A communication apparatus includes an acquisition unit that acquires a size of free space provided in each of a plurality of data transmission units of a first layer; an allocation unit that allocates to data of a second layer a contiguous sequence of free space from among the free space whose size is acquired by the acquisition unit, the contiguous sequence of free space being equal in size to the data of the second layer and provided in one data transmission unit of the first layer; and a multiplexing unit that multiplexes a plurality of pieces of data of the second layer into the plurality of data transmission units of the first layer according to the allocation of the free space by the allocation unit.