Contention-based Forwarding Research Articles

Evaluation of Greedy and CBF for ETSI non-area GeoNetworking: The impact of DCC

This paper evaluates the performance of the two ETSI non-area forwarding algorithms in the GeoNetworking specification: Greedy Forwarding and Non-Area Contention-Based Forwarding (CBF). Non-area forwarding occurs when a packet is sent to a geographical Destination Area from a node located outside of this area, e.g., when a vehicle wants to alert of hazardous events to other vehicles located in a distant geographical area. The evaluation has been carried out both in urban and highway scenarios and takes into account the complete ETSI Architecture, including the interaction with the Decentralized Congestion Control (DCC) mechanism. We have also compared ETSI-defined mechanisms with optimizations found in the literature. Our main findings are that Greedy Forwarding, when combined with DCC, is extremely ineffective even with optimizations, and Non-Area CBFs (both ETSI CBF and an optimized version called S-FoT+) outperform Greedy Forwarding both in highway and urban scenarios.

Studying and improving the performance of ETSI ITS contention-based forwarding (CBF) in urban and highway scenarios: S-FoT+

This paper evaluates the performance of ETSI ITS Contention-Based Forwarding (CBF) and ETSI Simple GeoBroadcast forwarding while disseminating warning messages over a Geographical Area in highway and urban scenarios. Our experimental evaluation considers the complete ETSI ITS architecture including the Decentralized Congestion Control (DCC) mechanism. We propose an enhanced CBF mechanism, named S-FOT+, which combines several improvements to the ETSI CBF algorithm. S-FoT+ has a similar or better performance than the ETSI forwarding algorithms regarding both reliability and end-to-end delay while requiring much fewer transmissions. The improvements are equally effective and efficient in both urban and highway scenarios with large Destination Areas. Finally, we evaluate the trade-offs that stem from using multi-hop broadcast mechanisms in urban settings with smaller Destination Areas when compared to single-hop broadcast. Results show that multi-hop mechanisms significantly improve coverage at the cost of an increased number of transmissions.

Evaluation and improvement of ETSI ITS Contention-Based Forwarding (CBF) of warning messages in highway scenarios

This paper evaluates the performance of the ETSI Contention-Based Forwarding (CBF) GeoNetworking protocol for distributing warning messages in highway scenarios, including its interaction with the Decentralized Congestion Control (DCC) mechanism. Several shortcomings of the standard ETSI CBF algorithm are identified, and we propose different solutions to these problems, which are able to reduce the number of transmissions by an order of magnitude, while reducing the message end-to-end delay and providing a reliability close to 100% in a large area of interest.

Volunteers Dilemma Game Inspired Broadcast Scheme for Vehicular Ad Hoc Networks

Multi-hop broadcast communication is one of the main schemes for supporting message dissemination in vehicular ad hoc networks. In this paper, we propose an efficient receiver-oriented broadcast scheme in which the receiving vehicles' probability of forwarding is modeled by the symmetric volunteer's dilemma game. Based on this game, the vehicles that receive the broadcast message are players. At least one of the players should pay a cost and be a volunteer to rebroadcast the message, and then all will benefit from this volunteering. Utilizing fuzzy logic techniques and considering information from the network layer about local density and probability of transmission, the contention window size at the MAC layer will be adjusted. We develop ns-3 simulations to evaluate the performance of the proposed volunteer's dilemma inspired broadcast (VDIB) scheme in terms of reachability, number of rebroadcasts per covered vehicle, number of bytes sent per covered vehicle, and per-hop delay. VDIB performance is compared with that of the distance-to-mean broadcast method, broadcast component of contention-based forwarding, distribution-adaptive distance with channel quality, statistical location assisted broadcast, fuzzy logic-based broadcast, bandwidth efficient fuzzy logic assisted broadcast, and intelligent hybrid adaptive broadcast protocols in both highway and urban environments.

