For companies in the automation industry, the development of real-time Ethernet to connect devices is of high economic interest to replace conventional fieldbus systems. Therefore, many approaches ...for adapting Ethernet to real-time requirements come from industrial applications. This is a challenging task as the original Ethernet standard IEEE 802.3 was not designed for real-time data transmission. Likewise, protocols basing on Ethernet like TCP, UDP, and IP do typically not consider real-time requirements. Hence, adaptations on several OSI layers become necessary to make the industrial system meet hard real-time requirements. For this purpose, a multitude of realtime capable Industrial Ethernet systems has been developed, which solve the problems of standard Ethernet- and TCP/IP- or UDP/IP-based communication in a variety of ways. This paper gives a summary of different Industrial Ethernet protocols for the real-time data transmission via Ethernet in automation environments. Advantages and disadvantages of these protocols are analyzed with regard to their sustainability in terms of their realtime capability, reliability, scalability, self-configuration of the network, and hardware requirements. Against the background of connected devices tremendously growing in number and computational power in the prospective "Industrial Internet", consequences for future developments are drawn.
Accurate people count estimation, potentially in real-time, both for indoor and outdoor environments, is said to be of major importance in the smart cities of tomorrow. Application areas, such as ...public transportation, urban analytics, building automation, as well as disaster management are all expected to benefit if they were to have a better understanding of occupancy in public premises. A large body of work has been concentrated into providing people counting solutions based on images captured by surveillance cameras. However, image-based approaches are costly, as they require devoted hardware installations, and are often privacy intruding. Thus, academic and industry researchers are looking into alternative solutions for people counting. In this paper, we present a comprehensive study of non-image-based people counting techniques. Our goal with this paper is twofold: 1) to serve as an introduction to everyone interested in gaining a better understanding on non-image-based people counting techniques and 2) to serve as a guideline to practitioners interested in implementing and testing specific solutions in their everyday practice. To this end, we provide a novel classification of available approaches, and outline the requirements they need to meet. We further discuss in detail different academic solutions, and provide comparisons between them. Furthermore, we provide a discussion on available industrial approaches and compare them to academic proposals. Finally, we discuss open challenges and future directions in the field of non-image-based people counting.
IEEE 802.11s introduces MAC-layer extensions to enable vendor-independent and inter-operable WLAN mesh networks. Featuring automatic device interconnection and routing, 802.11s networks provide a ...higher scalability, flexibility, and robustness compared to common centralized WLAN infrastructures. As logical Peer-to-Peer (P2P) networks exhibit many of the characteristics of physical WLAN mesh networks on the application layer, it is obvious to consider solutions where both technologies interact to leverage robust distributed wireless applications, such as collaborative data distribution and synchronization in future smart cities. Envisioned scenarios include the administration and update deployment to specific device groups or the distributed caching and delivery of on-demand multi-media content to selected end points within a city-area wireless mesh network. Nevertheless, common P2P protocols, such as BitTorrent (BT), do not consider the structure of the physical underlay as they were primarily designed to be used over wired communication networks, such as large parts of the Internet. Hence, the default BT peer selection mechanism does not adapt to the network topology and varying medium utilization in wireless multi-hop networks. We present MeNTor, a set of optimizations to enable underlay-aware BT peer selection in WLAN mesh networks. It relies on cross-layer integration of default 802.11s information, only requiring minor extension of the BT application layer without introducing any MAC-layer modifications or traffic overhead. Our solution was evaluated in a 25-node real-world mesh test bed, using 10 different seed/leecher placements and comparing 18 parameter combination variants of MeNTor. Results show that average download times can be reduced by 30–40%, depending on the seed/leecher placement and parameter combination variant. Finally, we recommend the variant that performed best across all scenarios as prospective default configuration.
Time (or clock) synchronization is a large and vital field of research, as synchronization is a precondition for many applications. A few example applications are distributed data acquisition, ...distributed databases, and real-time communication. First, this survey paper introduces the research area of time synchronization and emphasizes its relation to other research areas. Second, we give an overview of the state-of-the-art of time synchronization. Herein, we discuss both established protocol and research approaches. We analyze all techniques according to three criteria: used estimation algorithm, achievable synchronization accuracy, and the experimental conditions. In our opinion, this analysis highlights potential improvements. The most important question in this survey is as follows: which estimation method can be used to achieve which accuracies under which conditions? The intention behind this is to identify estimation methods that are particularly worth considering, as these already achieve good results in the wireless area but have not yet been examined in the wired area (and vice versa). This survey paper differs from other surveys in particular through the consideration of wireless and wired synchronization and the focus on estimation algorithms and their achievable accuracy.
