Performance Study of an Overlay Approach to Active Routing in Ad Hoc Networks

We motivate the use of the active technology for routing in ad hoc networks. We present an active architecture where passive and active nodes can operate together, avoiding any change in the legacy muti-hop routing protocol they use. We detail a basic reactive protocol which can be used to build any overlay on top of an ad hoc network. We model it as an active application called Re-Active Routing (RAR). RAR provides dynamic routing in dense and sparse active overlays. We investigate its performance in static and dynamic environments and show that it depends substantially on the active range, i.e. on the allowed maximal number of hops between two active nodes. For a well-chosen active range, RAR achieves good performance even if the mobility level is high and the overlay density is as low as 12.5 %. I. MOTIVATION This work is based on the conviction that the active and ad hoc technologies are complementary for building a very flexible network where users do not need a third party to communicate. An ad hoc network is defined as a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration [1]. In this environment, the only way for a node to reach another one which is not in its range is to use a multi-hop path passing through intermediate nodes. Various multihop routing protocols have been developed. They can first be classified in three categories: proactive, reactive and hybrid. Each class has its own assets; one should prefer a proactive protocol if the nodes mobility is low, a reactive one if the mobility is high. Some hybrid protocols are well-suited for large networks while some reactive protocols are not. Even if we only consider the reactive class, there is still a large panel of protocols, each more or less adapted to the network conditions and to the application needs, in terms, for example, of energy saving, path stability or control traffic amount. In order to communicate, all the nodes must of course share the same routing protocol. This is not a restriction in the context of sensor networks or disaster relief and more generally in situations where all the nodes are intended to be used for a specific application : the environment is known as well as the user’s needs and resources. However, within an heterogeneous environment, in terms of nodes resources (bandwidth, computing, memory and energy) and user’s needs, if the network conditions are not known a priori or varying, the requirement of choosing a routing protocol and imposing it to all nodes is a limitation. This can be overcome thanks to the active technology. With an active or programmable network element, it is possible to load new protocols or services automatically, and to remove protocols or services that are no longer useful, without service interruption. A reactive routing protocol could be fully injected or configured by an end user, following its needs, and it could be adapted to the network conditions and to the available resources in each intermediate node. Moreover, the active technology would allow a direct use of new protocols, avoiding the time consuming standardization process. Finally, thanks to it, nodes would not have to store plenty of protocols for other user’s needs. We assume that ad hoc networks, if spreading, will be progressivily deployed in a classical way, on passive nodes, after standardization of a few routing protocols. We present an architecture which allows the progressive introduction of the active technology by ad hoc users, simply upgrading software on their wireless devices. We adopted an overlay approach. All hosts share a common legacy routing protocol. Some users install an active platform on their node. These active nodes use the passive routing protocol for communication with neighbours. To