DXU 21 & DXU 11

I have few questions about DXU ports. Since DXU 11 has 2 ports, can each one of them be configured toward BSC, or one is necessery configured toward BSC and the other toward other BS.
If both can be configured toward BSC, how and where is it done.

And as far as DXU 21 is concerned, I understand that it has 4 E1/T1 ports. How they can be configured?

And one thing more can anyone tell me or send an DXU 21&DXU 11 block diagram, with interfaces described?

Thanks in advance