# Testing in loopback mode

To test the digital trunk application without connecting to the telephone network, connect the CG 6060 board in loopback mode. The following illustration shows the loopback configuration using a crossover cable to connect trunk 0 and trunk 1 on a four-trunk CG 6060 board:

The cross-over cable connects the transmit signals from one trunk to the receive signals on another trunk as shown.

If your board configuration uses two optional splitter cables to use trunks 2 and 3, you can connect the splitter cables in loopback mode. Use the cross-over cable to connect the transmit signals on one of the splitter cables to receive signals on the second splitter cable.