How to use the pynetdicom.PDU.AsynchronousOperationsWindowSubItem function in pynetdicom

def ToParams(self):
        tmp = AsynchronousOperationsWindowSubItem()
        tmp.MaximumNumberOperationsInvoked = \
                                    self.MaximumNumberOperationsInvoked
        tmp.MaximumNumberOperationsPerformed = \
                                    self.MaximumNumberOperationsPerformed
        return tmp

???
        
    Returns
    -------
    sub_item
        The PDU sub item type
    """
    ItemType = NextType(Stream)
    if ItemType == 0x52:
        return ImplementationClassUIDSubItem
    elif ItemType == 0x51:
        return MaximumLengthSubItem
    elif ItemType == 0x55:
        return ImplementationVersionNameSubItem
    elif ItemType == 0x53:
        return AsynchronousOperationsWindowSubItem
    elif ItemType == 0x54:
        return SCP_SCU_RoleSelectionSubItem
    elif ItemType == 0x56:
        return SOPClassExtentedNegociationSubItem
    elif ItemType is None:
        return None
    else:
        raise #'Invalid Sub Item', "0x%X" % ItemType

def MaximumOperationsInvoked(self):
        """
        See PS3.7 D3.3.3
        
        Optional
        
        Returns
        -------
        int
            Association Requestor's MaximumOperationsInvoked
        """
        for ii in self.UserData:
            if isinstance(ii, AsynchronousOperationsWindowSubItem):
                return ii.MaximumNumberOperationsInvoked

elif item_type == 0x21:
        return PresentationContextItemAC()
    elif item_type == 0x30:
        return AbstractSyntaxSubItem()
    elif item_type == 0x40:
        return TransferSyntaxSubItem()
    elif item_type == 0x50:
        return UserInformationItem()
    elif item_type == 0x52:
        return ImplementationClassUIDSubItem()
    elif item_type == 0x51:
        return MaximumLengthSubItem()
    elif item_type == 0x55:
        return ImplementationVersionNameSubItem()
    elif item_type == 0x53:
        return AsynchronousOperationsWindowSubItem()
    elif item_type == 0x54:
        return SCP_SCU_RoleSelectionSubItem()
    elif item_type == 0x56:
        return SOPClassExtendedNegotiationSubItem()
    elif item_type is None:
        # if we are at the end of stream
        return None
    else:
        raise ValueError("During PDU decoding we received an invalid "
                    "PDU type: %s" %pdu_type)