Hi, devang
Unlike a normal ethernet connection, in which there are four wires between two devices, ADSL only have 2 wires between them. In the four wires situation ,you have 2 wires for transmitting data and other 2 wires for receiving data. To connect two devices back-to-back, you just need to crossover the wires on the other side, then they can talk.But this strategy no more work for ADSL connection because ADSL has only two wires. ADSL uses a different strategy to make the communication work: it devides the frequency band of the wires into 3 category: low band, medium band, and high band. Then one device (we call it ATU-C:ADSL Termination Unit Central) uses the high band to transmit data to the other side(we call it ATU-R:ADSL termination Unit Remote)
and uses the medium band to receive data from the ATU-R.
For your case, you connect two ADSL cards (both of them are ATU-R) back to back. They will send data in the same band (a kind of collision) and expect to receive data in the same band (but no one will send data on that band). It just like you connect two NICs by using a straight through cable. It won't work just at the LAYER 1.
To make the connection successful at Layer 1, you will need to connect each of them to a ATU-C on the other side. (Typically on a ISP site, where they have a device called DSLAM which binds many ATU-Cs in one device.) Only after that you can have the possibilty to make them talk on Layer 2 and Layer 3.
Here is a webpage you can refer to.
http://www.cs.tut.fi/tlt/stuff/adsl/node6.html#kuspektri
Hope this help
SSLIN
