SUMMARYIn vehicular networks, safety and comfort applications are two quite different kinds of applications to avoid the emergency traffic accident and enjoy the non‐emergency entertainment. The comfort application drives the challenges of new non‐emergency entertainments for vehicular ad hoc networks (VANETs). The comfort application usually keeps the delay‐tolerant capability; that is, messages initiated from a specific vehicle at time t can be delivered through VANETs to some vehicles within a given constrained delay time λ. In this paper, we investigate a new mobicast protocol to support comfort applications for a highway scenario in VANETs. All vehicles are located in a geographic zone (denoted as zone of relevance (ZOR)) at time t; the mobicast routing must disseminate the data message initiated from a specific vehicle to all vehicles that have ever appeared in ZOR at time t. This data dissemination must be performed before time t + λ through the carry‐and‐forward technique. In addition, the temporary network fragmentation problem is considered in our protocol design. Also, the low degree of channel utilization is kept to reserve the resource for safety applications. To illustrate the performance achievement, simulation results are examined in terms of message overhead, dissemination success rate, and accumulative packet delivery delay. Copyright © 2012 John Wiley & Sons, Ltd.
Vehicular Ad hoc Network (VANET), a subclass of mobile ad hoc networks (MANETs), is a promising approach for the intelligent transportation system (ITS). The design of routing protocols in VANETs is important and necessary issue for support the smart ITS. The key difference of VANET and MANET is the special mobility pattern and rapidly changeable topology. It is not effectively applied the existing routing protocols of MANETs into VANETs. In this chapter, we mainly survey new routing results in VANET. The authors introduce unicast protocol, multicast protocol, geocast protocol, mobicast protocol, and broadcast protocol. It is observed that carry-and-forward is the new and key consideration for designing all routing protocols in VANETs. With the consideration of multi-hop forwarding and carryand- forward techniques, min-delay and delay-bounded routing protocols for VANETs are discussed in VANETs. Besides, the temporary network fragmentation problem and the broadcast storm problem are further considered for designing routing protocols in VANETs. The temporary network fragmentation problem caused by rapidly changeable topology influence on the performance of data transmissions. The broadcast storm problem seriously affects the successful rate of message delivery in VANETs. The key challenge is to overcome these problems to provide routing protocols with the low communication delay, the low communication overhead, and the low time complexity.
In 1991, Mark Weiser proposed ubiquitous computing that is based on the network environment [1]. It is to create a user centric computing and its environment that is different from the traditional ways and computing models [2]. Ubiquitous computing service aims to develop the various ranges of sensors and networks available to provide timeless services and user's location. A main issue of ubiquitous computing can be context awareness that it is able to provide various services to end users not only based on information but also based on potential contextual information [3].In this content, wireless sensor network (WSN) is a hot issue and new trend of ubiquitous computing technologies to implement the ubiquitous society. WSNs are expected to be applied in many long-term applications such as scientific exploration, preventive maintenance, disaster management, emergency management, security and surveillance, environmental monitoring, monitoring in domestic situations, civil, biological, a wide range of military, and health-care applications, and infrastructure protection. These applications require efficient and flexible sensor networks [4]. So WSNs are composed of a collection of many sensor nodes that are deployed in a sensor field, each of which collects data and relays them to the base station (called a sink node) where data can be analyzed, applied, and used efficiently. Generally, a sensor node is made of a sensing device, a processing unit, a transceiver, and a power unit. The main task can be summarized by three keys: sensing, computing, and communicating [5].A common architecture of WSNs is sink and sensor pair. The sensors deal with measuring the environmental status, which may change with time and space, collaborating with each sensor, and forwarding the measured data from the sensor to the sink. The sink is responsible for integrating, analyzing data received from sensors, and responding to users and applications [6].Many Researchers study and propose their manuscripts and system using WSNs.Hung et al. [7] propose a mechanism to maintain temporal coverage for the quality of monitoring (QoM) using WSNs. Generally, in WSN environment that can require many sensors with powerful energy, they suggest a method to improve energy efficiency.Adhikari [8] reviews designing a good MAC (medium access control) protocol for a WSN. That is, he highlights the importance of MAC in WSN when we implement energy efficient medium access rules among the low capacity sensor nodes.In this technical trend, a context-aware system and application can be hot issue in ubiquitous computing environment. That is, context-awareness techniques can provide both functional and nonfunctional system requirements. Aqeelur-Rehman et al. [9] review importance of context awareness in sensor network and ubiquitous computing. And they present an example that context-aware sensor grid framework should be composed of three layers, sensor network layer, grid computing layer, and context-aware application
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