Designing Redundant Terminal Bus in SIMATIC PCS 7 - Intel NIC Teaming vs SOFTNET-IE RNA (PRP) and SCALANCE X-204RNA

To establish a redundant terminal bus between SIMATIC PCS 7 OS Servers and Clients, two primary architectures are supported: Intel NIC Teaming (using certified Intel multi-port server adapters and Intel ANS drivers) or Parallel Redundancy Protocol (PRP according to IEC 62439-3) using SIMATIC NET SOFTNET-IE RNA software. Standard commercial adapters (such as Realtek RTL8139) cannot utilize Intel Teaming drivers; they require SOFTNET-IE RNA for NDIS-level PRP bonding or connection through hardware redundancy boxes such as SCALANCE X-204RNA.

Architecture of the PCS 7 Redundant Terminal Bus

The terminal bus in SIMATIC PCS 7 interconnects Engineering Stations (ES), redundant OS Server pairs, OS Clients, BATCH Servers, Route Control, and Process Historian:
* The Redundancy Objective:
A single network cable disconnect, switch failure, or adapter defect must not sever communication between the operating consoles and the plant automation servers.
* Separation of Terminal Bus and Plant Bus:
The Plant Bus connects OS Servers and Engineering Stations to controllers (S7-400 / CPU 410-5H) using CP 1623 / CP 1628 or standard network cards with Industrial Ethernet. The Terminal Bus operates as a separate logical and physical network to handle high-bandwidth operator graphics, trend streaming, and SQL database synchronization without impacting real-time controller polling.

Intel NIC Teaming vs SOFTNET-IE RNA (PRP IEC 62439-3)

Two distinct technological methods exist for establishing terminal bus adapter redundancy:
1. Intel NIC Teaming (Adapter Fault Tolerance - AFT / Switch Fault Tolerance - SFT):
* Mechanism: Operates via proprietary Intel ANS (Advanced Network Services) drivers. Two physical ports form a single logical adapter with a shared IP and MAC address. One link remains active while the standby link monitors connectivity via test beacons.
* Hardware Restriction: Supported only on certified Intel server-grade network chipsets (e.g., Intel I210, I350, PRO/1000). Commercial chipsets such as Realtek, Broadcom, or Marvell cannot use Intel ANS teaming.
2. Parallel Redundancy Protocol (PRP according to IEC 62439-3):
* Mechanism: Operates using SIMATIC NET SOFTNET-IE RNA (6GK1780-0AA00 / 6GK1780-0AA08-0AA0). SOFTNET-IE RNA creates a virtual network adapter above two independent standard NDIS physical Ethernet adapters.
* Operation: Transmits every Ethernet packet simultaneously across two independent physical LAN rings/switches (LAN A and LAN B). The receiving station accepts the first arriving frame and discards the duplicate. Switchover time is literally zero milliseconds (bumpless).
* Adapter Independence: Works with standard NDIS-compliant network cards, including non-Intel adapters, making it versatile across diverse PC station hardware.

Comparison Table: Intel Teaming vs SOFTNET-IE RNA vs SCALANCE X-204RNA

The table below outlines technical and commercial differences between terminal bus redundancy solutions:

Feature / MetricIntel NIC Teaming (AFT/SFT)SOFTNET-IE RNA (PRP)SCALANCE X-204RNA Hardware RedBoxUnderlying StandardProprietary Intel ANS / IEEE 802.3adIEC 62439-3 (PRP Clause 4)IEC 62439-3 (PRP Clause 4)Switchover Time1 to 3 seconds0 ms (Bumpless, duplicate discard)0 ms (Bumpless at network edge)NIC Hardware RequirementSpecific Intel Server NICs onlyAny standard NDIS Ethernet NICsSingle standard NIC on client/printerHost Software DriverIntel PROSet / ANS DriverSIMATIC NET SOFTNET-IE RNANone (External industrial hardware)License RequirementIncluded with Intel HardwareSoftnet-IE RNA Runtime License (6GK1780-0AA08-0AA0)None (Hardware purchase 6GK5204-0BA00-2KB2)Network InfrastructureSingle or dual switch with link trackingTwo completely independent LANs (LAN A & B)Two completely independent LANs (LAN A & B)Ideal ApplicationStandard PCS 7 IPC Industrial WorkstationsVirtualized servers & multi-vendor PC fleetsNetwork printers, thin clients, legacy IPCs

