Minn. R. 7810.5400
INTEROFFICE TRUNKS
Local interoffice trunks shall be provided so that at least 95 percent of telephone calls offered to the group will not encounter an all-trunks-busy condition. For toll connecting trunks, this figure shall be at least 97 percent. When the completion rate falls below 95 percent on a continuing basis investigative or corrective action should be initiated.