It determines which node the packet came from and which destination node the sender node want to ship it to. No computer knows where other computers are located, and packets are not despatched to each laptop. A Router identifies the vacation spot node handle to which a network packet must be despatched and it forwards it to the desired handle. Talking on the lowest degree of network communication, your file is converted to packets and every packet has the destination node address with it which is nothing however the IP tackle.
