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A Comparative Study of Various Routing Protocols in VANET
Rakesh Kumar, Mayank Dave
TL;DR
VANET routing must operate under unreliable communication, rapidly changing topology, variable vehicle density, and demanding reliability and security requirements. This paper surveys routing-protocol categories and representative protocols, comparing their forwarding methods, map and clustering requirements, mechanisms, applications, advantages, and disadvantages. It concludes with a tabular comparison and identifies clustering overhead and delay as limitations in highly mobile VANETs.
Problem
VANET routing must address unreliable wireless communication, rapidly changing topology, variable vehicle density, and potentially high reliability and security requirements.
Method
The paper surveys VANET routing categories and representative protocols, examining their forwarding methods, geographic information, connectivity mechanisms, clustering, and comparative characteristics.
Results
The paper provides a tabular comparison of routing protocols, including forwarding methods, digital-map and virtual-infrastructure requirements, and clustering characteristics.
Takeaways & Limitations
The comparison organizes topology-based, position-based, cluster-based, geocast, and broadcast protocols by the areas or applications where they are most suitable.
Takeaways & Limitations
Cluster-based routing incurs network delay and overhead during cluster formation in highly mobile VANETs.
Abstract
from arXiv · showhide
Vehicular Ad Hoc Networks (VANET) is a subclass of Mobile ad hoc networks which provides a distinguished approach for Intelligent Transport System (ITS). The survey of routing protocols in VANET is important and necessary for smart ITS. This paper discusses the advantages / disadvantages and the applications of various routing protocols for vehicular ad hoc networks. It explores the motivation behind the designed, and traces the evolution of these routing protocols. F inally the paper concludes by a tabular comparison of the various routing protocols for VANET.
3. Layered View Of Vehicular Networks
Vehicular networks support safety, intelligent transport, and passenger-comfort applications. Their required Quality of Service ranges from non-real-time to hard real-time, and applications may be wide-area or local.
- Application classes: Vehicular networks span applications from safety to passenger comfort.The paper classifies vehicular networks across five aspects in its layered view.
- Intelligent transport applications: Intelligent transport applications improve traffic-information delivery and traffic-detection efficiency through collaborative processing between vehicles.Examples include traffic monitoring, traffic management, platooning, vehicle tracking, and notification services.
- Comfort applications: Comfort applications address passenger convenience through parking management, distributed games or talks, and peer-to-peer applications.
- Requirements: VANET applications require QoS ranging from non-real-time to soft real-time and hard real-time communication.A timing failure may compromise soft-real-time service quality or lead to catastrophe in hard-real-time applications.
4. VANET Characteristics, Issues And Requirements
VANETs must support reliable communication in highly dynamic, infrastructure-independent environments. Road-constrained mobility, a shared control channel, and large density variations make wireless transmission challenging.
- Safety applications: Safety applications improve driving conditions and reduce accident chances by giving drivers more time and automatically applying brakes.
- Safety applications: Cooperative collision warning is a safety application identified for VANETs.
- Communication issues: VANET communication is unreliable, particularly for real-time communication, and cannot assume central coordination.A single shared control channel is therefore required at the MAC layer under the one-channel paradigm.
- Mobility: Vehicles move along roads in predefined directions, requiring mobility models specific to vehicular networks.This deterministic movement pattern makes wireless transmission challenging.
- Density and requirements: Vehicle density varies from sparse highways to areas exceeding 500 vehicles per kilometer, making both density extremes challenging.Vehicular applications also require potentially very high reliability and other nonfunctional guarantees.
5. Overview Of Routing Protocols
The paper groups VANET routing protocols into five categories and associates each category with the areas or applications where it is most suitable.
- Routing categories: VANET routing protocols are classified as topology-based, position-based, cluster-based, geocast, and broadcast protocols.
- Routing categories: The routing categories are characterized according to the area or application where each is most suitable.
- Routing categories: This classification provides the organizing framework for comparing routing protocols in VANETs.
a) Topology Based Routing Protocols
Topology-based routing uses existing network-link information for packet forwarding and is divided into proactive and reactive approaches. Proactive routing maintains next-hop information continuously, trading route-discovery avoidance for maintenance overhead and low latency for real-time applications.
- Topology-based protocols use existing network-link information to forward packets and divide into proactive and reactive approaches.
- i) Proactive routing protocols: Proactive routing maintains next-hop information in the background regardless of communication requests.Each node constructs and maintains a table whose entries indicate the next hop toward destinations.
