A method of operating a transmitting apparatus in a multimedia system, the method comprising: inputting at least one network layer packet; generating a link layer packet based on the at least one network layer packet; and transmitting the link layer packet, wherein the link layer packet includes a header and a payload, wherein the header comprises a base header including payload configuration information indicating a configuration of the payload, wherein if the payload configuration information is a first value, the payload configuring information indicates that the payload includes a single network layer packet and header mode information is included in the base header, the header mode information indicating whether an additional header for the single network layer packet is included in the header, wherein if the header mode information is a first value, the header mode information indicates that the additional header for the single network layer packet is included in the header, the additional header following the base header and including sub-stream identifier flag information indicating whether an optional header for sub-stream identification information is included in the header, wherein if the sub-stream identifier flag information is a first value, the sub-stream identifier flag information indicates that the optional header for the sub-stream identification information is included in header, the optional header following the additional header and including the sub-stream identification information indicating an identifier used to identify a specific sub-stream related to the at least one network layer packet in a link layer packet stream. inputting at least one network layer packet; generating a link layer packet based on the at least one network layer packet; and transmitting the link layer packet, wherein the link layer packet includes a header and a payload, wherein the header comprises a base header including payload configuration information indicating a configuration of the payload, wherein if the payload configuration information is a first value, the payload configuring information indicates that the payload includes a single network layer packet and header mode information is included in the base header, the header mode information indicating whether an additional header for the single network layer packet is included in the header, wherein if the header mode information is a first value, the header mode information indicates that the additional header for the single network layer packet is included in the header, the additional header following the base header and including sub-stream identifier flag information indicating whether an optional header for sub-stream identification information is included in the header, wherein if the sub-stream identifier flag information is a first value, the sub-stream identifier flag information indicates that the optional header for the sub-stream identification information is included in header, the optional header following the additional header and including the sub-stream identification information indicating an identifier used to identify a specific sub-stream related to the at least one network layer packet in a link layer packet stream. <EOS>