Ah.wnci-In this papcr. we introduce a solution for securing tlafa in Ad hoc nctworlii. \\'e esploit thc existence o f multiple paths hctwcen nodes in an A d hoc network to increase the robustness of depends on several paramcters and reaching a good security degree i s il hard task. Hucently, there arc several proposed snlutions trcating authentication. awilahilitp. secure routing and intrusion tlctecrion ctc. in ..\d hoc nctaorka. ,\II nverviea. of some current \ d~t i o n s . implementation details and experimental results are tliwu>sd in this papcr. fr. .inmittud . ' data confidentiality. I n Ad hoc networks, security and attacks. Nodes are easier to be stolen since they are mobile and the computing capacity is limited. That makes using heavy solutions. as PKI [4][5]. not very efficient. Also, A d hoc networks services are provisional and batteries are a limited alimentation resource that makes a Denial o f Service attack. by consumption o f energy, very possible [ 6 ] .

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In wireless networks, the radio link vulnerability attributed to effects such as noise, interference, free-space loss, shadowing and multipath fading, must be considered. MAC protocols developed for these networks do not take into account these perturbations. It was shown, in the literature, that 802.11 suffers from what is called 'the 802.11 anomaly'. This anomaly concerns two aspects: all nodes throughput, in a 802.11 network, falls to the worst one of all nodes and the bandwidth will be divided by the number of the mobile nodes of the network. In order to improve the quality of service of a BSS (Basic Service Set) and to solve 802.11 anomaly, Cross-layer approaches are developed. These approaches are especially based on information given by the Physical layer. In this study we propose a new cross-layer scheme: AMCLM (Adaptive Multi-services Cross-Layer MAC). The goal of this protocol is to improve the Quality-of-Service (QoS) of Mobile Nodes (MNs) connected in a BSS by a temporary disassociation of the ones for which the SNR (Signal to Noise Ratio) is under a defined threshold. In this way, the network's throughput is improved. Our approach aims to improve global networks QoS by unselfishness decisions of nodes. In order to show the benefit of our method, a performance evaluation of this protocol has been made. We have built the discrete Markov Chain associated to the behavior of AMCLM protocol to analyze the throughput of mobile nodes connected to the BSS.