Evaluation of Congestion-Enabled Forwarding With Mixed Data Traffic in Vehicular Communications

ITS-G5 is a communication system for vehicle-to-everything communication for road safety and traffic efficiency applications. On the lower layers, it is based on IEEE 802.11 standard and uses a simple ad hoc mode with a random medium access control scheme. Ad hoc networking is realized by a geographical routing scheme that provides single- and multi-hop communication over ITS-G5 links for periodic and event-driven broadcast messages. Specifically, contention-based forwarding ( CBF ) allows for efficient and reliable multi-hop packet transport by overhearing and timer-based transmission control. To cope with the channel congestion, decentralized congestion control (DCC) adjusts the message rate and ensures that the network load keeps below a predefined threshold of the bandwidth. To enforce a node’s message rate, a “ Gatekeeper” above the MAC and beneath CBF is added. Under high network load, this Gatekeeper introduces an additional queuing delay seen by CBF , which can cause its overhearing function to fail. This contribution studies multi-hop forwarding in the context of DCC with the Gatekeeper and LIMERIC as a rate adaptation algorithm. We propose a congestion-enabled forwarding scheme that, in comparison to existing approaches considering DCC and forwarding separately, restores the efficient operation of CBF , and improves the communication performance in terms of reliability and latency for mixed data traffic composed of single- and multi-hop packets with different priorities. The simulations show the performance improvements in a freeway scenario. An analysis assesses the boundary conditions for CBF and the Gatekeeper. Moreover, the analysis corroborates the simulation.

Improving Routing Performances to Provide Internet Connectivity in VANETs over IEEE 802.11p

In the intelligent transportation systems, many applications and services could be offered in the road via Internet. Providing these applications over vehicular ad hoc network (VANETs) technology may require good performances in routing. The channel fading and quality of received signal are the two main factors which affect the Mobile ad hoc network perfor-mances as well as mobility of vehicles, in terms of throughput and delay packets that are relevant to the performance evaluation of the routing protocols. In this paper, we propose an efficient relay selection scheme based on Contention Based Forwarding (CBF) and Fuzzy Logic System (FLS) that considers two important Quality of Service parameters such as link stability, and quality of received signal to select a potential relay vehicle, in order to improve the routing performances in the network. The simulation results show that the proposed relay selection scheme enhances throughput, and decreases packet delay and overhead comparing it with an existing link stability based routing protocol(MBRP) and M-AODV+.

On-demand Misbehavior Detection for Vehicular Ad Hoc Network

Maintaining communication links of an established communication path that extends between source and destination nodes is a significant challenge in Vehicular Ad Hoc Networks due to movement of the vehicles. Operations of Vehicular Ad Hoc Network rely on the collaboration of participating nodes to route data for each other. A critical requirement on the nodes is to cooperate with each other for successful data transmission. Thus, the impact of malicious and selfish users must be detected to ensure the operations of Vehicular Ad Hoc Network. In this article, we proposed On-demand Misbehavior Detection technique for vehicle-to-vehicle communication. We adapt two location-based routing protocols, Contention-Based Forwarding and Connectionless Approach for Streets, to our On-demand Misbehavior Detection. Various experiments are conducted to show the effectiveness and efficiency of the proposed On-demand Misbehavior Detection technique. The simulation and analytical results showed that the proposed technique is very effective in detecting misbehaving nodes.

Enhancing Relay Selection Scheme for Connecting VANETs to Internet Over IEEE 802.11p in Congested and Fading Environment Scenarios

For connecting vehicular ad hoc networks (VANETs) to the Internet over IEEE 802.11p, mobility parameters of vehicles such as speed, location, direction, are often used to connect vehicles to Road Side Units (RSUs) via more stable and less hop routes. On the one side, in the fading environment, these routes may suffer from continuous packet losses due to the frequent disconnection and extra network overhead may be incurred in the PHY, MAC, or network layer to establish them (routes) due to dynamic topology caused by channel fading as well as nodes mobility. In this paper, we propose to integrate into the relay selection scheme a routing metric which combines the impact of mobility parameters and channel fading, in order to select most stable and lowest fade routes. On the other side, in congested scenarios, pausing only on these movement parameters, one vehicle may be selected as a relay by large number of vehicles, if the number of relay requests exceeds the service capacity of the vehicle, it might get overloaded, and eventually dropping packets and enforcing re-transmissions may be happening. In this paper, we base on the fuzzy logic system between channel availability and queue occupancy to adapt the value of maximum forwarding time used in contention-based forwarding approach which is adopted in our relay selection scheme, in order to reduce as much as possible having overload relays in the network. The simulation results show that the proposed protocol enhances throughput and decreases overhead with a comparable end to end delay.

