private void UpdateState(MusicOnHoldServerState newState)
        {
            MusicOnHoldServerState oldState = _state;

            _state = newState;

            EventHandler <MusicOnHoldServerStateChangedEventArgs> stateChanged = this.StateChanged;

            if (stateChanged != null)
            {
                stateChanged(this, new MusicOnHoldServerStateChangedEventArgs
                                 (oldState, newState));
            }
        }
 internal MusicOnHoldServerStateChangedEventArgs(MusicOnHoldServerState previousState, MusicOnHoldServerState newState)
 {
     _previousState = previousState;
     _newState      = newState;
 }