PHY-Level Collision Avoidance

PHY-Level Collision Avoidance (PLCA) is a component of the Ethernet reconciliation sublayer (between the PHY and the MAC) defined within IEEE 802.3 clause 148.^[1] The purpose of PLCA is to avoid the shared medium collisions and associated retransmission overhead. PLCA is used in 802.3cg (10BASE-T1), which focuses on bringing Ethernet connectivity to short-haul embedded internet of things and low throughput, noise-tolerant, industrial deployment use cases.^[2]

In order for a multidrop 10BASE-T1S standard to successfully compete with CAN XL, some kind of arbitration was necessary. The linear arbitration scheme of PLCA somewhat resembles that of the Byteflight, but PLCA was designed from scratch to accommodate the existing shared medium Ethernet MACs with their busy sensing mechanisms.^[3]