This radio feature permits you to check servo operation without broadcasting a radio signal. A cable connects the transmitter to the receiver. Direct servo control is very useful for on-the-ground control checks.
DSC - Direct Servo Control

Futaba Description:
Direct Servo Control (DSC): High-end convenience feature which allows control/adjustment of servo function without sending signal through receiver. Requires optional DSC cord (FUTM4250) and DSC-compatible receiver such as R149DP and R113IP.