A network node (21), which is placed within a core network, stores a list of network elements (24) capable of forwarding a trigger message to a MTC device (10). The network node (21) receives the trigger message from a transmission source (30, 40) placed outside the core network, and then selects, based on the list, one of the network elements to forward the trigger message to the MTC device (10). The MTC device (10) validates the received trigger message, and then transmits, when the trigger message is not validated, to the network node (21) a reject message indicating that the trigger message is not accepted by the MTC device (10). Upon receiving the reject message, the network node (21) forwards the trigger message through a different one of the network elements, or forwards the reject message to transmission source (30, 40) to send the trigger message through user plane.