Showing papers on "Optimized Link State Routing Protocol published in 2007"

The Dynamic Source Routing Protocol (DSR) for Mobile Ad Hoc Networks for IPv4

Abstract: The Dynamic Source Routing protocol (DSR) is a simple and efficient routing protocol designed specifically for use in multi-hop wireless ad hoc networks of mobile nodes. DSR allows the network to be completely self-organizing and self-configuring, without the need for any existing network infrastructure or administration. The protocol is composed of the two mechanisms of "Route Discovery" and "Route Maintenance", which work together to allow nodes to discover and maintain source routes to arbitrary destinations in the ad hoc network. The use of source routing allows packet routing to be trivially loop-free, avoids the need for up-to-date routing information in the intermediate nodes through which packets are forwarded, and allows nodes forwarding or overhearing packets to cache the routing information in them for their own future use. All aspects of the protocol operate entirely on-demand, allowing the routing packet overhead of DSR to scale automatically to only that needed to react to changes in the routes currently in use. This document specifies the operation of the DSR protocol for routing unicast IP packets in multi-hop wireless ad hoc networks.

Securing vehicular ad hoc networks

Abstract: Vehicular networks are very likely to be deployed in the coming years and thus become the most relevant form of mobile ad hoc networks. In this paper, we address the security of these networks. We provide a detailed threat analysis and devise an appropriate security architecture. We also describe some major design decisions still to be made, which in some cases have more than mere technical implications. We provide a set of security protocols, we show that they protect privacy and we analyze their robustness and efficiency.

Social network analysis for routing in disconnected delay-tolerant MANETs

Abstract: Message delivery in sparse Mobile Ad hoc Networks (MANETs) is difficult due to the fact that the network graph is rarely (if ever) connected. A key challenge is to find a route that can provide good delivery performance and low end-to-end delay in a disconnected network graph where nodes may move freely. This paper presents a multidisciplinary solution based on the consideration of the so-called small world dynamics which have been proposed for economy and social studies and have recently revealed to be a successful approach to be exploited for characterising information propagation in wireless networks. To this purpose, some bridge nodes are identified based on their centrality characteristics, i.e., on their capability to broker information exchange among otherwise disconnected nodes. Due to the complexity of the centrality metrics in populated networks the concept of ego networks is exploited where nodes are not required to exchange information about the entire network topology, but only locally available information is considered. Then SimBet Routing is proposed which exploits the exchange of pre-estimated "betweenness' centrality metrics and locally determined social "similarity' to the destination node. We present simulations using real trace data to demonstrate that SimBet Routing results in delivery performance close to Epidemic Routing but with significantly reduced overhead. Additionally, we show that SimBet Routing outperforms PRoPHET Routing, particularly when the sending and receiving nodes have low connectivity.

Routing in vehicular ad hoc networks: A survey

Abstract: Vehicular ad hoc network (VANET) is an emerging new technology integrating ad hoc network, wireless LAN (WLAN) and cellular technology to achieve intelligent inter-vehicle communications and improve road traffic safety and efficiency. VANETs are distinguished from other kinds of ad hoc networks by their hybrid network architectures, node movement characteristics, and new application scenarios. Therefore, VANETs pose many unique networking research challenges, and the design of an efficient routing protocol for VANETs is very crucial. In this article, we discuss the research challenge of routing in VANETs and survey recent routing protocols and related mobility models for VANETs.

Securing Vehicular Ad Hoc Networks

Abstract: Ad hoc networks are a new wireless networking paradigm for mobile hosts. In this paper, we designed an intelligent transport system. The ITS (intelligent transport system) includes two big function modules: Information processing application system and Road condition information transferring system. The main task of the road condition information transferring module is in charge of the information exchange of the car inside, car to car and car to road. The module works in ad hoc network, we call the network VANET (vehicular ad-hoc network) . Vehicular networks are likely to become the most relevant form of mobile ad hoc networks. For the sake of insuring the system can run normally, the information can be transferring correctly and fleetly, the security of VANET (vehicular ad-hoc network) of the road condition information transferring system is crucial. So integrate the characteristics of ad hoc network itself, in the ITS of this paper, we concern the security issues of VANETs from some aspects and provide the appropriate solving measures. To make sure the ITS can be used under the security pattern.

