Redundancy is a much requested feature in telecom applications. IDT's recently released HD-LIU family products have built in fully internal termination features that enable total relay-less redundancy for HPS applications. However, earlier released ULIU (universal LIU) and transceiver (SuperJet) devices require an external resistor for different termination schemes. Based on different system conditions, different redundancy schemes are proposed. In each redundancy scheme proposal, it is assumed that transmit direction will be put in High-Z state for redundant card. The figure below shows a scheme used for designs that allow a separate I/O card on which magnetic component and an external resistor reside. In this configuration, primary card is in normal operation while Standby card is configured to be in high-impedance state. When primary card fails, standby card will be switched to “working mode” from high-impedance state within 2μs. The switch-over applies to both transmit and receive. Refer to application note AN-858 for more details. For other questions not addressed by the Knowledge Base, please submit a technical support request.