TSN adds determinism to standard 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. These protocols solve the reliability requirement. A different challenge remains: running multiple industrial protocols with different timing requirements on the same Ethernet network. TSN addresses this challenge.
Why TSN Exists
Section titled “Why TSN Exists”Today, PROFINET IRT requires dedicated switch hardware. EtherNet/IP uses standard switches but does not guarantee hard real-time latency. Each protocol needs a separate network segment. TSN (Time-Sensitive Networking) is a set of IEEE 802.1 standards. TSN adds deterministic, time-aware behavior to standard Ethernet. Hard real-time, soft real-time, and best-effort traffic 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. gPTP delivers sub-microsecond time synchronization across 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. Other traffic waits. This mechanism guarantees that best-effort traffic never delays real-time frames.
| 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 switch splits the lower-priority frame, transmits the high-priority frame, and then resumes the lower-priority frame. Frame preemption 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 time synchronization on devices and switches 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. MRP ties ring topology to industrial Ethernet most tightly. The next chapter provides a deep dive into MRP: ring operation, detected-inoperability handling, and configuration and troubleshooting 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.