A transmitting method of a transmitting apparatus, the method comprising: generating a ATSC 3.0 Link-Layer Protocol, ALP packet comprising a header and a payload, based on an input packet; and processing the generated ALP packet to generate a Baseband Packet, BBP, transmitted by the transmission apparatus, wherein the header comprises a base header, wherein the base header comprises a first field and a second field, wherein the first field comprises a value indicating a packet type of the input packet, wherein the second field comprises a first value or a second value, wherein the first value indicates that the ALP packet transmits one single, complete input packet, wherein the second value indicates that the ALP packet transmits a segment of an input packet or a plurality of input packets, wherein, if the second field comprises the first value, the base header comprises a third field which comprises a third value indicating that an additional header is not present or a fourth value indicating that the additional header is present, wherein, if the third field comprises the fourth value, the additional header comprises a fourth field, wherein the fourth field comprises a value indicating whether an optional header for a sub-stream identification is present, wherein, if the fourth field comprises a value indicating that the optional header for a sub-stream identification is present, the optional header comprises a fifth field which comprises a value indicating a substream identifier, and wherein the substream identifier indicates the ALP packet as being related to a substream corresponding to a specific service in an ALP stream that carries multiple services. generating a ATSC 3.0 Link-Layer Protocol, ALP packet comprising a header and a payload, based on an input packet; and processing the generated ALP packet to generate a Baseband Packet, BBP, transmitted by the transmission apparatus, wherein the header comprises a base header, wherein the base header comprises a first field and a second field, wherein the first field comprises a value indicating a packet type of the input packet, wherein the second field comprises a first value or a second value, wherein the first value indicates that the ALP packet transmits one single, complete input packet, wherein the second value indicates that the ALP packet transmits a segment of an input packet or a plurality of input packets, wherein, if the second field comprises the first value, the base header comprises a third field which comprises a third value indicating that an additional header is not present or a fourth value indicating that the additional header is present, wherein, if the third field comprises the fourth value, the additional header comprises a fourth field, wherein the fourth field comprises a value indicating whether an optional header for a sub-stream identification is present, wherein, if the fourth field comprises a value indicating that the optional header for a sub-stream identification is present, the optional header comprises a fifth field which comprises a value indicating a substream identifier, and wherein the substream identifier indicates the ALP packet as being related to a substream corresponding to a specific service in an ALP stream that carries multiple services.