A card, particularly a digital line card is provided for use with a chassis having a slot for receiving the digital line card. The chassis has an Ethernet bus for receiving packets from the line card and has a power supply and power strip for supplying power to the line card. The line card includes a public switched telephone network (PSTN) digital line input/output interface for sending digital signals over the PSTN and for receiving digital signals from PSTN. A line card control processor is connected to the digital line input/output interface. An Ethernet input/output is provided for sending packets over a local network corresponding to signals received from the telephone line and for receiving packets from the local network and forwarding received signals to the digital line input/output interface. The Ethernet input/output has a controllable backplane interface to the Ethernet bus including a switch normally active to direct data flow between the line card and the Ethernet bus, an Ethernet transceiver connectable to an Ethernet network, and an Ethernet link signal detector for detecting an Ethernet link signal at the Ethernet transceiver and deactivating the switch to isolate the line card from the Ethernet bus and to force data flow through the Ethernet transceiver. The card may also be part a network system with a chassis having a backplane Ethernet bus.