few thing need to be check
1) E1 card need to be check by giving loop, at that time you receiveing serial up , line up.
2) check cable , connectector ( RJ45 ),
3) Normally this happend due to high number of error
4) check the electrial earthing of your router.
5) Use only AT & T standard cable ( 1,2 & 4, 5 ).
I hope this will help you out.
Minu