The messages — what actually goes over the air.

The core North American V2V message, SAE J2735 ID 20, broadcast at a nominal 10 Hz. Part I carries mandatory state — position, speed, heading, acceleration, brake status, vehicle size, steering angle. Part II carries optional and event-driven data including hard-braking flags, path history and path prediction.

They serve the same purpose from two standards families. The BSM is fixed-rate at 10 Hz with a two-part structure; the CAM is adaptive between 1 and 10 Hz, triggered by change in the vehicle's state, and hands event-driven hazards to a separate message, the DENM. The field sets overlap heavily but are not identical, and the two are not interchangeable on the wire.

Signal Phase and Timing — the message an intersection broadcasts describing the current state of every signal movement and the time until it changes. Paired with MAP, which describes the intersection's lane-level geometry, it lets a vehicle work out which signal applies to its own approach.

A CPM shares what a station's own sensors have detected — a list of objects with position, velocity, dimensions and classification — rather than only the station's own state. It lets an equipped vehicle or roadside unit act as a sensor for unequipped road users, which is the main answer to the fitment-penetration problem. The SAE equivalent is the Sensor Data Sharing Message, ID 51.