Configuring PROFINET Redundancy Architectures on CPU 410-5H: S2 vs. R1 Topologies

In SIMATIC PCS 7 with CPU 410-5H, PROFINET field device redundancy is achieved using two distinct architectural models: System Redundancy (S2) and Hardware Redundancy (R1). S2 redundancy utilizes a single PROFINET High Feature (HF) interface module (e.g. ET 200SP IM 155-6 PN HF) that maintains dual logical Application Relationships (ARs) to both CPUs of the 410-5H over a single Media Redundancy Protocol (MRP) ring. R1 redundancy deploys dual physical interface modules in an active backplane rack (e.g. ET 200M IM 153-4 PN or ET 200SP HA IM 155-6 HA), providing complete physical hardware redundancy across dual independent PROFINET rings.

PROFINET Redundancy Paradigms in SIMATIC PCS 7

In process automation systems powered by the SIMATIC PCS 7 CPU 410-5H controller, fieldbus networks are rapidly transitioning from legacy PROFIBUS DP to Industrial Ethernet-based PROFINET IO.

In a fault-tolerant S7-400H / CPU 410-5H system, distributed I/O stations must survive CPU failover, cable breaks, and switch failures without interrupting process signals. To achieve this, PROFINET specifies two distinct layers of redundancy:
1. Network Path Redundancy (Layer 2): Governed by the Media Redundancy Protocol (MRP), healing physical cable breaks in under 200 ms.
2. Controller System Redundancy (Application Layer): Governed by PROFINET System Redundancy specifications, defining how an I/O device connects to both CPUs of a redundant controller pair.

System Redundancy S2: Single Interface with Dual Application Relationships

The S2 Redundancy model represents the standard, cost-effective redundancy approach for modern process plants:
* Hardware Configuration: A distributed I/O station (e.g. SIMATIC ET 200SP with IM 155-6 PN HF 6ES7155-6AU00-0CN0) has a single physical interface module equipped with two integrated network ports.
* Dual Application Relationships (AR):
- The interface module establishes a primary AR with the active master CPU (e.g. CPU 0) and a backup AR with the standby CPU (CPU 1).
- Cyclic process data is exchanged over the primary AR. If the master CPU fails, the device seamlessly switches its primary connection to the backup AR without losing process values or passivating I/O channels.
* Limitation: While S2 protects against controller failure and cable breaks (when wired in an MRP ring), a physical failure of the single interface module itself takes down the entire I/O station.

System Redundancy R1: Dual Interface with Physical Hardware Redundancy

The R1 Redundancy model represents maximum process availability for mission-critical applications:
* Hardware Configuration: An I/O station (e.g. SIMATIC ET 200M or SIMATIC ET 200SP HA) is equipped with two independent physical interface modules (IM 1 and IM 2) mounted on an active backplane bus.
* Physical Redundancy:
- IM 1 connects to PROFINET Ring 1 (governed by CPU 0).
- IM 2 connects to PROFINET Ring 2 (governed by CPU 1).
* Fault Tolerance: R1 survives the simultaneous loss of a CPU, a cable break, AND the complete physical destruction or hot-swapping of an interface module. One interface module can be removed under power while process control continues uninterrupted.

Media Redundancy (MRP) vs. System Redundancy (S2/R1)

Engineers frequently confuse Media Redundancy (MRP) with System Redundancy (S2):
* MRP (Ring Redundancy): Operates at Ethernet Layer 2. If a physical cable in the ring is cut, the MRP Redundancy Manager (CPU 410-5H or SCALANCE switch) unblocks its ring port within 200 ms, restoring network continuity. MRP does NOT protect against CPU failovers.
* S2 / R1 (System Redundancy): Operates at the application layer. It governs the logical S7-400H master/standby CPU relationship.
* In PCS 7, best practice combines both: Deploying S2 devices inside an MRP ring creates a resilient topology where a single cable cut is handled by MRP, and a CPU failover is handled by S2.