Single Attached Nodes (SAN) and Dual Attached Nodes (DAN) Topologies

When implementing a redundant terminal bus across an entire facility:
* Dual Attached Nodes (DAN P):
Stations equipped with two physical network cards running SOFTNET-IE RNA or Intel Teaming. Both OS Servers and primary OS Clients connect directly to both LAN A and LAN B switches.
* Single Attached Nodes (SAN):
Devices with only one network port (e.g., office printers, panel PCs, legacy engineering laptops). A SAN cannot connect to both LANs directly:
* If plugged into LAN A only, communication is lost if LAN A switches fail.
* Solution: Connect the SAN device through a SCALANCE X-204RNA (6GK5204-0BA00-2KB2) Redundancy Box (RedBox). The RedBox connects to LAN A and LAN B, duplicating outgoing frames and eliminating duplicate incoming frames transparently for the single-port node.

Step-by-Step Procedure to Implement SOFTNET-IE RNA on OS Stations

Install Physical Network Adapters:
Install two independent PCIe Ethernet adapters (or dual-port card) in the OS Server and OS Client stations.
Install SIMATIC NET SOFTNET-IE RNA:
Install the SOFTNET-IE RNA software package and transfer the license via Automation License Manager (6GK1780-0AA08-0AA0).
Configure the RNA Virtual Adapter:
* Open the RNA configuration utility in Windows Control Panel / SIMATIC NET.
* Bind Adapter 1 to RNA Network A and Adapter 2 to RNA Network B.
* Create the virtual adapter RNA0.
Assign IP Parameters:
Assign the plant static IP address, subnet mask, and default gateway to the virtual RNA0 adapter in Windows Network Connections. The physical adapters (Adapter 1 and Adapter 2) must have IP protocols disabled or set to unmanaged bindings.
Configure Network Switches:
Connect Adapter 1 ports to SCALANCE X switch infrastructure for LAN A. Connect Adapter 2 ports to independent SCALANCE X infrastructure for LAN B. Ensure no cross-links exist between LAN A and LAN B.
Set Simatic Shell Adapter:
Open Simatic Shell in Windows Explorer. Right-click and select Settings. Set the network adapter binding to the virtual RNA0 adapter. Restart the station.

Verification

To verify redundant terminal bus operation:
1. Open Simatic Shell on an OS Client. Confirm that the redundant OS Server pair is visible and accessible.
2. Start WinCC OS Runtime and open process graphic screens.
3. Initiate a continuous ping from the client to the server virtual RNA IP address: ping -t <Server_RNA_IP>.
4. Disconnect the physical network cable from Adapter 1 (LAN A).
5. Verify that zero ping packets are dropped, process graphic values continue updating without interruption, and no disconnection alarms appear in WinCC.
6. Reconnect Adapter 1 and disconnect Adapter 2 (LAN B). Confirm bumpless continuity.

Limitations and Operational Precautions

Commercial NIC Limitations: Consumer-grade NICs (such as Realtek RTL8139) lack industrial galvanic isolation and high-precision interrupt moderation, which can result in frame drops during high-volume SQL replication between WinCC servers. Use Siemens-approved industrial adapters.
No Inter-Switch Links: Under PRP / SOFTNET-IE RNA, LAN A and LAN B must remain completely isolated from each other. Never bridge LAN A and LAN B switches with a trunk cable, as this causes catastrophic broadcast storms.
Licensing Disclaimer: Final license quantities and MLFBs for SIMATIC NET SOFTNET-IE RNA (6GK1780-0AA08-0AA0) must be validated against the applicable Siemens catalog and authorized distributor quotation.