Actually, the Ascend uses a card stuffed with Rockwell *analog* chipsets. So
does Cisco's AS5200 and the USR Sportster.
The USR Courier and the Livingston use a DSP chip to implement the modem in
*software* (can you say firmware update?). The advantage of this is faster
turn around times for new feature implementations and bug fixes. If rockwell
discovers a bug in a critical portion of their chip, they have to spin a new
revision. Three months would be an optimistic guess for the time involved. Also,
it's kinda inconvenient to unsolder all those chips from the PC boards.
With a DSP implementation, the vendor distributes a firmware update - that's it.
There is a downside though. Manufacturers tend to select a DSP chip that can
just barely do the job. Along comes a new modulation scheme and it turns out
that the DSP that was originally built into the product doesn't have enough
horsepower to handle to new software. Telebit was guilty of that. They released
the T2500 with an enticing song and dance about how any future CCITT standard
would be just a prom change. Unfortunately, the TI chip inside wasn't fast
enough, so we got suckered into buying T3000's...