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Is IEEE 802.11p V2X Obsolete Before it is Even Deployed? 35 an addressing mechanism and rules for address configuration [5]. The Basic Transport Protocol (BTP) adds a mechanism for distinguishing different applications sharing the communication link. This achieved using ports, some of which are reserved for distinct applications like CAMs [6]. 3.3 The Common Data Dictionary The common data dictionary (CDD) [11] is an extensive set of basic definitions which are used to define messages for exchanging information between ITS-G5-compliant ITS-Ss. It only defines the basic data structures using ASN.1 syntax [14] but is not intended for independent usage; therefore, further relevant aspects like the encoding mechanism are not covered by the specification. The containers described in the following are built from elements of the CDD. 3.4 Cooperative Awareness Basic Service The CA basic service is part of the Facilities Layer which represents OSI layers 5 to 7[9]. Its task is to regularly broadcast information about an ITS-S’s parameters to surrounding ITS-Ss. The relevant standard document [7] defines the data structures, called containers, forming a CAM. Compliant ITS-Ss have to generate CAMs regularly according to rules determining the generation rate which are also defined in the standard. The data structures typically consist of mandatory and optional parameters. Depending on their dynamics, parameters are either considered high frequency or low frequency. CAMs therefore consist of high and low frequency containers, the latter of which only has to be sent every 500 ms while the prior is to be present in every CAM. Furthermore, the standard defines common basic and as well as extended data structures for vehicles and Roadside Units (RSUs). Additional containers for special purpose vehicles are specified containing further information like loaded dangerous goods. An ITS-S is required to generate between one and ten CAMs per second depending on its dynamics. The intent of this mechanism is to quickly communicate abrupt changes of a vehicle’s position and motion—like braking or avoiding an obstacle—to the surrounding ITS-Ss. Three conditions are defined mandating the instantaneous generation of a CAM, all regarding the respective values included into the last one generated: a difference in heading exceeding 4°, in position exceeding 4 m or in acceleration exceeding 0.5 m/s 2 . CAMs are encoded using the ASN.1 Unaligned Packed Encoding Rule (UPER) [15] which aims to create minimum size bit streams from data sets. They shall be transmitted in the CCH [7].
36 J. Hiltscher et al. 3.5 Security Services As information communicated between ITS-Ss is intended to be used for control applications, its reliability is of utmost importance. Mechanisms to prevent unauthorized participants from sending data to the network or altering transmissions are hence required. IEEE 1609.2 defines security services available to all layers of the communication stack [13]. ITS-G5 extends these to incorporate rules for the defined facility layer messages. A PDU, the security header, which encapsulates other PDUs like CAMs, and elliptical curve cryptographic services (encryption and digital signing) are defined in [12]. The specification requires CAMs to be digitally signed by the sending ITS-S so receivers can verify their integrity and detect unauthorized messages. The defined mechanisms are based on a certificate system where the authenticity of an ITS-S is warranted by trusted entities (Certificate Authorities, CAs), not all of which may be known by each ITS-S. Therefore mechanisms for resolving unknown certificates and verifying their authenticity are also defined. The security header is encoded according to the TLS RFC [3, 12]. 4 Evaluation Framework and Methodology For conducting this evaluation a custom simulation framework was developed. It extends Veins [20, 21], a simulation framework targeting IEEE 802.11p VANETs. Veins couples the popular traffic simulator SUMO [17] with the network simulator OMNeT++ [22]. The available framework simulates an IEEE 802.11p PHY, an IEEE 1609.4 MAC and the wireless communication between ITS-Ss. Veins was chosen over other simulation frameworks like iTETRIS [18] as it is actively being developed and the network definition mechanism of OMNeT++ is very intuitive for programmers. The latter point was important as extensions to the framework had to be made to adapt it to ITS-G5. We also developed custom C++ implementations of the data types and structures defined for the CDD, CAM and security header, the GeoNetworking and BTP PDUs and ASN.1 UPER and TLS encoders. Implementing the data types and structures defined in ITS-G5 was necessary as no C/C++ implementation was available. The encoders were implemented as the ones available as open source did not match our demands. To add ITS-G5 CAM support to Veins the existing MAC was extended to add the DCC mechanism and the CA basic service added. The Security basic service is not implemented completely as of now; the CAMs are encapsulated into a standard Security header containing signer information. Unknown certificate resolution will be added in the future. Using the developed framework we carried out simulation runs for different amounts of vehicles moving across a straight road with six lanes at a constant speed of 130 km/h (36.11 m/s). Vehicles were placed with a time gap of one second, i.e. 36.11 m apart to ensure each ITS-S is in the communication range of all others.
- Page 1 and 2: Lecture Notes in Mobility Tim Schul
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Is IEEE 802.11p V2X Obsolete Before it is Even Deployed? 35<br />
an addressing mechanism and rules for address configuration [5]. The Basic<br />
Transport Protocol (BTP) adds a mechanism for distinguishing different applications<br />
sharing the communication link. This achieved using ports, some of which are<br />
reserved for distinct applications like CAMs [6].<br />
3.3 The Common Data Dictionary<br />
The common data dictionary (CDD) [11] is an extensive set of basic definitions<br />
which are used to define messages for exchanging information between<br />
ITS-G5-compliant ITS-Ss. It only defines the basic data structures using ASN.1<br />
syntax [14] but is not intended for independent usage; therefore, further relevant<br />
aspects like the encoding mechanism are not covered by the specification. The<br />
containers described in the following are built from elements of the CDD.<br />
3.4 Cooperative Awareness Basic Service<br />
The CA basic service is part of the Facilities Layer which represents OSI layers 5 to<br />
7[9]. Its task is to regularly broadcast information about an ITS-S’s parameters to<br />
surrounding ITS-Ss. The relevant standard document [7] defines the data structures,<br />
called containers, forming a CAM. Compliant ITS-Ss have to generate CAMs<br />
regularly according to rules determining the generation rate which are also defined<br />
in the standard. The data structures typically consist of mandatory and optional<br />
parameters. Depending on their dynamics, parameters are either considered high<br />
frequency or low frequency. CAMs therefore consist of high and low frequency<br />
containers, the latter of which only has to be sent every 500 ms while the prior is to<br />
be present in every CAM. Furthermore, the standard defines common basic and as<br />
well as extended data structures for vehicles and Roadside Units (RSUs).<br />
Additional containers for special purpose vehicles are specified containing further<br />
information like loaded dangerous goods.<br />
An ITS-S is required to generate between one and ten CAMs per second<br />
depending on its dynamics. The intent of this mechanism is to quickly communicate<br />
abrupt changes of a vehicle’s position and motion—like braking or avoiding an<br />
obstacle—to the surrounding ITS-Ss. Three conditions are defined mandating the<br />
instantaneous generation of a CAM, all regarding the respective values included<br />
into the last one generated: a difference in heading exceeding 4°, in position<br />
exceeding 4 m or in acceleration exceeding 0.5 m/s 2 . CAMs are encoded using the<br />
ASN.1 Unaligned Packed Encoding Rule (UPER) [15] which aims to create minimum<br />
size bit streams from data sets. They shall be transmitted in the CCH [7].
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