Although we don't know if any DSLAM vendor has actually done so, given SDSL's HDSL heritage one can reasonably expect that someone has used the HDSL frame format in a flavor of SDSL. Given that there are different American and European HDSL standards and there are HDSL and HDSL-like systems with 1, 2 or 3 loops, one can speak of a generalised HDSL that encompasses all these variations, and this generalised HDSL can also potentially serve as a flavor of SDSL — that's what we call SDSL Flavor H.

The generalised HDSL frame format consists of N 64 kbps channels plus 16 kbps of overhead, where N can theoretically be any integer. Thus the physical bit rate of an SDSL Flavor H line (for the bitpump) would be N*64+16 kbps, which would reduce to N*64 kbps of payload after the framer removes the overhead. The payload could then be fed into an ATM TC-PHY or used as a bit stream, so we can have subflavors HA and HB. The HDSL frame structure preserves octet boundaries, so one could have octet-aligned ATM cells or octet-oriented HDLC.

Again we don't know if any DSLAM vendor has actually used SDSL Flavor H — perhaps not. It appears to not be supported by the M289xx chipset.

If anyone did implement SDSL Flavor H, it would probably be at 784 kbps, i.e., one loop out of a standard North American HDSL system. Such a service would be able to make use of standard HDSL repeaters, and that could have been one incentive for someone to implement Flavor H. (Theoretically SDSL Flavor H can use HDSL-style repeaters at any data rate, but since HDSL standards do not use any pre-activation data rate signaling, a standard commercial HDSL repeater product would be built for the standard HDSL data rates.) Thus if you find an SDSL flavor that's presented to the user as having only one data rate of 768 kbps, it might be Flavor H.