Can the built-in NT1 on a 2600 router be looped?

[admin_2]

I work for a telco. We have a DMS-100 switch and a customer of ours has a 2610 router with a ISDN BRI with us.

I have run a NT1 loopback test , but it doesn't seem to loop.

What is troubling is, the router will no longer sync with the switch, until the router is rebooted.

Does the NT-1 support loopback codes?

[#2]

The fixed HW versions are 800-01238-04 (for the NM-4B-U)

and 800-01239-04 (for the NM-8B-U). You can see the

version of the NM-4B-U or NM-8B-U using the IOS "show

diag" command.

I do not think that the BRI's support loopback codes from the network.