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How Simatic Shell Redundancy Settings Function and Why OS Clients Differ from OS Servers

How Simatic Shell Redundancy Settings Function and Why OS Clients Differ from OS Servers

In SIMATIC PCS 7, the 'Redundancy Settings' dialog inside Simatic Shell is designed exclusively for paired WinCC OS Servers and does not apply to OS Clients. On OS Servers, Simatic Shell Redundancy Settings configure the dedicated secondary communication path—such as a point-to-point serial COM connection or an isolated crossover network adapter—used by the CCRedAsServer daemon to monitor partner health and coordinate runtime database replication. On an OS Client equipped with dual network adapters, Simatic Shell must bind to exactly one network adapter on the terminal bus. To achieve physical cable and switch redundancy on an OS Client, you must configure operating system Network Interface Card (NIC) Teaming or deploy SIMATIC NET SOFTNET-IE RNA rather than configuring Simatic Shell redundancy.

Table of Contents

Functional Separation: OS Server Redundancy vs. OS Client Connectivity

In SIMATIC PCS 7 and WinCC SCADA systems, redundancy operates at two distinct network tiers:
1. Server-to-Server Redundancy (OS Server Pair): Two identical servers (WinCC Appl. and WinCC Appl. (Stby)) run in parallel. They synchronize process alarms, historical tag archives, and batch states across dedicated redundant channels.
2. Client-to-Server Redundancy (OS Clients): Clients communicate with the server pair across the terminal bus. If the master server fails, clients automatically redirect their data requests to the standby server.

A widespread engineering misunderstanding is attempting to use the Redundancy Settings menu inside Simatic Shell on an OS Client. That dialog exists solely to configure the private heartbeat synchronization channel between redundant OS Server partners.

How Simatic Shell Redundancy Settings Operate on OS Servers

On a redundant OS Server pair, Siemens mandates two independent communication channels between the servers to prevent split-brain scenarios (where both servers believe the partner is dead and attempt to operate as master):
* Primary Channel (Terminal Bus): The standard corporate/terminal network where clients connect.
* Redundancy Channel (Private Heartbeat): Configured via Simatic Shell Redundancy Settings using one of two approved physical methods:
- Method 1 (Dedicated Ethernet Adapter): A secondary network interface card in each server connected via a direct point-to-point crossover cable or isolated VLAN.
- Method 2 (Serial Connection): A null-modem serial cable connected between COM ports (e.g., COM1) using approved Siemens RS-232 pinouts (SIOS Entry ID 18866438).

In Simatic Shell > Redundancy Settings, the engineer selects the secondary adapter or COM port. The redundancy engine checks this path continuously. If the terminal bus cable is severed, the servers communicate over the redundancy channel, preventing uncoordinated archive splits.

OS Client Network Architecture: Why Dual IP Binding Is Unsupported

An OS Client operates as a terminal bus consumer. In Simatic Shell, an engineer must right-click Simatic Shell, select Settings, and choose the specific network adapter card:
* The Single-Adapter Rule: Simatic Shell can bind to only one network interface and IP address per station.
* Why Multi-Homing Fails: If an engineer equips an OS Client with two network cards connected to two separate terminal bus switches and assigns them separate IP addresses (e.g., 192.168.1.50 and 192.168.2.50), Simatic Shell can broadcast on only one card.
* Routing Asymmetry: Multicasting and NetBIOS name resolution become indeterminate, causing random server disconnects, broken faceplate loading, and high CPU utilization.

