Secure Communication over Heterogeneous Networks with Clustered Mobile Ad hoc Extensions Dimitrios Vogiatzis, Spyridon Vassilaras and Gregory S. Yovanof Athens Information Technology e-mail: {dvog, svas, gyov}@ait.edu.gr Abstract — In addition to classical security issues, clustered ad hoc networks face the possibility that some nodes may exhibit uncooperative behaviour. Therefore, misbehaviour detection and reputation mechanisms need to be implemented in order to reinforce node cooperation. In this paper, we address the issue of detecting non- cooperative behaviour during packet forwarding in heterogeneous networks with clustered mobile ad hoc extensions. The proposed solution incorporates end-to-end authenticated acknowledgments for each transmitted packet, combined with explicit authenticated alarms sent by legitimate nodes along the path to the source, every time they encounter a suspicious event. Low computational overhead is achieved by employing an adapted version of the TESLA symmetric key broadcast authentication protocol. Index Terms — Ad hoc Networks, Packet Forwarding, Clusters, Misbehaviour Detection, TESLA. 1. Introduction The emergence and adoption of wireless standards, such as the WLAN WiFi (IEEE 802.11a/b/g), WPAN Bluetooth (802.15.1) and 3G (UMTS/HDSPA) has boosted a vast range of applications and services, including Internet browsing, file transfer, messaging, news, games, entertainment, location based services, etc. At the same time, the wide deployment of these wireless technologies has contributed a lot to the advance and realization of the “always connected, best connected” vision. Unfortunately, despite this explosion in wireless connectivity, there is still increased need for capacity improvement, even in areas where coverage exists. This is especially true, for large urban areas and hotspots (airports, shopping malls, cafes, etc.), where multiple mobile users with different user profiles coexist and compete for network resources, trying to gain access to a variety of wireless services. It is widely acknowledged that the 4G generation of networks will not be based on the prevalence of a single – entirely new or existing – technology but rather on the coexistence, synergy and efficient cooperation of heterogeneous systems and networks. One of the most popular and promising type of network architecture is the clustered ad hoc architecture (Fig. 1). Due to its inherent organizational features, clustered ad hoc networks exhibit many benefits with respect to capacity, interference, frequency reuse and scalability. Fig. 1: Clustered Ad hoc architecture A typical scenario describing the deployment of a clustered ad hoc network is in hotspot areas, where a large number of mobile users with high traffic needs are in the transmission range of each other. To increase the total capacity of such highly dynamic networks, a clustered mobile ad hoc network architecture can be used. In such a setting, a specific set of Mobile Nodes (MNs) that are closely located and want to exchange data are organized into a cluster. Each cluster operates in a different frequency channel to avoid interference with neighbouring clusters. Through the use of power control, MNs limit their transmissions in shorter range. Thus, the network is capable of accommodating more users within the same area and transmissions inside a cluster can achieve higher bit rates. Many of the existing wireless systems operate already in a clustered fashion. For example, in Bluetooth data communication is performed through piconets interconnected with each other to form scatternets. Other systems, such as CANA [1] and CAMA [2] also operate in a clustered way, while at the same time future UWB systems, are believed to adopt a similar clustered type of architecture. The authors in [3] also envision heterogeneous ad hoc networks (using 802.11, Bluetooth and GPRS technologies) that are formed under the central supervision of a cellular network infrastructure. Therefore, it is obvious that clustered