CRC easy to compute in hardware. Block Codes Can add additional parity bits to a block to correct even more errors. Used in CD-ROM's. Hamming Codes Label 11 data bits and 4 parity bits as di and pi as shown below. 1111 Receiver computes parity and finds p1, p2, and p8 are wrong.
Receiver recomputes the remainder.
Divisors expressed as polynomials. If the block arrives correctly, new remainder is 0.