Hi.
I am unfamiliar with the nokia mux, but once you take care of the more obvious (correct time-slots, framing, switch-type) TEI-Assigned usually means that the protocol emulation is wrong.
The easy way to confirm this is to add
isdn protocol-emulate network
to s1/0:15. Don't forget to clear the interface aftwerwards
also check
debug isdn q921
The normal behaviour is to get one TX and one RX.
I have experienced several behaviours when one gets hung on TEI ASSIGNED.
If you get tons of BAD FRAME on the RX packets, you have the protocol emulation wrong.
If you only get TX packets, try to place a call and see if some RX packets show up. If they do and thay are BAD FRAME, change protocol emulation. On the other hand, if they do show up without BAD FRAME that's more weird..
Cheers,
F