How to Loopback Test

It is possible to configure a cable as a Loopback connector. For PRI you need to connect the Pins:

1-4
2-5

and for BRI:

3-4
5-6

When you plugin such a cable into an ISDN PRI or BRI Port which is configured as "TE" and "PTP", the L1 Link should get up and thus indicate that the BRI/PRI Port is working fine.