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In emergencies, can cell phone network overload be prevented?

High call volume temporarily flooded networks after last week's San Francisco quake

By Todd R. Weiss
November 5, 2007 12:00 PM ET

Computerworld - Within minutes of Tuesday's 5.6 magnitude earthquake that hit the San Francisco Bay Area, the number of cell phone calls on the Verizon Wireless network skyrocketed.

Twenty minutes after the 8:04 p.m. quake, instead of the normal 300,000 calls made between 8 p.m. and 9 p.m. in one area of Santa Clara County, the call volume soared to 2.3 million. Many of those calls were probably made by people trying to check on friends or relatives who lived in the vicinity of the temblor.

And many of those calls never got through because, as often happens after a major emergency, the huge number of cell phone calls overwhelmed systems that weren't built to handle such high demand. Instead of reaching their destinations, the calls received fast busy signals or messages saying that all circuits were busy.

The incident raises the question: Is this acceptable service? Or can the system be fixed so that every call can go through at anytime, no matter how many calls are being made?

It's not a yes or no answer.

Yes, it could be done, according to wireless carriers, but it would be expensive, and would lead to an overbuilt network that's needed only a few times each year.

"It's not appropriate or feasible," said Chuck Hamby, a spokesman for Verizon Wireless in Tampa, Fla., where hurricanes are a fact of life and frequently cause problems for cell phone networks. "You could build, at least theoretically, a network that has enough capacity for everyone in the United States to get on the phone at one time, but [the required switching facilities] would be the size of the Empire State Building."

Instead, wireless carriers build specific cell site buildings that can handle the capacity that's needed in each individual area, and that capacity can be increased as needed, he said.

Usually, those capacity needs are met because the wireless carriers monitor the call volumes to keep up with normal demands. But when a natural disaster or some other unusual incident occurs, demand peaks, causing the call congestion that hit the Bay Area Tuesday night. "Only in truly unusual events do you see this," Hamby said.

If cell phone systems were overbuilt to handle those occasional but huge spikes, more cell towers, which are controversial in many communities, would need to be built a lot and the added expense would be passed on to customers, he said. "That 60% overcapacity would then sit idle probably 364 days a year" until it's needed in an emergency. "It's probably not the best use of the resources."

Verizon said its systems in the Bay Area worked fine when the earthquake occurred and that all systems were back at normal performance levels 30 minutes after the event. None of its cell phone towers were damaged or lost power because of the quake, the company said.



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