Routing in Sparse Vehicular Ad Hoc Wireless Networks

Abstract: A vehicular ad hoc network (VANET) may exhibit a bipolar behavior, i.e., the network can either be fully connected or sparsely connected depending on the time of day or on the market penetration rate of the wireless communication devices. In this paper, we use empirical vehicle traffic data measured on 1-80 freeway in California to develop a comprehensive analytical framework to study the disconnected network phenomenon and its network characteristics. These characteristics shed light on the key routing performance metrics of interest in disconnected VANETs, such as the average time taken to propagate a packet to disconnected nodes (i.e., the re-healing time). Our results show that, depending on the sparsity of vehicles or the market penetration rate of cars using Dedicated Short Range Communication (DSRC) technology, the network re-healing time can vary from a few seconds to several minutes. This suggests that, for vehicular safety applications, a new ad hoc routing protocol will be needed as the conventional ad hoc routing protocols such as Dynamic Source Routing (DSR) and Ad Hoc On-Demand Distance Vector Routing (AODV) will not work with such long re-healing times. In addition, the developed analytical framework and its predictions provide valuable insights into the VANET routing performance in the disconnected network regime.

An Acknowledgment-Based Approach for the Detection of Routing Misbehavior in MANETs

Abstract: We study routing misbehavior in MANETs (mobile ad hoc networks) in this paper. In general, routing protocols for MANETs are designed based on the assumption that all participating nodes are fully cooperative. However, due to the open structure and scarcely available battery-based energy, node misbehaviors may exist. One such routing misbehavior is that some selfish nodes will participate in the route discovery and maintenance processes but refuse to forward data packets. In this paper, we propose the 2ACK scheme that serves as an add-on technique for routing schemes to detect routing misbehavior and to mitigate their adverse effect. The main idea of the 2ACK scheme is to send two-hop acknowledgment packets in the opposite direction of the routing path. In order to reduce additional routing overhead, only a fraction of the received data packets are acknowledged in the 2ACK scheme. Analytical and simulation results are presented to evaluate the performance of the proposed scheme

A survey of routing attacks in mobile ad hoc networks s ecurity i n w ireless m obile a d h oc a nd s ensor n etworks

Abstract: Recently, mobile ad hoc networks became a hot research topic among researchers due to their flexibility and independence of network infrastructures, such as base stations. Due to unique characteristics, such as dynamic network topology, limited bandwidth, and limited battery power, routing in a MANET is a particularly challenging task compared to a conventional network. Early work in MANET research has mainly focused on developing an efficient routing mechanism in such a highly dynamic and resource-constrained network. At present, several efficient routing protocols have been proposed for MANET. Most of these protocols assume a trusted and cooperative environment. However, in the presence of malicious nodes, the networks are vulnerable to various kinds of attacks. In MANET, routing attacks are particularly serious. In this article, we investigate the state-of-the-art of security issues in MANET. In particular, we examine routing attacks, such as link spoofing and colluding misrelay attacks, as well as countermeasures against such attacks in existing MANET protocols.

Detecting Blackhole Attack on AODV-based Mobile Ad Hoc Networks by Dynamic Learning Method.

Abstract: This paper analyzes the blackhole attack which is one of the possible attacks in ad hoc networks. In a blackhole attack, a malicious node impersonates a destination node by sending a spoofed route reply packet to a source node that initiates a route discovery. By doing this, the malicious node can deprive the traffic from the source node. In order to prevent this kind of attack, it is crucial to detect the abnormality occurs during the attack. In conventional schemes, anomaly detection is achieved by defining the normal state from static training data. However, in mobile ad hoc networks where the network topology dynamically changes, such static training method could not be used efficiently. In this paper, we propose an anomaly detection scheme using dynamic training method in which the training data is updated at regular time intervals. The simulation results show the effectiveness of our scheme compared with conventional scheme.

A survey of routing attacks in mobile ad hoc networks

Abstract: Recently, mobile ad hoc networks became a hot research topic among researchers due to their flexibility and independence of network infrastructures, such as base stations. Due to unique characteristics, such as dynamic network topology, limited bandwidth, and limited battery power, routing in a MANET is a particularly challenging task compared to a conventional network. Early work in MANET research has mainly focused on developing an efficient routing mechanism in such a highly dynamic and resource-constrained network. At present, several efficient routing protocols have been proposed for MANET. Most of these protocols assume a trusted and cooperative environment. However, in the presence of malicious nodes, the networks are vulnerable to various kinds of attacks. In MANET, routing attacks are particularly serious. In this article, we investigate the state-of-the-art of security issues in MANET. In particular, we examine routing attacks, such as link spoofing and colluding misrelay attacks, as well as countermeasures against such attacks in existing MANET protocols.

