Provided are a transmitting apparatus, a receiving apparatus and controlling methods thereof. The transmitting apparatus includes: at least one processor configured to implement a packet generator which generates a packet including a header and a payload based on a plurality of input packets; and a signal processor which signal-processes the generated packet, and a transmitter configured to transmit the signal-processed packet. A base field included in the header includes a first field set to a first value representing that the base field is a first length or a second value representing that the base field is a second length.