WCA September 2019

Operation technology for efficient maintenance of underground optical cable By Miho Akamatsu, Chihiro Kito, Koji Mine and Takashi Ebine, of Strategic Network Management Department, NTT East, Tokyo, Japan

Abstract NTT East is developing an efficient maintenance operation system for underground optical cable. Since water penetration gradually deteriorates optical fibre cable, maintenance engineers periodically monitor water penetration of the underground optical cables. Although they spend much effort on the maintenance works, such as searching locations of water penetration and repairing closures, it is difficult to prevent water penetration in all underground cables. The company has developed a new maintenance operation system that performs automatic optical pulse tests, which allows engineers to easily manage maintenance work. The system will be useful for efficient maintenance and quality maintenance of optical fibres. 1 Introduction The number of optical IP (Internet Protocol) service subscribers of NTT has exceeded 20 million and the life cycle of them already seems to have reached its peak [1] . The optical fibre coverage is 99 per cent, and the total length of the installed optical fibre cable is almost 1.2 million kilometres. On the other hand, the number of PSTN (Public Switched Telephone Networks) subscribers was 60 million at its peak, but the number has decreased to 20 million. However, the total length of 500,000 km of copper cable has not decreased until now. NTT plans to use the copper cable network for providing the IP service, and the maintenance for legacy equipment is continuously required. Furthermore, it is planning to continue using legacy copper cables for providing the IP service, so reducing the maintenance and management cost of copper cables is an important issue. It has constructed optical fibre networks, overlaid on copper cable networks, and is facing the task of realising efficient maintenance for the telecommunications equipment. It has intensively developed operation systems for optical network construction, while on the other hand, the maintenance operation system has not proved efficient enough. This paper describes the maintenance system which promotes efficiency of operation for the water penetration in the underground optical closure.

2 Issues for underground optical cable maintenance NTT has taken measures against water penetration by installing optical cables and closures with water-blocking functions. Whilst using several solutions for water penetration, ageing degradation and cable creeping can cause water penetration into the closures. In some underground sections, it has adopted an MT (Mechanically Transferable) connector for switching cables easily. Periodic water penetration detection is necessary, because the

Underground optical closure

Water sensor module

❍ ❍ Figure 1 : Optical cable maintenance system ❍ ❍ Figure 2 : Conventional maintenance work flow

Searching location of water • Waveform

Periodical test

Length by loss • Facilities information system

Manhole constitution

Repair plan

Order

Issue individual order

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Wire & Cable ASIA – September/October 2019