EuroWire July 2019

Technical Article

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

Underground optical closure

Water sensor module

▲ ▲ Figure 1 : Optical cable maintenance system ▼ ▼ Figure 2 : Conventional maintenance work flow

Searching location of water

Periodical test

• Waveform

Length by loss

• Facilities information system

Manhole constitution

Repair plan

Order

Issue individual order

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July 2019