Evaluation of MAC contention techniques for efficient geo-routing in vehicular networks

In this paper we provide a novel performance evaluation methodology and fair comparison of the most relevant MAC-network cross-layer proposals for efficient geo-routing in the context of vehicular networks. In particular, GeoNetworking, the standard European network layer protocol for vehicle-to-vehicle (V2V) communications, proposes Contention-Based Forwarding (CBF) as basic forwarding mechanism, which can be also implemented at MAC layer in order to optimize its operation. A categorization and unified formal description of different proposals for such contention-based mechanisms is provided. We not only qualitatively discuss them, but also derive a more precise mathematical description of the operation of the proposals. Then we put forward a common framework for the analysis of their performance in the critical scenario of emergency warning delivery. Interestingly, with this model the performance metrics can be computed even when each vehicle selects its contention slot in a different way, unlike other models. This approach is validated by a thorough evaluation of the selected proposals in single-hop and multi-hop scenarios under ideal propagation conditions with both the proposed model and simulations. Finally, these techniques are also evaluated under more realistic fading conditions and compared with the purely network-layer implementation of CBF.

A new link lifetime estimation method for greedy and contention-based routing in mobile ad hoc networks

Greedy and contention-based forwarding schemes were proposed for mobile ad hoc networks (MANETs) to perform data routing hop-by-hop, without prior discovery of the end-to-end route to the destination. Accordingly, the neighboring node that satisfies specific criteria is selected as the next forwarder of the packet. Both schemes require the nodes participating in the selection process to be within the area that confronts the location of the destination. Therefore, the lifetime of links for such schemes is not only dependent on the transmission range, but also on the location parameters (position, speed and direction) of the sending node and the neighboring node as well as the destination. In this paper, we propose a new link lifetime prediction method for greedy and contention-based routing which can also be utilized as a new stability metric. The evaluation of the proposed method is conducted by the use of stability-based greedy routing algorithm, which selects the next hop node having the highest link stability.

Contention-based forwarding with multi-hop connectivity awareness in vehicular ad-hoc networks

Recent vehicular routing proposals use real-time road traffic density estimates to dynamically select forwarding paths. Estimating the traffic density in vehicular ad hoc networks requires the transmission of additional dedicated messages increasing the communications load. These proposals are generally based on unicast sender-based forwarding schemes. The greedy nature of sender-based forwarding can result in the selection of forwarders with weak radio links that might compromise the end-to-end performance. To overcome these limitations, this paper presents TOPOCBF, a novel contention-based broadcast forwarding protocol that dynamically selects forwarding paths based on their capability to route packets between anchor points. Such capability is estimated by means of a multi-hop connectivity metric. The obtained results demonstrate that TOPOCBF can provide good packet delivery ratios while reducing the communications load compared to unicast sender-based forwarding schemes using road traffic density estimates.

Area Partition-Based Suppression Algorithm for Contention-Based Forwarding in Mobile Ad-Hoc Networks

Contention-Based Forward (CBF) has proven to achieve a very good performance in mobile ad-hoc networks. Compare with other greedy forward algorithm, CBF is much more robust and have low maintenance network overheads. On the other hand, the main issue of CBF is to avoid packet duplication. Duplication is very easy to occur due to the hidden nodes problem. In this paper we introduce an area partition-based suppression algorithm for CBF in mobile ad-hoc networks. This algorithm sets the transmission area of a node into two areas: suppression area and none-suppression area. In the none-suppression area, the algorithm still use the SS-CBF (Sender Suppression-CBF) algorithm, in the suppression area, this paper will use a new equation to avoid packet duplication. The result shows that the new protocol could reduce the network overheads and do not cost extra transmission time.

