The May 12, 2008 devastating earthquake in Sichuan Province, China impacted all lifelines. This paper provides a record of observed damage to the telecommunications systems in the earthquake disaster area in Sichuan as a result of the earthquake. A brief over view of the network, the components, and the standards used will be presented. Conclusions of importance of a secured network, and lessons learned will be discussed.
NETWORK, COMPONENTS, AND SERVICE PROVIDERS
The telecommunication network within China is similar to that in Europe and North America. Depending on the suppliers used, the installation methods and equipment differ from region to region. The fast pace of development in the past two decades introduced various high technology services as well as increased number of service providers. The previously state owned enterprises; China Telecom became a public company in 2002, about 15 years after the de-regulation of the telecommunication industry in North America. China Telecom, China Netcom (split off from China Telecom), China Unicom, and China Mobile are the largest service providers in China. China Mobile is the only service provider without landline service.
As it is more cost effective and quicker to provide cellular services in rural mountainous areas, China Telecom, China Unicom and China Mobile operate many cell sites in the earthquake disaster area. However, connecting all these cell sites to switching centers (called Central Offices in North America), both cables and microwave were used. Fiber optic cable is used extensively connecting cell sites and switching centers.
In the rural areas, one common characteristic of the cell sites is tall towers for the sectorized antenna. The taller tower also provides a better line of sight for microwave connection between the cell sites in the mountainous area. Most of the cell sites are situated on high ground to increase the coverage, which is enhanced by tall towers. It is quite common that the cell towers are located close to electric power transmission tower, Figure 1. There are obvious benefits: shared access, and proximity to power source. In North America there are more cell sites that use the power transmission tower for mounting the antenna as well as tapping power.
In the cities, most towers are located based on coverage and access to buildings that are not owned by the service providers, Figure 2. This practice is quite common in North America.
Figure 1. Cell site tower close to power transmission tower. Note that there is
no microwave dish on the cellular tower, indicating that landline is used to connect to another cell site or switching center.
Figure 2. The tower is supported by and associated equipment are located
in this commercial building that is not designed for lifeline facilities.
Cellular antenna
Microwave dish connecting the cell site to another cell site or switching center.
Both GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile) and CDMA (Code Division Multiple Access) technology are used in China. China Unicom network is CDMA based. Equipment manufacturers from Canada, Europe, Japan, and the United States were exclusive suppliers until 1998 when a Chinese manufacturer started marketing its own brand of cellular equipment that are developed since 1988. Therefore, in most cell sites there is a mix of electronic equipment from different countries. With the recent introduction of 3G (Third Generation) cellular services, the two cellular technologies will be converged as a single technology in delivering the services.
In most cases, installation of the equipment follows the supplier’s requirements and methods. Based on my observations, equipment from North America follows the Bell CORE (formerly Bell Lab) NEBS (New Equipment Building System) guidelines. Seismic installation requirements are based on the China Building Code seismic zoning map.
Unlike North America, there are different emergency call numbers in China. There is a number for fire department, 119, and there is one number for police department, 110. In a post disaster, multiple numbers most likely will aggregate network congestion.
PERFORMANCE
In general, lifelines in this earthquake did not perform well. Telecommunication service was not an exception. Normal network call volume typically increases immediately after a major disaster that creates the perception of telecommunication failure. In Deyang, the volume of daily busy hour calls increased 3 times its norm 500,000 calls. However, in both landline and cellular services, there were equipment building, tower and equipment failures in large cities as well as rural areas.
Most of the cell site buildings visited were unreinforced masonry (URM) and the equipment was not anchored, Figure 3. Coupled with building and equipment failure was the long duration of power loss. The batteries in the cell sites usually lasted two to three hours. Cellular service disruption in some areas within the earthquake impacted region lasted more than 60 days.
The mobile handsets depend on batteries to power the units. Usually these units when fully charged can last for a few days. With power outage in the earthquake impacted areas lasting as long as four the six weeks, even when the cell sites were repaired the hand sets did not function without power. In many communities, people with small gas power generators provided the people with free charging service.
Landline service in large cities in the earthquake impacted region performed reasonably well with inter-city call disruption of about 2 to 3 days, while intra-city call disruption was in the order 4 to 5 hours due to call volume. It is reasonable to assume that the inter-city service failure was mainly due to transmission network damage, Figure 4.
Hongkou cell sites. Two cell sites one owned by China Telecom and the other by China Mobile were located adjacent to each other and both sustained extensive damage to the buildings and the equipment inside. A new building was constructed by one of the companies to house new equipment to provide service (Figure 5), while the other company temporarily placed new equipment in the damaged building to provide service (Figure 6). A mobile power generator was used to supply power to operate the equipment due to a failed pole mount 10KV transformer near by. The 10KV transformer was replaced on the 27th of July (Figure 7).
As we traveled along the road to Hongkou, we saw many cell towers on either side of the road. We did not stop to visit all the cell sites, as it was extremely difficult and dangerous to access the cell towers on the hills. With the massive landslides and the strong shaking, there had to be some damage to the cell sites. It was not surprising that the duration of total service outage in this area was over 10 days. In fact one of the major service providers was still not available in some locations along the road to Hongkou during our visit in late July.
Figure 5. A new cell site building was built next to the damaged one on the
left.
Figure 6. The equipment in this damaged building was new, unanchored and
temporarily providing service with a limited number of channels.
