Extending the reach of ad hoc networks using layer 2 tunnels

Ad hoc wireless networking has been an active research area for the past several years. Reachability has been one of the bigger challenges encountered in the design of an efficient ad hoc wireless network. One of the solutions towards improving the reachability of ad hoc networks is the usage of a hierarchical approach [1]. The authors of [1] suggest that instead of a flat homogenous ad hoc network (which suffers from poor scalability), an ad hoc network with Mobile Backbone Nodes (MBN) be used. They argue that a large scale ad hoc network suffers not only from the limitation of available bandwidth but also “many hops” paths are prone to break and cause numerous packet drops. The nodes that form an MBN network communicate over a separate radio frequency than the actual ad hoc network. In [2] another solution is proposed for improving the reach of ad hoc networks by considering the use of hybrid networks. The authors of [2] suggest a network that uses both ad hoc connectivity and access points (AP). Access points give mobile hosts (MH) access to the nodes that are outside their transmission range. These APs are joined together via a wired network. Using their proposed routing protocol, an AP maintains information about routes to all MHs within its own zone. It uses this information to entertain any Route REQuests (RREQs) coming from other zones. The routing protocol works differently for APs and MHs. In both [1] and [2], the solution completely relies upon the routing protocols. To expand the reach of ad hoc networks, these solutions either extend the existing routing protocol (LANMAR in [1]) or consider a new routing protocol [2]. In this paper, the authors examine the reachability problem of ad hoc networks with respect to layer 2 mechanisms. Two specific cases were considered for the current work: (1) Two ad hoc networks connected via two or more border gateways via an infrastructured network. (2) A single ad hoc network with the provision for an alternate path between ad hoc nodes via an infrastructured network.