Configuring AS-OS Communication and Redundant WinCC Servers in SIMATIC PCS 7 - NetPro, Station Configurator, and S7ONLINE Setup

Establishing reliable AS-OS communication for redundant WinCC OS servers in SIMATIC PCS 7 requires precise configuration across NetPro, the local Station Configuration Editor, Simatic Shell, and the PG/PC Interface. In PCS 7, the engineering paradigm dictates that the S7ONLINE access point on all PC stations (ES, OS Server 1, and OS Server 2) must be set to 'PC internal.local.1'. This delegates communication routing to the Station Configuration Editor, allowing NetPro to centrally download network adapter bindings and virtual S7 connection tables without manual per-card driver adjustments. Redundant OS servers must have identical S7 connections configured to the AS, with dedicated redundancy pairing in WinCC Explorer and priority adapter binding in Simatic Shell on the terminal bus.

AS-OS Communication Architecture in Redundant Systems

In a SIMATIC PCS 7 distributed control system, Operator Stations (OS Servers) communicate with S7-400 or CPU 410-5H controllers across the Industrial Ethernet Plant Bus (System Bus). For redundant OS server architectures (OS Server 1 and OS Server 2):
1. Physical Redundancy: Each server is equipped with a network adapter (Standard IE adapter with Softnet or dedicated CP 1623 / CP 1613 with Hardnet) connected to the plant bus, and a secondary network adapter connected to the terminal bus.
2. Logical S7 Named Connections: In NetPro, identical S7 Named Connections are established between AS1 and OS1 (WinCC Appl.), and between AS1 and OS2 (WinCC Appl. stby).
3. Data Synchronization: During runtime, both OS servers independently poll process values and alarms from the AS across their respective plant bus connections. High-speed process value and alarm state synchronization between Server 1 and Server 2 occurs across a dedicated redundant network cable (serial cross-cable or dedicated Ethernet NIC) managed by the WinCC Redundancy option.

Misconfigurations in network interfaces, Station Configurator virtual racks, or NetPro downloads prevent the OS runtime from establishing communication, causing tags to display yellow exclamation marks or gray invalid statuses.

Role and Configuration of 'PC internal.local.1'

A frequent source of confusion during PCS 7 engineering is setting the PG/PC Interface to PC internal.local.1.

In standard STEP 7 / WinCC flexible engineering, users manually bind the S7ONLINE access point directly to the physical network card (e.g., TCP/IP -> Realtek PCIe...). However, in SIMATIC PCS 7:
- Centralized Station Management: All PC stations are modeled as virtual racks in the Station Configuration Editor (Station Configurator).
- The PC Internal Driver: Setting S7ONLINE to PC internal.local.1 directs all communication requests to the local SIMATIC station manager. The station manager then maps these requests to the physical hardware adapters based on the virtual rack index and the NetPro configuration downloaded from the ES.
- Remote Commissioning: This architecture allows the central Engineering Station to configure, reassign, and download network properties to remote OS servers and clients without physical intervention at each computer.

To configure this setting:
1. In Windows Control Panel, open Set PG/PC Interface.
2. Under Access Point of the Application, select S7ONLINE (STEP 7).
3. In the interface parameter assignment list, select PC internal.local.1.
4. Click OK to apply.

Step-by-Step Procedure: Configuring Redundant AS-OS Connections

Follow these systematic steps to configure and verify redundant AS-OS connections:

Step 1: Configure PC Stations in SIMATIC Manager

In the Component View of SIMATIC Manager, insert two PC Stations: OS_SRV1 and OS_SRV2.
In HW Config for OS_SRV1:
- Slot 1: Insert WinCC Appl.
- Slot 2: Insert communication module (e.g., IE General or CP 1623) assigned to the Plant Bus subnet.
In HW Config for OS_SRV2:
- Slot 1: Insert WinCC Appl. stby
- Slot 2: Insert identical communication module assigned to the Plant Bus subnet.
Save and Compile HW Config for both stations.

Step 2: Establish Redundant Partner Association

In SIMATIC Manager, right-click the WinCC Appl. object under OS_SRV1 and select Object Properties.
Switch to the Operating System or Redundancy tab.
Select OS_SRV2 / WinCC Appl. stby as the Redundant Partner OS. This automatically links the projects.

