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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.
The following subsection provides an overview of the DSRC architecture and protocol stack. Subsequent
annexes describe examples of how the message sets specified in this Standard might be used, which also
strongly influenced the philosophy of the message design. These message sets are presented in Section 5.
The particular message design techniques described in this Standard have allowed for the construction of a
dictionary of reusable, relevant data frames and data elements that support interoperability for currently
envisioned applications and are also intended to expedite the development of future message sets. The
standard data frames are presented in Section 6 of this Standard, and the data elements are specified in
Section 7. Data concepts reused from other areas of ITS work are presented in Section 8.
4.2
DSRC Overview
The WAVE communications system is designed to enable vehicle-to-vehicle and vehicle-to/from-
infrastructure communications in order to provide a common platform to achieve the safety, mobility and
commercial priorities described in Section 4.1. Interoperability is a fundamental requirement of this
common platform, and WAVE is designed to provide the required interoperable wireless networking
services for transportation. As well, the WAVE system uniquely supports the high-availability, low-
latency communications requirements of vehicle safety applications, such as pre-crash collision mitigation,
intersection collision avoidance and cooperative collision avoidance.
The physical layer (PHY) of the WAVE system is defined in IEEE P802.11p. In general, the WAVE PHY
provides a control channel (CCH) and multiple service channels (SCH). The range of this system is
generally considered to be line-of-sight distances of less than 1000 meters. The PHY has been optimized to
support usage by vehicles traveling at highway speeds.
IEEE P1609.4 provides enhancements to the IEEE 802.11 medium access control (MAC) that support
WAVE safety, mobility and private applications in a multi-channel system by specifying mechanisms for
prioritized access, channel routing, channel coordination and data transmission.
The upper layers of the network stack, up to the application layer, are defined in IEEE P1609.3. There are
two pathways through the WAVE upper layers above the LLC layer: the Wave Short Message Protocol
(WSMP) stack and the UDP/IP stack. IEEE 1609.3 describes networking services for applications running
over either of these stacks, as well as describing the operation of the WSMP stack. Transmissions on the
CCH are limited to WAVE Short Messages (WSM). Either WSMP stack or UDP/IP stack may be used for
communications on SCHs. The WSMP stack is generally used for broadcast applications.
IEEE P1609.2 defines secure message formats, and specifies how these secure messages are processed
within the WAVE system. These security services are designed to protect messages from attacks such as
eavesdropping, spoofing, alteration and replay, while respecting end users’ rights to privacy. The messages
covered in IEEE P1609.2 security procedures include WAVE management messages and application
messages, but do not yet include vehicle-originating safety messages. Security services for vehicle-
originating safety messages have not yet been specified in any standard, but will be required before vehicle
safety applications can be widely deployed.
4.3
Philosophy of Message Design
The DSRC message sets which are the subject of this standard are transported over the protocol stack of the
WAVE Short Message (WSM), a finite resource which must be conserved in order to promote the best
operations for all vehicles. While other protocol stacks also exist over the DSRC media (and are in fact
expected to simultaneously carry a variety of other ITS related information including such things as ATIS
information encoded in XML forms), the WSM is characterized by short length packet message traffic,
often broadcast to other vehicles in an un-acknowledged delivery mode. Dialogs and transactions do take
place, and such transaction can leave the control channel in order to use a service channel as needed, but
the general design goal is to maximize support for short broadcast style messages. To that end, a dense