WAVE: A Tutorial


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WAVE: A Tutorial

  1. 1. TOPICS IN AUTOMOTIVE NETWORKINGWAVE: A TutorialRoberto A. Uzcátegui, Universidad Nacional Experimental Politécnica “Antonio José de Sucre”Guillermo Acosta-Marum, Georgia Institute of Technology ABSTRACT (FCC) for 75 MHz of bandwidth in the 5.9-GHz band with the specific goal of supporting dedi- Intelligent transportation systems have been cated short-range communications (DSRC) for under development since at least the early 1990s. ITS. The FCC granted the request in October of The rationale behind the concept is to automate 1999. The DSRC-based ITS radio services the interactions among vehicles and infra- received 75 MHz of spectrum in the 5.85–5.925 structure to achieve high levels of security, com- GHz range. fort, and efficiency. Communications, in general, By July 2002, the ITSA was actively lobbying and networking, in particular, have been essen- the FCC on matters of licensing, service rules, tial elements in the evolution of these systems. and possible technologies for the ITS-DSRC The IEEE has developed a system architecture band. The ITSA recommended the adoption of known as WAVE to provide wireless access in a single standard for the physical (PHY) and vehicular environments. This article gives an medium access control (MAC) layers of the overview of the associated standards. The pre- architecture and proposed one developed by the sentation loosely follows the order of the layers American Society for Testing and Materials of the open systems interconnection model. (ASTM) based on IEEE 802.11 [1] (ASTM’s E2213-02 [2]). The FCC officially adopted this INTRODUCTION recommendation in the 2003–2004 timeframe. In 2004, an IEEE task group (task group p, In the Intermodal Surface Transportation Effi- or TGp of the IEEE 802.11 working group) ciency Act of 1991 (ISTEA), the United States assumed the role initiated by the ASTM and Congress mandated the creation of a program started developing an amendment to the 802.11 called Intelligent Vehicle Highway Systems standard to include vehicular environments. The (IVHS), whose main goals were to increase safe- document is known as IEEE 802.11p [3]. Anoth- ty, ameliorate congestion, reduce pollution, and er IEEE team (working group 1609) undertook conserve fossil fuels while vehicles use the the task of developing specifications to cover nation’s surface transportation infrastructure. additional layers in the protocol suite. At the Responsibility for the program was assigned to time of this writing, the IEEE 1609 standards set the U. S. Department of Transportation (DOT), consisted of four documents: IEEE 1609.1 [4], which sought the advice of the Intelligent Trans- IEEE 1609.2 [5], IEEE 1609.3 [6], and IEEE portation Society of America (ITSA) — a non- 1609.4 [7]. profit organization whose members come from Collectively, IEEE 802.11p and IEEE 1609.x industry and academia, as well as federal, state, are called wireless access in vehicular environ- and municipal government — to perform the ments (WAVE) standards because their goal, as assignment. By 1996, the DOT, the ITSA, and a whole, is to facilitate the provision of wireless several other interested parties had developed a access in vehicular environments. The conceptu- procedural framework wherein IVHS services al design they portray is called WAVE architec- (or intelligent transportation system [ITS] ser- ture in this article, and the systems that vices, as they are known today) could be system- implement it are referred to as WAVE systems. atically planned, defined, and integrated. Known The objective of this article is to give an as the National Intelligent Transportation Sys- overview of the IEEE WAVE standards. tems Architecture (NITSA), this framework has To the extent that the model applies, the pre- served as a master plan for ITS initiatives for the sentation of the material loosely follows the past 13 years. order of the layers in the open systems intercon- From the beginning, the NITSA recognized nection (OSI) model from the bottom up. In this wireless communications as a cornerstone for article, we consider only those OSI layers that the implementation of many ITS services. At the are covered by a WAVE standard. This content time, some applications, such as automated toll arrangement does not correspond to a monoton- collection, were performed using the spectrum ic progression of the numerical designations between 902 MHz and 928 MHz. Unfortunately, given by the IEEE to the related documents, but this band was too small and polluted to enable it does convey a general sense of the logical flow the envisioned evolution of IVHS communica- of information inside a WAVE system within the tions. Consequently, in 1997, the ITSA peti- confines of a sequentially written composition. tioned the Federal Communications Commission We organized the article as follows. First, we126 0163-6804/09/$25.00 © 2009 IEEE IEEE Communications Magazine • May 2009 Authorized licensed use limited to: Georgia Institute of Technology. Downloaded on May 21, 2009 at 19:29 from IEEE Xplore. Restrictions apply.
