Profinet vs Profibus: which one to choose?

Introduction: two generations of industrial communication

Profibus and Profinet are two industrial communication standards developed within the PI (Profibus & Profinet International) ecosystem and closely tied to the Siemens world. Although they share a name and philosophy, they belong to different technological generations: Profibus is a classic serial fieldbus, while Profinet is an industrial protocol over Ethernet.

Choosing correctly between them — or planning the migration from one to the other — has a direct impact on performance, cabling cost, diagnostic capability and the future of the installation. In this guide we compare both without bias and explain how to approach a real migration.

What is Profibus

Profibus (Process Field Bus) is a serial fieldbus based on RS-485 that has dominated industrial automation since the 1990s. Its two main variants are:

• Profibus DP (Decentralized Peripherals): fast communication between the PLC and distributed I/O, drives and field devices.
• Profibus PA (Process Automation): designed for process industries, with bus-powered devices and intrinsic safety for ATEX zones.

Key features of Profibus DP:

• Speed up to 12 Mbit/s (depending on segment length)
• Bus (line) topology with termination resistors at each end
• Up to 126 addresses (32 nodes per segment, extendable with repeaters)
• Shielded twisted-pair cable (typically the purple Profibus cable)
• Determinism through a master-slave, token-passing procedure

What is Profinet

Profinet (Process Field Network) is the industrial communication standard over Ethernet that Siemens and PI promote as the natural successor to Profibus. Because it is based on standard Ethernet, it leverages IT infrastructure and offers much more bandwidth and vertical integration with SCADA, MES and ERP systems.

Profinet defines several performance classes depending on real-time demands:

• Profinet RT (Real Time): software-based real time, sufficient for most factory automation applications.
• Profinet IRT (Isochronous Real Time): hardware-based isochronous real time, with nanosecond jitter, for Motion Control and axis synchronisation.
• TSN (Time-Sensitive Networking): the evolution over standard Ethernet that converges deterministic and non-deterministic traffic on the same network.

Key features of Profinet:

• 100 Mbit/s (Fast Ethernet) or higher, full-duplex
• Flexible topology: star, line, tree and ring (with MRP redundancy)
• Industrial Ethernet cabling (twisted pair or fibre optic)
• Advanced diagnostics, device names and IP addressing
• Direct integration with the IT world and protocols such as OPC-UA and MQTT

Profinet vs Profibus comparison table

When to choose Profibus?

• Expansions of existing installations already running on Profibus
• Process industry with Profibus PA and ATEX intrinsic-safety requirements
• Field devices or drives that only offer a Profibus interface
• Projects where maintenance staff are trained exclusively in Profibus
• Simple installations where Profibus bandwidth is more than enough

When to choose Profinet?

• New projects seeking future-proofing, scalability and bandwidth
• Motion Control applications requiring isochronous synchronisation (IRT)
• Installations that need network redundancy (MRP ring)
• Plants wanting vertical integration with SCADA, MES, ERP and OPC-UA
• Industry 4.0 environments with large data volumes and remote diagnostics
• When many devices coexist and detailed per-port diagnostics are needed

How to migrate from Profibus to Profinet

Migration does not have to be a radical overnight change. In practice, it is approached gradually to minimise downtime and make the most of the existing investment. These are the usual steps:

1. Audit of the current network: inventory of masters, slaves, drives and field devices, with their interfaces and obsolescence status.
2. Definition of the target architecture: Profinet topology (line or MRP ring), managed industrial switches and network segmentation.
3. Use of gateways (proxies): a link such as the Siemens IE/PB Link lets you integrate existing Profibus DP segments into the Profinet network, keeping the old slaves operational.
4. Phased replacement: Profibus nodes are replaced by Profinet equivalents during each scheduled maintenance stop, starting with the most critical or obsolete ones.
5. PLC and project upgrade: CPU migration (for example from S7-300 to S7-1500) and reconfiguration in TIA Portal with the new addressing.
6. Commissioning and diagnostics: validation of cycle times, redundancy tests and verification of advanced per-device diagnostics.

This phased approach modernises communication without prolonged production stoppages and spreads the investment over time.

Frequently asked questions

What is the difference between Profinet and Profibus?

Profibus is a serial fieldbus (RS-485) up to 12 Mbit/s with a bus topology; Profinet is a protocol over standard Ethernet (100 Mbit/s or more) with flexible topology, higher bandwidth, advanced diagnostics and direct integration with the IT world.

Can a Profibus device be connected to a Profinet network?

Yes. Using gateways or proxies (such as the Siemens IE/PB Link) existing Profibus DP slaves are integrated into a Profinet network, enabling a gradual migration without replacing all hardware at once.

Does Profinet replace Profibus?

For new projects Profinet is now the recommended option, but Profibus is still installed in millions of nodes and remains operational. Replacement is normally considered during modernisations, expansions or obsolescence cases.

Conclusion

There is no absolute winner: Profibus is still reliable and massively installed, while Profinet is the future-proof choice for bandwidth, topology flexibility, redundancy and Industry 4.0 integration. For new projects, the general recommendation is Profinet; for expansions of existing installations, Profibus or a phased migration is often the most cost-effective option.

For related content, you may be interested in our Siemens S7-1200 vs S7-1500 comparison or the PLC migration from S7-300 to S7-1500 guide, closely tied to Profibus-to-Profinet projects.

Planning an industrial network migration? Contact our team with no obligation.