in a cable network providing , among others , interactive video services , data cells carrying real - time data concerning , e . g ., trick mode commands initiated by a user are instantly transmitted to a headend facility for immediate processing . the invention is premised upon a recognition that such real - time data typically does not fully utilize the transport capacity of the data cells . in accordance with the invention , non - real - time data to be transmitted to the headend facility , although accorded a lower priority than the real - time data , is inserted into those underutilized data cells before their transmission , thereby fully exploiting the transport capacity of the data cells .