Method: Implementing Physical Network Redundancy on OS Clients

To achieve physical cable, switch, and adapter redundancy on an OS Client without violating Simatic Shell's single-adapter rule, implement one of the following two approved solutions:

Solution A: Operating System NIC Teaming (Recommended for Standard Networks)

Configure Windows Server or Windows 10 NIC Teaming (Load Balancing and Failover - LBFO):
1. In Windows, launch PowerShell as Administrator or open Server Manager > Local Server > NIC Teaming.
2. Select the two physical network adapters and create a new team named TerminalBus_Team.
3. Configure the Teaming mode:
- Teaming mode: Switch Independent.
- Load balancing mode: Address Hash or Dynamic.
- Standby adapter: None (all adapters active).
4. Assign your static terminal bus IP address, subnet mask, and DNS to the newly created virtual TerminalBus_Team adapter.
5. In Windows Explorer, right-click Simatic Shell > Settings, select TerminalBus_Team, and click OK.
6. Result: Windows transparently handles link failover in milliseconds; Simatic Shell sees only one persistent adapter.

Solution B: SIMATIC NET SOFTNET-IE RNA (PRP / HSR Redundancy)

For high-availability mission-critical plants:
1. Install the SIMATIC NET SOFTNET-IE RNA software package.
2. Connect the client's dual network adapters to two completely independent, parallel terminal bus networks (LAN A and LAN B) compliant with IEC 62439-3 Parallel Redundancy Protocol (PRP).
3. The RNA virtual adapter transmits duplicate frames simultaneously over both networks; the receiving server accepts the first frame and discards the duplicate with zero-millisecond failover time.
4. Bind Simatic Shell strictly to the virtual RNA Adapter.

Verification

To verify that terminal bus redundancy operates correctly on the OS Client:

  1. In Windows Explorer, open Simatic Shell. Verify that the local station and all OS Servers appear in the tree with active blue icons.
  2. Start WinCC Runtime on the OS Client. Confirm that all graphics screens load and dynamic tag values update.
  3. Execute a physical pull-test:
    - Physically unplug the primary network cable from the OS Client's first network adapter.
  4. Observe the network status and WinCC Runtime:
    - Verify that Windows reports the team remains online over the second adapter.
    - Confirm that WinCC Runtime exhibits zero disconnect popups, zero screen freezes, and continuous data updates.
  5. Reconnect the cable and verify automatic link reintegration.

Limitations and Operational Precautions

  • Do Not Enable Redundancy Settings on Clients: Selecting an adapter in Simatic Shell 'Redundancy Settings' on an OS Client will trigger internal initialization warnings in WinCC_Sys_01.log because client runtime lacks the server redundancy management components.
  • Switch Configuration Matching: If using Switch-Dependent NIC Teaming (such as LACP / 802.3ad), ensure the managed Industrial Ethernet switches (e.g., SCALANCE X-300/X-400) are explicitly configured with matching LAG trunk ports.
  • Avoid DHCP on Terminal Bus: All IP addresses on redundant terminal bus interfaces must be statically assigned. DHCP lease renewals can introduce transient socket delays that interrupt Simatic Shell heartbeats.

Engineer FAQ

What happens if I leave the Simatic Shell Redundancy Settings unconfigured on an OS Server?
The redundant server pair will rely entirely on the terminal bus for synchronization. If the terminal bus fails, both servers will attempt to become master, corrupting archive synchronization.

Can an OS Client communicate with an OS Server over a wireless (Wi-Fi) network?
Siemens does not support standard thick OS Clients over Wi-Fi due to jitter and packet loss. For wireless operator mobility, deploy SIMATIC WinCC WebUX or WebNavigator.

Does NIC Teaming require specialized industrial network cards?
No. Windows Switch-Independent NIC Teaming works with standard enterprise Intel or Realtek Gigabit server adapters as well as Siemens CP 1623/1628 cards.

Technical References

  • Siemens Industry Online Support Entry ID 18866438: Connecting a redundant WinCC server via a serial connection
  • Siemens Industry Online Support Entry ID 109742323: SIMATIC Process Control System PCS 7 Fault-Tolerant Process Control Systems Manual
  • SIMATIC HMI WinCC V7.5 Redundancy Manual (Document No. 6AV6392-1CA07-5AA0)

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Related Tags

  • https://industrialautomation.net/search?query=simatic-shell
  • https://industrialautomation.net/search?query=wincc-redundancy
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  • https://industrialautomation.net/search?query=network-teaming
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