Troubleshooting Offline (Red) Process Historian Status in WinCC States of Connected Servers

When the Process Historian (PH) displays in RED (Offline) within the WinCC 'States of Connected Servers' dialog on an OS Client while OS Servers and PH are actively communicating, the root cause is a client-level communication or package resolution failure. The OS Client monitors server states directly: if the PH Server Data package was not loaded into the OS Client project, if DNS/NetBIOS name resolution between client and PH fails, or if Windows Firewall blocks RPC ports (Port 135, dynamic RPC) and PH communication port 4224, the client reports PH offline despite active server archiving.

Executive Summary

In SIMATIC PCS 7 (V8.0 through V9.1), the Process Historian (PH) serves as the central long-term archive server for alarms, batch data, and analog process tags collected from distributed OS Server pairs. On OS Client consoles, the 'States of Connected Servers' window (@ServerState.pdl) provides real-time health indicators for all connected server entities. A frequent commissioning anomaly occurs where OS Servers archive data to PH successfully, but OS Clients display the Process Historian icon in RED (Offline). This article details the client-to-PH polling architecture, identifies firewall and name resolution obstacles, and outlines the step-by-step procedure to restore online server state.

Architecture and Fundamental Mechanics

Client-to-Historian Polling Mechanics and Communication Architecture:

Multi-Server State Evaluation (@ServerState.pdl):
The 'States of Connected Servers' window does not query the OS Servers to ask if the Process Historian is healthy.
Instead, each OS Client independently queries every server node for which it holds a loaded Server Package (.pck).
If an OS Client loads the Process Historian package (enabling direct long-term trend querying via WinCC Trend Control), the client's internal Split Screen Manager daemon initiates cyclic RPC/DCOM and TCP status polls directly to the Process Historian IP address/hostname.
Primary Root Causes of False 'Red/Offline' Status:
1. Missing or Stale PH Server Data Package on Client:
- If the PH server package was generated before network IP changes or was not imported into the OS Client project via Server Data -> Load..., the client cannot resolve the internal server GUID.
  2. Terminal Bus Name Resolution Failure (DNS / LMHOSTS):
- PCS 7 client-server communication depends strictly on forward and reverse NetBIOS/DNS hostname resolution over the Terminal Bus. If the client cannot ping the PH by its exact NetBIOS computer name, status queries fail.
  3. Firewall and Network Port Obstructions:
- Direct client-to-PH status queries require open ports on the Terminal Bus:
- TCP Port 135 (RPC Endpoint Mapper).
- Dynamic RPC ports (TCP 49152–65535).
- TCP Port 4224 (Process Historian Ready communication service).
- TCP Port 1433 (Microsoft SQL Server instance).
- If Windows Firewall or an intermediate network switch blocks these ports on the client, the client flags the PH as offline.
  4. Security Controller Misalignment:
- If the Siemens Security Controller was not executed following operating system updates, local DCOM permissions will deny status polling from remote client accounts.

Step-by-Step Implementation Procedure

Step-by-Step Procedure to Restore Process Historian Online Status on OS Clients:

Verify Hostname Resolution over Terminal Bus:
- Open Command Prompt on the OS Client.
- Ping the Process Historian by NetBIOS name (e.g. ping PH_SERVER01).
- Verify that the ping replies from the designated Terminal Bus IP address, not an external or plant bus address.
- If name resolution fails, update the Windows hosts and lmhosts files on the client (C:\Windows\System32\drivers\etc\hosts).
Verify Firewall and Port Accessibility:
- On both the OS Client and Process Historian, run the Siemens Security Controller (Start -> Siemens Automation -> Security Controller -> Repeat Settings).
- Ensure Windows Firewall rules allow inbound and outbound connections for WinCC, SQL Server, and Process Historian services.
- Test TCP port 4224 and 135 reachability from the client using PowerShell:
Test-NetConnection -ComputerName PH_SERVER01 -Port 4224
Regenerate and Reload Process Historian Server Package:
- On the Process Historian / Information Server station, open the SIMATIC Manager project representing the PH.
- In Component View, right-click the PH OS object -> select Server Data -> Generate.
- Open the OS Client project in SIMATIC Manager on the ES.
- Navigate to Server Data; right-click the existing PH package -> select Update... (or delete and reload via Load...).
- Confirm the package properties point to the correct computer name.
Download Updated Client Project:
- Close WinCC Runtime on the OS Client.
- Download the OS Client project from the ES to the target client station.
Reactivate Runtime and Verify Server State:
- Activate WinCC Runtime on the OS Client.
- Open the 'States of Connected Servers' window.

Verification

Verification Procedure:
1. Visual Status Check: In WinCC Runtime on the OS Client, open the 'States of Connected Servers' dialog. Confirm that the Process Historian icon indicates a green checkmark / 'Online' status.
2. Trend Access Test: Open a WinCC process picture containing a WinCC Trend Control bound to a long-term archived tag on the Process Historian. Verify that historical trend curves from previous months display seamlessly without data timeout banners.
3. Alarm History Check: Open the WinCC Alarm Journal. Select long-term archive view; verify historical alarms stored in PH populate immediately.

Limitations and Operational Precautions

Operational Precautions and Network Segmentation Guidelines:
- Dual-Homed Network Isolation: Process Historian nodes typically have two network cards: one connected to the Terminal Bus (OS Clients and OS Servers) and one connected to the corporate/office network (Information Server clients). Never route client runtime traffic over the corporate network interface.
- SIMATIC Service User Account: In workgroup environments, ensure the SiemensUser and Windows logon credentials have identical usernames and passwords across all participating stations to prevent DCOM authentication rejection.
- Server Data Updates: Whenever a server's network name or IP changes, all dependent OS Client server data packages must be regenerated and re-downloaded.

Engineer FAQ

Why does the OS Client show PH offline when OS Servers are archiving normally?

Because the OS Client queries the Process Historian directly across the Terminal Bus. If client-to-PH name resolution, firewall ports, or the loaded PH server package are invalid, the client flags PH offline independently of server status.

What TCP port is used by Process Historian Ready services?

TCP Port 4224 is used for Process Historian Ready communication.

How do I update the Process Historian server package on an OS Client?

Generate the package on the PH OS object in SIMATIC Manager, then right-click Server Data on the OS Client project and select 'Update...' before downloading to the client.

What tool configures Windows Firewall exceptions for PCS 7 automatically?

The Siemens Security Controller automatically configures all necessary Windows Firewall exceptions and DCOM security rights.

Where is the 'States of Connected Servers' picture located in WinCC?

The status screen is implemented in system picture @ServerState.pdl.

Technical References

Related Tags

Process Historian
Server State
WinCC Runtime
Terminal Bus
Firewall Ports

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Troubleshooting Offline (Red) Process Historian Status in WinCC States of Connected Servers