  2. 2. give a general description of the architecture of User services bundles User servicesa WAVE system. Then, we follow it with a briefdiscussion of the PHY layer and the MAC sub-layer (as addressed in IEEE 802.11p), the multi- Pre-trip travel information En route driver informationchannel coordination mechanism used in WAVE Route guidance(that sits atop the MAC sublayer, as specified in Ride matching and reservationIEEE 1609.4), and the WAVE services at the Travel and Traveler’s services informationnetwork- and transport-layer levels (as described traffic management Traffic controlin IEEE 1609.3). In the next two sections, we Incident managementdiscuss entities that have no counterpart in the Travel demand managementOSI model: the resource manager (IEEE 1609.1) Emissions testing and mitigationand the security services (IEEE 1609.2). We Highway rail intersectionfinalize the article with some comments aboutthe state of the art in research and development Public transportation managementin the field. Public transportation En route transit information management Personalized public transit Public travel security WAVE SYSTEM ARCHITECTURE OVERVIEW Electronic payment Electronic payment servicesImagine the following three scenarios: Commercial vehicle electronic clearance• An emergency-response vehicle, such as a Automated roadside safety inspection fire department truck, rapidly approaches Commercial vehicle Onboard safety and security monitoring an intersection with a four-way stop. As it operations Commercial vehicle administrative processes nears the intersection, a radio device on the Hazardous materials security and incident response truck sends an electronic message to similar Freight mobility devices located in all nearby vehicles to pre- empt the crossroad. The onboard computer Emergency notification and personal security Emergency of any of the receiving vehicles first alerts Emergency vehicle management management the driver about the emergency, and then, if Disaster response and evacuation necessary, autonomously slows down the car to avoid a collision. Longitudinal collision avoidance• As they drive by the welcome center of the Lateral collision avoidance town that a family is visiting for the week- Intersection collision avoidance Advanced vehicle end, a wireless transceiver in their minivan Vision enhancement for crash avoidance safety systems receives an announcement from an access Safety readiness point in the building, advertising free global Pre-crash restraint deployment positioning system (GPS) maps updated Automated vehicle operation with information about the tourist attrac- tions for that particular weekend. After Information Archived data receiving confirmation that the passengers management are interested in this particular information, the transceiver downloads the maps. Maintenance and Maintenance and construction operations• On the way to work and using the speech construction management user interface of her car, the doctor con- nects to her Web-based calendar applica- Table 1. User services considered in the version 6.1 of the NITSA. tion and listens to the list of appointments she has that day. The first scenario is an example of a public- By default, WAVE units operate indepen-safety application that implies vehicle-to-vehicle dently, exchanging information over a fixed(V2V) communications. The second and third radio channel known as the control channelones are instances of private applications that (CCH). However, they also can organize them-entail a vehicle-to-infrastructure (V2I) informa- selves in small networks called WAVE basic ser-tion exchange. The third one, in particular, vice sets (WBSSs), which are similar in nature toinvolves traditional Internet access. These are the service sets defined in IEEE 802.11 [1].but three of the potential uses of the WAVE WBSSs can consist of OBUs only or a mix oftechnology that is the focus of this article (see OBUs and RSUs (Fig. 1). All the members of aTable 1 for more uses). We use these three sce- particular WBSS exchange information throughnarios to provide concrete illustrations of the one of several radio channels known as serviceconcepts discussed in the rest of this section. channels (SCHs). Through the appropriate por- tals, a WBSS can connect to a wide-area net- COMPONENTS OF A WAVE SYSTEM work (Fig. 1).A WAVE system consists of entities called units(Fig. 1). Roadside units (RSUs) usually are COMMUNICATION PROTOCOLSinstalled in light poles, traffic lights, road signs, The WAVE architecture supports two protocoland so on; they might change location (for stacks, as shown in Fig. 2. In the terminology ofinstance, when transported to a construction the OSI model, both stacks use the same physi-site) but cannot work while in transit. Onboard cal and data-link layers, and they differ fromunits (OBUs) are mounted in vehicles and can each other in the network and transport layers.function while moving. The WAVE standards do not specify session,IEEE Communications Magazine • May 2009 127 Authorized licensed use limited to: Georgia Institute of Technology. Downloaded on May 21, 2009 at 19:29 from IEEE Xplore. Restrictions apply.
