.DSP is it. Rockwell refers to the Data Pump as the DSP alot.

I read carefully the document, first line of the Data Pump says, "The Data Pump driver is at the lowest end of the modem software..."

So its an INIT or DRVR in the software....

Also, the CTB is the communications toolbox that communicates with the driver to the internal modem. the CTB has a custom serial driver, so un-aware serial modem apps can treat the internal modem as if it were a serial port through emulation in the CTB.