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 N number of known data sequences are inserted in some regions among the plurality of regions, and wherein a transmission parameter is inserted between a first known data sequence and a second known data sequence, among the N number of known data sequences, detecting the transmission parameter from the mobile broadcast service data, symbol-decoding the received broadcast signal included in the mobile broadcast service data in block units, based upon the detected transmission parameter, extracting a video data from the mobile broadcast service data, parsing the extracted video data by a NAL unit, obtaining NAL unit type information from parsed NAL header, obtaining extension information of a NAL header, when data of a current NAL unit indicates scalable video coded data according to the NAL unit type information, and decoding the video data using the extension information of the NAL header, wherein the extension information of the NAL header includes at least one of temporal level information, quality level information, information indicating whether inter-layer prediction is used, and dependency information of the NAL unit.