CAN — Priority-Based Deterministic Arbitration:

Deterministic behavior is a critical requirement in safety-relevant and real-time automotive, commercial and industrial networks. While both CAN XL and Ethernet's 10BASE-T1S provide bounded latency operation, the mechanism by which determinism is achieved differs fundamentally.

CAN XL maintains classical CAN arbitration during the arbitration phase (≤1Mbps), where frames compete based on priority and the lower identifier value wins. Arbitration is non-destructive, meaning no bandwidth is wasted during contention and worst-case latency in CAN networks is governed primarily by:

• Priority assignment
• Maximum frame length of higher-priority traffic
• Overall bus utilization

Due to arbitration being priority-based, high-priority frames are guaranteed access ahead of lower-priority frames. Deterministic latency can therefore be engineered by system-level priority design and bus load budgeting.

Unlike time-slot systems, node count alone does not directly determine latency. Instead, worst-case delay depends on higher-priority traffic occupancy. With proper network design, high-priority traffic latency remains tightly bounded even as additional low-priority nodes are introduced.

10BASE-T1S — PLCA Slot-Based Determinism:

10BASE-T1S (IEEE 802.3cg) employs Physical Layer Collision Avoidance (PLCA), where a coordinator issues a beacon and each node receives a transmit opportunity in a round-robin sequence.

Key characteristics:

• Fairness-based scheduling
• Each node assigned a transmit opportunity per PLCA cycle
• Worst-case latency bounded by PLCA cycle duration and node count

Latency in PLCA systems scales approximately linearly with the number of active nodes and the configured transmit opportunity window. PLCA guarantees bounded access time, but does not provide priority preemption and all nodes are treated equally within the scheduling cycle.

CAN XL is optimized for systems requiring priority-driven safety messaging, preemptive access for critical traffic and deterministic arbitration under heavy load. 10BASE-T1S is optimized for fair bandwidth distribution, moderate real-time constraints and Ethernet-based protocol integration.

Both technologies provide bounded latency, but they solve determinism differently. CAN provides priority determinism while PLCA provides fairness determinism.