Group recommends 911 call-handling procedures to reduce service outages

WASHINGTON, D.C. — A telecommunications group told federal regulators that telecommunications providers and public agencies that handle 911 emergency calls should look at how their telephone trunk lines react in heavy calling periods to avoid cascading service outages.

The recommendation was only one made by the Alliance for Telecommunications Industry Solutions (ATIS), in a report by the organization’s Network Reliability Steering Committee (NRSC) done at the request of the Federal Communications Commission (FCC).

Emergency 911 systems are becoming increasingly overloaded as the number of calling devices explodes and budgets to handle calls at Public Safety Answering Points (PSAPs)  –  emergency responders’ call-handling facilities  –  are reduced. Those and other conditions, said ATIS in a report issued on Nov. 2,  have led to higher risks of overloading 911 systems during weather or other emergencies, resulting in abandoned or unanswered calls. The NRSC was asked by the FCC in May to review why telecommunications trunk lines hat serve PSAPs were being automatically removed during heavy calling volumes. The group made several recommendations to both telecommunications service providers and Public Safety Answering Points (PSAPs) for improvements to reduce 911 outages.

The study found that PSAPs receive emergency calls and, at times of heavy volumes, “wink” failures occur between service providers’ selective routers and PSAPs that temporarily disrupt trunk lines. A wink is a short signal carried over the network at the beginning and end of calls, explained the group. During a high call volume overload to 911, the time needed for the PSAP’s call handling equipment to be ready for the next 911 call can exceed the call set up time resulting in the PSAP’s equipment not providing the “wink,” said the study.

It said if all the other trunks remain busy  –  as is often the case during a heavy call volume event  –  the same call will again be offered to the same trunk. If the second offering results in a no-wink condition, the selective router trunk can automatically be taken out of service in what’s known as a double wink failure, said ATIS. That could lead to a cascading effect that takes out several, or all, trunk lines connected to local PSAPs, which happened during an East Coast blizzard in January 2011, said ATIS.

ATIS’ report made multiple recommendations to prevent these types of outages. Service providers should modifying their selective routers to prevent complete trunk groups from going out of service due to double wink failures, it said.

PSAPs and service providers should work together to develop overflow routing to backup PSAPs during high call volumes.

PSAPS and service providers should increase during high volume periods to minimize impact.

PSAPs should update their procedures to allow more calls to be handled during high volume periods, include hiring more call-takers during expected weather emergencies, or shifting focus to handling as many calls as possible rather than returning calls during these volume periods, it said.

“We appreciate the hard work of the NRSC on the 911 CAMA trunk overload issue,” said John Healy, Chief Statistician of the FCC’s Public Safety and Homeland Security Bureau. “Our collaboration should help prevent major 911 outages in the future and is a major step in improving the overall reliability of 911 networks.”

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