SDSL/2B1Q is the family of SDSL flavors which are based on a Bt8970 or RS8973 bitpump.
We do not consider IDSL to be a part of the SDSL/2B1Q family because even though it uses 2B1Q modulation, it uses an ISDN U interface transceiver rather than an HDSL-derived bitpump.
We recommend the following solutions for brain-friendly connectivity to SDSL/2B1Q lines:
For Flavor B the XSB-2000 SDSL to V.35 DSU is a good choice.
We have our own OSDCU hardware that does exactly the same thing as XSB-2000 for Flavor B, but is fully open source and is also planned to support operation as a Layer 2 converter for SDSL/ATM.
We also have the Hack-o-Rocket IP router implemented as an open source software hack on the CR201s hardware platform. It supports Flavor B and even Nokia, but it's extremely Spartan at the higher levels due to the hardware not being suited to run a more generic and modular network OS.
Our goal is to bring our OSDCU/VersaDSU to full completion (both bit-transparent DSU operation for Flavor B and a Layer 2 converter for Nokia SDSL/ATM); it would then fully supplant the XSB-2000. Combined with our HECGW project it would also supplant the primitive Hack-o-Rocket IP router.