Lars Landmark

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.

Performance analysis of the AODV ad hoc routing protocol in a dual radio network

Existing ad hoc routing protocols supports multiple radio interfaces, but they are designed for radio interfaces with similar properties. In contrast, in a typical usage scenario the interfaces will have different properties. There will be a need for longer range resulting in a lower bandwidth, while some applications will have higher capacity requirements but for nodes in close proximity. A solution may be to use one interface with low bandwidth and long range for example in the UHF band, whilst the other interface has a higher bandwidth and shorter range in the VHF or SHF band. Such a solution will not be energy efficient, so it will be feasible only for vehicle-mounted radios like in tactical military or emergency service networks. With the shortest path routing, the long range interfaces tend to be selected. The traffic is therefore shifted towards the links with the lowest capacity. Firstly, we analyze and illustrate the problem for the typical reactive routing protocol, AODV. Secondly, we propose two techniques that take the underlying radio capacity into account when a new route is established. Compared to original AODV, the proposed algorithms provide higher network throughput, less routing overhead, less end-to-end delay and still provides connectivity. The applicability to this approach is one of practical interest to scenarios where nodes are typically unevenly distributed; a network where some nodes only are reachable over long range radios, while others are also reachable over short range high capacity radios.

On improving connectivity and network efficiency in a heterogeneous military environment

In this article, we examine some major challenges to be solved in order to provide efficient end-to-end connectivity, resource management and QoS in a tactical military heterogeneous network (including the mobile edge). We briefly describe a selected set of possible solutions and mechanisms to improve inter-domain and intra-domain networking for the tactical heterogeneous network that will be further studied in the NATO STO IST-124/RTG-061 group “Heterogeneous tactical networks - improving connectivity and network efficiency”.

A Survey of QoS Multicast in Ad Hoc Networks

This survey on Quality of Service (QoS) in multicast ad hoc networks uses a framework based on the mechanisms in three important elements: resource estimations, multicast tree/mesh administration, and multicast routing. Our contribution is an exploration of the design space and an identification of areas that have not been fully explored. We discuss the design space of central mechanisms and classify proposed QoS multicast schemes according to the mechanisms they used. In addition, we summarize the scenarios used for evaluating their performance. Furthermore, we identify issues, mechanisms, and scenarios that have not been fully investigated in existing works. The paper provides a coherent understanding of design principles, conceptual operation, and evaluated scenarios of schemes designed for QoS multicast application in mobile ad hoc networks (MANETs). It also outlines new areas for future research in this field.

Alternative Packet Forwarding for Otherwise Discarded Packets

Packets in multihop wireless networks are often discarded due to missing routes, packet collision, unreachable next-hop or bit error. As a remedy to these problems, this paper presents alternative packet- forwarding mechanisms that will reduce the likelihood of discarding packets. In addition to this, a new packet-buffering solution is proposed. By combining these two methods, reduced packet loss was achieved in addition to preserved network resources. This was confirmed through simulations, where a comparison between our proposed solutions and standard forwarding showed up to 50% reduction in packet loss.

Testing and analyzing TCP performance in a wireless-wired mobile ad hoc test bed

TCP is the most used connection-oriented transport protocol in the Internet today. However, TCP has a number of problems when the connections are running over wireless links. This paper addresses some of them for wireless-wired ad hoc networking. We have made a real-life testbed for experimenting and analyzing TCP connections from a multi-homed ad hoc network into the global Internet. Through a set of experiments, we show how TCP behaves when switching gateways. The experiments are carried out in a mobile ad hoc network running a pro-active routing protocol, namely the OLSR protocol. The testbed and initial results are our first step for making an improvement to TCP for ad hoc networking.

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 connectionless multicast protocol for MANETs

In this paper, the connectionless multicast routing MCOM (Multipoint relay Connectionless Multicast) is introduced for mobile Ad hoc networks. MCOM adapts over a wide ranges of density of group members. It appears as unicast with few receivers and as flooding protocol, similar to Simplified Multicast Forwarding (SMF), with many receivers. MCOM utilizes the forwarding structure Multipoint relay (MPR) of the proactive unicast routing protocols as duplication points. In MCOM, addresses of MPRs are included in data packets instead of addresses of receivers as in the traditional connectionless multicast protocol Xcast. After receiving multicast packets from source, specific MPRs use SMF to deliver the packets to receivers. Two simulators NS-2 and nsclick were used to evaluate performance of protocols. The results from our studies demonstrate that MCOM is an efficient multicast protocols over a wide range of scenarios.

Routing Loops in Mobile Heterogeneous Ad Hoc Networks

Routing loops accounts for a fair share of packet loss in mobile networks, particularly so for heterogeneous mobile networks. Loops occur when nodes build routes based on inconsistent topology databases. The inconsistency is caused by, but not limited to, dissimilar transmission delay, lost signaling messages, mobility, traffic load, and dissimilar frequency for route update messages. The latter cause is a consequence of optimization of control traffic overhead in heterogeneous networks. These networks are networks that consist of links, or network segments, based on radios with unlike transmission technologies. Such networks typically operate in areas that enforce network topologies with non-optimal radio degree for some of the network types. This paper studies the phenomenon of routing loops in mobile heterogeneous networks. It is shown where the loops occur. Methods to reduce the occurrence of the loops, and ways to do local repair, are proposed.