Physical Layer Collision Avoidance (PLCA) is a generic reconciliation sublayer (gRS) used in Single-Pair Ethernet ( SPE). This sublayer is used to run deterministics to ensure high performance from the CSMA/ CD access method for different transmission types.
The goal of the PLCA method is to achieve high transmission performance with a low number of nodes using half- duplex and multidrop transmissions. Since the CSMA/CD access method causes random, indeterminable latency, it is of limited use for real-time applications in industrial and automotive engineering. In contrast, PLCA has guaranteed latency and higher throughput, like a Time-Sensitive Network( TSN).
PLCA relies on CSMA/CD and maps the Media Independent Interface( MII) signals onto the MAC layer primitives in such a way that collisions are avoided at the physical layer. PLCA dynamically searches for transmission possibilities in which one node at a time is allowed to send only one data packet over the transmission medium. Each node is assigned a unique identification number( ID). The identification number with the digitzero is assigned to the PLCA coordinator, who starts the cycle with a beacon. If no data is transmitted, the transmission possibility is passed on to the next node. The Reconciliation Sublayer( RS) detects when data is pending for transmission. Since the cycles are very short, the RS sublayer buffers the few data for a short time. Since the PLCA process avoids collisions on the physical media, the data flow is continuous without interruption. To ensure that nodes with higher identification numbers do not have to wait longer than others, the transmission option is passed on from one node to the next.