Gerald Wagenknecht

Flexible experimentation in wireless sensor networks

Virtual testbeds model them by seamlessly integrating physical, simulated, and emulated sensor nodes and radios in real time.

MARWIS: a management architecture for heterogeneous wireless sensor networks

In this paper we present a new management architecture for heterogeneous wireless sensor networks (WSNs) called MARWIS. It supports common management tasks such as monitoring, (re)configuration, and updating program code in a WSN and considers specific characteristics of WSNs and restricted physical resources of the nodes such as battery, computing power, memory or network bandwidth and link quality. To handle large heterogeneous WSN we propose to subdivide it into smaller sensor subnetworks (SSNs), which contains sensor node of one type. A wireless mesh network (WMN) operates as backbone and builds the communication gateway between these SSNs. We show that the packet loss and the round trip time are decreased significantly in such an architecture. The mesh nodes operate also as a communication gateway between the different SSNs and perform the management tasks. All management tasks are controlled by a management station located in the Internet.

BEAM: A Burst-aware Energy-efficient Adaptive MAC protocol for Wireless Sensor Networks

Low latency for packet delivery, high throughput, good reactivity, and energy-efficient operation are key challenges that MAC protocols for Wireless Sensor Networks (WSNs) have to meet. Since traffic patterns as well as network load may change during network lifetime, adaptability of the protocol stack, e.g. in terms of duty cycling, and the integration of reliable transport mechanisms are mandatory. So far, given that optimizations for energy-efficiency and performance parameters are contradicting, most MAC protocols proposed have concentrated on either one or the other. In order to close this gap, we designed BEAM (Burst-aware Energy-efficient Adaptive MAC).

SNOMC: An overlay multicast protocol for Wireless Sensor Networks

Using multicast communication in Wireless Sensor Networks (WSNs) is an efficient way to disseminate the same data (from one sender) to multiple receivers, e.g., transmitting code updates to a group of sensor nodes. Due to the nature of code update traffic a multicast protocol has to support bulky traffic and end-to-end reliability. We are interested in an energy-efficient multicast protocol due to the limited resources of wireless sensor nodes. Current data dissemination schemes do not fulfill the above requirements. In order to close the gap, we designed and implemented the SNOMC (Sensor Node Overlay Multicast) protocol. It is an overlay multicast protocol, which supports reliable, time-efficient, and energy-efficient data dissemination of bulky data from one sender to many receivers. To ensure end-to-end reliability, SNOMC uses a NACK-based reliability mechanism with different caching strategies.

TARWIS — A testbed management architecture for wireless sensor network testbeds

Research in the area of Wireless Sensor Networks (WSNs) has become more and more driven by real-world experimental evaluations rather than network simulation. Numerous testbeds of WSNs have been set up in the past decade, often with very much differing architectural design and hardware. The Testbed Management Architecture for Wireless Sensor Networks (TARWIS) presented in this paper provides the most crucial management and scheduling functionalities for WSN testbeds, independent from the testbed architecture and the sensor nodes operating systems. These functionalities are: a consistent notion of users and user groups, resource reservation features, support for reprogramming and reconfiguration of the nodes, provisions to debug and remotely reset sensor nodes in case of node failures, as well as a solution for collecting and storing experimental data. We describe the workflow of using a TARWIS on a WSN testbed over the entire experimentation life cycle, starting from resource reservation over experiment definition to the collection of real-world experimental data.

Performance evaluation of reliable overlay multicast in wireless sensor networks

Using multicast communication in Wireless Sensor Networks (WSNs) is an efficient way to disseminate code updates to multiple sensor nodes. For this purpose a multicast protocol has to support bulky traffic (typical traffic pattern for code updates) and end-to-end reliability. In addition, we are interested in energy-efficient operations due to the limited resources of WSNs. Currently no data dissemination scheme fits the requirements mentioned above. Therefore, we proposed the SNOMC (Sensor Node Overlay Multicast) protocol, an overlay multicast protocol, which supports reliable, time-efficient, and energy-efficient data dissemination of bulky data from one sender to many receivers. The protocols performance in terms of transmission time, number of totally transmitted packets and energy consumption is compared to other often cited data dissemination protocols. Our results show superior performance of SNOMC independent of the underlaying MAC protocol.

User and Machine Authentication and Authorization Infrastructure for Distributed Wireless Sensor Network Testbeds

The intention of an authentication and authorization infrastructure (AAI) is to simplify and unify access to different web resources. With a single login, a user can access web applications at multiple organizations. The Shibboleth authentication and authorization infrastructure is a standards-based, open source software package for web single sign-on (SSO) across or within organizational boundaries. It allows service providers to make fine-grained authorization decisions for individual access of protected online resources. The Shibboleth system is a widely used AAI, but only supports protection of browser-based web resources. We have implemented a Shibboleth AAI extension to protect web services using Simple Object Access Protocol (SOAP). Besides user authentication for browser-based web resources, this extension also provides user and machine authentication for web service-based resources. Although implemented for a Shibboleth AAI, the architecture can be easily adapted to other AAIs.

Hop-to-Hop Reliability in IP-Based Wireless Sensor Networks - A Cross-Layer Approach

To interconnect a wireless sensor network (WSN) to the Internet, we propose to use TCP/IP as the standard protocol for all network entities. We present a cross layer designed communication architecture, which contains a MAC protocol, IP, a new protocol called Hop-to-Hop Reliability (H2HR) protocol, and the TCP Support for Sensor Nodes (TSS) protocol. The MAC protocol implements the MAC layer of beacon-less personal area networks (PANs) as defined in IEEE 802.15.4. H2HR implements hop-to-hop reliability mechanisms. Two acknowledgment mechanisms, explicit and implicit ACK are supported. TSS optimizes using TCP in WSNs by implementing local retransmission of TCP data packets, local TCP ACK regeneration, aggressive TCP ACK recovery, congestion and flow control algorithms. We show that H2HR increases the performance of UDP, TCP, and RMST in WSNs significantly. The throughput is increased and the packet loss ratio is decreased. As a result, WSNs can be operated and managed using TCP/IP.

Testbed Evaluation of Sensor Node Overlay Multicast

The Sensor Node Overlay Multicast (SNOMC) protocol supports reliable, time-efficient and energy-efficient dissemination of data from one sender node to multiple receivers as it is needed for configuration, code update, and management operations in wireless sensor networks. SNOMC supports end-to-end reliability using negative acknowledgements. The mechanism is simple and easy to implement and can significantly reduce the number of transmissions. SNOMC supports three different caching strategies namely caching on each intermediate node, caching on branching nodes, or caching on the sender node only. SNOMC was evaluated in our in-house real-world testbed and compared to a number of common data dissemination protocols. It outperforms the selected protocols in terms of transmission time, number of transmitted packets, and energy-consumption.