi-statistical approach. The optical
47、power budget should take into account part or all of the following parameters: Receiver sensitivity (dBm) The mean optical power in the optical signal modulated by a pseudo-random electrical signal with a specified mark density at the input of the optical fibre pigtail of a receiver, below which the
48、 receive equipment would exhibit a bit error ratio higher than 10x. Receiver optical overload (dBm) The mean optical power in the optical signal modulated by a pseudo-random electrical signal with a specified mark density at the input of the optical fibre pigtail of the receiver, above which the rec
49、eive equipment would exhibit a bit error ratio higher than 10x. 4 ITU-T Rec. G.974 (07/2007) Dynamic range (dB) The difference between the receiver optical overload and the receiver sensitivity. Mean launched power (dBm) The mean optical power in the optical line signal at the output of the optical fibre pigtail of the transmitter. The equipment internal loss (dB) The optical section loss (dB) The system performance penalty (dB) Taking into account the difference between the perf