  3. 3. presentation, or application layers. However, of datagram length or complexity but very strict they do introduce two elements that do not fit ones in terms of latency and probability of error. easily within the boundaries of the OSI model: WSMP enables the application to send short the resource manager and the security services messages and directly control certain parameters blocks (Fig. 2). of the radio resource to maximize the probability The two stacks supported by WAVE are tra- that all the implicated parties will receive the ditional Internet Protocol version six (IPv6) and messages in time. However, WSMP is not a proprietary one known as WAVE Short-Mes- enough to support typical Internet applications, sage Protocol (WSMP). The reason for having and these are required to attract private invest- two protocol stacks is to accommodate high-pri- ment that would help spread, and ultimately ority, time-sensitive communications, as well as reduce, the cost of implementing the systems; more traditional and less demanding exchanges, hence the inclusion of IPv6. such as Transmission Control Protocol/User For reasons that will be explained in the next Datagram Protocol (TCP/UDP) transactions. An section, the WAVE architecture is based on the application like the crossroad pre-emption men- IEEE 802.11 standard [1], which specifies layer tioned before has scarce requirements in terms one and part of layer two of the protocol stack (Fig. 2). Given the differences between the oper- ating environment of an 802.11 wireless local area network (LAN) and a vehicular environ- ment such as any of the ones described at the RSU beginning of this section, an amendment to the standard was required, which is known as IEEE WBSS 3 802.11p. This norm specifies not only the data OBU WBSS 1 OBU transmission portion of the protocols but also the management functions associated with the corresponding layer (the physical layer manage- ment entity [PLME] and the MAC layer man- agement entity [MLME] blocks in Fig. 2). OBU OBU Unlike traditional wireless LAN stations, WAVE units might be required to divide their time between the CCH and the SCHs. There- fore, the WAVE protocol stack includes a sub- layer at the level of the OSI layer two, dedicated OBU WBSS 2 to controlling this multichannel operation. This sublayer (including the associated management functions) is specified in IEEE 1609.4. The remaining part of OSI layer two (the log- RSU ical link control [LLC]) follows the IEEE 802.2 WAN standard, as described in a later section. Portal At the level of the OSI layers three and four, IEEE 1609.3 specifies the aforementioned WSMP and explains how to incorporate tradi- Figure 1. Illustration of a WAVE system showing the typical locations of the tional IPv6, UDP, and TCP in the systems. That OBUs and RSUs, the general makeup of the WBSSs, and the way a WBSS can document also defines a set of management connect to a WAN through a portal. functions (labeled WAVE management entity [WME] in Fig. 2) that must be used to provide networking services. The remaining two blocks in Fig. 2 (resource manager and security services) do not fit easily Resource manager in the layered structure of the OSI model. They are covered by IEEE 1609.1 and IEEE 1609.2, OSI model respectively. layer 4 UDP/TCP In subsequent sections of this article, we WSMP OSI model IPv6 review the WAVE protocols specified in Table layer 3 Security 2, in the order given in the table. Protocols that WME services LLC appear in Fig. 2 but are not specific to WAVE OSI model Multichannel MLME (such as LLC, IPv6, TCP, and UDP) are men- layer 2 operation extension tioned without details. WAVE MAC MLME OSI model layer 1 WAVE PHY PLME PHY AND MAC LAYERS The WAVE PHY and MAC layers are based on Data Management IEEE 802.11a, and their corresponding standard plane plane is IEEE 802.11p [3]. There are several advan- IEEE 1609.1 IEEE 1609.3 IEEE 802.11p tages to basing the WAVE on 802.11 because it IEEE 1609.2 IEEE 1609.4 is a stable standard supported by experts in wire- less technology. A stable standard is required to Figure 2. WAVE communication stack indicating the standard that covers guarantee interoperability between vehicles each set of layers. The blocks marked resource manager and security services made by different manufacturers and the road- do not fit easily within the layered structure of the OSI model. side infrastructure in different geographic loca-128 IEEE Communications Magazine • May 2009 Authorized licensed use limited to: Georgia Institute of Technology. Downloaded on May 21, 2009 at 19:29 from IEEE Xplore. Restrictions apply.
