Police in Boston defended their communications system after two city councilors said department radio transmissions suffered a 30-minute “breakdown” during a burst of overnight violence early Monday in Dorchester when four people were shot .

That breakdown, Councilors Ed Flynn and Erin J. Murphy wrote in a letter Monday to the city’s police commissioner, Michael A. Cox , “demands immediate attention and accountability.”

Speaking to reporters after an unrelated event Tuesday, police Superintendent-in-Chief Phillip Owens said, “It was just one channel that went down.”

Owens said that officers immediately switched over to an alternate channel for communications, according to department protocol.

“Preliminary information I got, we’re working with Motorola to determine exactly what

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