Erlend Larsen

Gateway load balancing in future tactical networks

In future tactical networks, gateway nodes will have an important role in connecting different military communications platforms together to form a consolidated network. To increase capacity for upstream/downstream traffic as well as resiliency, more than one gateway should be deployed. In this context, performing gateway load balancing is vital in order to take full advantage of the resources available and thereby improve the performance. Previous work has shown that a number of factors such as the level of asymmetry, offered load, and gateway location may influence the performance of load balancing. However these parameters alone cannot explain why the performance of load balancing is high for certain topologies while it is very poor for others. Obviously, the specific layout of a topology also plays a crucial role on the efficiency of load balancing. We question what are the differences between topologies where load balancing is efficient from the topologies where it is inefficient? The work in this paper thus aims to find the answer to this question, and to explore the nature of performing load balancing in wireless multi-hop networks. Through the knowledge acquired we propose a Radio load based Load Balancing scheme (RLLB). Simulations of many randomly generated topologies show that the performance of RLLB is promising.

Performance analysis of gateway load balancing in ad hoc networks with random topologies

In wireless multihop networks such as MANETs or Wireless Mesh Networks (WMN), an Internet gateway (IGW) is a node that provides Internet connectivity, linking the wireless network with the global Internet. Congestion around the IGW represents a potential bottleneck for all Internet traffic that has to pass through the IGW. To alleviate this problem, the common solution is to have multiple IGWs in the network. However in order to take advantage of the capacity provided by multiple gateways, the routing protocol utilized must efficiently load balance the traffic among available IGWs such that the network performance is optimized. In this context, it is questioned to which extent it is possible to enhance the performance by utilizing a load balancing metric instead for the traditional shortest path metric. Furthermore, what are the factors that may set an upper limit for the performance that can be achieved. The aim of our investigation is to seek the answers to these questions through extensive simulations of a large number of random topologies. While a number of other studies have reported potential benefits of load balancing with some specific network topologies, to the best of our knowledge none have conducted similar studies covering a larger number of random topologies.

Optimized group communication for tactical military networks

In tactical networks there is a need for group communication applications, such as position and information sharing (Situational Awareness data), and Push-to-Talk (PTT) voice communication. This paper focuses on group communication in tactical military ad hoc networks, where most of the nodes are interested receivers. In this case, an efficient flooding protocol will be the best solution for the group communication. Efficient flooding can be achieved with the Simplified Multicast Forwarding (SMF) framework. The performance of SMF depends on the chosen forwarding algorithm. Two plausible alternatives are S-MPR and NS-MPR. The former is the more bandwidth efficient, while the latter is more robust to mobility. This paper investigates the limitations of the forwarding algorithms and investigates measures to mend S-MPRs mobility problem. Further, the paper suggests combining S-MPR and NS-MPR using the radio load as metric. Finally, the PTT and Situational Awareness (SA) traffic types are evaluated when run simultaneously, and a preemptive switch to S-MPR is proposed for the SA traffic. Through employing the methods suggested in this paper, the performance for PTT and SA traffic forwarded using SMF in tactical military networks can be increased.

Rerouting Time and Queueing in Proactive Ad Hoc Networks

In a MANET network where nodes move frequently, the probability of connectivity loss between nodes might be high, and communication sessions may easily loose connectivity during transmission. The routing protocol is designed to find alternative paths in these situations. This rerouting takes time, and the latency is referred to as the rerouting time. This paper investigates the rerouting time of proactive routing protocols and shows that the rerouting time is considerably affected by queueing. Simulations and analysis are conducted to explore the problem. Finally, we propose a MAC-layer solution that reduces the rerouting time problems due to queueing. Simulations and analysis show that the solution is so effective that it eliminates the entire problem in many situations.

Routing of internal MANET traffic over external networks

Many have proposed to connect Mobile Ad Hoc Networks (MANETs) to a wired backbone Internet access network. This paper demonstrates that a wired backbone network can be utilized for more than just providing access to the global Internet. Traffic between mobile nodes in the ad hoc network may also be routed via this backbone network to achieve higher throughput, and to reduce the load in the ad hoc network. This is referred to as transit routing. This paper proposes a cost metric algorithm that facilitates transit routing for some of the traffic flows between nodes in the MANET. The algorithm aims at carrying out transit routing for a flow only when it leads to improvements of the performance. The proposal is implemented and tested in the ns-2 network simulator, and the simulation results are promising.