Recently, cooperative autonomous underwater vehicles (AUVs) have been deployed in application areas such as surveillance and protection of maritime infrastructures for inspection and monitoring ...purposes. These cooperative methodologies require wireless transmission of data between the different AUVs operating in the underwater environment. Communication over ranges exceeding 100 m exclusively relies on underwater acoustic communication. However, the propagating acoustic waves suffer from several challenges due to the presence of path loss, multi-path propagation, the slow and variant propagation speed, background noise, and Doppler distortion. Since the power supply of the AUVs is limited, communication must be very energy efficient and energy constraints have to be known to be able to plan the mission of AUVs. Due to the difficulties of real experiments, the modeling and simulation of the energy consumption and underwater acoustic communication play an essential role in studying and developing these systems. We provide a modular simulation model for the energy consumption and acoustic underwater communication of AUVs implemented in the network simulator OMNeT++ using the INET framework. More specifically, we extend several INET modules in such a way as to reflect the characteristics of AUVs and underwater communication. We study and analyze the AUVs’ energy consumption and dependence of the message quality on different properties such as those mentioned above.
This survey addresses the question if existing realtime capable Internet technologies for wired communication can meet the requirements of future industrial IoT scenarios with a rising number of ...heterogeneous devices to be connected and increasing amounts of data to be exchanged in real-time. The development towards an industrial IoT is further referred to as Industry 4.0 in Germany and Industrial Internet in the USA, respectively. We first investigate selected widespread technologies at all layers of the ISO/OSI model with respect to their realtime capability, scalability and dynamic reconfiguration, standard compliance and platform complexity as well their capability to integrate non-real-time devices. On the one hand, we note that TSN technology at physical and link layer is standardized but exhibits very high platform complexity for the switches and is thus costly. Subsequently, it is hence discussed if purely software-based approaches can enable RT communication over Ethernet. Moreover, even though TSN-enabled network components can enforce real-time behavior, scheduling and routing algorithms for computing the respective network configuration are not part of the TSN standards. Those algorithms could be executed on a central SDN controller to achieve high performance and realtime capability, however, the scalability of such a centralized approach is limited by the fact that corresponding algorithms have exponential computational complexity. Hence, one of the future research directions outlined proposes to trade off distributed against centralized scheduling and routing approaches with regard to scalability and dynamic reconfiguration, real-time capability, and platform complexity. We conclude there is a need for the advancement of existing and for the development of new, possibly hybrid, real-time capable approaches that combine the advantages of centralized and distributed solution in order to meet all requirements.
WLAN mesh networks are one of the key technologies for upcoming smart city applications and characterized by a flexible and low-cost deployment. The amendment IEEE 802.11s introduces low-level mesh ...interoperability at the WLAN MAC layer. On the physical layer, IEEE 802.11n introduced major improvements such as HT data rates, MIMO techniques, and frame aggregation. However, building large-scale 802.11n/s testbeds and reproducible setups is challenging and costly. On the other hand, existing attempts for down-scaling real-world setups are limited to works without support for 802.11n and 802.11s. We therefore present Mini-Mesh, a miniaturized indoor 802.11n/s testbed. Following a transmission range scaling approach, we deploy a 6×6-node mesh grid on an area of only 1 m 2 . We validate the applicability of our method via comparative measurements, exhibiting a deviation of less than 6 % between a scaled indoor and unscaled outdoor setup. Based on these results, we parameterize a path loss model helping us to estimate outdoor dimensions for arbitrary indoor mesh topologies.
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 standard's 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.
The distributed computing of data is a challenging task in terms of the self-organizing task distribution and computing, especially if distributed computing systems are becoming very large and ...complex. Therefore, the distributed hash table (DHT)-based P2P system called DuDE has been developed to compute statistics of access nodes of Internet service providers in an efficient way. DuDE exploits the high failure resilience and scalability features of the DHT network Kad to achieve a high-performance distributed system, which avoids the bottlenecks of a centralized computing solution. To ensure highly available data, Reed-Solomon codes for reliable distributed data storage are utilized. For implementing DuDE, usual working steps of distributed computing have been extended to realize a highly scalable computing system. We have developed a simulation model for a large-scale DuDE network consisting of up to 9,000 access nodes for computing statistics. In this paper, simulation results are presented, which demonstrate that DuDE is able to almost linearly accelerate the distributed computing compared to a centralized solution while introducing low traffic overhead.
In the modern world, accurate crowd counting is integral to a multitude of applications, including urban planning, transportation management, and crowd control. The advent of opportunistic ...communication networks, which enable devices to sporadically exchange data in a decentralized fashion, has introduced a new set of challenges in crowd estimation. This paper delves into two opportunistic people counting protocols: UrbanCount and HeartBeatCount. UrbanCount, while a robust protocol in its own right, comes with certain limitations that hinder its real-world applicability. In response to these limitations, this paper introduces refinements to UrbanCount, making it more practical and effective. Additionally, a novel protocol called HeartBeatCount is presented, which significantly enhances crowd size estimation accuracy, particularly in sparse scenarios. Through an evaluation, we compare the performance of these protocols and conclude that HeartBeatCount offers a more resilient solution for opportunistic people counting in various real-world scenarios.
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