Step 3: Configure NetPro S7 Connections

Open NetPro.
Select the WinCC Appl. in OS_SRV1. In the lower connection table, insert a new connection:
- Partner: AS controller CPU (e.g., CPU 410-5H).
- Type: S7 connection (use S7 connection fault-tolerant only if connecting to redundant S7-400H CPUs via CP 1623).
Repeat the connection setup for WinCC Appl. stby in OS_SRV2 targeting the identical CPU.
Perform Network > Save and Compile. Resolve any compilation errors.
Download the network configuration to the AS controller, OS Server 1, and OS Server 2 via NetPro.

Step 4: Configure WinCC Redundancy Editor

Open the WinCC project on OS_SRV1.
Open the Redundancy editor in WinCC Explorer navigation tree.
Set Default Master to OS_SRV1 and Redundant Partner Server to OS_SRV2.
Select the dedicated connection adapter used for internal server synchronization.
Check Activate Redundancy. Click OK.

Diagnostic Matrix for AS-OS Communication Failures

Use this diagnostic reference table when AS-OS communication fails:

SymptomProbable CauseCorrective ActionStation Configurator shows Red CrossNetwork adapter disabled, MAC address mismatch, or missing driverVerify physical NIC state in Device Manager; re-index slot in Station ConfiguratorTags show yellow exclamation pointNetPro S7 connection not downloaded to AS or OSRe-download connection tables in NetPro to both AS and OS PC stationsConnection status: 'Is being set up'S7ONLINE not mapped to PC internal, or firewall blocking port 102Set PG/PC interface to PC internal.local.1; open TCP port 102 in Windows FirewallWinCC Redundancy does not synchronizeTerminal bus priority incorrect in Simatic ShellOpen Simatic Shell, select terminal bus adapter, enable encrypted communicationOS compiles with ISO instead of Named ConnectionConnection parameter set to MAC instead of IP/Named in OS Compile wizardIn SIMATIC Manager, run OS Compile wizard; explicitly select S7 Named Connection

Verification

To confirm that redundant AS-OS communication is operational:
1. Station Configurator Check: Open Station Configuration Editor on both OS servers; confirm that the WinCC Application and network card display the Yellow Pencil icon (indicating successful NetPro download) and status RUN.
2. WinCC Channel Diagnosis: Launch WinCC Channel Diagnosis on OS Server 1 and Server 2. Verify that the Named Connections channel indicates state Ready and the connection to the AS shows a green checkmark with cycle times below 50 ms.
3. Runtime Redundancy Verification: Open WinCC Runtime on both servers. In the internal tags @RedundancyState, verify that Server 1 reports Master (@RM_MASTER = 1) and Server 2 reports Standby (@RM_MASTER = 0).
4. Failover Test: Temporarily disconnect the plant bus network cable on Server 1. Confirm that Server 2 transitions seamlessly to Master without alarm loss or client freeze.

Limitations and Operational Precautions

Observe the following architectural precautions:
- For redundant OS systems, explicitly verify the licensing requirement for each server; each server requires separate identical WinCC Server RT, Process Object, and Redundancy licenses.
- Always validate final license quantities and MLFBs against the applicable Siemens catalog and authorized distributor quotation.
- Do not mix network adapters of different speeds or operational modes (e.g., standard NIC with Softnet paired with CP 1623 with Hardnet) across redundant servers, as latency disparities will cause synchronization timeouts.

Engineer FAQ

Why can't I go online to the PLC from the ES after setting PG/PC interface to PC internal.local.1?

If setting PC internal.local.1 breaks online connectivity, the Station Configuration Editor on the ES has not been properly loaded with the ES hardware configuration from NetPro. In SIMATIC Manager, perform a station download to the local ES station, or verify in Station Configurator that the ES network card matches the index assigned in HW Config.

What is the difference between an 'S7 connection' and an 'S7 connection fault-tolerant' in NetPro?

A standard 'S7 connection' runs over a single physical network route. An 'S7 connection fault-tolerant' utilizes redundant plant bus paths between redundant CP 1623 cards and redundant S7-400H CPUs, automatically switching communication paths without application interruption if one bus fails.

Do both redundant OS servers need separate WinCC licenses?

Yes. Both OS Server 1 and OS Server 2 require identical WinCC Server runtime licenses and identical PO count licenses. Additionally, the WinCC Redundancy license package (6AV6371-1CF07-0AX0) must be installed on each server.