Figure 7. On the right of the photo, a couple of repairmen were replacing a
10KV pole mounted transformer. The cell sites were a few meters from the pole.
Yingxiu cell site. This cell site (Figure 8) is located near Min Jiang. From an aerial photo on Xinhua News Net web site a day after the earthquake, the unreinforced masonry wall around the tower collapsed and the building housing the cellular equipment was damaged.
The top portion of the tower, where the antennas were mounted seemed to be new. A new satellite dish (Figure 9) was also installed under the tower. The equipment inside the repaired building was quite new, indicating that they replaced the damaged equipment. Some of the equipment was anchored with four 12 mm anchor bolts. A diesel power generator was also added. However, this power generator was not anchored and it had casters (Figure 10).
Shifeng cell sites. Many cell sites in Shifeng were severely damaged. New temporary cell sites (Figure 11) were installed to provide service to the communities, and particularly in the area where there were many factories damaged by strong shaking.
Figure 8. Yingxiu cell site Figure 9. Satellite dish under the tower
Figure 10. Backup power generator on casters in Yingxiu cell site.
Figure 11. Temporary cell site in Shifeng opposite to an area with many
Switching Center. We did not have the opportunity of visiting a switching center in the earthquake impacted areas. However, on our way to Nanba passing through the city called Jiangyou, we saw a telecommunication building with damaged exterior wall (Figure 12). The cell tower on the roof indicated that there was at least a cell site in this building. We did not stopped to investigate due to our tight schedule to Manba. From the investigation reported by China Earthquake Administration team, there were switching centers with toppled equipment and interior damage to the structure.
Figure 12. Damaged side wall of this telecom building.
Transmission and Distribution Systems. This network sustained the most extensive damage mainly due to landslides, rock falls and surface faulting. The continuous heavy rainfall right after the earthquake did not provide any relief. Basically wherever we went in the earthquake impacted region, we saw toppled utility poles, poles that were snapped in half, and landslide that swept away the ground supporting the pole. We also observed severed fiber optic cables on the side of the roads we travelled. Figures 13 to 16 show the various modes of failure.
Cables co-locating with bridges were severed when the bridge collapsed. Collateral damage by fallen trees and buildings were also observed.
Figure 13. Toppled utility pole with fiber optic cables in the fore ground
Figure 14. Pole snapped at about half height
Figure 15. Tree fell on the telecom cable as well as the power cables
Figure 16. This pole was hanging by the cables along the landslide created cliff
LESSONS LEARNED Equipment building. In both switching centers and cell sites, the building used to house the equipment should be constructed with a higher standard to resist damage by natural hazards in the area. In most cases, the equipment inside the building is worth much more than the cost of the building. It is also a revenue generating facility. This should be a good incentive to consider upgrading these building in the recovery action plans.
Distribution and Transmission network. A well-planned dispersed redundant network will be more resilient to disruption from natural disasters. The loop configuration that was developed during the introduction of fiber optic network in late 1990 and used by most countries would reduce the possibility of a facility totally disconnected from the network.
Co-locating. Telecommunication is not the only lifeline that uses a bridge to run cables across a river or a valley. Water and electric power also use the same access.
With the number of bridges collapsed, the telecommunication, power and water routed along these bridges were also damaged. Either avoid collocating with a bridge or design the routing along the bridge to anticipate surviving a bridge failure.
Electric Power. Electric power is usually the first lifeline that fails during a large earthquake. Although most switching centers and cell sites have their own battery reserve power, the batteries may not last longer than the power outage. For critical facilities, power generator is the only option. Remote cell sites or cell sites located in hard to access areas should have their own power generator to sustain operation. Remote power sensing is also helpful for emergency service management.
Emergency call facilities. It is not clear whether the service providers in the region operate a separate network to handle emergency call services. In China the emergency number to the Fire Department is different from that to the Police Department, 119 and 110 respectively. There is advantage to use one number for all emergency services (fire, police, and medical).
CONCLUSION
This was one of the biggest earthquakes that impacted a huge area with dense population in the world. Most of the towns, and villages are in the mountainous region. Telecommunication is one of means of connecting the communities to the outside world. One can imagine the anxiety of the people in these towns and villages that were disconnected from the rest of the world after the devastating earthquake. This disruption also made it extremely difficult for the emergency response organizations to plan their actions. The emergency response people need to know what types of resources are required by the people in the impacted areas.
A secured telecommunication system is needed in big cities as well as rural communities. The service providers should initiate a plan of actions to reduce repeated disruption and economic losses. The plan should include emergency response and recovery plans for disasters. Dispersed network redundancy in the rural areas will be an excellent option to prevent communities from total telecommunication isolation.
This is the best time for the service providers to upgrade their network components, such as equipment building, towers, transmission and distribution network, equipment anchorage, backup power generators, increase backup battery duration, and concentration.
REFERENCES
Tang, A. K., et al (2007) Preliminary Wenchuan EQ Investigation Phase I Report, http://www.asce.org/instfound/techcomm_tclee.cfm
Yuan, Y. F., Sun, B. T., et al, (Oct 2008) General Introduction of Engineering Damage of Wenchuan Ms 8.0 Earthquake, Journal of Earthquake Engineering and Engineering Vibration Vol. 28 Supplement, China Earthquake Administration report.
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