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Future Trends in Smart Homes and Buildings
Published in Richard Zurawski, Industrial Communication Technology Handbook, 2017
Wolfgang Kastner, Markus Jung, Lukas Krammer
CoAP uses a 4-byte binary header followed by binary options and the payload. Each message contains a message ID in order to detect duplicate messages and for optional reliability mechanism. CoAP marks messages as confirmable if an acknowledgment should be provided by the server. In this case, the server responds with an acknowledgment. If the acknowledgment is not received, the client retransmits the message for several times until an acknowledgment is returned. In order to avoid congestion, an exponential back-off mechanism is used. For some use cases, reliable messaging is not required; in this case, only one message is passed from the client to the server, which makes the communication more efficient but unreliable.
Energy-Efficient MAC Protocols for Wireless Sensor Networks
Published in Richard Zurawski, Networked Embedded Systems, 2017
Lucia Lo Bello, Mario Collotta, Emanuele Toscano
Packet back-off is configurable and is chosen from a linear range instead of the usual exponential back-off approach. Optional packet-by-packet link layer ACKs are provided to reliably transfer important data. Finally, low-power operation is achieved through an adaptive preamble sampling scheme able to reduce duty cycle and minimize idle listening. A node cycles between awake and sleep states. While awake, it listens a long preamble to assess whether it has to remain awake or can go back to sleep. RTS/CTS packets, due to their high overhead, are not used.
The Internet and TCP/IP
Published in Goff Hill, The Cable and Telecommunications Professionals' Reference, 2012
The timeout is taken to be RTT + 4D, where both 4 and 7/8 were chosen for computational ease. When TCP was devised, computers were not as cheap and powerful as they are now, so it was important to choose constants that could be multiplied quickly. Hence the timeout interval is dependent on the mean RTT and its deviation. If a timeout occurs it is doubled for each successive failure—this is known as “exponential backoff.” TCP timeout is followed by a slow start.
Context-aware Hybrid Adaptive Beaconing for Driver Behavior Dissemination in VANETs
Published in IETE Journal of Research, 2021
Rishu Chhabra, C. Rama Krishna, Seema Verma
With the proliferation in the count of automobiles and improvement in road infrastructure across the globe, to facilitate easy and fast movement of people and goods; a major challenge exists for the transportation systems to improve traffic safety and comfort. Intelligent Transportation Systems (ITS) is one of the major applications of VANET which comprises of Vehicle-to-Vehicle (V2V) communication and Vehicle-to-Infrastructure (V2I) communications. ITS primarily aims at making transportation safe, smart and coordinated. To achieve this, enhancement of IEEE 802.11 standard has been introduced as IEEE 802.11p. In order to support Wireless Access in Vehicular Environments (WAVE), IEEE 802.11p provides enhancements in PHY and MAC layer [1]. It acquires the PHY layer features from 802.11a. However, it reduces the transmission rate and limits the bandwidth from 20 MHz to 10 MHz [2]. In order to support different applications and contention-based differentiated channel access, VANET uses IEEE 802.11e based EDCA mechanism at the MAC layer. It depends on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with Binary Exponential Backoff for contention-based channel access [3].
Analysis of Ethernet Control Network
Published in IETE Journal of Research, 2023
Whenever two nodes in an Ethernet network transmit packets simultaneously, then the packets collide. Whenever a collision is detected, the two transmitting nodes wait a random length of time before retransmission. The standard binary exponential-backoff (BEB) algorithm determines the length of retransmission time [39]. If sixteen collisions are detected, then the node stops transmitting, and the data-packet losses occur.