High speed two wire modem

摘要

A two wire modem selects a carrier frequency in a baud rate from a predetermined plurality of carrier frequencies and baud rates to communicate with another modem over a communication media in a full duplex mode based on signal and echo characteristics of the communication media estimated by the modem. In addition, the processes of estimating channel characteristics and estimating range are combined in a common start up procedure comprising a plurality of successive time segments for a call modem to communicate with an answer modem over a communication media. Still further, a method is provided for switching from a primary communication media connection to a secondary connection of a data communications network for communication by first and second modems coupled to the network. More specifically, when a failure is detected in the primary connection, the secondary connection is qualified before switching thereto. Similarly, while communicating over the secondary connection, the primary connection is qualified so that communication may be restored thereto at some later time.