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ISBN: 978-972-8939-25-0 © 2010 IADISfor P2MAN. Through simulations in NS-2 (Fall & Varadhan), we show that our solution minimizes roguepeers activities.The remainder of the paper is organized as follows. In Section 2 we confront the state of the art with ourapproach. In Section 3 we detail our solution. In Section 4 we describe our simulation-based study andpresent our results. We conclude this work in Section 5, where we also point out future work.2. RELATED WORKS2.1 P2P Content Distribution on MANETsDistribute contents on MANETs is a difficult problem and some proposals employ a sort of peer-to-peerprotocols to accomplish content distribution. Prior works are basically adaptations of standard P2Palgorithms to MANETs (Kortuem et al., 2001; Klemm et al., 2003; Androutsellis-Theotokis & Spinellis,2004). We highlight the recent efforts to deal with BitTorrent on MANETs (Rajagopalan et al, 2006; Sbai &Barakat, 2009; Krifa, et al., 2009). Implement a popular protocol like BitTorrent on MANETs may result inimmediate acceptance and there would be fewer efforts to educate users. However, many P2P contentdistribution protocols present known drawbacks when running on MANETs, as follows.Popular P2P protocols have the Internet as their native habitat, contrasting with a MANET scale of justdozens to hundreds nodes. Regarding the scale, some works (Ding & Bhargava, 2004; Pucha et al., 2004)have adapted the Distributed Hash Table and other P2P location technologies to MANETs. Also, MANETshave intrinsic infrastructure problems that those P2P systems are not concerned with. For instance, BitTorrentemploy unicast, which is costly in MANETs due to the handshake efforts, disregards potential security issuesdue to a shared radio channel infrastructure, and assumes that if a node can achieve a good throughput withits neighbor, there is no other metric cost to be considered. In a MANET, due to the mobility and thecooperative hop by hop nature, a peer transmission may cost too much (i.e., excessive collision, contention)for the entire network, since each P2P transmission may have an undesired impact in neighboringtransmissions. Due to the dynamic nature of a MANET, P2P content distribution protocols need to beadapted to be trackerless.Moreover, it has been shown that TCP like protocols (Holland & Vaidya, 1999) perform poorly inmultihop wireless networks (i.e., packet losses due to link failures are misunderstood as congestion). Inefforts to solve that problem, Anastasi et al. (2009) have developed a new cross-layer transport protocol (i.e.,TPA) to be an efficient reliable protocol for MANETs. In fact, recent P2P solutions to distribute contents onMANETs leverage mostly on cross-layer approaches, which are basically protocols of one layer exchanginginformation with a protocol from another layer. For instance, there are some works that employ crosslayeringon overlay unicast and multicast routing at the application layer (Lee et al., 2006; Passarela et al.,2006; Yi et al., 2008). This practice is becoming usual, but it violates the OSI standard model. This is themain reason why we have not developed P2MAN as a cross-layer approach.2.1.1 Peer-to-MANETPeer-to-MANET (P2MAN) is a multicast based content distribution protocol for mobile ad hoc networks.P2MAN is designed to mitigate MANET’s constraints, achieving good performance by taking advantage ofP2P concepts and MANETs’ capabilities. Since MANETs usually employ unreliable broadcasts on a sharedradio channel, in P2MAN we propose the application of unreliable multicast transmissions instead of reliableunicast transmissions to distribute contents on MANETs. Likewise, we have not considered a reliabletransport protocol. Instead, we adopted UDP as transport protocol. P2MAN uses multicast groups to delivercontents, and a special multicast group, called Public Channel (PC), to accomplish all control functions.When a P2MAN node starts, it joins the PC for exchanging control messages. All nodes willing to shareany content are PC members. Content location is not cached at any node. Instead, to search for any content, anode queries the PC without the need for a network-wide flooding of control messages. In case any activepeer has the content, the peer is reachable through the PC group, and a reply is propagated back through thePC group. The reply also carries metadata generated by the content owner, having detailed information aboutthe file.220