In a memo Monday, City Manager Harry Black blamed the Comtech system's "instability" for the other outages, too.
"Because the Comtech system was inadequate, calls were lost," Black wrote. "That is unacceptable."
The city paid Cincinnati Bell more than $1 million at the start of the contract for 911 service in 2009 and pays an additional $6,750 per month. The city renewed the contract for five more years in 2014, but the deal can be terminated at any time with written notice 30 days in advance, according to the memo.
Cincinnati Bell has been working with the city to address the problems, but city officials will also issue a request for proposals to determine the best solution, Black wrote.
There have also been issues with 911 calls coming from cellphones, according to the memo. Those problems have been happening across the country, and the FCC is investigating them.