Troubleshooting 'No Connection to Data Server!' Alarm and Terminal Bus Network Adapter Lockups in WinCC

The 'No Connection to Data Server!' alarm in SIMATIC PCS 7 WinCC indicates that the local WinCC runtime process has lost RPC/DCOM communication with the active WinCC Data Server (CCDataServer.exe) or that the underlying Terminal Bus network adapter has entered a disabled or locked socket state. This frequently occurs when WinCC runtime is terminated abnormally (e.g. using reset_wincc or forced task killing), leaving orphaned SQL database handles and exhausted Winsock sockets. Subsequent restarts fail as the Windows network stack drops the adapter, triggering a forced Windows reboot prompt. To resolve this: gracefully deactivate WinCC, perform a full cold reboot of the station, verify Terminal Bus IP and Simatic Shell multicast settings, and redownload the OS project from the ES.

Executive Summary

In high-availability SIMATIC PCS 7 architectures utilizing redundant WinCC OS Servers, operators rely on seamless failover when one server is deactivated for maintenance. A critical failure scenario occurs when an OS server fails to deactivate cleanly, prompting maintenance personnel to execute emergency kill scripts such as reset_wincc.vbs. Following reboot, the server encounters hanging autostart routines, triggers a high-priority 'No Connection to Data Server!' alarm, and suffers a sudden network adapter lockout where Windows prompts for a forced restart. This article diagnoses the underlying Winsock socket exhaustion and DCOM connection failures, and outlines the correct recovery procedure to restore redundant server synchronization.

Architecture and Fundamental Mechanics

WinCC Data Server Architecture, DCOM Channel Mechanics, and Winsock Lockups:

Role of CCDataServer in WinCC Runtime:
In PCS 7 OS client-server and server-redundant topologies, CCDataServer.exe (and CCDataServer_x64.exe) manages data arbitration between the WinCC Graphics Runtime (pdlrt.exe), Alarm Logging, Tag Logging, and the partner redundant server.
When a client or standby server activates, it initializes a DCOM connection across the Terminal Bus to the Data Server service running on the master server.
If this communication channel fails or times out during initialization, WinCC raises the internal system alarm 'No Connection to Data Server!' and halts process visualization.
Hazards of Abrupt Process Termination (reset_wincc.vbs):
When WinCC deactivation hangs, using reset_wincc.vbs or killing processes via Windows Task Manager terminates executables abruptly without closing SQL Server connection pools, releasing shared memory segments, or clearing Winsock port bindings.
Orphaned TCP sockets remain trapped in the TIME_WAIT or FIN_WAIT_2 states. Upon immediate system reboot, the Windows network driver encounters hardware socket resource exhaustion or driver stalls, frequently disabling the physical Terminal Bus network interface card (NIC).
When SIMATIC NET detects the sudden loss of the primary network adapter while communication stacks are active, it triggers a critical operating system protection event: 'An error has occurred that requires a restart of computer'.
Terminal Bus Recovery Philosophy:
A cold reboot (complete power cycle or hardware shutdown) is necessary to reset the onboard NIC firmware and clear corrupted Windows Winsock socket tables.

Step-by-Step Implementation Procedure

Perform Controlled Hardware Power Cycle (Cold Reboot):
* Do not repeatedly warm-reboot Windows. Perform a clean Windows shutdown, power off the physical IPC, and wait 60 seconds to completely discharge motherboard capacitors and reset the Intel NIC hardware state machine.
* Power on the station and log on with the designated SIMATIC Windows user account.
Verify Terminal Bus Network Adapter State and IP Configuration:
* Open Windows Network Connections (ncpa.cpl).
* Verify that the Terminal Bus network adapter is enabled, healthy, and configured with its static IP address and subnet mask.
* In Device Manager, verify that the network adapter properties -> 'Power Management' has the option 'Allow the computer to turn off this device to save power' unchecked.
Configure Simatic Shell Terminal Bus Binding:
* Open Windows File Explorer and navigate to This PC -> Simatic Shell.
* Right-click Simatic Shell and select Settings.
* Verify that the selected network adapter is the dedicated Terminal Bus NIC (never the Plant Bus or a disabled NIC).
* Ensure that encrypted communication settings (or multicast broadcast settings) match across all OS Servers, OS Clients, and the Engineering Station.
Detach Residual SQL Databases and Re-Download OS Project:
* If the WinCC project remains unopenable or locked, open SQL Server Management Studio.
* Confirm that no orphaned CC_... databases from aborted sessions remain stuck in 'In Recovery' mode.
* From the Engineering Station in SIMATIC Manager, perform a clean OS project download to the standby server: Right-click OS Server -> PLC -> Download -> Entire OS.
Activate WinCC Runtime and Verify Redundancy Sync:
* Open WinCC Explorer on the restored OS server.
* Activate WinCC Runtime manually (or allow Autostart).
* Monitor the startup sequence; confirm that CCDataServer.exe initializes cleanly without alarms.
* Open the WinCC Redundancy Control dialog; verify that archive synchronization between Server A and Server B completes.

Verification

Verify Network Adapter Health and Server Synchronization:
1. In WinCC Runtime alarm banner, confirm that 'No Connection to Data Server!' does not appear.
2. In Windows Network Connections, verify that the Terminal Bus adapter remains steadily connected without disconnect events.
3. In Simatic Shell, confirm that all partner OS servers and clients appear with green operational status.
4. In the WinCC diagnostic directory (<WinCC_Dir>\Diagnostics), verify that CCDataServer.log reports clean DCOM binding and zero connection drops.

Limitations and Operational Precautions

Operational Precautions and Emergency Recovery Rules:
- Never run reset_wincc.vbs while an OS project is actively communicating if graceful deactivation is possible; allow WinCC up to 5 minutes to flush archive segments before intervening.
- Always maintain a separate physical network for the Terminal Bus (OS client-server communication) and the Plant Bus (AS-OS communication) to prevent network broadcast flooding from disabling server interfaces.

Engineer FAQ

What causes the 'No Connection to Data Server!' alarm in WinCC?

It indicates that WinCC runtime processes cannot establish DCOM/RPC communication with the local or remote CCDataServer service, typically due to network adapter lockups, firewall blocks, or killed database services.

Why did Windows force a computer restart after the adapter failed?

SIMATIC NET communication protocols monitor network interface integrity. A sudden hardware drop of the primary communications card causes a kernel-level protection fault requiring a system restart.

Why is a cold shutdown recommended over a warm restart?

A cold shutdown completely depowers the physical network controller, clearing locked hardware registers and Winsock socket queues that survive soft reboots.

What tool checks Simatic Shell network binding?

Open Windows Explorer, right-click 'Simatic Shell', select Settings, and verify the assigned Terminal Bus adapter.

Can power management disable network adapters on industrial IPCs?

Yes. Windows power-saving defaults can put network adapters to sleep during low-activity periods; disable 'Allow computer to turn off this device' in adapter properties.