Practical Routing in Delay-Tolerant Networks

Abstract: Delay-tolerant networks (DTNs) have the potential to interconnect devices in regions that current networking technology cannot reach. To realize the DTN vision, routes must be found over multiple unreliable, intermittently-connected hops. In this paper we present a practical routing protocol that uses only observed information about the network. We designed a metric that estimates the average waiting time for each potential next hop. This learned topology information is distributed using a link-state routing protocol, where the link-state packets are "flooded" using epidemic routing. The routing is recomputed each time connections are established, allowing messages to take advantage of unpredictable contacts. A message is forwarded if the topology suggests that the connected node is "closer" to the destination than the current node. We demonstrate through simulation that our protocol provides performance similar to that of schemes that have global knowledge of the network topology, yet without requiring that knowledge. Further, it requires significantly less resources than the alternative, epidemic routing, suggesting that our approach scales better with the number of messages in the network. This performance is achieved with minimal protocol overhead for networks of approximately 100 nodes.

Broadcasting in VANET

Abstract: In this paper, we report the first complete version of a multi-hop broadcast protocol for vehicular ad hoc networks (VANET). Our results clearly show that broadcasting in VANET is very different from routing in mobile ad hoc networks (MANET) due to several reasons such as network topology, mobility patterns, demographics, traffic patterns at different times of the day, etc. These differences imply that conventional ad hoc routing protocols such as DSR and AODV will not be appropriate in VANETs for most vehicular broadcast applications. We identify three very different regimes that a vehicular broadcast protocol needs to work in: i) dense traffic regime; ii) sparse traffic regime; and iii) regular traffic regime. We build upon our previously proposed routing solutions for each regime and we show that the broadcast message can be disseminate efficiently. The proposed design of the distributed vehicular broadcast (DV-CAST) protocol integrates the use of various routing solutions we have previously proposed.

A survey of QoS routing solutions for mobile ad hoc networks

Abstract: In mobile ad hoc networks (MANETs), the provision of quality of service (QoS) guarantees is much more challenging than in wireline networks, mainly due to node mobility, multihop communications, contention for channel access, and a lack of central coordination. QoS guarantees are required by most multimedia and other time- or error-sensitive applications. The difficulties in the provision of such guarantees have limited the usefulness of MANETs. However, in the last decade, much research attention has focused on providing QoS assurances in MANET protocols. The QoS routing protocol is an integral part of any QoS solution since its function is to ascertain which nodes, if any, are able to serve applications? requirements. Consequently, it also plays a crucial role in data session admission control. This document offers an up-to-date survey of most major contributions to the pool of QoS routing solutions for MANETs published in the period 1997?2006. We include a thorough overview of QoS routing metrics, resources, and factors affecting performance and classify the protocols found in the literature. We also summarize their operation and describe their interactions with the medium access control (MAC) protocol, where applicable. This provides the reader with insight into their differences and allows us to highlight trends in protocol design and identify areas for future research.

A survey on real-world implementations of mobile ad-hoc networks

Abstract: Simulation and emulation are valuable techniques for the evaluation of algorithms and protocols used in mobile ad-hoc networks. However, these techniques always require the simplification of real-world properties such as radio characteristics or node mobility. It has been shown that this may lead to results and conclusions which do not reflect the behavior of ad-hoc networks in the real world. Various prototype implementations demonstrate that even simple protocols such as flooding do not behave as it was predicted by earlier simulation. To overcome this problem, real-world experiments are required. In this paper, we present a survey on existing real-world implementations of mobile ad-hoc networks. We report on the technology used for the implementations as well as on key findings from experiments conducted with these implementations.

