A Secure Characteristics of Wireless Ad-Hoc Networks

Introduction To Wireless Ad-Hoc Networks

An ad-hoc network is a self-configuring network of wireless links connecting mobile nodes. These nodes may be routers and/or hosts. The mobile nodes communicate directly with each other and without the aid of access points, and therefore have no fixed infrastructure. They form an arbitrary topology, where the routers are free to move randomly and arrange themselves as required. First, the devices can freely move in the network, second, the devices can leave and join the network at any time. This type of network can change constantly. Finally, the network disappears when the last devices leave the network (Arkko, J. et al., 2004). The decentralized nature of wireless ad hoc networks makes them suitable for a variety of applications where central nodes cannot be relied on, and may improve the scalability of wireless ad hoc networks compared to wireless managed networks, though theoretical and practical limits to the overall capacity of such networks have been identified. Minimal configuration and quick deployment make ad hoc networks suitable for emergencies like natural disasters or military conflicts. The presence of a dynamic and adaptive routing protocol will enable ad hoc networks to be formed quickly (Buddhikot, M. et al., 2003).

Isolated wireless ad-hoc networks are not suitable for today’s applications that require accessing services in the Internet. To overcome this limitation, one or more devices in the wireless ad-hoc network can provide a gateway to an external network. This external network can be the Internet or a local area network (LAN), which may or may not be an infrastructured network. Wireless networks are more vulnerable to misuse than wired networks. In a wireless network, all devices share the same radio band. If two or more devices transmit simultaneously, the communication fails. In addition, a malicious device may be present in the network. It can analyze the communication in the network and do several attacks by sending invalid data. It can masquerade as another device, or it may do various Man-in-the-Middle (MitM) or Denial-of-Service (DoS) attacks. In particular, it can even block all communication by constantly interfere the transmission. Several security mechanisms partially protect communication in WLAN. WLAN may provide security on the lower layers that corresponds the physical and link layers of the Open Systems Interconnection (OSI) reference model. These mechanisms protect communication authenticity, integrity and confidentiality by using cryptographic methods. Moreover, these mechanisms depend on the WLAN technology. On the other hand, security can be provided independently on upper layers. However, none of these mechanisms protect against DoS attacks because it is impossible to prevent a malicious device from interfering the transmission in a wireless ad-hoc network. It is also possible that not all devices can communicate directly in the wireless ad-hoc network. Such a scenario is shown in Fig. 1. in which device B can communicate with devices A and C directly, but devices A and C cannot communicate directly. This has an impact on the network-layer and application-layer protocols. In the network-layer, not all devices can communicate directly with each other by using IP addresses. Moreover, some applications do not work unless the communication is link-local. For example, Dynamic Configuration of IPv4 Link-Local addresses requires link-local communication to successfully configure and maintain IPv4 addresses.

Figure 1.

Communication link between different networks using gateway

Routing enables communication between devices that cannot communicate directly. In the ad-hoc network, this is done by using an ad-hoc routing protocol. There are two types of routing protocols for ad-hoc networks: Proactive and Reactive. In proactive routing, routes are actively maintained, and they are available when needed. In reactive routing, routes are discovered on demand. An ad-hoc network can be isolated, or it can have a gateway that provides a connection to another network. Consequently, the devices must be able to communicate when the gateway is available and when it unavailable.