TSN is the future of industrial Ethernet
TSN adds determinism to standard Ethernet. PROFINET and EtherNet/IP are both adopting TSN.
10.4 Time-Sensitive Networking (TSN)
The previous chapter covered HSR and PRP for zero-recovery-time redundancy. Those protocols solve the reliability problem but do not address a different challenge: running multiple industrial protocols with different timing requirements on the same Ethernet network. TSN solves this.
Why TSN Exists
Section titled “Why TSN Exists”Today, PROFINET IRT requires dedicated switch hardware. EtherNet/IP uses standard switches but cannot guarantee hard real-time latency. Each protocol needs its own network segment. TSN (Time-Sensitive Networking) is a set of IEEE 802.1 standards that add deterministic, time-aware behavior to standard Ethernet, allowing hard real-time, soft real-time, and best-effort traffic to share the same wire.
The TSN Standards Suite
Section titled “The TSN Standards Suite”| Standard | Feature |
|---|---|
| IEEE 802.1AS-2020 | Time synchronization (gPTP) |
| IEEE 802.1Qbv | Scheduled traffic (time-aware shaper) |
| IEEE 802.1Qbu | Frame preemption |
| IEEE 802.1CB | Frame replication and elimination (FRER) |
| IEEE 802.1Qcc | Stream reservation and configuration |
gPTP (generalized Precision Time Protocol) is a constrained PTP profile that provides sub-microsecond time synchronization across all TSN devices.
IEEE 802.1Qbv — Time-Aware Shaper
Section titled “IEEE 802.1Qbv — Time-Aware Shaper”The time-aware shaper divides time into repeating cycles. Each cycle is divided into time slots assigned to specific traffic classes. During a Class A slot, only Class A frames transmit. All other traffic waits. This guarantees that real-time frames are never delayed by best-effort traffic.
| Time Slot | Traffic Class | Duration |
|---|---|---|
| 0 to 100 us | Class A: Hard real-time (motion control) | 100 us |
| 100 to 300 us | Class B: Soft real-time (I/O) | 200 us |
| 300 to 1000 us | Class C: Best effort | 700 us |
IEEE 802.1Qbu — Frame Preemption
Section titled “IEEE 802.1Qbu — Frame Preemption”Frame preemption allows a high-priority frame to interrupt the transmission of a lower-priority frame. The lower-priority frame is split, the high-priority frame transmits, and then the lower-priority frame resumes. This reduces worst-case latency for high-priority frames.
TSN in Industrial Protocols
Section titled “TSN in Industrial Protocols”The IEC/IEEE 60802 profile defines a common TSN configuration for industrial automation. PROFINET and EtherNet/IP devices coexist on the same TSN network using this shared profile.
| Feature | PROFINET IRT | TSN |
|---|---|---|
| Cycle time | 250 us | 31.25 us (theoretical) |
| Standard | Proprietary (PI) | IEEE 802.1 (open) |
| Multi-vendor | Limited | Yes (with common profile) |
| Maturity | Production-ready | Emerging (2020s) |
Key Takeaways
Section titled “Key Takeaways”Time synchronization is required
TSN requires all devices and switches to be time-synchronized via gPTP (IEEE 802.1AS).
What Comes Next
Section titled “What Comes Next”Chapters 9 and 10 covered the protocols and topologies of industrial networking. The protocol that ties ring topology to industrial Ethernet most tightly is MRP. The next chapter provides a deep dive into MRP: how the ring operates, how failures are detected, and how to configure and troubleshoot MRP on Hirschmann switches.
References
Section titled “References”- IEEE 802.1AS-2020 — Timing and Synchronization for Time-Sensitive Applications
- IEEE 802.1Qbv-2015 — Enhancements for Scheduled Traffic
- IEC/IEEE 60802:2023 — TSN Profile for Industrial Automation
- Belden. (2022). TSN: The Future of Industrial Networking. Belden White Paper.