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The IEEE 802.11 standard defines the specifications of the media access control (MAC) and physical (PHY) layers for vehicular ad hoc networks (VANETs). In IEEE 802.11, distributed coordination function (DCF) is the fundamental access technique, which employs a carrier sense multiple access with collision avoidance (CSMA/CA) mechanism to access the medium. In addition, request to send (RTS)/ clear to send (CTS) mechanism is used to overcome hidden vehicular nodes problem. In this paper, an analytical model is developed to evaluate the performance of the IEEE 802.11 MAC for VANETs. The algorithm of CSMA/CA and RTS/CTS mechanism are presented. Markov chain model based analytical analysis is presented to investigate the performance. Parameters that can influence the performance such as vehicles velocity, vehicle density, contention window size, maximum retransmission limit etc. are considered. The relationship between the performance metrics and parameters are derived. Throughput, packet dropping rate (PDR) and delay expressions are obtained. Moreover, numerical results are demonstrated to verify the analysis. The comparison between CSMA/CA and RTS/CTS access mechanisms is presented. [ABSTRACT FROM AUTHOR]

Wireless Sensor Networks (WSN) are very popular area of interest both in academic studies and industrial applications since they can work individually without additional maintenance and can be deployed in diverse applications. However, the limited source of the nodes cannot guarantee a sufficient level of security and also complicates the design and the implementation of the algorithms/protocols. DoS (Denial of Service) attacks that manipulate vulnerabilities of access protocol by disrupting network communication or arising exceptional cases and cutting network's lifetime are primary threats for wireless sensor networks. S-MAC (Sensor Medium Access Control) and its derivatives (T-MAC [1], D-MAC [2] etc.) which, are the most common medium access protocols designed for WSNs, are vulnerable against such attacks. In this paper, we have implemented the design of the AR-MAC (Attack Resistant MAC) protocol that detects the types of jammers and maintains the appropriate solution for each jammer type. By means of the new MAC protocol designed, the WSNs have been more robust to DoS attacks in MAC layer and the lifetime of the nodes have been extended under such attacks without additional hardware. [ABSTRACT FROM AUTHOR]