Japan assesses network damage
Following the March 11 earthquake in Japan, the national telecoms network appears to have fared well. Despite a burst of traffic after the quake as customers attempted to contact friends and family, traffic management was able to prevent disruption to emergency communications, causing some congestion for ordinary customers. Several submarine cables were damaged, but Japan’s international infrastructure is highly diverse, and service disruption was manageable.
Japan’s major telcos have been able to restore some fixed and mobile services in the worst affected areas, but the remaining problems will be harder to fix. We expect that some new problems will emerge in the coming weeks as stressed or damaged infrastructure fails, both on land and undersea.
Power shortages have led to rolling blackouts across the country, and these have disrupted access to fixed broadband and VoIP as terminal devices have been left without power.
Earthquakes damage telecommunications infrastructure in several ways. The vibrations from the quake, apart from shaking electronic equipment and civil infrastructure, can cause soil to liquefy, stressing or breaking pits, ducts, and cables. Liquefied soil can also enter pits and ducts.
Residual shearing, compression, and tension stresses in surrounding rock and soil also damage infrastructure, which can result in failure days or weeks after the initial earthquake.
Damaged ducts and pits can allow water to enter the system, which causes other failures, and undersea cables are particularly vulnerable to this threat. As a result, it is highly likely that further failures will occur.
The two key infrastructure failures were the loss of fixed backhaul routes servicing fixed and mobile communications in the earthquake affected area, and losses of power as generator fuel and battery backups were depleted. On March 14, the Japan Times quoted NTT East, the main service provider in northeastern Japan, which stated that 880,000 fixed lines were out of service in the region.
It also quoted the Internal Affairs and Communications Ministry, which stated that 11,400 mobile base stations were inoperative. Nationally, the majority of infrastructure remained functional, and data centers seem to have been largely unaffected.
While there was some disruption to international communications due to several reported cable breaks, international connectivity was surprisingly robust, particularly in comparison to the Taiwan earthquake of 2006, which severely disrupted communications in that country.
Since the earthquake, significant progress has been made towards repairing the damage. While fixed service disruptions are still a problem, service is gradually being restored. NTT DoCoMo, which reported that 6,720 of its mobile base stations were inoperative on March 12, announced that only 2,130 were still inoperative on March 15.
KDDI initially had 3,800 base stations out of service, which it has since reduced to 1,500, while Softbank has reduced its number of inoperative base stations from 3,786 to 1,157. Traffic restrictions are in place in areas where capacity is still limited.
Progress in repairing mobile communications has been faster than for fixed communications. This may be because operators have prioritized the mobile network, and if so, this makes perfect sense.
Fixed communications have been vulnerable to the rolling power blackouts across the country, which have been caused by power shortages arising from damage to power plants. As VoIP terminals and broadband modems are inoperative without mains power, it has meant that users are relying heavily on mobile communications.
It is likely that operators have focused on the easiest repairs, and will find the remaining base stations harder to fix. Operators have resorted to using temporary base stations in the worst affected areas to support emergency teams. Mobile data traffic restrictions remain in place in many areas as the remaining infrastructure is stretched to the limit.
The robustness of Japan’s network was due to two main factors.
The density and diversity of the networks within and out of Japan creates many redundancy paths, which prevented major service disruption outside of the worst affected areas.
Operators have installed specialized civil works which can cope with earthquakes, having learned many lessons from the Kobe earthquake of 1995.
Flexible underground conduits between street infrastructure and buildings, sliding joints for ducts to relieve axial forces, and flexible joints in manhole and other access tunnels have become commonplace in new installations since 1995.
However, none of these initiatives have helped the vulnerability of fixed communications devices to power disruption. Even if operators can keep their fiber infrastructure operational, it is of little use if power for terminal devices is not maintained. This problem is likely to grow as the number of networked consumer devices for the fixed network grows.