- i) Proactive routing protocols: Proactive routing avoids route discovery because destination routes are stored, but incurs maintenance overhead and provides low latency for real-time applications.
ii) Reactive/Ad hoc based routing
Reactive routing establishes routes only when communication requires them, maintaining only active routes to reduce network burden. It uses a flooded route-discovery phase and includes AODV, PGB, DSR, and TORA.
- Reactive routing opens routes only when communication is necessary and maintains only routes currently in use.This reduces the burden on the network compared with continuously maintained routing information.
- Route discovery floods query packets through the network until a path is found.
- The reactive routing protocols listed are AODV, PGB, DSR, and TORA.
b) Position Based Routing Protocols
Position-based routing selects forwarding hops using geographic information rather than maintaining a global source-to-destination route. The section covers greedy V2V and delay-tolerant protocols, including GPCR, CAR, DIR, MOVE, VADD, and SADV.
- Position-based routing forwards packets to the one-hop neighbor closest to the destination using geographic positioning information.It does not require creating and maintaining a global route from source to destination.
- 1) Position Based Greedy V2V Protocols: Greedy V2V routing forwards messages to the farthest neighbor toward the destination and requires positions for the intermediate node, neighbors, and destination.These protocols are also called min-delay routing protocols because they aim to reach the destination quickly.
- 2) Greedy Perimeter Coordinator Routing (GPCR): GPCR uses street intersections as routing points through restricted greedy forwarding and a repair strategy, without requiring an external static street map.
- 3) Connectivity Aware Routing Protocols (CAR): CAR caches successful source-destination routes, predicts destination movement, and uses beacon-based velocity information and temporary guard messages.Its recovery strategies address routing errors caused by communication gaps or guards, while guards provide virtual information.
- 5) Delay Tolerant Protocols: Delay-tolerant protocols address sparse networks where establishing end-to-end routes is difficult; the listed protocols are MOVE, VADD, and SADV.
- 6) Motion Vector Routing Algorithm (MOVE): MOVE targets sparse VANETs with intermittent connectivity, using position, heading, and destination information to predict forwarding progress.It uses less buffer space and is designed for vehicles transferring sensor-network data to a base station.
- 7) Vehicle Assisted Data Delivery (VADD): VADD carries and forwards packets in sparse networks using vehicle movement, requiring vehicle position and an external static street map.Packets operate in Intersection, StraightWay, or Destination modes based on node location.
- 8) Static Node Assisted Adaptive Routing Protocol (SADV): SADV reduces message-delivery delay in sparse networks and adapts to varying traffic density by measuring message-delivery time.It assumes GPS-based vehicle positions and access to an external static street map.
c) Cluster Based Routing
Cluster-based routing organizes vehicles into clusters with designated cluster heads that broadcast packets within each cluster. It can improve scalability, but cluster formation creates delay and overhead in highly mobile VANETs.
- Cluster-based routing groups nodes into clusters and designates a cluster head to broadcast packets to the cluster.
- Cluster-based routing can provide good scalability for large networks.
- Cluster formation incurs network delays and overhead in highly mobile VANETs.The approach requires creating a virtual network infrastructure through node clustering to provide scalability.
- The routing protocols listed for clustered networks are COIN and LORA_CBF.
d) Broadcast Routing
Broadcast routing shares traffic, weather, emergency, road-condition, advertising, and announcement information among vehicles.
- Broadcast routing disseminates traffic, weather, emergency, and road-condition information among vehicles.
- It also supports delivery of advertisements and announcements.
- The surveyed broadcast protocols include BROADCOMM, UMB, V-TRADE, and DV-CAST.
e) Geo Cast Routing
Geo cast routing delivers packets to vehicles within a specified geographical region while limiting dissemination outside that region.
- Geo cast is a location-based multicast protocol targeting all nodes within a Zone of Relevance (ZOR).
- Vehicles outside the ZOR are not alerted, avoiding unnecessary reactions.
- A forwarding zone limits packet flooding to reduce message overhead and network congestion.
6. Conclusion
The conclusion compares surveyed VANET routing protocols using forwarding methods, map and infrastructure requirements, clustering, and recovery strategies. It distinguishes delay-bounded protocols from other protocols and notes clustering’s role in scalability and coordination.
- 6. Conclusion: Table 2 compares protocols by their initial forwarding decision, distinguishing delay-bounded methods from wireless multi-hop forwarding.
- 6. Conclusion: Digital maps provide street-level maps and traffic statistics, and are mandatory for some cluster-based routing protocols.
- 6. Conclusion: Virtual infrastructure created through node clustering provides scalability, with cluster heads coordinating secure inter-cluster and intra-cluster communication.
- 6. Conclusion: Recovery strategy serves as a criterion for judging routing-protocol performance in unfavorable situations.