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Wireless Architecture Considerations
Published in Ali Youssef, Douglas McDonald II, Jon Linton, Bob Zemke, Aaron Earle, Wi-Fi Enabled Healthcare, 2014
Ali Youssef, Douglas McDonald II, Jon Linton, Bob Zemke, Aaron Earle
Unicast, Multicast, and Broadcast IPv4 was originally designed for wired networks. Many functions of the IP protocol are not ideally suited to the 802.11 protocol. The 802.11 designers did their best to work with IPv4, as it was the de facto standard. IPv4 has three types of frames, unicast, multicast, and broadcast. Unicast frames are sent from one address to another address. Over the wireless medium, the unicast frames are sent at the highest PHY rate that the client selects based on a number of criteria. By contrast multicast and broadcast traffic are flooded out to every device on the same subnet. On a WLAN, these packets are flooded out of every AP in the same IP broadcast domain. Unlike the unicast frame, these are transmitted at the lowest supported PHY rate. On an 802.11g network, this is the difference between as much as 54 Mbps and 1 Mbps. The broadcast 802.11 frames requires as much as 54 times as much transmission time as the unicast frame. If enough clients are producing these emissions, even infrequently, this could create severe performance problems on the WLAN. Many problems that can be found on wireless networks are an army of mice rather than a fire-breathing dragon. Figures 2.2 and 2.3 show two different packet captures of client devices sitting idle. At first glance this would seem inert. However, if 500 clients multiply this traffic, it is suddenly alarming. So, it is imperative to minimize this traffic whenever possible.
Multiple Access Methods for Communications Networks
Published in Jerry D. Gibson, The Communications Handbook, 2018
Using such frame removal supervisor nodes, the system interconnectivity patterns can be divided (statically or dynamically) into a number of modes. Under an extensively divisive mode, the supervisory stations allow only communications between stations that are located between two neighboring supervisory stations to take place. Under a less divisive connectivity mode, the system is divided into longer disjoint communications segments. Under a full broadcast mode, each frame is broadcast to all network stations. Depending on the network traffic pattern, time cycles can be defined such that a specific mode of operation is invoked during each time cycle.
Network Protocol Architectures
Published in Mário Marques da Silva, Cable and Wireless Networks, 2018
A switch is responsible for the distribution of frames (instead of packets) within a LAN, based on the destination MAC address† (instead of the IP address). Note that the MAC address is composed of 48 bits and represented by six groups of two hexadecimal digits (e.g., 00-1f-33-ac-c5-bb). In fact, a switch learns the MAC address of each device connected to each interface. Every time a frame is received in a certain interface, if this interface is not associated with any MAC address, the mapping is added to the table. Such a MAC address table maps interfaces to MAC addresses.
Ethernet-Based Servo-Hydraulic Real-Time Controller and DAQ at ELSA for Large Scale Experiments
Published in Journal of Earthquake Engineering, 2022
Marco Peroni, Pierre Pegon, Francisco Javier Molina, Philippe Buchet
The different slaves are connected among themselves and/or the Master Control Unit simply with two cables: an industrial robust and shielded EtherCAT® bus and a power supply cable creating the control network. At this point, it is worth remembering that EtherCAT® passes the Ethernet frame sent by the EtherCAT® master through all EtherCAT® slave nodes rather than sending specific frames data to each of them. The master is the only device in an EtherCAT® network that is allowed to send new frames. Each slave only reads and writes the data addressed to it in a specific area within the frame before transmitting the frame to the next slave in few nanoseconds. The frame is then sent back by the last slave and returns to the master after passing through all slaves again. The bandwidth is dramatically improved since one Ethernet frame per cycle is generally sufficient for sending and/or getting all the slave data.
Development and validation of finite element impact models of high-density UAS components for use in air-to-air collision simulations
Published in Mechanics of Advanced Materials and Structures, 2020
Kalyan Raj Kota, Trent Ricks, Luis Gomez, Jaime Espinosa de los Monteros, Gerardo Olivares, Thomas E. Lacy
The component FE models developed in this study were later incorporated into a structurally complete FW-UAS FE model. Just for illustration purposes, the side view image of a 128.6 m/s (250 knots) FW-UAS impact to a 1.59 mm thick aluminum target panel (at time, t = 5 ms) is shown in Figure 34. The FEs for the motor, battery, and payload subassemblies are highlighted in color while all other FW-UAS FEs are gray. The relatively high-density motor, battery, and camera remained mostly intact and continued roughly on the initial projectile trajectory. The motor essentially acted as a sharp penetrator and was mostly intact after penetration. The size of the hole created from the motor penetration increased as the remainder of the FW-UAS impacted the target panel (t = 5.0 ms). As a result, the battery and camera were mostly intact after passing through the target panel. These results suggested that a 1.59 mm thick target panel would not significantly prevent the FW-UAS penetration at 128.6 m/s. As a consequence, the high mass motor, battery, and camera pose a significant threat to any underlying structure or payload (e.g., ribs, frames, fuel tanks). The details of the development of the structurally complete FW-UAS FE model and the FW-UAS/flat-plate impact simulations will be discussed in future publication.
Dynamic modelling and analysis of 3-axis motion compensated offshore cranes
Published in Ships and Offshore Structures, 2018
Shenghai Wang, Yuqing Sun, Haiquan Chen, Jialu Du
Figure 6 depicts the three coordinate frames introduced to develop a mathematical model of the crane tip–rope–payload system: x0y0z0 denotes the inertial frame; xQyQzQ is defined in such a manner that the origin Q is fixed to crane tip, xQ-axis, yQ-axis and zQ-axis are parallel to x0-axis, y0-axis and z0-axis, respectively. Let Lr be the length of the rope. Let M represent the payload. Let β and ψ be in-plane angle and out-plane angle, respectively. Let 0aQ = [0Qx0Qy0Qz]T be the linear acceleration of Q in x0y0z0.