V.44 Data Compression Software

V.44, the new data compression software recently ratified by the ITU-T, improves on the existing V.42bis standard. Depending on the kind of data, compression ratios of 6:1 are attainable with V.44. When V.42 is combined with GAO’s V.92 softmodem, full advantage of both standards is realized by way of greater total throughput. For example, with a V.92 upstream connection speed of 48 kbps and 6:1 data compression the data transfer rate becomes 288 kbps. Due to physical limitations, hardware modems that depend on the use of serial ports are often limited to a maximum transfer rate of 115.2 kbps. GAO’s V.44 software consists of both an encoder and decoder. Encoding uses a dictionary consisting of a root-array of all characters, a node tree, and a history. Input is matched against previously input strings, and if a string is matched it is transferred as a codeword and an attempt is made to create a longer string in the dictionary. The decoder recreates the original string from the binary-tree dictionary.