IEEE 1609.4:2011 pdf free download – IEEE Standard for Wireless Access in Vehicular Environments (WAVE)一Multi-channel Operation
4.1 Overview
WAVE provides a communication protocol stack optimized for the vehicular environment, employing bothcustomized and general-purpose eiements. IEEE P1609.0 provides a description of the WAVE systemarchitecture and operations. To operate over multiple wireless channels while in operation withOCBEnabled, there is a need to perform channel coordination. OCBEnabled indicates operation outside thecontext of a basic service set as specified in IEEE Std 802.11p (by setting dot11OCBEnabled to TRUE)(i.e., WAVE operation).
Channel coordination is specified in this standard and consists of additional features for OCBEnabledoperations in the MAC sublayer specified in IEEE Std 802.11p. Both data plane and management planefeatures are included as shown in Figure 1. These features are introduced in 4.2 and 4.3 and specified inClause 5 and Clause 6.
4.2 Reference model
The basic reference model relevant to this standard is shown in Figure 1. WAVE supports both IP- andnon-IlP-based data transfers，although individual devices might support only one networking protocol.Non-IP-based data transfers are supported through the WAVE Short Message Protocol (WSMP) specifiedin IEEE Std 1609.3.Channel coordination is a collection of enhancements to the IEEE 802.11 MAC, andinteracts with the IEEE 802.2 LLC and IEEE 802.11 PHY. The WAVE Management Entity (WME) andcorresponding network services are specified in IEEE Std 1609.3.WAVE security services are specified inIEEE P1609.2.
The MAC and PHY layers conceptually include management entities, called MAC sublayer managementand PHY layer management entities (MLME and physical layer management entity [PLMEJ, respectively).These management entitics provide the layer management service interfaces through which layermanagement functions may be invoked. In Clause 6, this document specifies extensions to the IEEE 802.11MAC sublayer management entity (MLME; as amended by IEEE Std 802.11p) to provide channelcoordination. The interactions between the various entities are through service access point(SAPs) acrosswhich defined primitives are exchanged; see Clause 7.
5.1 General
WAVE devices shall communicate outside the context of an IEEE 802.11 basic service set (i.e.withdot11OCBEnabled equal true), as specified in IEEE Std 802.11p.
An example of a WAVE multi-channel MAC internal architecture is shown in Figure 2. This referencedesign architecture is used to specify the following transmit operations: channel routing, data queueing andprioritization， and channel coordination; however,actual implementations may depart from this exampledesign. A WAVE MAC entity uses one or more instances of the MAC sublayer entity specified inIEEE Std 802.11, as amended by IEEE Std 802.11p, operating outside the context of a basic service set,with the extensions defined herein. There are two IEEE Std 802.11p MAC entities in the example designdescribed in this clause: one for the CCH and one for the SCH. Data is prioritized according to accesscategory (directly related to user priority), as indicated by the queues shown in Figure 2, which providedifferent contention and transmission parameters for different priority data frames. Prioritization is furtherspecified in 5.4.
There are three types of information exchanged on the WAVE medium: management frames, data frames,and control frames.Control frames may be used per IEEE Std 802.11 and are not addressed in thisstandard.Management frames used by WAVE enter the data plane at the MAC layer. The primary management frames are the TA frame specified in IEEE Std 802.11p and the VSA frame specified inIEEE Std 802.11 and amended by IEEE Std 802.11p.Timing Advertisement frames are used to distributetime synchronization information. VSA frames are used to exchange management information such asWAVE Service Advertisements (WSAs). VSAs and TAs may be transmitted on any channel.
For higher layer data exchanges,WAVE supports both the WSMP specified in IEEE Std 1609.3 and IPversion 6. Data frames containing WSMs (as indicated by the Ethertype) may be exchanged among deviceson either the CCH or an SCH; however, data frames containing lP datagrams are only allowed on servicechannels. The management process of accessing the CCH or an SCH is specified in 6.3.