V2X

Question 1

SPaT

Answer 1

Signal, Phase, and Timing

Information about traffic signals: What phase an intersection is on, and how much time remains.

Question 2

MAP

Answer 2

A MAP message defines the intersection geography (literally a map), and is used in conjunction with a SPaT message to understand the state of the intersection

Question 3

BSM

Answer 3

Basic Safety Message

A message sent out usually at a 10Hz rate (10x a second) by a vehicle’s OBU on its given position and status.

Question 4

RSU

Answer 4

Roadside Unit
Broadcasts and receives V2X radio messages at an intersection, and communicates with the traffic controller and other services via Ethernet

Question 5

OBU

Answer 5

Onboard Unit
V2X device on a vehicle that communicates with RSUs and other OBUs. Typically sends BSMs, and listens for SPaT+MAP (and other BSMs).

Question 6

DSRC

Answer 6

Dedicated Short Range Communication
Wireless standard for sending V2X messages over radio. Has been largely replaced with CV2X although we still offer DSRC at Mcity.

Question 7

CV2X

Answer 7

Wireless standard for sending V2X messages over radio. This replaced DSRC and utilizes cellular technology

Question 8

J2735

Answer 8

SAE standard message set for V2X. This contains the definitions for “SPaT”, “MAP”, etc. (used by both DSRC and CV2X)

Question 9

IFM / IMF

Answer 9

Immediate Forward Message / Immediate Message Forward (interchangeable)
The function on an RSU to broadcast messages received via Ethernet across its radio link (usually the receiving port is UDP 1516)

Question 10

SRM

Answer 10

The function on an RSU to periodically broadcast messages that are stored locally on the device, such as MAP messages once per second. (As opposed to IMF)