  4. 4. Standard OSI model Protocols Purpose of the standard document layer numbers Specifies the PHY and MAC functions required of an IEEE 802.11 WAVE PHY and MAC IEEE 802.11p 1 and 2 device to work in the rapidly varying vehicular environment Provides enhancements to the IEEE 802.11p MAC to support Multichannel operation IEEE 1601.4 2 multichannel operation WAVE networking services IEEE 1609.3 Provides addressing and routing services within a WAVE system 2, 3, and 4 Describes an application that allows the interaction of OBUs with limited computing resources and complex processes WAVE resource manager IEEE 1609.1 N/A running outside the OBUs in order to give the impression that the processes are running in the OBUs WAVE security services IEEE 1609.2 Covers the format of secure messages and their processing N/A Table 2. A list of the protocols that compose the WAVE communications stack, in the order in which they are presented in this article, with the designation of the standard that covers each one of them, a brief description of the purpose of the norm, and the correspond- ing layers in the OSI model.tions. It also guarantees that the standard will be er. In [9, 10], we can find measurement andmaintained in concert with other ongoing devel- modeling studies showing the uniqueness ofopments in the 802.11 family, which enhances these high mobility channels. In [11], we find asynergies in chipset design to help ensure detailed description of the latest draft of thiseconomies of scale. However, we require a dif- standard.ferent version of the 802.11 because we mustsupport:• Longer ranges of operation (up to 1000 m) MULTICHANNEL OPERATION• The high speed of vehicles A WAVE device must be able to accommodate• Extreme multipath environments an architecture that supports a control channel• Multiple overlapping ad hoc networks with and multiple-service channels. The channel coor- extremely high quality of service (QoS) dination is an enhancement to IEEE 802.11• The nature of the applications MAC and interacts with IEEE 802.2 LLC and• A special type of beacon frame IEEE 802.11 PHY. In the standard [7], we find The main requirements, characteristics, the services that are used to manage channelchanges, and/or improvements for 802.11p are as coordination and to support MAC service datafollows [8]: unit (MSDU) delivery. There are four services• Communications in a highly mobile environ- provided in the standard. The channel routing ment service controls the routing of data packets from• 10-MHz channels; one-half the data rates of the LLC to the designated channel within chan- 802.11 nel coordination operations in the MAC layer.• Control channel and six service channels The user priority service is used to contend for• Unique ad hoc mode medium access using enhanced distributed chan-• Random MAC address nel access (EDCA) functionality derived from• High accuracy for the received signal IEEE 802.11e [12]. The channel coordination strength indication (RSSI) service coordinates the channel intervals accord-• 16 QAM used in the high-speed mobile ing to the channel synchronization operations of environment the MAC layer so that data packets from the• Spectral mask modification MAC are transmitted on the proper radio fre-• Option for a more severe operating envi- quency (RF) channel. Finally, the MSDU data ronment transfer service consists of three services: control• Priority control channel data transfer, service channel data trans-• Power control fer, and data transfer services. The design of We have noted several times that the high these three services is concerned mostly with giv-mobility and extreme multipath environments ing a higher priority and direct access to thepresent unique challenges in a WAVE system. WSMP, for which the MAC must be able toThe main reason for unique challenges is that identify the type of data packet (WSMP or IP)the wideband V2V or V2I channel is “doubly indicated by its EtherType in accordance withselective.” This means that its frequency the IEEE 802.2 header.response varies significantly over the signalbandwidth, and its time fluctuations happen in FUNCTIONAL DESCRIPTIONthe course of a symbol period. Because WAVE There are two types of information exchanges inuses orthogonal frequency division multiplexing the WAVE medium: management frames and(OFDM), these variations present significant data frames. The primary management frame isdesign challenges in the channel-estimation and the WAVE announcement defined in [7].frequency-offset-detection systems of the receiv- WAVE announcement frames are permitted toIEEE Communications Magazine • May 2009 129 Authorized licensed use limited to: Georgia Institute of Technology. Downloaded on May 21, 2009 at 19:29 from IEEE Xplore. Restrictions apply.
