Deletes a Virtual Circuit connection (unidirectional).

        :param port1: input port
        :param dlci1: input DLCI
        :param port2: output port
        :param dlci2: output DLCI

def unmap_vc(self, port1, dlci1, port2, dlci2):
        """
        Deletes a Virtual Circuit connection (unidirectional).

        :param port1: input port
        :param dlci1: input DLCI
        :param port2: output port
        :param dlci2: output DLCI
        """

        if port1 not in self._nios:
            raise DynamipsError("Port {} is not allocated".format(port1))

        if port2 not in self._nios:
            raise DynamipsError("Port {} is not allocated".format(port2))

        nio1 = self._nios[port1]
        nio2 = self._nios[port2]

        yield from self._hypervisor.send('frsw delete_vc "{name}" {input_nio} {input_dlci} {output_nio} {output_dlci}'.format(name=self._name,
                                                                                                                              input_nio=nio1,
                                                                                                                              input_dlci=dlci1,
                                                                                                                              output_nio=nio2,
                                                                                                                              output_dlci=dlci2))

        log.info('Frame Relay switch "{name}" [{id}]: VC from port {port1} DLCI {dlci1} to port {port2} DLCI {dlci2} deleted'.format(name=self._name,
                                                                                                                                     id=self._id,
                                                                                                                                     port1=port1,
                                                                                                                                     dlci1=dlci1,
                                                                                                                                     port2=port2,
                                                                                                                                     dlci2=dlci2))
        del self._active_mappings[(port1, dlci1)]