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SAE J2735-Draft-Rev15 [issued: 01-30-07]
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164 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
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.
10.
Application And Use With DSRC
The messages in this application are transmitted using the Wave Short Message Protocol (WSMP) stack in a
single attempt unicast mode on a Service Channel (SCH) determined by the Roadside Equipment (RSE) sent to
the RSE that has determined to receive this type of message (based on ACID value and running a suitable
application). Upon reception of such messages they are examined for content and relevance regardless of the
senders ACM.
This is a provider application that employ’s a Wave Basic Service Set (WBSS) announced by the RSE as per
IEEE 1609.4 Clause 5.3. A confirm-before-join operation is not required by the application in order to join and/or
send Probe Data snapshots. When the application receives a WME-Notification.ind (indicating a WBSS
has been joined) from the Wave Management Entity (WME), it will request access to the WBSS to send all
available snapshots.