The SuperLooperâ„¢ ISDN (BRI) Loopback Jack and Plug is used to check ISDN (BRI) cabling for broken or shorted wires and network interfaces for the simplest functionality. When installing primary network backbone circuits, the simple check of an ISDN (BRI) interface or jumper cable using the SuperLooperâ„¢ ISDN (BRI) Loopback Jack and Plug can save hours of infrastructure downtime.