A device for generating a block sequence number in a communication system
for transmitting frames comprised of a block sequence number and a
succeeding data field. The block sequence number is assigned to every
block unit corresponding to a multiple of the byte to transmit the
increased number of data bits, so that the data bits in at least one of
the frames can be verified in byte unit at a receiving side. A difference
D is calculated between a first byte sequence number A of m bits
indicating a first byte of transmission data and a second byte sequence
number B of m bits indicating data of the first byte in a second block
succeeding a first block to which the transmission data belongs. The first
byte sequence number A is converted to a block sequence number of n bits
smaller in number than m bits using difference D.
