I checked the following link.
T1 CSU/DSU and modem are layer 1 device
NIC is a layer 2 device, but SDSL module card requires an external modem.
What layer device ADSL and SDSL module, layer 1 or 2 device?
ADSL, SDSL, DSL are layer 1 , you may also find more detailed information at the ITU-T link bellow.