On Leveraging Partial Paths in Partially-Connected Networks

Mobile wireless network research focuses on scenarios at the extremes of the network connectivity continuum where the probability of all nodes being connected is either close to unity, assuming connected paths between all nodes (mobile ad hoc networks), or it is close to zero, assuming no multi-hop paths exist at all (delay-tolerant networks). In this paper, we argue that a sizable fraction of networks lies between these extremes and is characterized by the existence of partial paths, i.e. multi-hop path segments that allow forwarding data closer to the destination even when no end-to-end path is available. A fundamental issue in such networks is dealing with disruptions of end-to-end paths. Under a stochastic model, we compare the performance of the established end-to-end retransmission (ignoring partial paths), against a forwarding mechanism that leverages partial paths to forward data closer to the destination even during disruption periods. Perhaps surprisingly, the alternative mechanism is not necessarily superior. However, under a stochastic monotonicity condition between current v.s. future path length, which we demonstrate to hold in typical network models, we manage to prove superiority of the alternative mechanism in stochastic dominance terms. We believe that this study could serve as a foundation to design more efficient data transfer protocols for partially-connected networks, which could potentially help reducing the gap between applications that can be supported over disconnected networks and those requiring full connectivity.Comment: Extended version of paper appearing at IEEE INFOCOM 2009, April 20-25, Rio de Janeiro, Brazi

A Robust Path Metric for Mobile Wireless Networks

Abstract — In this paper, we propose and evaluate a path metric to select robust paths in mobile wireless networks. This path metric selects paths that offer a good trade-off between long routes consisting of many reliable links and short routes consisting of only few but unreliable links. In contrast to the widely used minimum hop count metric, which chooses arbitrarily among those paths with minimum length, our path metric estimates the reliability of a link based on the measured received signal strength (RSSI). Every node determines a preferred signal strength and assigns each neighbor a link cost depending on how close to this strength its RSSI value is. Using simulations with realistic mobility traces of a large city, we compare our path metric to the minimum hop count metric. With nodes moving at car speed, using our metric increases the average route lifetime by a factor of 7 and reduces the packet loss ratio due to route breaks during communication by a factor of up to 15. I

Globs in the Primordial Soup The Emergence of Connected Crowds in Mobile Wireless Networks

In many practical scenarios, nodes gathering at points of interest yield sizable connected components (clusters), which sometimes comprise the majority of nodes. While recent analysis of mobile networks focused on the process governing node encounters (“contacts”), this model is not particularly suitable for gathering behavior. In this paper, we propose a model of stochastic coalescence (merge) and fragmentation (split) of clusters. We implement this process as a Markov chain and derive analytically the exact stationary distribution of cluster size. Further, we prove that, as the number of nodes grows, the clustering behavior converges to a mean field, which is obtained as a closed-form expression. This expression translates the empirical merge and split rate of a scenario, a microscopic property, to an important macroscopic property—the cluster size distribution—with surprising accuracy. We validate all results with synthetic as well as real-world mobility traces from conference visitors and taxicabs with several thousand nodes

Routing Packets into Wireless Mesh Networks

Wireless mesh networks are a promising way to provide Internet access to fixed and mobile wireless devices. In mesh networks, traffic between mesh nodes and the Internet is routed over mesh gateways. On the forward path, i.e., from mesh nodes to Internet nodes, for all mesh nodes only route information for one destination, the gateways, needs to be maintained. However, on the backward path from the Internet to mesh nodes, an individual route for every mesh node is required. In this paper we investigate protocols for backward path routing in wireless mesh networks. Using simulation experiments with realistic mobility patterns of pedestrians and cars in cities, we compare three protocols, each of which represents a routing protocol family: (i) AODV with an extension for mesh networks, a reactive routing protocol, (ii) FBR, a proactive routing protocol, and (iii) GSR, a source routing protocol. Our results indicate that FBR has the highest packet delivery ratio but is not scalable to the network size. The extended AODV seems to be neither scalable nor does it achieve a high packet delivery ratio. A good compromise is provided by GSR, which is the most scalable to the network size and still achieves a high packet delivery ratio