/**
     * The method is called by a ProtocolProvider implementation whenever a change in the
     * registration state of the corresponding provider had occurred.
     *
     * @param evt ProviderStatusChangeEvent the event describing the status change.
     */
    public void registrationStateChanged(RegistrationStateChangeEvent evt) {
      if (logger.isDebugEnabled())
        logger.debug(
            "The provider changed state from: " + evt.getOldState() + " to: " + evt.getNewState());

      if (evt.getNewState() == RegistrationState.REGISTERED) {
        opSetPersPresence =
            (OperationSetPresenceSipImpl)
                sipProvider.getOperationSet(OperationSetPersistentPresence.class);
      }
    }