analog communication device assigned to the assignee hereof and incorporated herein by reference in the system described herein the analog modem rather than transmitting only in the pcm modulation mode transmits in a pulse amplitude modulation mode during the startup procedure the purpose of utilizing pulse amplitude modulation in the startup mode is to be able to characterize the communications channel in the simplest and most robust of manners by sending a limited number of analog levels to the digital modem this permits the analog modem to be set appropriately to accommodate impairments in the communications channel based on measurements taken at the digital modem the startup procedure is described in the above mentioned u s patent application it is the purpose of the startup procedure to measure the channel characteristics at the digital modem and to transmit parameters to the analog modem for configuring the transmitter structure of the analog modem in one embodiment the startup procedure begins with the sending of a set of signals in the upstream direction over the communications channel to the digital modem via pulse amplitude modulation or pam it is this set of training signals which can be utilized to determine the characteristics of the upstream direction of the communications channel once received by digital modem the digital modem receives signals sent by the analog modem and based upon the received signals calculates the characteristics of the communications channel in the upstream direction it will be noted that the signals the analog modem sends to the digital modem will likely be altered in such a way that the.