Two recent natural disasters have tested cellular networks in different ways. A 5.8-magnitude earthquake followed by Hurricane Irene struck the Eastern U.S. Call surges by cell phone users after the earthquake made voice communications difficult, if not impossible. Power outages caused by Hurricane Irene presented a different set of challenges to cellular providers. Cellular SCADA demonstrated its reliability in both instances.
Earthquakes are unannounced phenomena that leave little time to react and no time to prepare. Disasters that happen without warning often cause "mass calling events" that are essentially communications traffic jams. Cellular voice service was disrupted in Washington D.C. and surrounding areas for over an hour after the earthquake due to high call volume, which has prompted a Federal Communications Commission inquiry.
Because text data over cellular has lower bandwidth requirements than voice, text (SMS) messages were able to transmit during the disruption when voice was not. The new "Get Tech Ready" Web resource from the Federal Emergency Management Agency recommends sending text messages during emergencies because they "often have the ability to work in the event of a phone service disruption." While different than SMS, Mission SCADA has similar bandwidth requirements and utilizes the same cellular data networks for its service making it reliable during mass calling events.
Mission customers in Maryland and Virginia reported that they maintained connectivity throughout the earthquake when voice communications were down. In fact, the Mission RTU closest to the epicenter (within 22 miles) did not show a single disconnection or lost message. Mission RTUs in the Washington D.C. area maintained connectivity as well.
Hurricanes stress networks in very different ways. During and after a hurricane, disruptions in cellular communications can be caused by flooding that disconnects circuitry, power outages that last long enough to drain backup power sources or high winds that cause damage to infrastructure. Because the hurricane path is forecast well in advance, cellular providers have time to prepare. Carriers prepare by prepositioning crews and equipment for rapid deployment to repair damaged infrastructure.
After Hurricane Irene, 466,000 Baltimore Gas and Electric customers in Annapolis, Md., and greater Anne Arundel County experienced power outages. Over half the homes in the county were without power at the height of the storm. The city of Annapolis uses Mission to monitor lake levels.
Marcia Patrick, acting director of public works, reported, "We never lost communications with the Mission system and were able to keep a constant watch on levels in case we needed to notify residents of an emergency."
Approximately 1,400 cell sites were offline and more than 1,000 additional cell sites were operating on backup power in the hardest hit states of Maryland, North Carolina and Virginia. Cell towers are frequently equipped with backup power sources that enable them to continue operating until power is restored. When towers are damaged, carriers deploy COWs (cell sites on wheels) to provisionally replace offline towers until they are repaired.
The key to maintaining cellular network connectivity when a hurricane hits is preparedness. Overall, voice and data communications fared well throughout Hurricane Irene due to the rapid emergency response of cell carriers. According to a CNET and CBS News report titled, "Cell Phones 1, Hurricane Irene 0," the preparations paid off.
Cellular-based SCADA claims victory during natural disasters