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SAE J2735-Draft-Rev29 [issued: 12-11-08]
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248 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
Annex D: Traveler Information Message Use and Operation
Traveler Information Introduction
Traveler Information is designed to enable broadcast advisory messages to the vehicle driver based upon
location and situation relevant information. Messages are prioritized both for delivery and presentation
based on the type of the advisory. Presentation to the driver may be in the form of text, graphics, or audio
cues.
Examples include traveler advisories (traffic information, traffic incidents, major events, evacuations, etc.)
and road signs. Traveler advisories are dynamic and temporary in nature. Conversely, road sign messages
emulate their physical counterparts and are static in nature. Differences are discussed in this document.
The message, developed by the SAE-DSRC Traffic and Traveler Information Subcommittee discussed
earlier in this standard, describes the payload of the Traveler Information Message. This Annex describes
how[CH12] [RS13]the On-Board Unit (OBU) will receive traveler information as well as how an OBU could
utilize the data prior to presentation to the driver[RS14]. The format and mode of the presentation to the
driver is left to the developer.
Traveler Information Packet Structure
The following text describes the format of a packet containing multiple individual advisories or road signs.
(Refer to Figure 1: Packet Format, on the following pages)
Packet Structure
Multiple traveler advisories or road signs may be packaged into a single packet for transmission. However,
it is recommended practice not to mix advisories and road signs within the same packet since road signs are
essentially stable whereas advisories require frequent updates. [CH16]
Each packet has a unique Packet ID. If a vehicle’s OBU has processed a packet with a particular ID, it can
then ignore subsequent packets with that same ID, updated packets will have a different ID. The
recommended Packet ID structure is an octet string which is a combination of an agency identifier in the
most significant byte and timestamp in the subsequent bytes. An example of this recommended Packet ID
structure in shown below[CH18].
packetID
OCTET STRING (SIZE(9)),
-- PacketID (9-Byte ID)
--Recommended packetID structure
Byte 1
Bytes
2-3
Byte 4
Byte 5
Byte6
Byte7
Bytes 8-
9
Agency
ID
Data Frame Header
All individual message (data frame) headers are of a common format. However, individual messages are
either of type “advisory” or “road sign”. If it is an advisory, the message ID consists of a 2-byte Advisory
Number. This Advisory Number can be used to connect to additional message content transmitted in the
ATIS message format over the TCIP/IP stack, if available. If it is a road sign, the message ID is a
7
Here OBE is used, elsewhere OBU is used, pick one and stick with it.