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PHY-Level Collision Avoidance
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<h2 id="operation">Operation</h2> <p>Under a PLCA scheme all <a href="/facts/Network_node/LBp2vNcJ">nodes</a> are assigned unique sequential numbers (IDs) in the range from 0 to N. Zero ID corresponds to a special "coordinator" node that during the idle intervals transmits the synchronization <i>beacon</i> (a special <a href="/facts/Heartbeat_(computing)/b8fgB0JJ">heartbeat</a> frame). After the beacon (within <i>PLCA cycle</i><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>) each node gets its transmission opportunity (TO). Each opportunity interval is very short (typically 20 bits), so overhead for the nodes that do not have anything to transmit is low.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> If the PLCA circuitry discovers that the node's TO cannot be used (the other node with a lower ID have started its transmission and the media is busy at the beginning of the TO for this node), it asserts the "local collision" input of the MAC thus delaying the transmission. The condition is cleared once the node gets its TO. A standard MAC reacts to the local collision with a <a href="/facts/Exponential_backoff/pk2cAbqm">backoff</a>, however, since this is the first and only backoff for this frame, the backoff interval is equal to the smallest possible frame - and the backoff timer will definitely expire by the time the TO is granted, so there is no additional loss of performance.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Internet_of_things/rwwGAxn3">Internet of things</a> (IOT)</li></ul> <h2 id="sources">Sources</h2> <ul><li>Cena, Gianluca; Scanzio, Stefano; Valenzano, Adriano (2023-04-26). <i>Composite CAN XL-Ethernet Networks for Next-Gen Automotive and Automation Systems</i>. 2023 IEEE 19th International Conference on Factory Communication Systems (WFCS). IEEE. <a href="/facts/ArXiv_(identifier)/H6EtgnBe">arXiv</a>:<a href="https://arxiv.org/abs/2306.09498">2306.09498</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1109%2Fwfcs57264.2023.10144116">10.1109/wfcs57264.2023.10144116</a>.</li> <li>Beruto, Piergiorgio; Orzelli, Antonio (2018). <a href="https://www.ieee802.org/3/cg/public/July2018/PLCA%20overview.pdf"><i>802.3cg draft 2.0 PLCA (Clause 148) Overview</i></a> (PDF). San Diego, CA: IEEE 802.3 Plenary Meeting.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"PLCA FAQ" (PDF). IEEE. July 2018. <a href="https://www.ieee802.org/3/cg/public/July2018/PLCA%20FAQ.pdf" target="_blank">https://www.ieee802.org/3/cg/public/July2018/PLCA%20FAQ.pdf</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Beruto & Orzelli 2018. - Beruto, Piergiorgio; Orzelli, Antonio (2018). 802.3cg draft 2.0 PLCA (Clause 148) Overview (PDF). San Diego, CA: IEEE 802.3 Plenary Meeting. <a href="https://www.ieee802.org/3/cg/public/July2018/PLCA%20overview.pdf" target="_blank">https://www.ieee802.org/3/cg/public/July2018/PLCA%20overview.pdf</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Cena, Scanzio & Valenzano 2023. - Cena, Gianluca; Scanzio, Stefano; Valenzano, Adriano (2023-04-26). Composite CAN XL-Ethernet Networks for Next-Gen Automotive and Automation Systems. 2023 IEEE 19th International Conference on Factory Communication Systems (WFCS). IEEE. arXiv:2306.09498. doi:10.1109/wfcs57264.2023.10144116. <a href="https://arxiv.org/abs/2306.09498" target="_blank">https://arxiv.org/abs/2306.09498</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Beruto & Orzelli 2018. - Beruto, Piergiorgio; Orzelli, Antonio (2018). 802.3cg draft 2.0 PLCA (Clause 148) Overview (PDF). San Diego, CA: IEEE 802.3 Plenary Meeting. <a href="https://www.ieee802.org/3/cg/public/July2018/PLCA%20overview.pdf" target="_blank">https://www.ieee802.org/3/cg/public/July2018/PLCA%20overview.pdf</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Cena, Scanzio & Valenzano 2023. - Cena, Gianluca; Scanzio, Stefano; Valenzano, Adriano (2023-04-26). Composite CAN XL-Ethernet Networks for Next-Gen Automotive and Automation Systems. 2023 IEEE 19th International Conference on Factory Communication Systems (WFCS). IEEE. arXiv:2306.09498. doi:10.1109/wfcs57264.2023.10144116. <a href="https://arxiv.org/abs/2306.09498" target="_blank">https://arxiv.org/abs/2306.09498</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Beruto & Orzelli 2018. - Beruto, Piergiorgio; Orzelli, Antonio (2018). 802.3cg draft 2.0 PLCA (Clause 148) Overview (PDF). San Diego, CA: IEEE 802.3 Plenary Meeting. <a href="https://www.ieee802.org/3/cg/public/July2018/PLCA%20overview.pdf" target="_blank">https://www.ieee802.org/3/cg/public/July2018/PLCA%20overview.pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> </ol>