A method of testing trunks grouped in tributaries to evaluate interoffice transmission quality across a TDM network of all trunks in the office. The method includes performing a testing cycle testing only one trunk in each tributary in the central office to verify transmission quality. Testing includes setting up an interoffice connection to the one trunk, performing a transmission test on the one trunk. The method can also include attempting a connection to every trunk in each tributary in the testing cycle. The method can also include performing a plurality of testing cycles until all trunks in the central office have been tested, wherein each testing cycle includes testing one untested trunk in each tributary.