Abstract: A device for establishing boundaries in a bit stream is disclosed, which converts a first number of bits of the bit stream into a second number of bits (that is, the CRC is determined) and compares the second number of bits with a third number of bits of the bit stream. The converting means comprises discounting means for discounting the effect on the conversion process of at least one bit situated outside the first number of bits. The device establishes the boundary of the bit stream after a minimal time span, even for very high bit rates per bit shift.