IEEE 1609.3:2007 pdf free download – IEEE Trial-Use Standard for Wireless Access in Vehicular Environments(WAVE) – Networking Services
4.2.1 Channel types
For the purposes of this standard，WAVE distinguishes between two classes of radio channel: a singlecontrol channel(CCH), and multiple service channels (SCH). By default,WAVE devices operate on theCCH, which is reserved for short, high-priority application and system control messages. Service channelvisits are arranged between devices via a WBSS in support of general-purpose application data transfers.See IEEE Std 1609.4 for more information.
4.2.2 Communication protocols
WAVE accommodates two protocol stacks: standard Internet Protocol (IPv6) and the unique WAVE shortmessage protocol (WSMP)designed for optimized operation in the WAVE environment.WAVE shortmessages (WSMs) may be sent on any channel. lP traffic is allowed only on SCHs. In addition to thesetraffic types, system management frames are sent on the CCH as described in IEEE Std 1609.4.
The wSMP allows applications to directly control physical layer characteristics, e.g., channel number andtransmitter power, used in transmitting the messages. A sending application also provides the MAC addressof the destination device, including the possibility of a broadcast address. WSMs are delivered to the correctapplication at a destination based on Provider Service ldentifier (PSID). WSMs are designed to consumeminimal channel capacity and are allowed on both the CCH and SCHs.
A WBSS is established to support traffic to/from specific applications, and its presence is announced forother devices with compatible applications to join.A persistent WBSS is announced periodically, and couldbe used to support an ongoing service of indefinite duration,such as general Internet access. A non-persistent WBSS is announced only on WBSS initiation, and might be used to support a WBSS with limitedduration.
More on the use of WBSS in WAVE is found in IEEE Std 1609.4.
4.2.4 Device wBss roles
Devices take the role of either provider or user on a given WBSS. This is determined by the role chosen bythe requesting application. The provider device generates the announcements that inform other devices ofthe existence of the WBSS and the presence of the associated application service(s). The user role isassumed by any devices that join the WBSS based on receipt of the announcement. A device may changeroles as it participates on different WBSSs over time.Application roles are covered in Clause 6. The termsprovider and user do not imply any particular behavior of the applications once the WBSs is initiated orjoined.
The WBSS announcement indicates the presence of one or more applications providing services. A user ofsuch services joins the WBSs for all of the application services that apply, thus allowing a single device tosimultaneously support multiple applications.Also, a service provider could have multiple users joined withthe wBSs at any one time, each of which uses any possible combination of the application services beingprovided.
4.2.5 Priorities
The concept of priority is used in multiple ways.Applications have an application priority level, which isused by WAVE networking services to help decide which applications have first access to thecommunication services.An example of a conflict would be two applications, each with the concurrent needto announce or join a WBSS on a different channel. In this situation,WME would use application priority tochoose which application(s) to service, as specified in Clause 6. In addition, the lower layers use a separateMACtransmission priority to prioritize packets for transmission on the medium.IP packets are assigned theMAC priority associated with the traffic class of the generating application.The MAC priority for WSMpackets is assigned by the generating application on a packet-by-packet basis.Any relationship betweenapplication and transmission values is within the application, and outside the scope of this standard.SeeIEEE Std 1609.4 for more on MAC transmission priority.