http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5948952&tag=1
Abstract. Vehicular networking has significant potential to enable diverse applications associated with traffic safety, traffic efficiency and infotainment ... basic characteristics, applications, requirements, challenges, proposed solutions
Intelligent Transportation Systems (ITS) that aim to streamline the operation of vehicles, manage vehicle traffic, assist drivers with safety and other information, along with provisioning of convenience applications for passengers are no longer confined to laboratories and test facilities of companies.
vehicular networks are poised to become the most widely distributed and largest scale ad hoc networks
the requirements imposed by such applications on the vehicular networking architecture
decrease the probability of traffic accidents and the loss of life of the occupants of vehicles
primarily provide information and assistance to drivers to avoid such collisions with other vehicles … by sharing information between vehicles and road side units which is then used to predict collisions.
Such information can represent vehicle position, intersection position, speed and distance heading
information exchanged … moreover … to locate hazardous locations on roads, such as slippery sections or potholes
example applications
focus on improving the vehicle traffic flow, traffic coordination and traffic assistance and provide updated local information, maps and in general, messages of relevance bounded in space and/or time.
... fixed infrastructure routing, ... topological prefixes and
therefore cannot be adapted to follow geographical routing.
... to integrate the concept of physical location into the current
design of Internet that relies on logical addressing
DNS (Domain Name System) is extended by including a “geographic” data base, which contains the full directory information down to the level of IP addresses of each base station and its coverage area represented as a polygon of coordinates.
security model … flexible … allowing to integrate previously found attacks
security concepts that can be used to support the data trust and verification are categorized into proactive security and reactive security concepts.
Tamper-proof GPS [123] proposes a system, where each vehicle has a tamper-proof GPS receiver, which can register its location at all times and provides this information to other nodes in the network in an authentic manner.
With verifiable multilateration [123], the verification of the vehicle location is accomplished using the roadside infrastructure and by using multilateration and distance bounding
Another challenge-response system involves the use of logic reception of beacons [125], which involves synchronized acceptor and rejector nodes.
Secure localization can be considered as an efficient solution for the DOS attacks associated with localization.
The multi-hop communication between source and destination can be performed in either V2V, V2I, or hybrid fashion. Messages are forwarded to a destination by making use of multiple intermediate vehicles as relay nodes.
Driver safety related applications are the most important motivating applications for VANETs.
flooding seriously suffer from broadcast storm problem where large amount of bandwidth is consumed by excess number of retransmissions. When node density is high, this leads to large number of collisions and high channel contention overhead.
The main challenge in designing forwarding algorithms for VANETs is to provide reliable packet transmission with minimum delay, maximum throughput, and low communication overhead.
Most existing algorithms target only subset of these requirements within specific environment setups.
categorize all delay-aware protocols based on the layer in which the appropriate steps are being taken
Delay constraints at the level of application layer are necessary due to the requirements to support emergency warning messages.
The QoS support for multimedia applications in VANETS is studied in [164] by considering three different types of packet flows: audio, video, and data packets.
A mobile peer-to-peera (P2P) file sharing system that targets VANETs is introduced in CodeTorrent [165].
P2P systems are designed for IP address-based network, and they are not readily applicable for VANETs. The challenges here include high node mobility, error-prone wireless channel, and security-risk of information sharing.
Designing routing protocols with delay-bound and delay-guarantee characteristics is challenging due to high vehicular mobility.
The Incident Warning System (IWS) [172] utilizes direct wireless communication to transfer a variety of packets including traffic incidence reports, text messages, JPEG images etc. … requirements are handled by using two different frequencies: long range frequency to reserve the channel; and short range frequency to transmit the packets.
The primary challenge in designing protocols is to provide good delay performance under the constraints of high vehicular speeds, unreliable connectivity, and fast topological changes.
individual solutions may lead to conflict between layers and among other nodes.
When an emergency event occurs, the channel utilization is likely to degrade due to massive broadcast of emergency messages.
A vehicle collision warning communication (VCWC) [183] ... of cooperative collision warning system that is enabled by vehicle-to-vehicle communication. It aims to give low latency warning message transmission at the initial state of an emergency event.
Whenever a node has a backlogged emergency message, it raises an out-of-band busy tone signal, which can be sensed by vehicles located within two hops. Vehicles with lower priority messages defer their channel access whenever the busy tone signal is sensed.
In [186], a novel pulse-based control mechanism has been proposed to provide strict priority for emergency messages.
cross-layer protocols that operate in multiple layers to provide priorities among different flows and different applications.
The motivation behind such a cross-layer design is to support real-time and multimedia applications which require a reliable end-to-end connectivity with QoS requirements. Cross-layer designs also help in congestion avoidance.