An apparatus for content delivery across a plurality of heterogeneous networks some of which include a source node and in-network subscriber nodes one of which is a gateway node of and between one heterogeneous network and another heterogeneous network that includes an out-of-network subscriber node, the apparatus comprising: a plurality of communication interfaces communicably coupleable to respectively the plurality of heterogeneous networks; and a processor and a memory storing executable network node instructions that, in response to execution by the processor, cause the apparatus to at least: store a database of unified identity codes, UICs, for respective categories of information, and in association with the UICs, in-network addresses of the in-network subscriber nodes subscribed to the respective categories of information, the gateway node being an in-network subscriber node to enable the out-of-network subscriber node to subscribe to at least one of the respective categories of information; receive from the source node, a query including a UIC for a category of information to which one or more in-network subscriber nodes are subscribed; and in response thereto, retrieve from the database using the UIC, one or more in-network addresses for the one or more in-network subscriber nodes; and reply to the query with the one or more in-network addresses for use by the source node to transmit content to the one or more in-network subscriber nodes, and in at least one instance in which the one or more in-network subscriber nodes include the gateway node and the one or more in-network addresses include the in-network address thereof, for the gateway node to route the content to the out-of-network subscriber node, wherein the memory stores further executable instructions that, in response to execution by the processor, cause the apparatus to further at least: store a reference table including the UICs for the respective categories of information, the reference table also stored for use by the source node to generate the query, or one or more of the in-network subscriber nodes or out-of-network subscriber node to request to subscribe to the category of information. a plurality of communication interfaces communicably coupleable to respectively the plurality of heterogeneous networks; and a processor and a memory storing executable network node instructions that, in response to execution by the processor, cause the apparatus to at least: store a database of unified identity codes, UICs, for respective categories of information, and in association with the UICs, in-network addresses of the in-network subscriber nodes subscribed to the respective categories of information, the gateway node being an in-network subscriber node to enable the out-of-network subscriber node to subscribe to at least one of the respective categories of information; receive from the source node, a query including a UIC for a category of information to which one or more in-network subscriber nodes are subscribed; and in response thereto, retrieve from the database using the UIC, one or more in-network addresses for the one or more in-network subscriber nodes; and reply to the query with the one or more in-network addresses for use by the source node to transmit content to the one or more in-network subscriber nodes, and in at least one instance in which the one or more in-network subscriber nodes include the gateway node and the one or more in-network addresses include the in-network address thereof, for the gateway node to route the content to the out-of-network subscriber node, store a database of unified identity codes, UICs, for respective categories of information, and in association with the UICs, in-network addresses of the in-network subscriber nodes subscribed to the respective categories of information, the gateway node being an in-network subscriber node to enable the out-of-network subscriber node to subscribe to at least one of the respective categories of information; receive from the source node, a query including a UIC for a category of information to which one or more in-network subscriber nodes are subscribed; and in response thereto, retrieve from the database using the UIC, one or more in-network addresses for the one or more in-network subscriber nodes; and reply to the query with the one or more in-network addresses for use by the source node to transmit content to the one or more in-network subscriber nodes, and in at least one instance in which the one or more in-network subscriber nodes include the gateway node and the one or more in-network addresses include the in-network address thereof, for the gateway node to route the content to the out-of-network subscriber node, wherein the memory stores further executable instructions that, in response to execution by the processor, cause the apparatus to further at least: store a reference table including the UICs for the respective categories of information, the reference table also stored for use by the source node to generate the query, or one or more of the in-network subscriber nodes or out-of-network subscriber node to request to subscribe to the category of information.