The Common Digitizer 2, also known as the CD-2, is an electronic computer that takes raw (analog) siginals from a search radar and a beacon radar system (thus the term 'common') and digitizer the analog information into a digital format. It then places the information into 'tracks' (i.e., range, bearing, altitude, and aircraft ID) and sends this information to FAA Air Traffic Control Centers (also know as Air Route Traffic Control Centers - "ARTCC") for display to air traffice controllers.

The CD-2 is a second generation of digitizer being that it was a dual channel device that offered redundancy in case of a single channel failure. It's predicessor was called "Common Digitizer" (CD), it did the same job but was only a single channel, thus when it failed the ARTCC was without aircraft display input.

AFJAM11-213 3.2.1.2.1

The originating Base operations submits a flight data message specifying the fix where the ALTRV begins, followed by the amount of time required to fly from the ALTRV entry point to the ALTRV exit point, followed by the exit point and remainder of route.

example: (entry point) abc 136050/d2+30..xyz (exit point)