A receiving system and a data processing method are disclosed. The receiving system includes a signal receiving unit, an FIC handler, a manager, and a decoding unit. The signal receiving unit receives multiple Reed-Solomon (RS) frames comprising desired mobile service data for multiple ensembles and fast information channel (FIC) data including an indicator field, wherein the indicator field indicates whether or not the desired mobile service data are delivered through the multiple ensembles. The FIC handler obtains the indicator field from the FIC data. The manager determines at least one ensemble based upon the indicator field. And, the decoding unit decodes IP streams of the desired mobile service data from the RS frame of the determined ensemble.