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SAE J2735-Draft-Rev26 [issued: 09-18-08]
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This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
Basic Encoding Rules which were developed to allow one (and only one) encoding for any specific
message content. The DER style follows the normal byte-aligned Tag-Length-Value format of BER for
ASN, consult any textbook on ASN for further³ details.
5. Message Sets
This section defines the structure of the DSRC message sets. Each message set shall be further divided into
specific messages and elements as defined in this clause and those that follow. Typically, these messages
are made up of message content internal to this document (made up of entries that are either atomic or
complex) and message content external to this document (from other functional areas and companion
volumes).
Definitions for these messages are presented in the following subclauses. The ASN is presented in a
section called "ASN.1 Representation," formerly called "Format." In a similar manner, the equivalent
XML expression is presented in a section called "XML Representation" which follows the translation rule
set cited in Clause Two (SAE J2630).
Regarding equivalent entries to be placed into a data registry. The mapping between data elements and
analogous meta data entries have been explained in other ITS stds. In addition, some meta information is
constant in this entire standard and need not be repeated with each entry here. These include the sponsor
and steward of the entries [SAE], the registration status [registered once the standard is adopted] and the
revision date [the date of the standards adoption]. The class name is always ITS.
The productions of ASN.1 which follow shall be considered normative in nature. While the majority of the
normative content is reflected in the actual syntax of the ASN.1 some entries also have additional
statements in the ASN.1 comments which shall be considered to be normative as well. In addition, the
commentary provided with each entry may also provide additional normative restrictions on the proper use
of the entry which shall be followed. The XML productions follow directly from the ASN.1 specifications
and the same rules shall be applied.
5.1 Message: MSG_RoadSideAlert
Use: This message is used to send alerts for nearby hazards to travelers. Unlike most messages which use
the LRMS profiles to describe the areas affected, this message likely applies to the receiver by the very fact
that it is received. In other words, it does not use LRMS. Typically transmitted over the Dedicated Short
Range Communications (DSRC) media, this message provides simple alerts to travelers (both in vehicle
and with portable devices). Typical example messages would be "bridge icing ahead" or "train coming" or
"ambulances operating in the area." The full range of ITIS phrases are supported here, but those dealing
with mobile hazards, construction 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
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The DSRC committee has developed a (freely available) users guide to illustrate the proper use the
messages, and part of that guide provides additional data on the rules of encoding used in the message set.
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