Björn Konieczek

ViPMesh: A virtual prototyping framework for IEEE 802.11s wireless mesh networks

WLAN mesh networks are characterized by their flexible and low-cost deployment, scalability, and self-healing capabilities. The new WLAN standard IEEE 802.11s introduces low-level mesh interoperability. However, building large-scale real-world test beds and reproducible setups is challenging and costly. In the majority of research works, network simulation is preferred over practical measurements. Here, the main disadvantage exists in simplified device and protocol models restricting the comparability to practical implementations. In contrast, using device emulation still requires the simulation of wireless channel and environment models. Consequently, a combination of both emulation and simulation is needed to enable virtual prototyping of real applications and protocols in WLAN mesh networks. Nevertheless, the computation of complex wireless channel effects requires a decoupling of wall clock and simulation time. Therefore, we present ViPMesh, a virtual prototyping framework for IEEE 802.11s and its Linux reference implementation. ViPMesh relies on WLAN device emulation and nested virtualization using QEMU and Linux containers to support the analysis of real applications on top of an unmodified protocol stack. Adopting an alternative time source approach for QEMU, ViPMesh acts as discrete-event simulator. It further integrates channel and environment models with support for IEEE 802.11n MIMO techniques, high throughput modes, multi-channel operation, and node mobility. To the best of our knowledge, this is the first approach that combines the IEEE 802.11s reference implementation with the described simulation features. The functionality of ViPMesh is demonstrated in different example scenarios.

Design and development of a management solution for wireless mesh networks based on IEEE 802.11s

The broad availability of WLAN-capable off-the-shelf hardware lets WLAN mesh networks appear as promising technology for future distributed wireless applications. Featuring automatic device discovery, interconnection and routing, they provide a higher scalability, flexibility, and robustness compared to common centralized WLAN infrastructures. Besides these advantages, characteristics such as variable network topologies and link qualities imply new technical challenges for administration and real-world operation. Adopted in late 2011, IEEE 802.11s appears as new WLAN standard amendment, enabling vendor-independent mesh networks based on the widespread WLAN technology. However, network monitoring and management fall out of the standardization scope and are therefore not specified. In this paper, we present a novel 802.11s management solution based on the SNMP protocol. It covers dynamic mesh bootstrapping, error recovery, status monitoring and remote configuration. The presented solution was implemented and evaluated in a real-world testbed comprising more than 10 mesh nodes.

Evaluating Cross-Layer Cooperation of Congestion and Flow Control in IEEE 802.11s Networks

The new standard IEEE 802.11s enables vendor-independent wireless mesh networks based on the 802.11 WLAN technology. Transmission Control Protocol (TCP) is the most widespread transport protocol for reliable data delivery and still the basis for many network applications. TCP supports different mechanisms for flow and congestion control. However, designed for wired networks, it does not consider the dynamics of wireless networks and especially multi-hop wireless mesh networks. In addition, 802.11s provides own mechanisms such as Automatic Repeat Request (ARQ) for frame retransmissions to hide wireless loss from the upper layers. Being transparent to each other, retransmission schemes on both layers may interfere and operate redundantly, if not properly adjusted. We study the effects of ARQ retry limit variation on TCP throughput in a real-world multi-hop 802.11s test bed. As a result, we suggest ARQ adaptation based on the 802.11s standards Airtime Link Metric (ALM) for path selection, serving as indicator for overall frame travel time. Our proposed approach solely relies on standard features and imposes no modifications to 802.11s or TCP.

Integration of QoS Parameters from IEEE 802.11s WLAN Mesh Networks into Logical P2P Overlays

Adopted in late 2011, IEEE 802.11s comes as the first industry standard to enable vendor-independent and inter-operable WLAN mesh networks. Featuring automatic device interconnection and routing, they provide a higher scalability, flexibility, and robustness compared to common centralized WLAN infrastructures. The 802.11s standard defines mandatory support of the Hybrid Wireless Mesh Protocol (HWMP) and Airtime Link Metric (ALM) for MAC-layer routing. While 802.11s covers the physical network underlay, Peer-to-Peer (P2P) protocols are an equivalent on the application level. In contrast to centralized client/server communication, they establish a fail-safe and scalable logical network overlay for, e.g., distributed content sharing, streaming, search, or synchronization. Thus, P2P networks exhibit many of the characteristics of physical WLAN mesh networks. It is obvious to consider joint solutions, where both technologies are combined to leverage future distributed local area wireless applications. Nevertheless, common P2P protocols, such as BitTorrent, do not consider the structure of the physical underlay while performing topology management. Furthermore, they are primarily designed to be used over wired communication networks such as large parts of the Internet. When deployed over WLAN mesh networks with their quickly varying channel conditions, BitTorrent shows severe performance drawbacks. We present a cross-layer approach based on 802.11s and BitTorrent, that optimizes application layer peer selection by considering the mesh standards routing metric ALM. Our solution was implemented and evaluated in a real-world testbed. Results show that average download time can be reduced by up to 20% already in small network setups.