Contention-Based Forwarding의 신뢰성 향상 방안

무선 단말과 자동차 산업의 발전으로 도로 위의 차량들이 데이터 전달의 주체가 되는 차량 애드 혹 네트워크(Vehicular Ad hoc Networks, VANET)에 대한 연구가 활발하다. 차량에 의해 전달되는 데이터는 승객/운전자의 안전 및 교통 혼잡에 영향을 주는 긴급한 정보를 포함하고 있으므로 빠르고 신뢰성 있게 전달되어야 하고, 이를 위한 라우팅 프로토콜은 VANET의 성능에 큰 영향을 미친다. 이에 본 논문에서는 데이터 전달에 참여하는 차량의 이동 방향이 성능이 미치는 영향을 살펴보고, 이를 기반으로 신호등이 있는 도로에서 빠르고 신뢰성 있게 메시지를 전파하기 위해 CBF(Contention-Based Forwarding)를 확장하는 방안을 제안한다. 제안하는 방안은 신호등이 있는 도로에서 메시지 전파의 신뢰성을 높이면서도 전달 차량 간의 위치 관계 변화에 의한 라우팅 루프와 메시지 전달이 중단되는 등의 문제를 발생시키지 않는다. 또한 시뮬레이션을 통하여 제안하는 방안을 적용한 CBF(R-CBF)와 기존 연구 중 메시지 전달의 신뢰성을 향상시키되 메시지 전파 방향과 반대로 이동하는 차량을 전달 차량으로 선택하는 G-SRMB의 성능을 비교하여 R-CBF가 G-SRMB에 비해 메시지 전파 지연 시간을 최대 38% 감소시키고, 불필요한 재전송 없이 동작함을 확인하였다. Due to recent advances in wireless devices and the automotive industry, Vehicular Ad hoc Networks (VANETs) have emerged as a very promising technology for transferring data collected on the road by moving cars. The delivered data may contain emergency information which affects the safety of passengers and drivers as well as the traffic congestion, and the routing protocols have thus a significant impact on the performance of VANETs. In this paper, we study the impact of movement direction of the participating cars which forward data packets on the performance of data delivery and present a new approach which extends the contention-based forwarding (CBF). The proposed reliable CBF (R-CBF) increases the reliability of data deliver on the traffic lights installed roads and reduces the overall propagation delay without routing loops or interruption of data forwarding that may be caused by changes of relative positions of involving cars in routing. Simulation demonstrates that the R-CBF diminishes propagation delay by 38% in comparison to G-SRMB which forwards data to moving cars in the backward direction and eliminates unnecessary retransmissions.

Adapting contention-based forwarding to urban vehicular topologies for active safety applications

Contention-based forwarding (CBF) is a broadcasting technique used to disseminate emergency messages for traffic safety applications in intelligent transportation systems. Its design hypotheses have however been based on three major assumptions: uniform vehicular topology, nonfading channels and homogeneous communication capabilities. Realistic vehicular urban topologies do not comply with any of them, making CBF select relays, which may not exist, may not be reached or may not be optimal due to heterogeneous transmit capabilities. In this paper, we propose to adapt CBF to such challenging environment by first employing two different mechanisms as a function of the topology and second by considering the dissemination capabilities of the relays, allowing for example road-side units or tall vehicles to preferably act as relays when necessary. Our protocol, called Bi-Zone Broadcast, is evaluated in a realistic urban environment and showed to provide around 46 % improvement in dissemination delay and 40 % reduction in overhead compared to plain CBF or flooding. We finally shed light to other aspects of CBF that remain unsolved and should be addressed in future work to further improve the reliability of dissemination protocols for traffic safety protocols.

