V.42bis

V.42bis

(communications, standard)An extension of the ITU-T V.42standard modem protocol to included compression using aLempel-Ziv related technique, which detects frequentlyoccurring character strings and replaces them with tokens.This is similar to the Unix compress utility. Typicalcompression for text is 50% or better; with nearly 20% gainfrom synchronous conversion this gives reduces transmissiontime by almost 60%.

V.42bis

An ITU standard (1989) for analog modem data compression. It uses the BTLZ technique to achieve up to a 4:1 ratio. V.42bis implies the V.42 error checking protocol.