A software adaptation of a Time Division Multiplexing (TDM) telecommunications line and trunk group control sub-system is described. The adaptation permits this legacy software to run under various operating systems and provide essential functions to a packet based switching system. This method of reuse permits continual use of proven and dependable software features to operate under new packet based topologies. The legacy software runs in a new soft-switch environment with minimal redesign. Timer and interrupt functions are altered to comply with off-the-shelf operating systems. Error recovery and restart operations are isolated to remove awareness from the operating system but still permit the legacy software to recover in conventional manner.