There is disclosed a system for transmitting data to users. The system includes nodes interconnected by at least one data network. The nodes are organized hierarchically to comprise a root node and at least two child nodes. The data transmission characteristics of communication with each of the child nodes are different. The root node is configured to: receive data transmission preferences of a particular user; receive data to be transmitted to the particular user; and transmit a selected subset of the data to at least one of the child nodes. The subset selected based on at least the received data transmission preferences and the data transmission characteristics, to permit the particular user to obtain data from the child nodes according to the data transmission preferences. The at least one of the child nodes being configured to: receive data from the root node; and transmit at least part of the received data to the user.