A method of transmitting broadcast signals, includes link layer processing input packets to generate link layer packets, wherein a link layer packet of the link layer packets includes a header and a payload, wherein the payload of the link layer packet includes a segment of an input packet or concatenated input packets, wherein the header of the link layer packet includes a first field for identifying whether the payload includes the segment or the concatenated input packets, wherein the header further includes a second field for identifying a number of the concatenated input packets and third fields that are included in the header in the same order as the concatenated input packets present in the payload in response to the first field representing that the payload includes the concatenated input packets, and wherein the third fields represent a length of each of the concatenated input packets.