4. The method of claim 1 further comprising storing a history index which records when the nodes are used to represent subsequent strings of data.
1. A method of compressing digital data for transmission over a communications channel, the method comprising: determining strings of digital data; assigning a fixed size code word to a string of digital data; storing the fixed size code word and corresponding string of digital data in a dictionary as a node; storing subsequent fixed size code words as new nodes in the dictionary representing subsequent different strings of digital data ahead of the node storing the first fixed sized code word; examining a subsequent part of digital data for the string of digital data; and deleting the fixed size code word's node from the dictionary and adding the fixed size code word's node to the dictionary when a match is made between the string of digital data and the subsequent part of the digital data.