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SAE J2735-Draft-Rev18 [issued: 06-26-07]
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197 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
4.
Sending Probe Data Message Sets To An RSE
When a vehicle encounters an RSE that advertises Application Class ID (ACID) 5 and Application Class
Mark (ACM) 3, the OBE will send a single Probe Data Message Set, comprised of several individual
messages, on the Service Channel indicated by the RSE. Probe Data snapshots that were generated due to
Triggered Events are sent first since they, more than likely, contain information about roadway conditions
that approaching drivers need to be aware of. Stop and Start snapshots are sent next followed by time
interval snapshots. The OBE will then purge all snapshots from memory and continue to collect snapshots
as described above. The OBE will send another Probe Data Message Set when it encounters another RSE
that advertises ACID/ACM 5/3.
NOTE: Each individual snapshot contains the location and time as to when the snapshot was taken.
However, as mentioned above the messages discussed here only describe the payload of the Probe Data
Message. Therefore, it assumed that the Header of each Probe Message will contain the vehicle’s current
location and the current time.
5.
Probe Data Message Sets Received By An RSE
When an RSE receives a Probe Data Message Set it will send the data to the RSE’s primary Network
Access Point (NAP). The NAP then forwards the data to the Service Delivery Node (SDN) which
maintains Subscriber Registration and Subscription information and publishes the data to all valid
subscribers such as a local Traffic Operation Center or third party Content Service Providers.
6.
Vehicle Anonymity
Probe snapshots forwarded to an SDN publish/subscribe service will contain no record of the originating
vehicle nor will there be any information that directly links one snapshot with another snapshot (even those
contained within the same probe message).
7.
Probe Data Security
Probe Data Message Sets are sent, unicast, to the RSE. The RSE will NOT send an acknowledgement back
to the OBE; therefore, if the message does not get through it’s lost. All Probe Messages will be
authenticated to ensure message validity and protect their contents. Key management is assumed to be
handled by another layer, such as the IEEE 1609.2 Security Layer
8.
Vehicle-Based Data Lifecycle
After “Key-On”, vehicles begin gathering Probe Data snapshots once they have traveled the “Key-On
Threshold” distance (default is 500m) at which time they will collect snapshots based on the time interval
or trigger events as described above or based on parameters contained in a Probe Data Management
Message received from an RSE. All snapshots are purged from vehicle memory as they are sent to an RSE
and on “Key-Off”.
9.
Probe Data Message Management
If desired, the RSE can issue a Probe Data Management Message to vehicles within its communications
range. This message is used to request additional Probe Data Messages, Modify the interval between
snapshots, or change Trigger threshold values. Once the time interval contained in the message has expired
or the vehicle leaves the reception range of the RSE that initiated the Probe Data Management Message, the
vehicle will revert back to its original setting for the collection of Probe Data snapshots.