From Theory to Practice: Fundamental Properties and Services of Mobile Ad Hoc Networks

Mobile Ad Hoc Networks (MANETs) by definition operate without pre-established infrastructure. On the one hand side, this can be seen as an advantage since it makes them usable in situations where an infrastructure is not available, such as, e.g., in settings of emergency response. On the other hand, the lack of infrastructure poses difficult challenges to protocol design and software architecture for such networks. One example is wireless media access. In contrast to traditional wireless networks where nodes communicate through base stations, there is no dedicated network component to control the media access of the nodes in MANETs. This makes scheduling wireless transmissions complicated and affects the overall throughput capacity of the network. Another example are application level services. Many advanced applications on MANETs require basic services such as, e.g., DNS, SIP and SLP to operate. These services, however, typically rely on centralized components for storing the required networking information, components that are not available in MANETS. In this thesis, we study several problems occurring in MANETs at different places in the network stack. The first part studies fundamental properties of MANETs on the physical and data link layer, such as, e.g., capacity, connectivity, quality of service, etc. Understanding the behavior of those properties is important because they describe the limitations applications face in MANETs. Fundamental properties like connectivity and capacity have been in the focus of research over the past years. The novelty of the work presented in this thesis is that we use a formal model approach combined with Monte-Carlo methods. The approach chosen has a two-fold advantage: it is protocol independent and, at the same time, the computations are performed on a network model that is based on realistic physical properties. In the thesis we show how such an approach can be used to study the complex interactions between different interference and signal propagation models on the throughput capacity of a network. The second part of the thesis studies ad hoc networks from a system perspective. Thereby our goal is to provide a networking infrastructure that transparently hides the complexity of the underlying ad hoc network to upper layers. We believe that the ability to run traditional Internet-based applications in ad hoc networks is the key for MANETs to become ubiquitous. This dissertation presents several network abstractions and services that support this goal. First, we present the design and implementation of a virtual network interface which allows to integrate nodes equipped with different media access technologies into one single IP based MANET. The virtual interface accounts for the fact that today’s devices become more and more heterogeneous, particularly with respect to their wireless access technology. Second, we present the architecture of several fundamental networking services which allow Internet-based applications to run transparently in MANETs. Opening ad hoc networks for Internet applications such as chat or VoIP is an important step towards MANETs to be used in the everyday life. For each of the networking services, DNS, SIP and SLP, we show how they provide a smooth MANET-Internet phase transition. The core building block of those networking services is MAND, a distributed system for storing and searching key/value pairs. MAND is highly efficient as distribution of both tuples and requests happens based on piggybacking onto routing messages that the MANET network uses anyway, thus causing no additional message traffic. The thesis evaluates MAND together with the services built on top. The evaluation is done on a 30 node testbed and on a deployment of 20 Nokia N800 handheld devices. As a last part of this thesis, we present a social networking application for ad hoc networks. AdSocial allows users within a MANET to discover each other and browse through other people’s personal profile. AdSocial also integrates chat, VoIP and video. Similar to other networking services described in this thesis, AdSocial uses the MAND system to advertise user information, thus not imposing any additional traffic load.