This will damage your router. Step 3 Connect the ISDN cable provided with the NT1 to the NT1. Step 4 Connect the other end of the ISDN cable to the ISDN wall jack. The U port connects to the telephone service provider network using the internal NT1. Figure 3-4 shows the ISDN U port connection.
Caution Always connect the red cable to the red U port on the router.
Do not connect the cable to a yellow Ethernet port. This will damage your router. To connect an ISDN line to the U port on a router, complete the following steps. Step 1 Connect the red ISDN U cable to the red port labeled ISDN U on the rear panel of your router. Step 2 Connect the other end of the red ISDN U cable to the ISDN wall socket.