Prediction-Based Routing for Vehicular Ad Hoc Networks

Abstract: Development in short-range wireless LAN (WLAN) and long-range wireless WAN (WWAN) technologies have motivated recent efforts to integrate the two. This creates new application scenarios that were not possible before. Vehicles with only WLAN radios can use other vehicles that have both WLAN and WWAN radios as mobile gateways and connect to the Internet while on the road. The most difficult challenge in the scenario is to deal with frequent route breakages due to dynamic mobility of vehicles on the road. Existing routing protocols that are widely used for mobile ad hoc networks are reactive in nature and wait until existing routes break before constructing new routes. The frequent route failures result in a significant amount of time needed for repairing existing routes or reconstructing new routes. In spite of the dynamic mobility, the motion of vehicles on highways is quite predictable compared to other mobility patterns for wireless ad hoc networks, with location and velocity information readily available. This can be exploited to predict how long a route will last between a vehicle requiring Internet connectivity and the gateway that provides a route to the Internet. Successful prediction of route lifetimes can significantly reduce the number of route failures. In this paper, we introduce a prediction-based routing (PBR) protocol that is specifically tailored to the mobile gateway scenario and takes advantage of the predictable mobility pattern of vehicles on highways. The protocol uses predicted route lifetimes to preemptively create new routes before existing ones fail. We study the performance of this protocol through simulation and demonstrate significant reductions in route failures compared to protocols that do not use preemptive routing. Moreover, we find that the overhead of preemptive routing is kept in check due to the ability of PBR to predict route lifetimes.

An Improved Vehicular Ad Hoc Routing Protocol for City Environments

Abstract: The fundamental component for the success of VANET (vehicular ad hoc networks) applications is routing since it must efficiently handle rapid topology changes and a fragmented network. Current MANET (mobile ad hoc networks) routing protocols fail to fully address these specific needs especially in a city environments (nodes distribution, constrained but high mobility patterns, signal transmissions blocked by obstacles, etc.). In our current work, we propose an inter-vehicle ad-hoc routing protocol called GyTAR (improved greedy traffic aware routing protocol) suitable for city environments. GyTAR consists of two modules: (i) dynamic selection of the junctions through which a packet must pass to reach its destination, and (ii) an improved greedy strategy used to forward packets between two junctions. In this paper, we give detailed description of our approach and present its added value compared to other existing vehicular routing protocols. Simulation results show significant performance improvement in terms of packet delivery ratio, end-to-end delay, and routing overhead.

Comparative Study of Reactive and Proactive Routing Protocols Performance in Mobile Ad Hoc Networks

Abstract: The mobility of nodes in mobile ad hoc networks (MANETs) results in frequent changes of network topology making routing in MANETs a challenging task. Some studies have been reported in the literature to evaluate the performance of the proposed routing algorithms. However, since the publication of experimental standards for some routing protocols by IETF, little activity has been done to contrast the performance of reactive against proactive protocols. This paper evaluates the performance of reactive (AODV, DSR) and proactive (OLSR) routing protocols in MANETs under CBR traffic with different network conditions. Our results, contrarily to previously reported studies conducted on the same routing protocols, show the superiority of proactive over reactive protocols in routing such traffic at the cost of a higher routing load.

A Distributed Joint Channel-Assignment, Scheduling and Routing Algorithm for Multi-Channel Ad-hoc Wireless Networks

Abstract: The capacity of ad hoc wireless networks can be substantially increased by equipping each network node with multiple radio interfaces that can operate on multiple non-overlapping channels. However, new scheduling, channel-assignment, and routing algorithms are required to fully utilize the increased bandwidth in multi-channel multi-radio ad hoc networks. In this paper, we develop a fully distributed algorithm that jointly solves the channel-assignment, scheduling and routing problem. Our algorithm is an online algorithm, i.e., it does not require prior information on the offered load to the network, and can adapt automatically to the changes in the network topology and offered load. We show that our algorithm is provably efficient. That is, even compared with the optimal centralized and offline algorithm, our proposed distributed algorithm can achieve a provable fraction of the maximum system capacity. Further, the achievable fraction that we can guarantee is larger than that of some other comparable algorithms in the literature.

Prevention of Blackhole Attack in MANET

Abstract: An ad hoc network is a collection of mobile nodes that dynamically form a temporary network. It operates without the use of existing infrastructure. One of the principal routing protocols used in ad-hoc networks is AODV (ad-hoc on demand distance vector) protocol. The security of the AODV protocol is compromised by a particular type of attack called 'black hole' attack. In this attack a malicious node advertises itself as having the shortest path to the node whose packets it wants to intercept. To reduce the probability it is proposed to wait and check the replies from all the neighboring nodes to find a safe route. Computer simulation using glomosim shows that our protocol provides better performance than the conventional AODV in the presence of Black holes with minimal additional delay and Overhead.

