Upstream DOCSIS® carriers use predistortion data to cancel linear distortion. Equalization is a required step in a digital transmission system to remove linear distortion. In continuous DOCSIS downstream transmissions the equalization is done in the cable modem (CM) receiver, but in DOCSIS upstream the burst transmissions are pre-distorted by the CM so that they arrive at the cable modem termination system (CMTS) receiver with linear distortion removed. The predistortion is adjusted during a periodic process called ranging, which occurs about every 20 to 30 seconds.