what is the function of the crc in the fcs
The IEEE 802.3 standard that defines the basic Ethernet framing defines the FCS field in Section 3.2.9 as follows: A cyclic redundancy check (CRC) is used by the transmit and receive algorithms to generate a CRC value for the FCS field. The FCS field contains a 4-octet (32-bit) CRC value. This value is computed as a function of the contents of the protected fields of the MAC frame: the Destination Address, Source Address, Length/ Type field, MAC Client Data, and Pad (that is, all fields except FCS).