Multihop Ad Hoc Networking: The Reality

Abstract: In this article we show that, although pure general-purpose MANET (mobile ad hoc networks) does not yet exist in the real world, the multihop ad hoc networking paradigm was successfully applied in several classes of networks that are penetrating the mass market. We present as examples mesh, opportunistic, vehicular, and sensor networks, where the multi-hop ad hoc paradigm is applied in a pragmatic way to extend the Internet and/or to support well-defined application requirements. We contrast these successful areas of ad hoc networking to the lack of impact of pure general-purpose MANET, demonstrating how a more pragmatic approach is a winner

A graph theoretic framework for preventing the wormhole attack in wireless ad hoc networks

Abstract: Wireless ad hoc networks are envisioned to be randomly deployed in versatile and potentially hostile environments. Hence, providing secure and uninterrupted communication between the un-tethered network nodes becomes a critical problem. In this paper, we investigate the wormhole attack in wireless ad hoc networks, an attack that can disrupt vital network functions such as routing. In the wormhole attack, the adversary establishes a low-latency unidirectional or bi-directional link, such as a wired or long-range wireless link, between two points in the network that are not within communication range of each other. The attacker then records one or more messages at one end of the link, tunnels them via the link to the other end, and replays them into the network in a timely manner. The wormhole attack is easily implemented and particularly challenging to detect, since it does not require breach of the authenticity and confidentiality of communication, or the compromise of any host. We present a graph theoretic framework for modeling wormhole links and derive the necessary and sufficient conditions for detecting and defending against wormhole attacks. Based on our framework, we show that any candidate solution preventing wormholes should construct a communication graph that is a subgraph of the geometric graph defined by the radio range of the network nodes. Making use of our framework, we propose a cryptographic mechanism based on local broadcast keys in order to prevent wormholes. Our solution does not need time synchronization or time measurement, requires only a small fraction of the nodes to know their location, and is decentralized. Hence, it is suitable for networks with the most stringent constraints such as sensor networks. Finally, we believe our work is the first to provide an analytical evaluation in terms of probabilities of the extent to which a method prevents wormholes.

A static-node assisted adaptive routing protocol in vehicular networks

Abstract: Vehicular networks have attracted great interest in the research community recently, and multi-hop routing becomes an important issue. To improve data delivery performance, we propose SADV, which utilizes some static nodes at road intersections in a completely mobile vehicular network to help relay data. With the assistance of static nodes at intersections, a packet can be stored in the node for a while and wait until there are vehicles within communication range along the best delivery path to further forward the packet, which reduces the overall data delivery delay. In addition, we let adjacent nodes measure the delay of forwarding data between each other in real time, so that the routing decision can adapt to changing vehicle densities. Our simulation results show that SADV outperforms other multi-hop data dissemination protocols, especially under median or low vehicle density where the network is frequently partitioned.

Ad Hoc Mobile Wireless Networks Routing Protocols - A Review

Abstract: Mobile ad hoc networks(MANET) represent complex distributed systems that comprise wireless mobile nodes that can freely and dynamically self organize into arbitrary and temporary ad-hoc network topologies, allowing people and devices to seamlessly internet work in areas with no preexisting communication infrastructure e.g., disaster recovery environments. An ad-hoc network is not a new one, having been around in various forms for over 20 years. Traditionally, tactical networks have been the only communication networking application that followed the ad-hoc paradigm. Recently the introduction of new technologies such as Bluetooth, IEEE 802.11 and hyperlan are helping enable eventual commercial MANET deployments outside the military domain. These recent revolutions have been generating a renewed and growing interest in the research and development of MANET. To facilitate communication within the network a routing protocol is used to discover routes between nodes. The goal of the routing protocol is to have an efficient route establishment between a pair of nodes, so that messages can be delivered in a timely manner. Bandwidth and power constraints are the important factors to be considered in current wireless network because multi-hop ad-hoc wireless relies on each node in the network to act as a router and packet forwarder. This dependency places bandwidth, power computation demands on mobile host to be taken into account while choosing the protocol. Routing protocols used in wired network cannot be used for mobile ad-hoc networks because of node mobility. The ad-hoc routing protocols are divided into two classes: table driven and demand based. This paper reviews and discusses routing protocol belonging to each category.

A survey on congestion control for mobile ad hoc networks

Abstract: Congestion control is a key problem in mobile ad hoc networks. The standard congestion control mechanism of the Transmission Control Protocol (TCP) is not able to handle the special properties of a shared wireless multi-hop channel well. In particular, the frequent changes of the network topology and the shared nature of the wireless channel pose significant challenges. Many approaches have been proposed to overcome these difficulties. In this paper, we give an overview over existing proposals, explain their key ideas and show their interrelations. Copyright © 2007 John Wiley & Sons, Ltd.

