911 Services

Risks of overloading 911 systems during weather or other emergencies is increasing thanks to the changing call patterns including increased traffic on wireless networks, finds a report from Alliance for Telecommunications Industry Solutions (ATIS (News - Alert)).

ATIS’ Network Reliability Steering Committee (NRSC) made several recommendations to both telecommunications service providers and Public Safety Answering Points (PSAPs) for improvements to reduce 911 outages.

These recommendations were derived based on the review conducted by ATIS in May under the instruction of the Federal Communications Commission (FCC (News - Alert)). The review analyzed why certain trunk lines serving PSAPs were being removed from service during heavy calling volumes.

When call volume increases, “wink” failures can occur between service providers’ selective routers and PSAPs that temporarily disrupt trunk lines. A wink is defined as a short signal carried over the network at the beginning and end of calls.

“During a high call volume overload to 911, the time needed for the PSAP’s customer premise equipment to be ready for the next 911 call can exceed the maximum call setup time resulting in the PSAP’s equipment not providing a wink,” ATIS officials noted.

If all the other trunks remain busy, the same call will again be offered to the same trunk. If this second offering results in a no-wink condition, the selective router trunk will be taken out of service – a situation known as a double wink failure. This situation results in a cascading effect that takes several or all trunk lines connected to local PSAPs out of service, which happened during an East Coast blizzard in January 2011.

“911 communications links are vital, particularly during emergencies,” said Susan Miller (News - Alert), ATIS’ president and CEO, in a statement. “There are important steps that service providers and PSAPs can take to prevent emergency communications networks from becoming overloaded and failing.”

ATIS’ report has outlined a set of recommendations to prevent these types of outages. It says service providers modifying their selective routers must prevent complete trunk groups from going out of service due to double wink failures.

The second recommendation states PSAPs and service providers working together must develop overflow routing to backup PSAPs during high call volumes. They must also facilitate increased communications between service providers and PSAPs during high volume periods to minimize impact, the third recommendation stated.

Lastly ATIS suggests updated procedures that would allow PSAPs to handle more calls during high volume periods must be adopted. This could include employing 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.

"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, in a statement. “Our collaboration should help prevent major 911 outages in the future and is a major step in improving the overall reliability of 911 networks."