Modifying check codes in data packet transmission.

摘要

Disclosed is a method and circuit for modifying the check code (CRC1) of a data packet based on a first seed (14) to accommodate the addition or subtraction of a header (H2a,H2b). A number of bits, which include a second seed (17), an exclusive OR function of the first seed (14) and a portion (H2a) of a header (H2a, H2b) , and a string of zeros (21) dependent upon the length of an incoming data packet (16), is sent through a CRC generator. The resulting CRC calculation and the incoming packet check code (CRC1) are exclusive ORed to produce a modified check code (CRC2) taking into account the addition or subtraction of the header. <IMAGE>