Protocols, mobility models and tools in opportunistic networks: A survey

In opportunistic networks, instead of assuming an end-to-end path as in the traditional Internet model, messages are exchanged opportunistically when an encounter happens between two nodes. In the last years, several forwarding algorithms to efficiently decide when to forward messages were proposed. Those protocols are commonly suitable to a specific scenario, which has led to the creation of new subtypes of networks. Two different examples are pocket switched networks – PSN and vehicular networks – VANETs, since those networks have different features like a specific mobility pattern and intermittent connectivity. In this article we present an overview of opportunistic networks, proposing a taxonomy which encompasses those new types of network. We discuss the commonly used tools, simulators, contact traces, mobility models and applications available. Moreover, we analyzed a set of forwarding protocols to map the approach used by the research community to evaluate their proposals in terms of mobility, contacts and traffic pattern, reliability of simulations and practical projects. We show that although researchers are making efforts to use more realistic contact models (e.g., using real traces) the traffic pattern is generally disregarded, using assumptions that may not fit real applications.