Anders Lindgren

Probabilistic routing in intermittently connected networks

We consider the problem of routing in intermittently connected networks. In such networks there is no guarantee that a fully connected path between source and destination exist at any time, rendering traditional routing protocols unable to deliver messages between hosts. We propose a probabilistic routing protocol for such networks.

Probabilistic Routing in intermittently connected networks

In this paper, we address the problem of routing in intermittently connected networks. In such networks there is no guarantee that a fully connected path between source and destination exists at any time, rendering traditional routing protocols unable to deliver messages between hosts. There does, however, exist a number of scenarios where connectivity is intermittent, but where the possibility of communication still is desirable. Thus, there is a need for a way to route through networks with these properties. We propose PRoPHET, a probabilistic routing protocol for intermittently connected networks and compare it to the earlier presented Epidemic Routing protocol through simulations. We show that PRoPHET is able to deliver more messages than Epidemic Routing with a lower communication overhead.

Opportunistic content distribution in an urban setting

This paper investigates the feasibility of a city-wide content distribution architecture composed of short range wireless access points. We look at how a target group of intermittently and partially connected mobile nodes can improve the diffusion of information within the group by leveraging fixed and mobile nodes that are exterior to the group. The fixed nodes are data sources, and the external mobile nodes are data relays, and we examine the trade off between the use of each in order to obtain high satisfaction within the target group, which consists of data sinks. We conducted an experiment in Cambridge, UK, to gather mobility traces that we used for the study of this content distribution architecture. In this scenario, the simple fact that members of the target group collaborate leads to a delivery ratio of 90%. In addition, the use of external mobile nodes to relay the information slightly increases the delivery ratio while significantly decreasing the delay.

Evaluation of quality of service schemes for IEEE 802.11 wireless LANs

This paper evaluates four mechanisms for providing service differentiation in IEEE 802.11 wireless LANs, the point coordinator function (PCF) of IEEE 802.11, the enhanced distributed coordinator function (EDCF) of the proposed IEEE 802.11e extension to IEEE 802.11, distributed fair scheduling (DFS), and Blackburst using the ns-2 simulator. The metrics used in the evaluation are throughput, medium utilization, collision rate, average access delay, and delay distribution for a variable load of real time and background traffic. The PCF performance is comparably low, while the EDCF performs much better. The best performance is achieved by Blackburst. The DFS provides relative differentiation and consequently avoids starvation of low priority traffic.

Quality of service schemes for IEEE 802.11 wireless LANs: an evaluation

This paper evaluates four mechanisms for providing service differentiation in IEEE 802.11 wireless LANs. The evaluated schemes are the Point Coordinator Function (PCF) of IEEE 802.11, the Enhanced Distributed Coordinator Function (EDCF) of the proposed IEEE 802.11e extension to IEEE 802.11, Distributed Fair Scheduling (DFS), and Blackburst. The evaluation was done using the ns-2 simulator. Furthermore, the impact of some parameter settings on performance has also been investigated. The metrics used in the evaluation are throughput, medium utilization, collision rate, average access delay, and delay distribution for a variable load of real time and background traffic. The simulations show that the best performance is achieved by Blackburst. PCF and EDCF are also able to provide pretty good service differentiation. DFS can give a relative differentiation and consequently avoids starvation of low priority traffic.

The evolution of a DTN routing protocol - PRoPHETv2

Research within Delay- and Disruption Tolerant Networks (DTN) has evolved into a mature research area. PRoPHET is a routing protocol for DTNs that was developed when DTN research was in its infancy and which has been studied by many. In this paper we investigate how the protocol can evolve to meet new challenges that has been identified through research and practical experience. We propose some minor modifications to the routing metric calculations done in PRoPHET which has potential to alleviate some issues and improve the performance of the protocol. Using these modifications, we define an updated version of the protocol called PRoPHETv2. We run simulations to verify the operation of the protocol and compare its performance against the original version of the protocol as well as some other routing protocols. The evaluations are done using both traces from an existing DTN deployment and a synthetic mobility model. Since the basic mechanisms of the protocol remain the same, migrating existing implementations to the new version of PRoPHET is possible with limited effort.

The quest for a killer app for opportunistic and delay tolerant networks: (invited paper)

Delay Tolerant Networking (DTN) has attracted a lot of attention from the research community in recent years. Much work have been done regarding network architectures and algorithms for routing and forwarding in such networks. At the same time as many show enthusiasm for this exciting new research area there are also many sceptics, who question the usefulness of research in this area. In the past, we have seen other research areas become over-hyped and later die out as there was no killer app for them that made them useful in real scenarios. Real deployments of DTN systems have so far mostly been limited to a few niche scenarios, where they have been done as proof-of-concept field tests in research pro jects. In this paper, we embark upon a quest to find out what characterizes a potential killer applications for DTNs. Are there applications and situations where DTNs provide services that could not be achieved otherwise, or have potential to do it in a better way than other techniques? Further, we highlight some of the main challenges that needs to be solved to realize these applications and make DTNs a part of the mainstream network landscape.

Quality of Service Schemes for IEEE 802.11: A Simulation Study

This paper analyzes and compares four different mechanisms for providing QoS in IEEE 802.11 wireless LANs. We have evaluated the IEEE 802.11 mode for service differentiation (PCF), Distributed Fair Scheduling, Blackburst, and a scheme proposed by Deng et al. using the ns-2 simulator. The evaluation covers medium utilization, access delay, and the ability to support a large number of high priority mobile stations. Our simulations show that PCF performs badly, and that Blackburst has the best performance with regard to the above metrics. An advantage with the Deng scheme and Distributed Fair Scheduling is that they are less constrained, with regard to the characteristics of high priority traffic, than Blackburst is.

Networking in the land of northern lights: two years of experiences from DTN system deployments

The Sámi Network Connectivity (SNC) project was started to enable Internet connectivity for the Sámi population of reindeer herders in the Laponia region in northern Sweden. In this area, no infrastructure and thus, no Internet connectivity is normally available. Thus, DTN functionality is used to enable connectivity through the use of mobile relays. This paper describes deployments and field tests done within the SNC project and its continuation SNC+1, in which a Delay-Tolerant Networking system was deployed in the target region. During these deployments, the PRoPHET routing protocol, and three different applications were deployed and tested sucessfully.

Impact of communication infrastructure on forwarding in pocket switched networks

Recently, it has been established on multiple experimental data sets that human contact processes exhibit heavy-tailed inter-event distributions. This characteristic makes it difficult to transport data with a finite transfer time in a network of mobile devices, relying on opportunistic contacts only. Using various experimental data sets, we analyze how different types of communication infrastructure impact the feasibility of data transfers among mobile devices.The first striking result is that the heavy tailed nature of the contact processes persists after infrastructure is introduced. We establish experimentally that infrastructure improves significantly multiple opportunistic contact properties, relevant to opportunistic forwarding algorithms. We discuss how infrastructure can be used to design simpler and more efficient (in terms of delay and number of hops) opportunistic forwarding algorithms. In addition to this, for the first time in a study like this, the communication pattern of nodes is taken into account in the analysis. We also show that node pairs that have a real-life history of communication have contact properties that are better for opportunistic message forwarding to each other than what other node pairs have.