DSC = Direct Servo Control
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.

The cord hooks up from the TX to the RX and lets you adjust/test servos without sending signal from TX. This was a nice feature when everyone was running FM and you had to worry about interference.

This is the cord for my 3PK -

http://www3.towerhobbies.com/cgi-bin...?&I=LXH457&P=7