Abstract: Expansion of unidirectional datacasting includes the use of backchannel communication link(s) for clients communication with the datacasting infrastructure, producing a closed-loop or bidirectional system, possibly for both the acknowledgement of datacasting message receipts and a request-response service over datacasting. In one implementation, a server creates a message including a data object and a data object identifier associated with the data object. The server datacasts the message via the broadcast medium to client device(s). A given client device receives the message datacasted by the server via the broadcast medium, creates a given message including the data object identifier, and sends the given message to the server via a given backchannel. The server receives the given message including the data object identifier from the given client device via the given backchannel and records the receipt of the given message for the data object identifier.