A read-write enumerated value configuring the physical layer data format, PLCP or HEC, used on the DS3-ATM interface, defaulting to hec. This mapping must match what the connected ATM equipment or carrier network uses, since a mismatch prevents ATM cells from being correctly framed over the DS3 line even though the raw DS3 signal is fine. When connecting to carrier equipment that requires PLCP framing, the admin would change cmDS3AtmCellMapping from its hec default to plcp to establish correct ATM cell delineation.