In the case of packet transmission, a packet transmission apparatus divides packet data, which are received from its preceding communication apparatus, into a plurality of blocks each having a fixed block size (predetermined block size), and assigns the blocks to a plurality of transmission lines. Accordingly, the packet transmission apparatus can increase transmission capacity by use of the plural transmission lines.
In the case that a size of the packet data, which are received from the communication apparatus, is not an integral multiple of the fixed data block size, if dividing the packet data into the blocks each having the fixed block size, n (n is any integer) blocks each having the fixed block size, and one block including residual data, whose size is smaller than the fixed block size, are generated.
In the case of a method according to a related art, by carrying out a padding process in which dummy data are added to the residual data, the packet transmission apparatus makes the size of the residual data adjusted to the fixed block size. Then, the packet transmission apparatus transfers data for which the padding process is carried out. The method has a problem that data transmission efficiency is lowered, since the transferred data includes a block which has an area unused for data transmission.
In order to solve the problem, PTL 1 discloses an art to set a size of packet data, which are sent by a communication apparatus, to be equal to or smaller than MTU (Maximum Transfer Unit) defined between the communication apparatus and a transmission destination apparatus, and to be an integral multiple of a block size which is applied to a low rank transmission line. By using the method, it is avoided to generate the residual data in the division process carried out by the packet transmission apparatus which receives the packet data from the communication apparatus. Therefore, it is possible to avoid generation of the block which includes the unused area.