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SAE J2735-Draft-Rev15 [issued: 01-30-07]
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116 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
zones, and roadside events are the ones most frequently expected to be found in use.
This message is for the alerting of roadway hazards; not for vehicle cooperative communications, mayday, or other
safety applications (see SAE J2735 for these). It is generally presumed that each receiving device is aware of its
own position and heading, but this is not a requirement to receive and understand these messages. Nor is having
a local base map.
The space vector section of the message gives a simple vector for where the hazard is located (fixed or moving)
and can be used to filter some messages as being not applicable. Consider a "train approaching" message which
indicates the train is in fact traveling away from the receiver. The basic messages types themselves are
represented in the standard ITIS codes send only in their integer representation formats. This ITIS list is national in
scope, never outdated (items can only be added), and in this use does not allow local additions, refer to SAE
J2540.1 for the complete code list. A priority level for the message is also sent, which may be matched to various
other priorities in the cockpit to determine the order and type of message presentation to minimize driver
distraction. Message transmission priority is typically handled in the IEEE 1609 standard layer in the application
stack and is a function of the application type. A duration field provides a gross level for the range (distance) of
applicability for the message over distance. For example, some messages are no longer meaningful to the traveler
once the vehicle has moved a distance down the roadway link.
In many cases a complex event will also be explained in the other ATIS messages, and a linkage value is given in
those cases when such data is available. Note that this message is often hard coded in transmission, that the
byte ordering is known and fixed, and therefore no tagging is required to denote internal elements. The tail element
is not used when transmitted over DSRC media and using the Wave Short Message (WSM) protocol to preserve
the fixed and known byte size of the message. The message in this form is exactly 37 bytes in length.
ASN.1 Representation:
RoadSideAlert ::= SEQUENCE {
typeEvent ITIS.ITIScodes,
-- a category and an item from that category
-- all ITS stds use the same types here
-- to explain the type of the
-- alert / danger / hazard involved
-- two bytes in length
description SEQUENCE (SIZE(8)) OF ITIS.ITIScodes,
-- eight ITIS code entries to further
-- describe the event, give advice, or any
-- other ITIS codes
-- non used positions are set to zero
-- 16 bytes in length
priority Priority,
-- the urgency of this message, a relative
-- degree of merit compared with other
-- similar messages for this type (not other
-- message being sent by the device), nor a
-- priority of display urgency
-- one byte in length
extent Extent,
-- the spatial distance over which this
-- message applies and should be presented
-- to the driver
-- one byte in length
spaceVector SpaceVector,
-- a compact summary of the position,
-- heading, rate of speed, etc of the
-- event in question. Including stationary
-- and wide area events.
-- 15 bytes in length
furtherInfoID FurtherInfoID
-- a link to any other incident
-- information data that may be available
-- in the normal ATIS incident description