O-CTP: Hybrid opportunistic collection tree protocol for Wireless Sensor Networks

Radio interference or deliberate jamming attacks can cause highly unpredictable communication in Wireless Sensor Networks (WSNs). Most prevalent WSN platforms consist of low-cost hardware with no effective measures against these threats. Most proposed countermeasures require a more advanced hardware design or radical changes to the 802.15.4 MAC protocol. These alternatives can be very difficult or even impossible to apply to existing WSN designs. In this paper we do not attempt to change the hardware or the MAC protocol. Instead we investigate how WSN routing protocols behave when the network is affected by interference. The paper proposes enhancements of CTP, the de-facto tree-based routing protocol for WSN, using opportunistic routing. We compare our approach with a wide range of protocols: CTP, TYMO, MultihopLQI, broadcast and geographic opportunistic routing in a real-life TelosB testbed subjected to different interference levels. The results show that our hybrid protocol, O-CTP, both improves the data delivery rate and reduces the cost when compared to standard routing protocols.

Routing with transmission buffer zones in MANETs

Dealing with link breaks in MANETs is a challenge for the routing protocol. This paper proposes a mechanism to reduce the negative impact of link breaks on the routing. The transmission area of a node is divided into a safe zone close to the node and an unsafe zone (i.e. buffer zone) near the end of the transmission range. The probability is high that link breaks occur with neighboring nodes located in the buffer zone, while links to neighboring nodes in the safe zone are expected to be more stable. Thus, neighbors in the safe zone are preferred as relay nodes, while neighbors in the buffer zone are only used if necessary to avoid network partitioning. The main cost of this mechanism is that the mean number of hops between two nodes is higher than without the mechanism, but simulations show that the solution offers increased throughput.

Preemption mechanisms for push-to-talk in ad hoc networks

Using push-to-talk applications in ad hoc networks is not straightforward. There are no inherent mechanisms to support priority of the voice traffic, to avoid great jitter and packet loss in face of large background traffic loads. This paper presents three preemption mechanisms that can be applied to support push-to-talk traffic in multi-hop ad hoc networks. The mechanisms differ in the way the background traffic is treated: discard, buffering and inter-scheduling. It is shown that there is a trade-off between the impact on the background traffic and the service for the push-to-talk traffic. Discarding or buffering the background traffic leaves the push-to-talk traffic with very little impact by the background traffic, while inserting the low priority packets in the interval between the high priority packets incurs some cost to the push-to-talk traffic.

A radio load based load balancing scheme with admission control

In mobile ad hoc networks (MANETs) where there exist multiple Internet gateways, performing load balancing among available gateways is vital in order to take full advantage of the network capacity and improve the performance. However, performing load balancing in a wireless environment is very challenging due to the inherently interfering and unreliable nature that characterize wireless communication. Additionally, the dynamic in ad hoc networks due to node mobility makes it even more difficult. This paper explores the feasibility of performing load balancing in ad hoc networks both in static and mobile topologies, and proposes the RLAC scheme, that jointly performs the task of load balancing and admission control. RLAC relies on radio load information provided by the underlying MAC-layer to make routing decisions. Simulations with RLAC on a considerable number of random topologies, both static and mobile, show that the proposed scheme has a potential to improve performance with respect to the aggregated throughput.

Cost metric algorithm for transit routing in MANETs with internet connectivity

Many have proposed to connect Mobile Ad Hoc Networks (MANETs) to a wired backbone Internet access network. This paper demonstrates that a wired backbone network can be utilized for more than just providing access to the global Internet. Traffic between mobile nodes in the ad hoc network may also be routed via this backbone network to achieve higher throughput, and to reduce the load in the ad hoc network. This is referred to as transit routing. This paper proposes a cost metric algorithm that facilitates transit routing for some of the traffic flows between nodes in the MANET. The algorithm aims at carrying out transit routing for a flow only when it leads to improvements of the performance. The proposal is implemented and tested in the ns-2 network simulator, and the simulation results are promising.