Widespread problems with cellphone service around Boston on Monday after the Marathon bombings put the limits of the nation’s wireless network into sharp relief, as the nation’s top carriers were unable to cope under the heaviest loads during the most crucial moments.
Verizon Wireless, AT&T, and Sprint were all overwhelmed by the surge in traffic, leaving many at the scene of the explosions unable to contact family or friends, and blocked other callers in the area or outside Boston from checking on those attending the Marathon.
Hari Balakrishnan, a computer science professor at the Massachusetts Institute of Technology, said the shortcomings Monday demonstrate that wireless networks have to be upgraded to function better during disasters, when authorities and people most need to use mobile phones.
“We ought to be investing in designing disaster relief networks,” said Balakrishnan, who leads MIT’s Networks and Mobile Systems groups. “We have to make more flexible networks.”
While nationwide wireless coverage has vastly improved since the attacks of 9/11, after which much of the cellphone service in New York failed, the use of cellphones and smartphones has become much more commonplace, too. And wireless networks have not been able to withstand sudden increases in calling loads during natural disasters such as hurricanes Sandy and Irene, the earthquake in Virginia in 2011, or the attack in Boston on Monday.
Currently, wireless towers are designed to only handle a certain amount of call volume, and call blocking can occur when too many calls are made from a certain geographic location or via a certain network’s cell tower.
But Balakrishnan said that during intense calling periods, cellular carriers should be able to deploy additional technology, such as routing overflow calls to nearby Wi-Fi networks. Researchers have been studying models that could work more efficiently during these kinds of emergencies, he said, and the technology exists to deploy them.
“It’s time to make it real,” said Balakrishnan.
The Federal Communications Commission, which regulates the wireless industry, would not comment on the performance of the local cell networks Monday.
Wireless network providers said they had boosted coverage prior to the Marathon in anticipation of intense usage, which may have kept the networks from collapsing completely under the flood of calls.
In normal conditions, the cell coverage in the Back Bay area in Boston is considered to be good, according to RootMetrics, a Bellevue, Wash., company that measures mobile coverage around the country.
But wireless carriers would have to invest potentially billions of dollars to upgrade networks to handle every tidal wave of traffic that would follow an event like Monday’s bombing — an investment that RootMetric chief executive Bill Moore said would not be practical.
“They can’t build networks for the fraction of the percent of cases that something like this would happen,” said Bill Moore, chief executive officer of RootMetrics. “If every cellular company built for a terrorist attack, they would spend so much on infrastructure that no one would be able to afford services.”
While many callers were left unable to dial out on cellphones, emergency officials and first responders do have priority calling on wireless networks that can allow them to get through during heavy-use periods.
On Monday the cellphone overload did not hamper efforts on the ground, said Peter Judge, a spokesman for the Massachusetts Emergency Management Agency.
Much of the emergency communication was done via radio, he said.
Still, wireless carriers such as Verizon did turn up capacity after the explosion to enable additional calling, the company said Tuesday.
None of the carriers would comment on Monday’s call traffic or whether they need to increase capacity in the event of an emergency.
Verizon Wireless, AT&T, Sprint, and T-Mobile all reported that their network services returned to normal on Tuesday.