Abstract: Methods, apparatus and computer program products are disclosed for structuring Protocol Data Units (PDU). A method comprises: structuring a protocol data unit to include at least one special field in a header part of the protocol data unit and a padding part of the protocol data unit, wherein the at least one special field part indicates a length of the header part and wherein a length of the padding part is based at least on the indicated length of the header part; mapping the protocol data unit onto the trans port block scheduled for transmission between a source entity and a target entity, and transmitting the transport block from the source entity.