  5. 5. be transmitted only in the CCH. Other IEEE the WSMP checks that the length of the WSM is In the data plane, 802.11 management frames may be utilized in valid (or not) and passes it to the LLC layer for the SCH. For data exchanges, data frames con- delivery over the radio link (or not). Upon the WAVE architec- taining WAVE short messages (WSMs) can be receipt of an indication from the LLC of a ture supports two exchanged among devices on both the CCH and received WSM, the WSMP passes it to the desti- protocol stacks: the SCH; however, IP data frames are permitted nation application (local or remote) by way of a only in an SCH, and SCH exchanges require the second primitive WSM- traditional IPv6 and corresponding devices to be members of a WaveShortMessage.indication. the unique WSMP. WBSS. For control channel priority, the EDCA parameter set is optimized for WSMP data trans- MANAGEMENT-PLANE SERVICES Both of them oper- fer. A predetermined EDCA parameter set must Management-plane services specified in IEEE ate atop a single LLC be used for all WAVE devices when operating in 1609.3 are collectively known as the WME and layer. This dual con- the CCH. For service channel priority, the include: EDCA parameter received within the WAVE • Application registration figuration serves to announcement frame of the provider must be • WBSS management accommodate high- used. Channel coordination utilizes a synchro- • Channel usage monitoring nized scheme based on coordinated universal • IPv6 configuration priority, time-sensi- time (UTC). This approach assures that all • Received channel power indicator (RCPI)tive communications, WAVE devices are monitoring the CCH during monitoring as well as less a common time interval (CCH interval). When a • Management information base (MIB) main- WAVE device joins a WBSS, this channel syn- tenance demanding, transac- chronization approach also assures that the tional exchanges. members of that WBSS are utilizing the corre- Application Registration — All the applica- sponding SCH during a common time interval tions that expect to use the WAVE networking (SCH interval). The sum of these two intervals services first must register with the WME. Each comprises the sync interval. application registers with a unique provider ser- vice identifier (PSID). Registration information is recorded in three tables, namely: NETWORKING SERVICES • The ProviderServiceInfo table, which In the IEEE 1609.3 standard [6], we find the contains information about the applications specification of the functions associated with the that provide a service. LLC, network, and transport layers of the OSI • The UserServiceInfo table, which con- model, and the standard calls them WAVE net- tains information about the services that working services (Fig. 2). are of interest to applications residing in We can functionally divide the WAVE net- the local unit. working services into two sets: • The ApplicationStatus table, which • Data-plane services, whose function is to contains, among other things, the IP carry traffic addresses and ports of the applications for • Management-plane services, whose func- notification purposes when they reside out- tions are system configuration and mainte- side the local unit. nance WBSS Management — The WME is in charge DATA-PLANE SERVICES of initiating a WBSS on behalf of any applica- In the data plane, the WAVE architecture sup- tion that provides a service. This may require ports two protocol stacks: traditional IPv6 and one or more of the following operations: the unique WSMP. Both of them operate atop a • Link establishment single LLC layer. This dual configuration serves • Addition or removal of applications from to accommodate high-priority, time-sensitive dynamic WBSSs communications (through WSMP), as well as • Inclusion (provider side) and retrieval (user less demanding, transactional exchanges side) of security credentials (through UDP/TCP/IP). • WBSS termination At the LLC layer, WAVE devices must imple- • Maintenance of the status of each applica- ment the type 1 operation specified in [13], the tion in the context of a particular WBSS Sub-Network Access Protocol (SNAP) specified in [14], and the standard for transmission of IP Channel Usage Monitoring — Although the datagrams over IEEE 802 networks specified in standard does not specify how to do it, it man- RFC 1042. dates that the WME tracks the SCHs usage pat- WAVE devices must implement IPv6, as terns so that it can choose a channel that is less specified in RFC 2460, UDP as defined in RFC likely to be congested when it must establish a 768, and TCP as per RFC 793. Manufacturers WBSS. are free to implement any other Internet Engi- neering Task Force (IETF) recommendation IPv6 Configuration — This service is for man- they wish, as long as it does not hinder interop- aging the link local, global, and multicast IPv6 erability with other WAVE devices. addresses of the unit as indicated in the corre- Implementations of WSMP must support a sponding IETF RFCs. short-message-forwarding function consisting of two primitives. Upon receipt of the primitive RCPI Monitoring — Any application can query WSM-WaveShortMessage.request from a a remote device about the strength of the local (residing on the same device) or a remote received signal. The WME sends the corre- (residing outside the WAVE device) application, sponding request on behalf of the querying130 IEEE Communications Magazine • May 2009 Authorized licensed use limited to: Georgia Institute of Technology. Downloaded on May 21, 2009 at 19:29 from IEEE Xplore. Restrictions apply.
