Lukas Krammer

A new approach for robot motion planning using rapidly-exploring Randomized Trees

In the last few years, car-like robots became increasingly important. Thus, motion planning algorithms for this kind of problem are needed more than ever. Unfortunately, this problem is computational difficult and so probabilistic approaches like Probabilistic Roadmaps or Rapidly-exploring Randomized Trees are often used in this context. This paper introduces a new concept for robot motion planning especially for car-like robots based on Rapidly-exploring Randomized Trees. In contrast to the conventional method, the presented approach uses a pre-computed auxiliary path to improve the distribution of random states. The main contribution of this approach is the significantly increased quality of the computed path. A proof-of-concept implementation evaluates the quality and performance of the proposed concept.

On the security of security extensions for IP-based KNX networks

The traditional areas of building automation like heating, ventilation and air conditioning as well as lighting and shading are more and more extended by services requiring a more robust security infrastructure like alarm-and access control systems. Additionally, building automation networks get integrated into existing IP-based networks, or even communicate directly over the Internet. Therefore, the attack surface of building automation systems has increased dramatically. This requires a solid security architecture and a profound knowledge of possible attack vectors. This work reviews two security extensions for KNXnet/IP regarding their individual security properties. Thereby, it is pointed out that the current version of the draft specification, called KNXnet/IP Secure, lacks some relevant details and has certain limitations concerning the provided level of security.

Limiting constraints for ZigBee networks

Wireless communication has many interesting applications in the field of home and building automation. Besides proprietary solutions of different vendors, ZigBee has gained acceptance in this domain. Since in particular in building automation a high amount of nodes needs to be covered, the question about the applicability of ZigBee for large networks may arise. For this reason, this paper analyzes the constraints regarding ZigBees network size. Furthermore, relations to other automation domains are established, where the proposed concepts can be used too. Starting with a scalable and regular network structure, the limits of ZigBee are figured out analytically. This analysis is then backed up by the results of an OMNeT++ simulation. Moreover, the simulation allows reasoning on further performance-related criteria for ZigBee networks.

Dependability demands and state of the art in the internet of things

The number of devices connected to the Internet of Things (IoT) has steadily been increasing over the last years and so has the variety of applications. There is no sign for this trend to weaken. A broad subset of them imposes requirements on attributes, such as availability, reliability, safety and many more. These attributes are commonly subsumed under the term dependability. In this paper we first give a brief introduction to dependability. Three application scenarios typical for the IoT are presented and their demands for each dependability attribute are discussed. Furthermore, an overview of the current state of the art is presented. Last, a summary of required technologies and future research topics to enable dependability in the IoT is given.

A software-based redundancy concept for building automation networks

Reliability in automation networks is an important topic. Thus, redundant communication is fundamental in this context. In contrast to other automation domains, building automation networks facilitate Ethernet and IP communication and require reliable and predictable communication that are ideally based on standard network technologies. Since automation components are often based on commonly used operating systems, software-based solutions come into play. However, pure software-based solutions are inefficient and often infeasible due to limited processing resources. Thus, a hybrid redundancy concept is proposed that facilitates standard hardware components in combination with lightweight software modules. This paper presents a new redundancy mechanism for Ethernet networks based on a ring topology. This approach makes use of VLAN-capable Ethernet switches in combination with software modules for controlling the network traffic. Thereby, VLANs are used to provide physical redundancy by preventing from Ethernet loops. The proposed concept can therefore be used on different platforms and provides a transparent and reliable communication channel for automation applications. The concept is theoretically analyzed. Finally, a proof-of-concept shows the feasibility.

A fault-tolerant backbone for IEEE 802.15.4 based networks

IEEE 802.15.4 is a well-accepted standard for realizing wireless control networks. Besides the immediate use by an application, many industrial automation and building automation technologies are based on this standard. However, wireless networks have significant drawbacks. One major drawback is the range, since many automation systems are spread over a wide area or are even located in different facilities. In some cases, gateways are used to bridge the wireless clusters. However, a gateway strongly depends on the application. This paper introduces a transparent backbone for seamless communication in IEEE 802.15.4. The proposed solution is capable of connecting a large number of wireless clusters. The concept does not depend on a specific backbone medium. It only requires a pairwise connection among all backbone nodes. Thus, any fieldbus protocol or even Ethernet (IP) can be used. Since many applications are safety-critical, the backbone allows placing two or more wireless interfaces in one cluster and tolerates faults of backbone devices.