HaRTKad: A P2P-based concept for deterministic communication and its limitations

Real-time systems play a major role in the realm of industrial automation. It is predicted for the number of smart interconnected devices that participate in such systems to grow significantly in the future. This development is also referred to as Industrial Internet of Things (IIoT) or Industry 4.0. The high number of devices results in highly distributed applications. Therefore, it is no longer sufficient for each device to be real-time capable. In fact, the influence of the communication on the overall timing behavior of the applications grows. Taking this into account, a variety of real-time capable Ethernet approaches called Industrial Ethernet (IE) emerged. However, the established IE solutions rely on proprietary hardware and/or non standard conform protocol adaptations. This leads to very expensive hardware and incompatibilities with other IE solutions or common Ethernet, and thus degrades the interoperability. HaRTKad describes a purely software-based P2P approach that allows deterministic communication over common Ethernet. Although it solely relies on well-known standards and allows real-time communication, it suffers from a multitude of problems. In this paper, the low network utilization, the handling of hash collisions and the traffic prioritization are revealed as the most significant limitations of HaRTKad and possible solutions to these problems are presented.

Algorithmic approach to estimate variant software latencies for latency-sensitive networking

Recently, there has been the arise of latency-sensitive IoT applications, e.g., in the field of telemedicine or Industrial Internet. Such applications have stringent latency requirements. The entire end-to-end latency between two devices is composed of several individual latencies: the software latency of the application, the software latency in the networking stack, the hardware latency on wire, and the hardware latency in switches. The hardware latencies are relatively invariant (constant). Contrary, the software latency is highly variant and thus hard to determine. However, the software-introduced latency is crucial for latency-sensitive applications, since the end-to-end latency equals the sum of all latencies between two devices. In the literature, different investigations based on simulations as well as practical test-beds using specialized hardware are proposed. In contrast, we propose a novel method using no specialized hardware that precisely estimates the latency in the networking software (precision: approx. 144μs). Our approach bases on the measurement of round-trip times between several devices and solving the resulting system of equations to estimate the latency of every individual device. Compared to the state-of-the-art the proposed method has also several advantages regarding scalability and resiliency.

AKadeMesh: Software-defined overlay adaptation for the management of IEEE 802.11s networks

The new standard amendment IEEE 802.11s enables low-level interoperability for future WLAN mesh networks. Support of the Hybrid Wireless Mesh Protocol (HWMP) and the Airtime Link Metric (ALM) for MAC-layer routing is mandatory. Its default distance vector routing mode facilitates scalability but also results in a limited network view per mesh node. Moreover, mesh mechanisms operate transparently to higher layers which makes the management and optimization of 802.11s networks a challenging task. Available on every standard-compliant node, ALM offers the potential to derive mesh topology information. We present AKadeMesh (Adaptive Kad-enhanced Mesh), a cross-layer approach specifically designed for 802.11s networks. It is based on the P2P protocol Kad and dynamically adapts its logical overlay to the physical mesh underlay by directly considering ALM. The resulting topology-aware P2P overlay is used to realize logical clustering for the distributed management of 802.11s networks, thereby maintaining unrestrained interoperability to the mesh standard. Our solution was implemented and evaluated in a real-world test bed. Results demonstrate its practical feasibility and verify the expected clustering benefit.

Towards a TDMA-based real-time extension for the constrained application protocol

Current IoT protocols, like the Constrained Application Protocol (CoAP), do not yet provide real-time behavior for the inter-device communication. In this paper, we propose a real-time extension for the CoAP standard that defines interfaces for the time synchronization among nodes and the time slot management. These interfaces enable a controlled exclusive network access based on a Time Division Multiple Access (TDMA) approach. With this extension, it is possible to realize access control on the application layer without the modification of lower layer protocols. The described interfaces are prototypically implemented within the jCoAP communication stack and evaluated in a multi-device real-world testbed. In our prototype, we used established algorithms for the time synchronization. The results, reveal the weaknesses of the chosen synchronization algorithm. However, the interface definition allows the usage of more accurate algorithms.

Applying the BaaS reference architecture on different classes of devices

This paper presents how the reference architecture of the ITEA2 project Building as a Service (BaaS) could be applied on different classes of devices to show its flexibility and suitability for the heterogeneous environment of building automation systems. For this purpose technologies are identified and discussed that could be used for the implementation. The approach of the reference architecture is applied on three different classes of devices that are used in todays building automation systems or are intended to be used in the future. The selected devices span the range from a small sensor node up to a high performance system.