US Patent 7639001 Built-in test for high speed electrical networks

An apparatus for providing auxiliary signals on a high speed electrical signal network is provided such that the auxiliary signals may be used for independent monitoring or communication of monitored information without affecting data or bit error rates for the primary high speed data signals. The auxiliary signals may be used as part of a built-in testing of a network, including electrical time-domain reflectometry measurements to determine fault locations in a network.