C135 PCS 7 (PCS7)
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How to Configure S7 Named Connections for Redundant OS Server Pairs in SIMATIC NetPro

How to Configure S7 Named Connections for Redundant OS Server Pairs in SIMATIC NetPro

In a redundant SIMATIC PCS 7 OS Server architecture, the Standby Server failing to establish communication with the AS while the Master Server communicates normally occurs when the S7 Named Connection names in NetPro are configured with different names on each PC Station. WinCC OS Redundancy requires identical logical connection names across both redundant partner stations (e.g., both named OSS_AS01). When connection names mismatch, WinCC Tag Management assigns the Master's connection name to the Standby Server, where it appears read-only and fails to communicate. Configuring identical connection names from each PC Station to the AS in NetPro resolves the fault.

Table of Contents

S7 Named Connection Mechanics in Redundant OS Systems

In SIMATIC PCS 7 high-availability architectures, supervisory visualization is delivered by redundant pairs of Operator Stations (OS Server Master and OS Server Standby). Both servers communicate simultaneously with the Automation Stations (AS) across the Plant Bus using S7 Named Connections.

How S7 Named Connections Operate

  • Unlike classic IP/port-addressed connections, an S7 Named Connection is an application-level communication route coordinated between SIMATIC NetPro, Station Configuration Editor, and the WinCC s7chn.chn protocol driver.
  • In WinCC Tag Management, all AS process tags are mapped under a single logical connection object (e.g., Named Connections -> OSS_AS01).
  • Because a redundant server pair shares an identical project database generated by the OS Compiler, both server runtimes execute using the identical logical connection name in WinCC Tag Management.

Root Cause Analysis for Standby Server Connection Failure

Engineers configuring redundant servers in NetPro often make an intuitive naming distinction:
* On PC Station 1 (PCS7OSS01), they create an S7 connection to AS01 and name it: OSS01_AS01.
* On PC Station 2 (PCS7OSS02), they create an S7 connection to AS01 and name it: OSS02_AS01.

The Resulting Communication Breakdown

  1. OS Compilation Mapping: During OS compilation, SIMATIC Manager compiles the Master OS database and creates the logical connection using Server 1's NetPro name (OSS01_AS01).
  2. Replication to Standby: When the project is replicated to the Standby Server (via Project Duplicator or OS download), WinCC on Server 2 loads the database and attempts to initialize the connection named OSS01_AS01.
  3. Local Route Missing: Server 2's local Station Configurator only knows a connection named OSS02_AS01. The communication channel driver reports that the requested connection name does not exist on this computer, leaving the connection state dead.
  4. Read-Only Lock in WinCC: In WinCC Tag Management, the connection properties are greyed out (read-only) because connection topologies are managed exclusively from Step 7 NetPro.
  5. Database Editing Trap: Manually modifying SQL database tables in SQL Server Management Studio to change the connection name is dangerous, as the next OS compile or delta download will overwrite manual edits.

Step-by-Step NetPro Configuration Procedure

To configure S7 Named Connections properly and restore communication on the Standby Server:

Step 1: Open NetPro and Inspect PC Station Connections

  1. In SIMATIC Manager, open NetPro.
  2. Locate the two redundant PC Stations:
    * Master OS PC Station (e.g., PCS7OSS01 hosting WinCC Application).
    * Standby OS PC Station (e.g., PCS7OSS02 hosting WinCC Application (stby)).
  3. Select the WinCC Application on Server 1: inspect the connection table at the bottom of NetPro.
  4. Select the WinCC Application (stby) on Server 2: inspect its connection table.

Step 2: Harmonize Connection Names

  1. Double-click the connection on Server 1:
    * Verify the Connection Type is S7 connection (or S7 fault-tolerant connection if AS 410-5H).
    * Note the Local Connection Name: e.g., OSS_AS01.
  2. Double-click the connection on Server 2:
    * Change the Local Connection Name to be exactly identical: OSS_AS01.
    (Note: NetPro permits identical connection names because they originate from different PC Station endpoints).

Step 3: Save, Compile, and Download NetPro Connections

  1. In NetPro, select menu Network -> Save and Compile....
  2. Select Check and compile all; verify zero errors.
  3. Download the connection tables to both PC Stations:
    * Select PCS7OSS01 -> PLC -> Download to Current Project -> Selected Connections.
    * Select PCS7OSS02 -> PLC -> Download to Current Project -> Selected Connections.

Step 4: Recompile the OS and Download

  1. In SIMATIC Manager, right-click the OS Server object and select Compile.
  2. In the OS Compilation Wizard, select Changes only (with 'Tags and messages' enabled) or Entire OS.
  3. Download changes to both OS Servers. Both servers will now bind to OSS_AS01 with complete success.

Redundant Server Connection Parameters and Architecture Matrix

The following table outlines the proper NetPro connection naming conventions for redundant PCS 7 systems:

Network EntityPC Station 1 (Master)PC Station 2 (Standby)Required Consistency RuleHardware ObjectWinCC ApplicationWinCC Application (stby)Must be configured as redundant pairNetPro Connection NameOSS_AS01OSS_AS01Must be 100% Identical StringTarget Automation StationAS01 (CPU 410-5H / S7-400)AS01 (CPU 410-5H / S7-400)Both connect to the same ASNetwork InterfaceCP 1623 / IE GeneralCP 1623 / IE GeneralIdentical card types recommendedWinCC Logical ConnectionNamed Connections -> OSS_AS01Named Connections -> OSS_AS01Automatically shared via OS database

Enforcing identical connection names eliminates communication failover anomalies.

Verification

To verify that both redundant servers connect simultaneously to the controller:
1. Open WinCC Explorer on the Master Server (PCS7OSS01) in runtime; navigate to Tag Management -> Named Connections.
2. Verify that OSS_AS01 shows a green checkmark indicating active communication.
3. Open WinCC Explorer on the Standby Server (PCS7OSS02) in runtime; navigate to Tag Management -> Named Connections.
4. Confirm that OSS_AS01 shows a green checkmark on the Standby Server as well.
5. In WinCC Explorer, verify that the @RM_MASTER and @RM_SERVER_STATE tags confirm proper redundant synchronization.

Limitations and Operational Precautions

  • Never use SQL Server Management Studio to alter connection names directly in the WinCC database; any subsequent OS compilation will overwrite manual changes and corrupt project consistency.
  • In fault-tolerant redundant AS architectures (CPU 410-5H / S7-400H), ensure the connection type in NetPro is selected as 'S7 fault-tolerant connection' spanning both redundant plant bus subnets.
  • When downloading connections in NetPro to an active OS server, ensure the WinCC runtime channel is not actively locked by configuration dialogs.
  • Station names in HW Config and PC Station names in Station Configuration Editor must match the physical Windows computer hostnames exactly.

Engineer FAQ

Why does NetPro allow two different stations to have the exact same connection name?

Because the connection name is local to each station's communication context. In redundant PCS 7 servers, identical connection names are mandatory so the single compiled OS database can execute identically on both nodes.

Why is the connection name greyed out in WinCC Tag Management?

In SIMATIC PCS 7, connections under 'Named Connections' are system-managed by SIMATIC Manager. They are intentionally locked against manual editing in WinCC Explorer to prevent desynchronization with NetPro.

Can the Standby Server communicate with the AS if the Master Server is powered off?

Yes. Both servers maintain completely independent physical S7 connections to the AS controllers; redundant failover does not depend on the partner server's physical connection.

Technical References

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Related Tags

  • S7_Named_Connections
  • OS_Redundancy
  • NetPro
  • Standby_Server
  • WinCC_Tag_Management
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