How to configure PPPOA DSL on Cisco IOS Router

Hi, René, first sorry for my broken English but I am a Spanish speaker, let me tell you that your explain are excellent about the dsl configuration, but I have a doubt I am trying to configure two router cisco 857 back to back another way to say that you know is stand alone, or it is necessary something clock signal from DSLAM to ADSL router, it is just an idea because here I have a case where two building have just two wire connection between them, what do you think is it possible or not, I was trying but it doesn´t work maybe you can help me .

Thank you a lot and greetings from Central America …