A Survey of Routing Protocols that Support QoS in Mobile Ad Hoc Networks

Abstract: The explosive growth in the use of mobile devices coupled with users' desires for real-time applications has provided new challenges in the design of protocols for mobile ad hoc networks. Chief among these challenges to enabling real-time applications for mobile ad hoc networks is incorporating support for quality of service (QoS), such as meeting bandwidth or delay constraints. In particular, it is important that routing protocols incorporate QoS metrics in route finding and maintenance to support end-to-end QoS. This article extensively and exclusively studies the issues involved with QoS-aware routing and presents an overview and comparison of existing QoS-aware routing protocols. In addition, the open issues that must be addressed to fully support QoS-aware routing are discussed.

DARWIN: distributed and adaptive reputation mechanism for wireless ad-hoc networks

Abstract: Mobile ad-hoc networks are deployed under the assumption that participating nodes are willing to forward other nodes' packets. In reputation-based mechanisms cooperation is induced by means of a threat of partial or total disconnection from the network if a node is non-cooperative; however packet collisions and interference may make cooperative nodes appear selfish sometimes. In this paper we use a simple network model to first study the performance of some proposed reputation strategies and then present a new mechanism that we call DARWIN (Distributed and Adaptive Reputation mechanism for WIreless ad-hoc Networks). The idea is to avoid a retaliation situation after a node has been falsely perceived as selfish so cooperation can be restored quickly. We prove that our strategy is robust to imperfect measurements, is collusion-resistant and can achieve full cooperation among nodes.

Variable-Range Transmission Power Control in Wireless Ad Hoc Networks

Abstract: In this paper, we investigate the impact of variable-range transmission power control on the physical and network connectivity, on network capacity, and on power savings in wireless multihop networks. First, using previous work by Steele (1988), we show that, for a path attenuation factor a = 2, the average range of links in a planar random network of A m2 having n nodes is ~aradicA/n1. We show that this average range is approximately half the range obtained when common-range transmission control is used. Combining this result and previous work by Gupta and Kumar (2000), we derive an expression for the average traffic carrying capacity of variable-range-based multihop networks. For a = 2, we show that this capacity remains constant even when more nodes are added to the network. Second, we derive a model that approximates the signaling overhead of a routing protocol as a function of the transmission range and node mobility for both route discovery and route maintenance. We show that there is an optimum setting for the transmission range, not necessarily the minimum, which maximizes the capacity available to nodes in the presence of node mobility. The results presented in this paper highlight the need to design future MAC and routing protocols for wireless ad hoc and sensor networks based, not on common-range which is prevalent today, but on variable-range power control

A Cross Layered MAC and Clustering Scheme for Efficient Broadcast in VANETs

Abstract: In this paper, we illustrate the design of a cross-layered MAC and clustering solution for supporting the fast propagation of broadcast messages in a vehicular ad hoc network (VANET). A distributed dynamic clustering algorithm is proposed to create a dynamic virtual backbone in the vehicular network. The vehicle-members of the backbone are responsible for implementing an efficient messages propagation. The backbone creation and maintenance are proactively performed aiming to balance the stability of backbone connections as well as the cost/efficiency trade-off and the hops-reduction when forwarding broadcast messages. A fast multi-hop MAC forwarding mechanism is defined to exploit the role of backbone vehicles, under a cross-layered approach. Simulation results show the effectiveness of the mutual support of proactive clustering and MAC protocols for efficient dissemination of broadcast messages in VANETs.

On the Routing Problem in Disconnected Vehicular Ad-hoc Networks

Abstract: Vehicular ad hoc wireless network (VANET) exhibits a bipolar behavior in terms of network topology: fully connected topology with high traffic volume or sparsely connected topology when traffic volume is low. In this work, we develop a statistical traffic model based on the data collected on 1-80 freeway in California in order to study key performance metrics of interest in disconnected VANETs, such as average re-healing time (or the network restoration time). Our results show that, depending on the sparsity of vehicles, the network re-healing time can vary from a few seconds to several minutes. This suggests that, a new ad hoc routing protocol will be needed as the conventional ad hoc routing protocols such as dynamic source routing (DSR) and ad hoc on-demand distance vector routing (AODV) will not work with such long re-healing times.