PROFINET Redundancy Architecture Comparison Matrix

The following matrix compares PROFINET redundancy configurations on CPU 410-5H:

Architecture MetricStandard PROFINET (Non-Redundant)S2 RedundancyR1 RedundancyInterface Modules per Rack1 Standard IM1 High Feature (HF) IM2 Redundant IMs (HA)Active Connections to 410-5H1 AR (Single CPU)2 ARs (Master + Standby)2 ARs per IM (4 ARs Total)Cable Fault ToleranceZero (Line drops)Full (Inside MRP Ring)Full (Dual Isolated Rings)CPU Failover SupportDisconnects on failoverBumpless Failover (<100 ms)Bumpless Failover (<50 ms)Interface Module Hot-SwapStation trips offlineStation trips offlineBumpless Hot-Swap in RUNHardware CostLowestModerate (Standard for PCS 7)High (Mission-Critical Plants)Typical Distributed I/OET 200SP Basic / StandardET 200SP HF / ET 200MP HFET 200M Redundant / ET 200SP HA

Step-by-Step Configuration Workflow for S2 on CPU 410-5H

To configure S2 System Redundancy in STEP 7 HW Config:
1. Configure CPU 410-5H PROFINET Subnet:
- In HW Config, select the integrated PROFINET interface (X5/X8) on CPU 0 and CPU 1.
- Assign both interfaces to a common Industrial Ethernet subnet (e.g. PROFINET_Plant_Bus).
2. Configure MRP Ring Parameters:
- In CPU PROFINET Interface properties, select the Media Redundancy tab.
- Set Redundancy Role to Manager (Auto).
- Designate Port 1 and Port 2 as Ring Ports.
3. Insert S2-Capable Distributed I/O:
- From the Hardware Catalog, select an S2-certified module:
PROFINET IO -> I/O -> ET 200SP -> IM 155-6 PN HF (6ES7155-6AU00-0CN0).
- Drag and drop the IM onto the PROFINET master system.
4. Enable System Redundancy in Module Properties:
- Open properties of the IM 155-6 PN HF.
- Under the Redundancy tab, ensure the checkbox System Redundancy is active.
- Verify that the station shows connections linking to both CPU 0 and CPU 1.
5. Compile and Download:
- Save and Compile HW Config.
- Download the hardware configuration to the CPU 410-5H controller pair.

Verification

Verify PROFINET S2 redundancy operation and failover:
1. Open STEP 7 HW Config online: Verify the ET 200SP station displays status Available and OK.
2. Inspect physical hardware: Verify that IM 155-6 PN HF displays green RN (Run) and LK1 / LK2 LEDs.
3. Test Controller Redundancy Failover:
- In STEP 7, toggle the active master CPU from CPU 0 to CPU 1.
- Observe field outputs (e.g. energized valves or motor contactors): Confirm zero dropout or chattering during CPU switchover.
4. Test Media Redundancy (Cable Break):
- Disconnect one Ethernet cable from the MRP ring.
- Confirm that the MRP ring heals and communication continues without passivating I/O channels.

Limitations and Operational Precautions

Standard PROFINET interface modules (Basic and Standard tiers, e.g. IM 155-6 PN ST) do NOT support S2 redundancy; attempting to connect them to CPU 410-5H will cause communication faults on the standby CPU.
The maximum number of PROFINET IO devices on a CPU 410-5H MRP ring is typically 64 devices to maintain a guaranteed 200 ms ring reconfiguration time.
For hardware procurement, verify exact part numbers: High Feature modules (e.g. 6ES7155-6AU00-0CN0) are required for S2. Consult an authorized Siemens distributor for procurement schedules.

Engineer FAQ

Can I connect third-party PROFINET devices to CPU 410-5H using S2?

Yes, provided the third-party device vendor explicitly certifies S2 system redundancy support in its GSDML file. If a third-party device only supports single ARs, it must be connected via an intermediary gateway (e.g. PN/PN Coupler).

What is the difference between S1 and S2 in PROFINET terminology?

S1 denotes a non-redundant connection (single device, single controller AR). S2 denotes system redundancy (single device with dual ARs communicating with redundant controllers).

Does CPU 410-5H require external CP cards for PROFINET communication?

No. CPU 410-5H features two high-performance onboard PROFINET interfaces (2 ports each) supporting full S2, MRP, and PROFINET IO communication natively without external CP 443-1 cards.