The data compression algorithm reduces the volume of data to less than the toolkit level. The rendering stream is scanned for sequences of commands that are reversed engineered into both application and toolkit level routines. These routines are entered into dictionaries shared by both the encoding (server) and decoding (client) ends. Long sequences of rendering commands are sent by simple reference to the dictionary entries from the server to the client.
More details can be found on the URL:
http://www.ascender.com/remote-graphics