Elias Weingärtner

A Performance Comparison of Recent Network Simulators

A widespread methodology for performance analysis in the field of communication systems engineering is network simulation. While ns-2 has established itself as virtually the standard network simulation tool, other network simulators have gained more and more attention during the last years. In this paper, we briefly survey new developments in the field of network simulation and conduct a performance comparison study by implementing an identical simulation set-up in five simulators, namely ns-2, OMNet++, ns-3, SimPy and JiST/SWANS. Our results reveal large differences according to both run-time performance and memory usage.

Synchronized network emulation: matching prototypes with complex simulations

Network emulation, in which real systems interact with a network simulation, is a common evaluation method in computer networking research. Until now, the simulation in charge of representing the network has been required to be real-time capable, as otherwise a time drift between the simulation and the real network devices may occur and corrupt the results. In this paper, we present our work on synchronized network emulation. By adding a central synchronization entity and by virtualizing real systems for means of control, we can build-up network emulations which contain both unmodified x86 systems and network simulations of any complexity.

Secure Wi-Fi sharing at global scales

The proliferation of broadband Internet connections has lead to an almost pervasive coverage of densely populated areas with private wireless access points. To leverage this coverage, sharing of access points as Internet uplinks among users has first become popular in communities of individuals and has recently been adopted as a business model by several companies. However, existing implementations and proposals suffer from the security risks of directly providing Internet access to strangers. In this paper, we present the P2P Wi-Fi Internet Sharing Architecture PISA, which eliminates these risks by introducing secure tunneling, cryptographic identities, and certificates as primary security concepts. Thus, PISA offers nomadic users the same security that they expect from a wired Internet connection at home. Based on its three fundamental mechanisms, PISA achieves a flexibility which opens significant advantages over existing systems. They include user mobility, anonymity, service levels with different performance and availability characteristics, and different revenue models for operators. With this combination of key features, PISA forms an essential basis for global, seamless, and secure Wi-Fi sharing for large communities.

An Adaptive Codec Switching Scheme for SIP-Based VoIP

Contemporary Voice-Over-IP (VoIP) systems typically negotiate only one codec for the entire VoIP session life time. However, as different codecs perform differently well under certain network conditions like delay, jitter or packet loss, this can lead to a reduction of quality if those conditions change during the call. This paper makes two core contributions: First, we compare the speech quality of a set of standard VoIP codecs given different network conditions. Second, we propose an adaptive end-to-end based codec switching scheme that fully conforms to the SIP standard. Our evaluation with a real-world prototype based on Linphone shows that our codec switching scheme adapts well to changing network conditions, improving overall speech quality.

ProMoX: A protocol stack monitoring framework

In this paper, we present a preliminary glance on our framework for protocol stack monitoring using Xen (ProMoX). ProMoX uses the Xen hypervisor to virtualize entire instances of operating systems which may execute any arbitrary protocol implementation. By utilizing system virtualization for external monitoring, ProMoX can transparently inspect any protocol state and performance metrics of protocol implementations carried by a guest operating system. This way, ProMoX supports both the indentification of faults within early prototypes as well as the evaluation of new protocol designs.

A blueprint for switching between secure routing protocols in wireless multihop networks

A plethora of (secure) routing protocols exists for wireless multihop networks. These protocols are mostly tailored to meet the performance and security requirements of specific application scenarios. As a result, the protocols cannot easily be adapted to novel application demands, organically growing networks, etc. We argue that the modular design of routing protocols and security mechanisms can remove the key limitations of todays monolithic routing protocols. We show the feasibility of a modular routing approach for wireless multihop networks using the example of a wireless mesh network. In particular, we demonstrate that a dynamic switch between protocol modules is possible at runtime by means of simulation as well as testbed experimentation. We further demonstrate that the security associations and the key material can be reutilized for bootstrapping novel protocol modules, thus minimizing the control overhead.

Time accurate integration of software prototypes with event-based network simulations

The concept of network emulation brings together the flexibility of network simulations and the accuracy of real-world prototype implementations. However, this approach suffers from the fundamental problem of simulation overload which occurs if the simulation is not able to execute in real-time. We tackle this problem with a concept we call Synchronized Network Emulation It enables the time accurate integration of implementations with network simulations of any complexity.

Towards Network Centric Development of Embedded Systems

Nowadays, the development of embedded system hardware and related system software is mostly carried out using virtual platform environments. The high level of modeling detail (hardware elements are partially modeled in a cycle-accurate fashion) is required for many core design tasks. At the same time, the high computational complexity of virtual platforms caused by the detailed level of simulation hinders their application for modeling large networks of embedded systems. In this paper, we propose the integration of virtual platforms with network simulations, combining the accuracy of virtual platforms with the versatility and scalability of network simulation tools. Forming such a hybrid toolchain facilitates the detailed analysis of embedded network systems and related important design aspects, such as resource effectiveness, prior to their actual deployment.

Content delivery overlays

Content Delivery Overlays (CDOs) are used to organize the transport of application data between content sources and end users in an efficient way. In fact, the delivery of content in today’s Internet is already well supported by CDOs and ContentDelivery Networks like Akamai [9]. A famous example for a CDO that employs P2P mechanisms is Octoshape [3] which delivers live video broadcasts to hundreds of thousands of viewers in the Internet. In this Chapter we first discuss how such CDOs may be evaluated using a benchmark in general. This discussion is specially aligned with Content Delivery Overlay technologies that are based on open protocols and communication technologies. Typical examples for such CDOs are BitTorrent, which is a CDO for bulk data transfer, and CDO software such as Tribler [8], which is designed for the effective sharing of media content. A benchmark of video streaming systems is later described in Chapter 9. The second part of this Chapter discusses a platform for benchmarking BitTorrent clients. It is based on the SliceTime [11] environment and the VODSim [10] BitTorrent simulation model. The remainder of this Chapter then demonstrates how this platform can be applied for benchmarking legacy BitTorrent software clients.

Can P2P swarm loading improve the robustness of 6LoWPAN data transfer

The recent arrival of 6LoWPAN, an IPv6 variant for low-power wireless devices, allows for the development of IP-based applications for low-power wireless networks like sensor networks. As these networks often suffer from unreliable radio channels or frequent node failure, the question arises how 6LoWPAN-based applications can be hardened against such issues. In this paper, we examine if well-known concepts from the research domain of P2P networks can be applied for increasing the robustness of 6LoWPAN networks. For this purpose, we design and implement a straightforward P2P system for data sharing that is adapted to the low system capabilities of a typical 6LoWPAN device. Our preliminary evaluation shows that P2P mechanisms like swarm loading are able to improve the robustness of a 6LoWPAN application.