Olov Schelén

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.

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.

Performance of QoS agents for provisioning network resources

We have designed an agent-based architecture for quantitative service provisioning in differentiated services capable networks. For each link-state routing domain in the network there is a topology-aware QoS agent (also known as a bandwidth broker) responsible for admission control. The architecture provides resource reservations for aggregated virtual leased lines between network domains. In this paper, we present performance measurements for resource provisioning in a prototype QoS agent. This includes an evaluation of two data structures for advance reservations and accompanying algorithms. We also compare the cost for on-demand route computations with pre-computation of routes. The objective in this paper is to evaluate the performance of end-to-end admission control within a single link-state routing domain. In a domain with 15 routers, 28 transition networks and 64 stub networks, our prototype performs approximately 25000 end-to-end admission decisions per second. The results show that an ordinary PC can be used for running a QoS agent that performs path-sensitive admission control and maintains per link resource reservations in a link-state routing domain.

Sharing Resources through Advance Reservation Agents

We propose an architecture where clients can make advance reservations through agents responsible for advance admission control. The agents allocate resources in the routers just before they are ne ...

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.

Advance Reservations for Predictive Service

We extend a measurement-based admission control algorithm suggested for predictive service to provide advance reservations for guaranteed and predictive service while keeping the attractive features of predictive service. The admission decision for advance reservations is based on information about flows that overlap in time. For flows that have not yet started, the requested values are used, and for those that have already started measurements are used. This allows us to estimate the network load accurately for the near future. To provide advance reservations we ask users to include durations in their requests. We provide simulation results to show that predictive service with advance reservations provides utilization levels significantly higher than those for guaranteed service.

An agent-based architecture for advance reservations

The authors propose an architecture where clients can make advance reservations through agents. For each routing domain in the network there will be an agent responsible for admission control on behalf of the routers in the domain. Requests involving several routing domains are forwarded for admission control with agents along the path for the requested service. Agents maintain hard reservation state using a reliable protocol for agent intercommunication. Agents start allocating resources for advance reservations in the routers by setting up forwarding state shortly before resources are needed for packet fop warding. Resources are made available for advance reservations by means of rejecting further immediate requests and ultimately by preempting some immediate reservations. They have shown that the risk of preemption can be kept very low. Thus, agents can set up packet classifiers and schedulers in their routers, allowing routers to get on with their main task, packet forwarding.

Aggregating resource reservations over multiple routing domains

Presents an agent-based architecture for resource reservations. For each domain in the network, there is an agent that is responsible for admission control. The architecture provides scalable per-link resource reservations in agents and low per-packet overhead in routers. The key ideas are the following. First, reservations from different sources to the same destination are aggregated as their paths merge toward the destination. Second, an agent in charge of resources at the final destination can generalize reservations for specific end-points so that they are valid for any end-point in the destination domain, thereby allowing more aggregation. Third, agents can do bulk reservations in advance with neighboring agents, thereby allowing aggregation over time. Fourth, agents are responsible for setting up policing points at edge routers for checking commitments. Agents can minimize the per-packet policing overhead in routers by varying the granularity of policing over time.