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SAE J2735-Draft-Rev29 [issued: 12-11-08]
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This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
Probe Data Message Sets Received By an RSU
When an RSU receives a Probe Data Message Set it will send the data to the RSU’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.
Local systems, if authorized, can subscribe to probe data directly from the RSU. This will allow local
systems and signal controllers to use probe data directly and significantly reduce bandwidth requirements.
Vehicle Anonymity
Probe snapshots when sent to the RSU and forwarded to an SDN publish/subscribe service normally will
contain no record
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of the originating vehicle nor will there be any information that directly links one
snapshot with another snapshot. To aid anonymity:
The collection of snapshots does not begin until 500m after the vehicle start up. All snapshots are
purged from vehicle memory as they are sent to an RSU and when vehicle is turned off.
Probe Data Security
Probe Data Message Sets are sent, unicast, to the RSU. The RSU will NOT send an acknowledgement
back to the OBU; 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
Probe Data Message Management
This message is broadcast from the RSU to all vehicles. Its purpose is to change the snapshot generation
characteristics of the OBU. For example, the OBU can be instructed to take snapshots more frequently and
transmit them more often. It does not change the snapshot message.
Probe management is temporary. By default a probe message management process ceases when a new
RSU that supports probe messages is contacted. This case overrides the termination settings below.
Probe messages can be set to terminate as follows:
A time-based duration expires
A distance-based length has been traversed, or
A vehicle is out-of-range of the current RSU
When a probe management message terminates the default conditions again operate in the OBU unless or
until a new probe management message is received. Probe management messages can perform the
following functions either singly or in combination:
Control the production of snapshots by either distance or time
Direct the management message to vehicles moving in specified directions
Control how often snapshots are transmitted
Be applied to only a random sample of vehicles
Modify the thresholds of when event snapshots are triggered
Modify the thresholds of start/stop snapshots
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Some pubic fleet vehicle types may provide additional identity information.