Experimental Evaluation of Techniques to Lower Spectrum Consumption in Wi-Red

Seamless redundancy layered atop Wi-Fi has been shown able to tangibly increase communication quality, hence offering industry-grade reliability. However, it also implies much higher network traffic, which is often unbearable as the wireless spectrum is a shared and scarce resource. To deal with this drawback the Wi-Red proposal includes suitable duplication avoidance mechanisms, which reduce spectrum consumption by preventing transmission on air of inessential frame duplicates. In this paper, the ability of such mechanisms to save wireless bandwidth is experimentally evaluated. To this purpose, specific post-analysis techniques have been defined, which permit to carry out such an assessment on a simple testbed that relies on plain redundancy and do not require any changes to the adapters' firmware. As results show, spectrum consumption decreases noticeably without communication quality is impaired. Further saving can be obtained if a slight worsening is tolerated for latencies.Comment: preprint, 13 page

Seamless Link-level Redundancy to Improve Reliability of Industrial Wi-Fi Networks

The adoption of wireless communications and, in particular, Wi-Fi, at the lowest level of the factory automation hierarchy has not increased as fast as expected so far, mainly because of serious issues concerning determinism. Actually, besides the random access scheme, disturbance and interference prevent reliable communication over the air and, as a matter of fact, make wireless networks unable to support distributed real-time control applications properly. Several papers recently appeared in the literature suggest that diversity could be leveraged to overcome this limitation effectively. In this paper a reference architecture is introduced, which describes how seamless link-level redundancy can be applied to Wi-Fi. The framework is general enough to serve as a basis for future protocol enhancements, and also includes two optimizations aimed at improving the quality of wireless communication by avoiding unnecessary replicated transmissions. Some relevant solutions have been analyzed by means of a thorough simulation campaign, in order to highlight their benefits when compared to conventional Wi-Fi. Results show that both packet losses and network latencies improve noticeably.Comment: preprint, 13 pages (Winner of the "2017 Best Paper Award for the IEEE Transactions on Industrial Informatics"

Fixed-Length Payload Encoding for Low-Jitter Controller Area Network Communication

The controller area network (CAN) bit stuffing mechanism, albeit essential to ensure proper receiver clock synchronization, introduces a significant, payload-dependent jitter on message response times, which may worsen the timing accuracy of a networked control system. Accordingly, several approaches to overcome this issue have been discussed in literature. This paper presents a novel software payload encoding scheme, which is able to guarantee that no stuff bits will ever be added to the data field by the CAN controller during transmission and, hence, lessens jitters considerably. Particular care has been put in its practical implementation and its subsequent evaluation to show how the simplicity and inherent high performance of the scheme make it suitable even for low-cost, embedded architectures

On a Software-Defined CAN Controller for Embedded Systems

Controller Area Network (CAN) technology is nowadays ubiquitous in vehicular applications and is also gaining popularity in other contexts, for instance, embedded and industrial automation systems. The recent standardization of CAN with flexible data rate (CAN FD), as well as other academic proposals, have highlighted the usefulness of enhancing the CAN physical and data link layers to attain better performance and other features. This paper describes a portable software-defined CAN controller called SDCC. Besides being handy as a research tool for experimenting with novel protocol concepts at the data link layer, SDCC is also fully capable of real-time execution. Hence, it can interact with real-world CAN devices through a physical bus interface

CAN With eXtensible In-Frame Reply: Protocol Definition and Prototype Implementation

Controller area network (CAN) has been the de facto standard in the automotive industry for the past two decades. Recently, CAN with flexible data-rate (CAN FD) has been standardized, which achieves noticeably higher throughput. Further improvements are still possible for CAN, by exploiting its peculiar physical layer to carry out distributed operations among network nodes, implemented as atomic transactions mapped on quasi-conventional frame exchanges. In this paper, a proposal is made for an extension to the CAN protocol, termed CAN with eXtensible in-frame Reply (CAN XR), which enables upper protocol layers to define new custom services devoted to, e.g., network management, application-specific functions, and high-efficiency data transfer. The key point is that CAN XR retains full backward compatibility with CAN, therefore, there is no need to change the protocol specification once again

Wireless Sensor Networks and TSCH: a compromise between Reliability, Power Consumption and Latency

7siReliability, power consumption, and latency are the three main performance indicators of wireless sensor networks. Time slotted channel hopping (TSCH) is a promising technique introduced in the IEEE 802.15.4 standard that performs some steps ahead in the direction of the final dream to meet all the previous requirements at the same time. In this article, a simple and effective mathematical model is presented for TSCH that, starting from measurements performed on a real testbed, permits to characterize both the network and the surrounding environment. To better characterize power consumption, an experimental measurement campaign was purposely performed on OpenMote B devices. The model, which was checked against a real 6TiSCH implementation, can be employed to predict network behaviour when configuration parameters are varied, in such a way to satisfy different application contexts. Results show that, when one of the three above indices is privileged, unavoidably there is a worsening of the others.openopenScanzio, Stefano; Vakili, Mohammad Ghazi; Cena, Gianluca; Demartini, Claudio Giovanni; Montrucchio, Bartolomeo; Valenzano, Adriano; Zunino, ClaudioScanzio, Stefano; Vakili, Mohammad Ghazi; Cena, Gianluca; Demartini, Claudio Giovanni; Montrucchio, Bartolomeo; Valenzano, Adriano; Zunino, Claudi

Supporting Security Protocols on CAN-Based Networks

The ever-increasing variety of services built on top of the Controller Area Network (CAN), along with the recent discovery of vulnerabilities in CAN-based automotive systems (some of them demonstrated in practice) stimulated a renewed attention to security-oriented enhancements of the CAN protocol. The issue is further compounded nowadays because, unlike in the past, security can no longer be enforced by physical bus segregation. This paper describes how CAN XR, a recently proposed extension of the CAN data-link layer, can effectively support the distributed calculation of arbitrary binary Boolean functions, which are the foundation of most security protocols, without necessarily disclosing their operands on the bus. The feasibility of the approach is then shown through experimental evaluation and by confirming its applicability to a shared key generation protocol proposed in literature

Optimized event notification in CAN through in-frame replies and Bloom filters

Thanks to its distributed and asynchronous medium access control mechanism, CAN is the ideal choice for interconnecting devices in event-driven systems. When timing requirements of applications are not particularly demanding, as in the case of, e.g., reactive and proactive maintenance, constraints on event delivery can be relaxed, so that their notification may rely on best-effort approaches. In this paper, a number of techniques are taken into account for notifying events in such a kind of systems, and their performance has been evaluated. Besides conventional CAN, a recent proposal for extending this protocol, termed CAN XR, is considered. Moreover, the adoption of Bloom filters to cope with rare events in very large systems has also been evaluated

Event Notification in CAN-based Sensor Networks

Preventive and reactive maintenance require the collection of an ever-increasing amount of information from industrial plants and other complex systems, like those based on robotized cells, a need that can be fulfilled by means of a suitable event notification mechanism. At the same time, timing and delivery reliability requirements in those scenarios are typically less demanding than in other cases, thus enabling the adoption of best-effort notification approaches. This paper presents, evaluates, and compares some of those approaches, based on either standard CAN messaging or a recently proposed protocol extension called CAN XR. In the second case, the combined use of Bloom filters is also envisaged to increase flexibility. Results show that the latter approaches are advantageous in a range of event generation rates and network topologies of practical relevance