This read-write enumerated value selects the line signalling method for a user port, such as loopStart(1), loopReverseBattery(2), groundStart(3), or ddiPbx. It matters because the connected telephone equipment, whether a simple analog phone or a PBX trunk, expects a specific signalling method to correctly detect off-hook, ringing, and call supervision. Setting this to groundStart(3) would be required if the port connects to a PBX trunk expecting ground-start signalling instead of the ordinary loop-start used by a standard phone.