V.42bis supports data compression during data transmission. The compression works with a variant of the LZW algorithm: LZBT algorithm, Lempel-Ziv British Telecom.
V.42bis is an effective method for data compression, specified for asynchronous data transmission with the modem; in most applications it is combined with V.42 error protection. Depending on the data structure, compression factors up to 3 are possible.
In addition, V.42bis offers Adverse Channel Enhancement( ACE) for transmission optimization and compensation of noisy transmission lines.