  6. 6. application. The MLME, not the WME, of the commands issued by the RM allow the RMAs toremote unit answers this request. read, write, reserve, and release portions of this WAVE applications memory space.MIB Maintenance — The WME maintains a The RM concept reduces the complexity of face unique safetyMIB that contains system-related and applica- the OBUs by freeing them from the requirement constraints becausetion-related information. The system-related of executing applications onboard the vehicle. of their wide rangeinformation includes network information This was considered a simple way of reducing(router, gateway, and Domain Name Service their production costs, increasing their reliability, of operation.[DNS] data, among other types), address infor- and facilitating the interoperability of units pro- For example, safetymation (such as local MAC addresses), and duced by different manufacturers.other values, such as registration port, forward- applications are timeing port, WSM maximum length, and so on. The critical; therefore,application-related information includes the SECURITY SERVICES the processing andProviderServiceInfo, UserServiceInfo, WAVE applications face unique safety con-and ApplicationStatus tables previously straints because of their wide range of operation. bandwidth overheadmentioned, as well as channel information, like For example, safety applications are time criti- must be kept to achannel number, data rate, and transmit power cal; therefore, the processing and bandwidthlevel. overhead must be kept to a minimum. For other minimum. applications, the potential audience may consist of all vehicles on the road in North America; RESOURCE MANAGER therefore, the mechanism used to authenticateIn the IEEE 1609.1 standard [4], we find the messages must be as flexible and scalable as pos-definition of a WAVE application called the sible. In each case, we must protect messagesresource manager (RM), whose purpose is to from eavesdropping, spoofing, alterations, andgive certain processes access to the system com- replay. We also must provide owners the right tomunication resources. privacy to avoid leaking of personal, identifying, The RM is located in either an RSU or an or linkable information to unauthorized parties.OBU. It receives requests from applications that In the IEEE 1609.2 standard [5], we find therun in computers that are located remotely from security services for the WAVE networking stackits host unit. These applications are called and for applications that are intended to runresource management applications (RMAs). The over the stack. Mechanisms are provided togoal of the RMAs is to use the resources of one authenticate WAVE management messages, toor more OBUs. The RM acts as a broker that authenticate messages that do not requirerelays commands and responses between the anonymity, and to encrypt messages to a knownRMAs to the appropriate OBUs. A software recipient. Services include encryption usingentity called the resource command processor another party’s public key and non-anonymous(RCP) that resides in the OBU executes the authentication. Confidentiality (encrypting a mes-commands sent by the RM on behalf of the sage for a specific recipient) avoids the intercep-RMAs. tion or altering of a message. Authenticity A summary of the operation of the RM layer (confirmation of origin of the message) andis as follows. Each RMA registers with the RM integrity (confirmation that the message has notwith which it interacts and specifies, among been altered in transit) avoid tricking a recipientother things, the list of resources that it must into accepting incorrect message contents. Inuse. The RM registers with the WME of its host WAVE, anonymity for end users is also aunit as a provider. When the RMA becomes requirement. Cryptographic mechanisms provideactive, the provider’s WME initiates a WBSS most of these security requirements, and theirand announces, along with other pertinent infor- three main families are secret-key or symmetricmation, that there is an RMA wishing to use the algorithms, public-key or asymmetric algorithms,specified set of resources. The WME of an OBU and hash functions.receiving the announcement notifies the RCPabout the RMA and its list of desired resources. SYMMETRIC ALGORITHMSIf there is a match within the set of resources it When two entities (traditionally called Alice andadministers, the RCP asks the WME of its unit Bob) want to communicate, they both use secretto join the WBSS and registers as a user. Once data known as a key. Alice uses the key to encryptthis is done, the RCP responds directly to the her message; Bob has the same key and canRM. The RM then notifies the RMA that it is in decrypt it. To provide authenticity and integrity,the presence of an RCP that has some or all of Alice uses the key to generate a cryptographicthe resources that the application requires. An checksum or message integrity check (MIC), andexchange between the RMA and the RCP the MIC only passes the check if Bob uses thebegins, by way of the RM. This takes place until correct key. A message can be encrypted-only,the RMA decides to terminate the session, issu- authenticated-only, or both. The standard usesing the appropriate commands to the RCP, the advanced encryption standard — counterwhich acknowledges the termination. with cipher block chaining (CBC) MIC (AES- The resources that the RMAs may control CCM) mechanism.include, but are not limited to, read/write memo-ry; user interfaces that are included as part of ASYMMETRIC ALGORITHMSthe OBU; specialized interfaces to other onboard We use a keypair, known as the public key andequipment; and optional vehicle-security devices the private key, which are mathematically relatedconnected to the OBU. All these resources are so that it is extremely difficult to determine themapped into the memory space of the unit. The private key, given only the public key. For anIEEE Communications Magazine • May 2009 131 Authorized licensed use limited to: Georgia Institute of Technology. Downloaded on May 21, 2009 at 19:29 from IEEE Xplore. Restrictions apply.