Hierarchical concept for IP-based resilient communication in building automation

In building automation, IP-based communication is commonly used. However, availability and reliability recently gained importance in this domain since even safety critical applications (e.g., fire alarm systems) are integrated in building automation networks. Usually, IP-based communication systems, as they are used in functional buildings, do not provide redundancy mechanisms. However, redundancy and deterministic behavior is crucial for a reliable communication system. For different reasons, building automation networks facilitate standard network technologies and components. Nevertheless, such networks are required to be flexible and scalable ranging from small buildings up to areas of buildings by additionally being efficient regarding communication overhead. This paper presents a new hierarchical system concept which provides a homogeneous communication infrastructure to the automation devices. The concept is based on physical Ethernet-ring topologies which represent the bottom level. However, the design and selection of such protocols is out of scope. The rings are connected by a special kind of Router in a redundant way which represents the next level. To establish a connection between dislocated network segments, a reliable backbone communication mechanism is introduced, that can be seen as top level of the hierarchy. In contrast to other technologies, this concept can be statically configured and does not need dynamic reconfiguration in case of a fault. It tolerates one single fault per ring and provides deterministic and local fault handling. The concept is theoretically analyzed; a proof-of-concept shows the feasibility.

Reliable IP based communication for fire alarm systems

With the increasing popularity of the Internet, Ethernet and IP networks are commonly used as backbone technologies in the domain of building automation. For the area of networked fire alarm systems, however, dependability aspects need to be met and reliable communication must be guaranteed to satisfy functional and normative constraints. Due to the economic pressure in this domain, it is desirable to rest system architectures on conventional network technologies and commercial off-the-shelf whenever possible. Moreover, fire alarm systems shall even be integrated into existing installations. The paper defines necessary requirements for communication systems to satisfy the according standards. Subsequently, a ring-based approach with different communication procedures addressing these requirements is presented and theoretically analyzed with regards to failure models of the underlying components.

A generic dependability layer for building automation networks

This paper introduces a concept for bringing dependability into the area of building automation. The proposed approach is able to extend existing building automation networks with dependability features. For this purpose, the communication stack of a particular system is extended by adding an intermediate layer. This so-called dependability layer is transparent to allow seamless integration. Thereby, reliability is addressed in terms of fault tolerance by offering redundant network topologies. A heartbeat mechanism and an acknowledgment procedure as well as a specific message format satisfy the safety requirements. Moreover, the dependability layer offers security mechanisms that establish a secured channel among communicating nodes.

Efficient broadcast authentication for Wireless Sensor and Actuator Networks

In the last decade, broadcast authentication for Wireless Sensor and Actuator Networks (WSANs) has evolved to a prosperous research topic. There basically exist two different approaches to verify a messages originator. On the one hand, public-key cryptography is well-suited to sign and verify messages. However, this may not be feasible for low-cost, lowpower nodes with limited processing capabilities as can be found in WSANs. On the other hand, schemes that are based on symmetric-key cryptography require some kind of asymmetry which is crucial for broadcast authentication. Plenty of them are based on the TESLA protocol. TESLA achieves asymmetry by the use of one-way key chains with delayed disclosure of keys by requiring time synchronization. However, the authentication delay introduced by TESLA leads to some major disadvantages. This paper addresses the security demands of WSANs and proposes a broadcast authentication scheme allowing instantaneous message authentication. The basic scheme is further extended with a probabilistic model. The proposed concept is theoretically analyzed and the improvement of the security level is examined. Furthermore, storage requirements and the computational effort are investigated and compared to other approaches. Finally, a typical use case, i.e., streetlight management, is depicted.