1 Gbit/s for PROFINET: the benefits and risks

GBIT, Guidelines, network, PROFINET, Switch

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With the rapid developments in industrial automation, the need for bandwidth-growth and integration of networks keeps increasing. PROFINET, as a communication standard based on ethernet, allows for multiple data rates, including Gigabit Ethernet. In this article we’ll discuss the advantages, considerations and the potential risks of 1 Gbit ethernet for PROFINET networks, as described by the PROFINET Design Guideline.

Why should we need 1 Gbit/s for PROFINET

Higher bandwidth and performance

The guideline states that higher data rates, for example, 1 Gbit/s, provide larger available bandwidth and reduce congestion and delay in switches. This is especially valuable with significant data amounts, such as video streams or debug information together with real-time process communication. Further, the fast links ensure larger transfers are accomplished more quickly which minimizes the impact on time-critical traffic.

Enable converged networks

Today’s devices often include additional services—like OPC UA, MQTT, or video monitoring. Gigabit Ethernet provides enough bandwidth for both the PROFINET real-time traffic as well as the non-real-time services. This is essential for the realization of converged networks, whereby in the near futre TSN (Time-Sensitive Networking) mechanisms will isolate the real-time traffic from other streams.

Future-Proofing and Scalability

The guideline points out technology improvements now allow increased data speeds, such as 1 Gbit/s, to work with PROFINET. The use of Gigabit links at backbone or aggregation layers provides for future growth, added devices, and increased data levels without requiring significant redesigns.

Use cases for 1Gbit/s

Backbone Connections Between Switches: The guideline recommends the use of Gigabit Ethernet for interconnections between switches, whether or not the field devices operate at 100 Mbit/s. This eliminates bottlenecks and provides for future plant extensions.

High-Data Applications: Quality control based on cameras and data analytics, for example, benefit from Gigabit speed. A camera that requires up to 150 Mbit/s for video streaming requires a gigabit backbone to maintain performance.

Considerations when using 1Gbit/s for PROFINET

Device Compatibility

Not all devices used for PROFINET support 1 Gbit/s. Though switch and backbone links may usually operate at Gigabit rates, many of the field devices only support 100 Mbit/s. This creates intermixed link speeds, which requires thorough planning.

Risks of congestion

The use of different link speeds over a single network raises the possibility of congestion loss for switches. For example, bursts from a 1 Gbit/s uplink onto several 100 Mbit/s or 10 Mbit/s links would limit switch buffers and cause packet loss. This is critical for real-time traffic, as it does not support retransmission.

The guideline describes three main scenarios of congestion:

Congestion loss due to prioritization of messages (RT vs. NRT traffic)
Congestion loss due to input / output unbalance port count wise (many inputs for one output)
Congestion loss due to input / output unbalanced link speed wise (high speed uplink-low speed downlink)

Switch Requirements

Switches for mixed-speed environments must support:

Ingress rate limiting against buffer overflow
Priority queues by IEEE 802.1Q for real-time traffic

If these conditions are not met, it can lead to occasional or permanent communication failures, especially in time-critical applications.

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Network Design Complexity

While Gigabit connections improve speed, they also correspondingly increase design complexity. Engineers must:

Calculate critical load points of the topology
Ensure line depth and update times stay within limits
Document all mixed-speed intervals and ensure performance in high-load scenarios.

Best Practices

Use 1 Gbit/s for backbone connections between switches or aggregation layers, but not for links to single devices.
Avoid unnecessary mixed-speed transitions; when needed, ensure congestion control.
Test network performance using load calculation software and follow the recommended limits for network load (below 20% for cyclical RT traffic).

Conclusion

The use of 1 Gbit/s links for PROFINET networks offers specific advantages in terms of bandwidth, network scaling and supporting converged architectures.

However, these advantages do have a downside: the design is complex, especially when it comes to connections with different speeds and congestion control.

By complying to the PROFINET design guideline, engineers can leverage Gigabit Ethernet while maintaining the real-time functionality necessary for industrial automation.