  7. 7. encrypted message to Bob, Alice uses Bob’s pub- however, that the field is closed to new research The goals of safety, lic encryption key. Bob, who knows the corre- and development contributions. Submissions on sponding private decryption key, is the only one data dissemination, security, applications, comfort, and energy who can decrypt it. For an authenticated mes- testbeds, channel modeling, MAC protocols, and efficiency that sage to Bob, Alice uses her own private signing many other subjects are sent in significant num- motivated legislators key. A cryptographic checksum generated by a bers to conferences and symposia on WAVE private key is known as a digital signature. Bob (e.g., the International Conference on Wireless to call for the uses Alice’s public verification key to prove that Access in Vehicular Environments [WAVE] or creation of an it is her message. Digital signatures are particu- the IEEE International Symposium on Wireless larly useful for securing communications with Vehicular Communications [WiVEC]). intelligent parties that have not been encountered previous- At the time of this writing, experimental ITS ground-transporta- ly, such as when broadcasting to a dynamically networks have been implemented in California, tion system in 1991 changing population. Michigan, New York, and Virginia to display and test applications for collision avoidance, are as valid today as HASH FUNCTIONS traffic management, emergency response sys- they were then, A cryptographically secure hash function maps tems, real-time traveler information, and e-com- an arbitrary-length input into a fixed-length out- merce [15]. The goals of safety, comfort, and if not more so. put (the hash value), such that it is computation- energy efficiency that motivated legislators to ally infeasible to find an input that maps to a call for the creation of an intelligent ground- specific hash value and two inputs that map to transportation system in 1991 are as valid today the same hash value. The standard makes use of as they were then, if not more so; and in the cur- the Secure Hash Algorithm (SHA)-1 hash func- rent global economic climate, ITS may be favor- tion, defined in Federal Information Processing ably poised to help create jobs while upgrading Standard (FIPS) 180-1. the transportation infrastructure. Many stake- holders from industry, government, and ANONYMITY academia are betting on this [15], and, as this Broadcast transmissions from a vehicle operated article shows, WAVE technology has an impor- by a private citizen should not leak information tant role to play in the process. that can be used to identify that vehicle to unau- thorized recipients. Public safety vehicles do not ACKNOWLEDGMENTS generally require anonymity. A vehicle can use The authors thank Dr. Wai Chen for inviting broadcast or transactional applications. In both them to write this tutorial for the series “Topics cases, the use of these applications should not in Automotive Networking” of the IEEE Com- compromise anonymity. Additionally, the head- munications Magazine. They also thank Dr. Wei- ers in a transmitted packet might reveal informa- dong Xiang for inviting them to WAVE 2008: tion about the sender (e.g., a fixed source MAC The First International Conference on Wireless address). A truly anonymous system must Access in Vehicular Environments to give the remove this compromising information. The cur- tutorial on which this article is based. rent standard is focused on protecting message payloads and does not provide techniques for making the message headers anonymous. In REFERENCES addition, mechanisms for providing anonymous [1] IEEE Std 802.11, “IEEE Standard for Information Tech- authenticated broadcast messages are not given. nology-Telecommunications and Information Exchange Between Systems-Local and Metropolitan Area Net- works-Specific Requirements — Part 11: Wireless LAN CONCLUDING REMARKS Medium Access Control (MAC) and Physical Layer (PHY) Specifications,” 2007. This article presented a tutorial overview of the [2] ASTM E 2213, “Standard Specification for Telecommu- nications and Information Exchange between Roadside IEEE standards for WAVE, namely, IEEE and Vehicle Systems — 5GHz Band Dedicated Short 802.11p, IEEE 1609.1, IEEE 1609.2, IEEE Range Communications (DSRC) Medium Access Control 1609.3, and IEEE 1609.4. We presented the (MAC) and Physical Layer (PHY) Specifications,” 2002. material from the perspective of the OSI model, [3] IEEE P802.11p/D3.0, “Draft Amendment to Standard for Information Technology-Telecommunications and Infor- highlighting both the common points and the mation Exchange between Systems-Local and divergences between the two systems. Metropolitan Area Networks-Specific Requirements — The WAVE architecture is built on the ubiq- Part 11: Wireless LAN Medium Access Control (MAC) uitous IEEE 802.11 standard, which gives and Physical Layer (PHY) Specifications-Amendment 7: Wireless Access in Vehicular Environment,” 2007. WAVE the backing of a sizeable community of [4] IEEE P1609.1, “Trial-Use Standard for Wireless Access in wireless experts and enough market momentum Vehicular Environments (WAVE) — Resource Manager,” to make possible the production of complying 2006. devices without having to recover considerable [5] IEEE P1609.2, “Trial-Use Standard for Wireless Access in Vehicular Environments (WAVE) — Security Services for sunk costs. Basing WAVE on IEEE 802.11 Applications and Management Messages,” 2006. implies that many design choices already were [6] IEEE Std P1609.3, “IEEE Trial-Use Standard for Wireless made when the standardization process started, Access in Vehicular Environments (WAVE)-Networking but the WAVE environment and applications Services,” 2007. [7] IEEE P1609.4, “Trial-Use Standard for Wireless Access in are sometimes so different from those of tradi- Vehicular Environments (WAVE) — Multi-Channel Oper- tional wireless LANs that changes and adapta- ation,” 2006. tions were inevitable. This article highlighted [8] “Conversion of ASTM E 2213-03 to IEEE 802.11x For- many of them and gave justifications for the less mat,” Doc. IEEE 802.11-04-0363-00-wave, Mar. 2004. [9] G. Acosta-Marum and M. A. Ingram, “A BER-Based Par- obvious. titioned Model for a 2.4-GHz Vehicle-to-Vehicle Express- All of the standards reviewed in this article way Channel,” Int’l. J. Wireless Personal Commun., July are near final approval. This does not mean, 2006.132 IEEE Communications Magazine • May 2009 Authorized licensed use limited to: Georgia Institute of Technology. Downloaded on May 21, 2009 at 19:29 from IEEE Xplore. Restrictions apply.