Towards intelligent contention-based geographic forwarding in wireless sensor networks

Contention-based geographic forwarding (CGF) is a state-free communication paradigm for data delivery in multihop wireless sensor networks. CGF is robust to frequent topology changes, scalable to large-scale node deployment and applicable to data-centric applications and resource constrained networks. However, CGF may experience significant performance degradation under unreliable links. In this work, we present the intelligent CGF (ICGF) to combat the channel variation. IGCF combines the advantages of both cooperative and contention-based forwarding, involving multiple neighbours of the sender into the local forwarding to improve the transmission reliability. ICGF differs from existing work in that it extends the cooperation scope intelligently, by sending one additional control message on demand. For this reason, the probability of cooperation void in ICGF is decreased and the single-hop packet progress is increased. The authors conduct extensive simulations to study the performance of the proposed ICGF compared with existing protocols. Simulation results demonstrate that ICGF improves the end-to-end data delivery delay, energy efficiency and data delivery ratio.

An Opportunistic Forwarding Scheme Exploiting both Long Progress and Adaptive Rate in Wireless Networks

In Mobile Ad hoc Networks (MANET) geographic routing is characterized by local forwarding decision. Links with a long progress are preferred under the greedy forwarding rule. However in a real system long links tend to have a high packet loss rate due to multipath fading. A sub-optimal solution may separately exploit path diversity or rate adaptation. In this paper we study channel efficiency of multi-hop forwarding and try to jointly optimize rate adaptation and forwarder selection in geographic routing by the tradeoff between progress and instantaneous rate. We define a new metric-Bit Transfer Speed (BTS)-as the ratio of the progress made towards the destination to the equivalent time taken to transfer a payload bit. This metric takes overhead, rate and progress into account. Then we propose a packet forwarding scheme that Opportunistically exploits both long Progress and Adaptive Rate (OPAR) by a cross-layer design of routing and MAC. In OPAR each node selects for a packet the forwarder with the highest BTS. The forwarder changes as local topology (progress), packet size (overhead ratio) or channel state (data rate) varies. Simulation results show that compared with the normalized advance (NADV) [7] scheme and contention-based forwarding (CBF) [17] scheme, OPAR has lower packet loss and can effectively reduce channel occupation time by over 30% in the scenario with moderate mobility speeds.

Beacon-Less Geographic Routing in Real Wireless Sensor Networks

Geographic Routing (GR) algorithms require nodes to periodically transmit HELLO messages to allow neighbors to know their positions (beaconing mechanism). Beacon-less routing algorithms have recently been proposed to reduce the control overheads due to these messages. However, existing beacon-less algorithms have not considered realistic physical layers. Therefore, those algorithms cannot work properly in realistic scenarios. In this paper we present a new beaconless routing protocol called BOSS. Its design is based on the conclusions of our open-field experiments using Tmote-sky sensors. BOSS is adapted to error-prone networks and incorporates a new mechanism to reduce collisions and duplicate messages produced during the selection of the next forwarder node. We compare BOSS with Beacon-Less Routing (BLR) and Contention-Based Forwarding (CBF) algorithms through extensive simulations. The results show that our scheme is able to achieve almost perfect packet delivery ratio (like BLR) while having a low bandwidth consumption (even lower than CBF). Additionally, we carried out an empirical evaluation in a real testbed that shows the correctness of our simulation results.

Contention-based forwarding for mobile ad hoc networks

Existing position-based unicast routing algorithms which forward packets in the geographic direction of the destination require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically. Due to mobility, the information that a node receives about its neighbors becomes outdated, leading either to a significant decrease in the packet delivery rate or to a steep increase in load on the wireless channel as node mobility increases. In this paper, we propose a mechanism to perform position-based unicast forwarding without the help of beacons. In our contention-based forwarding scheme (CBF) the next hop is selected through a distributed contention process based on the actual positions of all current neighbors. For the contention process, CBF makes use of biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. We propose three suppression strategies which vary with respect to forwarding efficiency and suppression characteristics. We analyze the behavior of CBF with all three suppression strategies and compare it to an existing greedy position-based routing approach by means of simulation with ns-2. Our results show that CBF significantly reduces the load on the wireless channel required to achieve a specific delivery rate compared to the load a beacon-based greedy forwarding strategy generates.