Sometimes, requesting that the sender retransmit data whenever there is an error is too costly, so Forward Error Correction is used. Extra information is sent along with each transmission so that certain types of errors can be fixed without requiring data to be retransmitted. This idea depends on the use of Hamming distance to assess which of several possible codewords from a dictionary was the most likely codeword originally sent. Much of this material is based on content from the book Data and Computer Communications by William Stallings.