  8. 8. [10] G. Acosta-Marum and M. A. Ingram, “Six Time- and Frequency-Selective Empirical Channel Models for BIOGRAPHIES Vehicular Wireless LANs,” Proc. 1st IEEE Int’l. Symp. ROBERTO A. UZCA TEGUI (ruzcategui@unexpo.edu.ve) received ´ Wireless Vehic. Commun. (WiVec 2007), Baltimore, MD, a B.Sc. degree in electronic engineering, summa cum Sept. 30–Oct. 1, 2007. laude, from the Universidad Nacional Experimental Politéc-[11] D. Jiang and L. Delgrossi, “IEEE 802.11p: Towards nica “Antonio José de Sucre” (UNEXPO), Barquisimeto, an International Standard for WAVE,” Proc. IEEE Venezuela. He received a Master of Science in electronic Vehic. Tech. Conf., Singapore, May 11–14, 2008, pp. engineering from the Universidad Simón Bolívar, Caracas, 2036–40. Venezuela, and a Master of Science in electrical engineer-[12] IEEE Std 802.11e/D13.0, “IEEE Standard for Informa- ing from the Georgia Institute of Technology, Atlanta. Cur- tion Technology — Telecommunications and Informa- rently, he is a professor in the Department of Electronic tion Exchange between Systems-Local and Metropolitan Engineering of the Universidad Nacional Experimental Area Networks-Specific Requirements — Part 11: Wire- Politécnica “Antonio José de Sucre.” His research interests less LAN Medium Access Control (MAC) and Physical include wired and wireless networks, OFDM, MIMO sys- Layer (PHY) Specifications: Medium Access Control tems, and channel modeling. (MAC) Enhancements for Quality of Service (QoS),” draft standard. GUILLERMO ACOSTA-MARUM (gacosta@gatech.edu) received[13] IEEE Std 802.2, “IEEE Standard for Information Tech- Bachelor (with Honors) and Master of Engineering degrees nology-Telecommunications and Information Exchange from Stevens Institute of Technology in 1985 and 1987, between Systems-Local and Metropolitan Area Net- and an M.B.A. from the ITAM in 1996. He received his works-Specific Requirements — Part 2: Logical Link Ph.D. from the School of Electrical and Computer Engineer- Control,” 1998. ing at the Georgia Institute of Technology, Atlanta, in[14] IEEE Std 802, “IEEE Standard for Local and Metropoli- 2007. He has been an adjunct instructor in electrical engi- tan Area Networks: Overview and Architecture,” 2001. neering at the Instituto Tecnológico Estudios Superiores de[15] ITS America, “Letter to the Speaker of the U.S. House Monterrey Campus Estado de Mexico (ITESM-CEM), the of Representatives, Honorable Nancy Pelosi,” Mar. Universidad Iberoamericana, and Georgia Tech. His research 2009; http://www.itsa.org/itsa/files/pdf/ITSAEconStim- interests include wireless LAN, wireless MAN, OFDM, Pelosi.pdf MIMO, and channel modeling.IEEE Communications Magazine • May 2009 133 Authorized licensed use limited to: Georgia Institute of Technology. Downloaded on May 21, 2009 at 19:29 from IEEE Xplore. Restrictions apply.