The present invention provides a method of processing data in digital broadcasting system. The method includes receiving a broadcast signal including mobile broadcast service data and main broadcast service data, wherein the mobile broadcast service data configures a data group, wherein the data group is divided into a plurality of regions, wherein known data sequences are linearly inserted in some regions among the plurality of regions, and wherein initialization data are inserted at a beginning portion of each known data sequence, the initialization data being used for initializing a memory included in a trellis encoder of a digital broadcast transmitting system, detecting known data included in the received broadcast signal, channel-equalizing the received mobile broadcast service data corresponding to the detected known data, using the detected known data, extracting a video data from the mobile broadcast service data, parsing the extracted video data by a NAL unit and decoding the parsed video data based on header information of the parsed NAL unit.