Matthias Frank

Link stability in mobile wireless ad hoc networks

We develop adaptive metrics to identify stable links in a mobile wireless networking environment based on the analysis of link durations in several different mobility scenarios. Our metrics only rely on online statistical evaluation of observed link durations. Neither do they require information on signal strength, radio conditions, or spacing of the mobile devices, nor do they depend on the availability of additional hardware such as GPS receivers or a synchronisation of the devices. We demonstrate the ability of the metrics to select stable links with a high probability in a wide range of scenarios.

Modelling mobility in disaster area scenarios

This paper provides a model that realistically represents the movements in a disaster area scenario. The model is based on an analysis of tactical issues of civil protection. This analysis provides characteristics influencing network performance in public safety communication networks like heterogeneous area-based movement, obstacles, and joining/leaving of nodes. As these characteristics cannot be modelled with existing mobility models, we introduce a new disaster area mobility model. To examine the impact of our more realistic modelling, we compare it to existing ones (modelling the same scenario) using different pure movement and link based metrics. The new model shows specific characteristics like heterogeneous node density. Finally, the impact of the new model is evaluated in an exemplary simulative network performance analysis. The simulations show that the new model discloses new information and has a significant impact on performance analysis.

Handoff support for mobility with IP over Bluetooth

The BLUEPAC (BLUEtooth Public ACcess) concepts present ideas for enabling mobile Bluetooth devices to access local area networks in public areas, such as airports, train stations and supermarkets. The proposed protocols support mobility on OSI layer 3. This paper concentrates on the necessary layer 2 protocol concepts for supporting mobility and handoffs between different access points. Furthermore, we present the necessary adaptations for allowing IP datagrams to be exchanged between the mobile Bluetooth devices and access points. The BLUEPAC protocol concepts have been implemented above a Bluetooth emulation system to test their feasibility. First results clearly showed the importance of minimizing the handoff duration to allow efficient operation of upper layer protocols such as TCP.

Adaptive scatternet support for Bluetooth using sniff mode

Future applications of Bluetooth are likely to include ad-hoc networking. Therefore, it is desirable to interconnect multiple Bluetooth piconets to form a scatternet. Up to now, there is no extensive proposal for scatternet support available. We present and analyze an adaptive scheme for scatternet scheduling that is based on the sniff mode and thus does not require substantial modification of the current Bluetooth specification. The suitability of our approach is shown by first simulation results.

Human mobility in MANET disaster area simulation - a realistic approach

Disaster areas have been figured out as a typical usage scenario for mobile wireless ad-hoc networks (MANETs). In contrast to this, there are no specific mobility or traffic models for MANETs. We present a realistic approach to realize mobility in disaster areas based on tactical issues of civil protection. The new model is analyzed and compared to Gauss-Markov and random waypoint mobility models. Furthermore, we present first simulation results. The mobility model analysis as well as the simulation are based on two real disasters that occurred in Germany in 1999 and 2001. We show that disaster area scenarios have specific characteristics. Thus, they should be considered in MANET performance evaluation.

On things to happen during a TCP handover

This paper gives a survey on the impact of handover between heterogeneous links to the performance of TCP and elaborates on the effects TCP is challenged at the moment of a handover. Moreover, we propose several approaches to improve the performance of TCP in these situations and present an evaluation of these approaches by means of simulation.

Modelling Voice Communication in Disaster Area Scenarios

This paper deals with voice communication models for disaster area scenarios. The goal is to design models that can be used to generate realistic push to talk traffic for single talk groups. The modelling is based on an analysis of empirical measurements during a catastrophe maneuver. The analysis shows that the time series comprise heavy load periods and significant correlations. Based on these characteristics, different Markov and semi-Markov models are considered. Synthetic traffic streams for the different models are generated and evaluated by visual and statistical analysis. Finally, a case study outlines the impact of the different traffic models in network performance simulation

Performance analysis of TCP handover in a wireless/mobile multi-radio environment

The European Union funded projects DRIVE (Dynamic Radio for IP Services in Vehicular Environments) and OverDRiVE (Spectrum Efficient Uni- and Multicast Over Dynamic Radio Networks In Vehicular Environments) aim at enabling spectrum-efficient high-quality wireless IP communication in a heterogeneous multi-radio environment to deliver in-vehicle multimedia services. The IPv6 based network architecture for IP over multi-radio access networks and traffic control aspects has been developed in the DRiVE project. This paper presents relevant results of a performance analysis by simulation of the TCP handover behavior in the DRiVE multi-radio environment. Furthermore, the OverDRiVE project extends the scenario to mobile networks in larger vehicles like busses or trains, which imposes further interesting challenges on the IP-based network infrastructure and their protocols. The TCP handover evaluation will be continued in both the DRiVE and OverDRiVE scenarios.

End-to-end QoS management for delay-sensitive scalable multimedia streams over DiffServ

The migration of the Internet from classic computer communication to a platform for multimedia applications with real-time communication requires end-to-end improvements of the network-level service. The proposal known as Differentiated Services is a very promising approach for implementing quality of service in the Internet and is being discussed and developed. The challenge is to deliver end-to-end QoS on top of Differentiated Services considering multiple concurrent application level data streams. We propose a QoS management system for multimedia servers that benefits from the scaling properties of layered media streams. This enables the system to map application QoS demands to available network resources and to adapt the quality of individual streams according to inter-stream QoS dependencies.

Practical experiences with a transport layer extension for end-to-end bandwidth regulation

The paper presents an extension of the transport layer to control the bandwidth used by data flows in heterogeneous networks in case of network congestion. The regulation mechanism is operating on an end to end basis. It does not depend on a negotiation of quality of service (QoS) parameters prior to the data transmission. Instead it uses a relative QoS concept based on a classification of data flow requirements specified by the application. The paper describes the concept of the mechanism for Regulation Of Bandwidth in Intra-Networks (ROBIN) and presents first measurement results with a prototype implementation of ROBIN.